Document:

<PAGE>   1
                                                                   EXHIBIT 4.01

                                   ENRON CORP.

                                    AS ISSUER

                                       AND

                            THE CHASE MANHATTAN BANK

                                   AS TRUSTEE

                                    INDENTURE

                          Dated as of February 7, 2001

                                 $1,907,698,000

                 ZERO COUPON CONVERTIBLE SENIOR NOTES DUE 2021*

--------
*    Plus an option to purchase up to $381,540,000 additional Principal Amount
     at Maturity of such Zero Coupon Convertible Senior Notes due 2021 from the
     Issuer to cover over-allotments.

<PAGE>   2

                                TABLE OF CONTENTS
<TABLE>
<CAPTION>
                                                                                                               PAGE
                                                     ARTICLE 1

                                    DEFINITIONS AND INCORPORATION BY REFERENCE

<S>                                                                                                              <C>
   SECTION 1.01.   Definitions....................................................................................1

   SECTION 1.02.   Other Definitions..............................................................................8

   SECTION 1.03.   Incorporation by Reference of Trust Indenture Act..............................................8

   SECTION 1.04.   Rules of Construction..........................................................................8

                                                     ARTICLE 2

                                                  THE SECURITIES

   SECTION 2.01.   Form of Securities.............................................................................9

   SECTION 2.02.   Title and Terms................................................................................9

   SECTION 2.03.   Denominations.................................................................................10

   SECTION 2.04.   Forms Generally...............................................................................10

   SECTION 2.05.   Execution, Authentication and Delivery........................................................10

   SECTION 2.06.   Registrar and Paying Agent....................................................................11

   SECTION 2.07.   Transfer and Exchange.........................................................................11

   SECTION 2.08.   Replacement Securities........................................................................12

   SECTION 2.09.   Outstanding Securities........................................................................13

   SECTION 2.10.   Temporary Securities; Exchange of Global Security for Definitive Securities...................13

   SECTION 2.11.   Book-entry Provisions for Global Securities...................................................14

   SECTION 2.12.   Cancellation..................................................................................14

   SECTION 2.13.   Special Transfer Provisions...................................................................15

   SECTION 2.14.   CUSIP Numbers.................................................................................18

   SECTION 2.15.   Legend on Restricted Securities...............................................................18

                                                     ARTICLE 3

                                                    REDEMPTION

   SECTION 3.01.   Notices to Trustee............................................................................18

   SECTION 3.02.   Selection of Securities To Be Redeemed........................................................19

   SECTION 3.03.   Notice of Redemption..........................................................................19

   SECTION 3.04.   Effect of Notice of Redemption................................................................20

   SECTION 3.05.   Deposit of Redemption Price...................................................................20

   SECTION 3.06.   Securities Redeemed in Part...................................................................20

   SECTION 3.07.   Conversion Arrangement on Call for Redemption.................................................20

   SECTION 3.08.   Purchase of Securities at Option of the Holder................................................21

   SECTION 3.09.   Repurchase of Securities at Option of the Holder upon Fundamental Change......................28

   SECTION 3.10.   Effect of Purchase Notice or Fundamental Change Repurchase Notice.............................35

   SECTION 3.11.   Deposit of Purchase Price or Fundamental Change Repurchase Price..............................36

   SECTION 3.12.   Securities Purchased or Repurchased in Part...................................................36
</TABLE>

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                                TABLE OF CONTENTS

<TABLE>
<S>                                                                                                              <C>
   SECTION 3.13.   Covenant to Comply With Securities Laws Upon Purchase or Repurchase of Securities.............36

   SECTION 3.14.   Repayment to the Issuer.......................................................................37

                                                     ARTICLE 4

                                                     COVENANTS

   SECTION 4.01.   Payment of Securities.........................................................................37

   SECTION 4.02.   Financial Information; SEC Reports............................................................37

   SECTION 4.03.   Corporate Existence...........................................................................38

   SECTION 4.04.   Restrictions on Liens.........................................................................38

   SECTION 4.05.   [Intentionally omitted].......................................................................40

   SECTION 4.06.   Exempted Indebtedness.........................................................................40

   SECTION 4.07.   Waiver of Certain Covenants...................................................................41

   SECTION 4.08.   Compliance Certificate........................................................................41

   SECTION 4.09.   Further Instruments and Acts..................................................................41

   SECTION 4.10.   Calculation of Original Issue Discount........................................................41

                                                     ARTICLE 5

                                                SUCCESSOR COMPANIES

   SECTION 5.01.   Merger and Consolidation......................................................................42

                                                     ARTICLE 6

                                               DEFAULTS AND REMEDIES

   SECTION 6.01.   Events of Default.............................................................................42

   SECTION 6.02.   Acceleration..................................................................................44

   SECTION 6.03.   Other Remedies................................................................................44

   SECTION 6.04.   Waiver of Past Defaults.......................................................................44

   SECTION 6.05.   Control by Majority...........................................................................45

   SECTION 6.06.   Limitation on Suits...........................................................................45

   SECTION 6.07.   Rights of Holders to Receive Payment..........................................................45

   SECTION 6.08.   Collection Suit by Trustee....................................................................45

   SECTION 6.09.   Trustee May File Proofs of Claim..............................................................46

   SECTION 6.10.   Priorities....................................................................................46

   SECTION 6.11.   Undertaking for Costs.........................................................................46

   SECTION 6.12.   Waiver of Stay or Extension Laws..............................................................47

                                                     ARTICLE 7

                                                      TRUSTEE

   SECTION 7.01.   Duties of Trustee.............................................................................47

   SECTION 7.02.   Rights of Trustee.............................................................................48

   SECTION 7.03.   Individual Rights of Trustee..................................................................49

   SECTION 7.04.   Trustee's Disclaimer..........................................................................49

   SECTION 7.05.   Notice of Defaults............................................................................49
</TABLE>

                                       ii

<PAGE>   4

                                TABLE OF CONTENTS

<TABLE>
<S>                                                                                                             <C>
   SECTION 7.06.   Reports by Trustee to Holder..................................................................49

   SECTION 7.07.   Compensation and Indemnity....................................................................49

   SECTION 7.08.   Replacement of Trustee........................................................................50

   SECTION 7.09.   Successor Trustee by Merger...................................................................51

   SECTION 7.10.   Eligibility; Disqualification.................................................................51

   SECTION 7.11.   Preferential Collection of Claims Against Issuer..............................................51

                                                     ARTICLE 8

                                              DISCHARGE OF INDENTURE

   SECTION 8.01.   Discharge of Liability on Securities..........................................................51

   SECTION 8.02.   Application of Trust Money....................................................................52

   SECTION 8.03.   Repayment to Issuer...........................................................................52

                                                     ARTICLE 9

                                                    AMENDMENTS

   SECTION 9.01.   Without Consent of Holders....................................................................52

   SECTION 9.02.   With Consent of Holders.......................................................................53

   SECTION 9.03.   Compliance with Trust Indenture Act...........................................................54

   SECTION 9.04.   Revocation and Effect of Consents and Waivers.................................................54

   SECTION 9.05.   Notation on or Exchange of Securities.........................................................55

   SECTION 9.06.   Trustee To Sign Amendments....................................................................55

                                                    ARTICLE 10

                                           SPECIAL TAX EVENT CONVERSION

   SECTION 10.01.   Optional Conversion to Semi-annual Coupon Note Upon Tax Event................................55

   SECTION 10.02.   Paying Agent To Hold Money in Trust..........................................................56

   SECTION 10.03.   Securityholder Lists.........................................................................56

   SECTION 10.04.   Payment of Interest; Interest Rights Preserved...............................................56

                                                    ARTICLE 11

                                                    CONVERSION

   SECTION 11.01.   Conversion Privilege.........................................................................58

   SECTION 11.02.   Conversion Procedure.........................................................................60

   SECTION 11.03.   Fractional Shares............................................................................61

   SECTION 11.04.   Taxes on Conversion..........................................................................61

   SECTION 11.05.   Company to Provide Stock.....................................................................61

   SECTION 11.06.   Adjustment for Change In Capital Stock.......................................................62

   SECTION 11.07.   Adjustment for Rights Issue..................................................................62

   SECTION 11.08.   Adjustment for Other Distributions...........................................................64

   SECTION 11.09.   When Adjustment May Be Deferred..............................................................65

   SECTION 11.10.   When No Adjustment Required..................................................................65

   SECTION 11.11.   Notice of Adjustment.........................................................................66

   SECTION 11.12.   Voluntary Increase...........................................................................66
</TABLE>

                                      iii
<PAGE>   5

                                TABLE OF CONTENTS

<TABLE>
<S>                                                                                                             <C>
   SECTION 11.13.   Notice of Certain Transactions...............................................................66

   SECTION 11.14.   Reorganization of Company; Special Distributions.............................................66

   SECTION 11.15.   Company Determination Final..................................................................67

   SECTION 11.16.   Trustee's Adjustment Disclaimer..............................................................67

   SECTION 11.17.   Simultaneous Adjustments.....................................................................67

   SECTION 11.18.   Successive Adjustments.......................................................................68

   SECTION 11.19.   Rights Issued in Respect of Common Stock Issued Upon Conversion..............................68

   SECTION 11.20.   Restriction on Common Stock Issued Upon Conversion...........................................68

                                                    ARTICLE 12

                                                   MISCELLANEOUS

   SECTION 12.01.   Trust Indenture Act Controls.................................................................69

   SECTION 12.02.   Notices......................................................................................69

   SECTION 12.03.   Communication by Holders with Other Holders..................................................70

   SECTION 12.04.   Certificate and Opinion as to Conditions Precedent...........................................70

   SECTION 12.05.   Statements Required in Certificate or Opinion................................................70

   SECTION 12.06.   When Securities Disregarded..................................................................71

   SECTION 12.07.   Rules by Trustee, Paying Agent and Registrar.................................................71

   SECTION 12.08.   Legal Holidays...............................................................................71

   SECTION 12.09.   Governing Law................................................................................71

   SECTION 12.10.   No Recourse Against Others...................................................................71

   SECTION 12.11.   Successors...................................................................................71

   SECTION 12.12.   Multiple Originals...........................................................................72

   SECTION 12.13.   Table of Contents;  Headings.................................................................72

   SECTION 12.14.   Severability.................................................................................72

EXHIBIT A: FORM OF SECURITY......................................................................................A-1
EXHIBIT B: FORM OF TRANSFER CERTIFICATE FOR TRANSFER
           FROM GLOBAL SECURITY OR DEFINITIVE SECURITY
           TO DEFINITIVE SECURITY................................................................................B-1
EXHIBIT C: FORM OF NON-DISTRIBUTION LETTER FOR
           INSTITUTIONAL ACCREDITED INVESTORS....................................................................C-1
EXHIBIT D: FORM OF PURCHASE NOTICE...............................................................................D-1
EXHIBIT E: FORM OF FUNDAMENTAL CHANGE REPURCHASE
           NOTICE................................................................................................E-1
EXHIBIT F: FORM OF TRANSFER CERTIFICATE FOR TRANSFER
           OF RESTRICTED COMMON STOCK............................................................................F-1
</TABLE>

                                       iv
<PAGE>   6

                  INDENTURE, dated as of February 7, 2001, by and between, ENRON
CORP., an Oregon corporation (the "Issuer" or the "Company"), and THE CHASE
MANHATTAN BANK, a New York banking corporation, as trustee (the "Trustee").

                  Each party agrees as follows for the benefit of the other
party and for the equal and ratable benefit of the Holders of the Issuer's Zero
Coupon Convertible Senior Notes due 2021 (the "Securities"):

                                    ARTICLE 1

                   DEFINITIONS AND INCORPORATION BY REFERENCE

                   SECTION 1.01. Definitions.

                  "Accreted Conversion Price" means with respect to a Security
per $1,000 of Principal Amount at Maturity, as of the date of determination, the
quotient of (i) the sum of the Issue Price plus Original Issue Discount accrued
to such date (or, if the Issuer has exercised its option to convert the
Securities to semi-annual coupon notes following the occurrence of a Tax Event,
the Restated Principal Amount) divided by (ii) the Conversion Rate in effect on
such date.

                  "Affiliate" of any specified Person means any other Person,
directly or indirectly, controlling or controlled by or under direct or indirect
common control with such specified Person. For the purposes of this definition,
"control" when used with respect to any Person means the power to direct the
management and policies of such Person, directly or indirectly, whether through
the ownership of voting securities, by contract or otherwise; and the terms
"controlling" and "controlled" have meanings correlative to the foregoing.

                  "Agent Members" has the meaning specified in Section 2.11.

                  "Average Quoted Price" has the meaning specified in Section
11.01.

                  "Board of Directors" means the Board of Directors of the
Issuer or any committee thereof duly authorized to act on behalf of the Board of
Directors of the Issuer.

                  "Business Day" means each day which is not a Legal Holiday.

                  "Capital Stock" of any Person means any and all shares,
interests, rights to purchase, warrants, options, participations or other
equivalents of or interests in (however designated) equity of such Person,
including any preferred stock, but excluding any debt securities convertible
into such equity.

                  "Clearstream" has the meaning specified in Section 2.01.

                  "Closing Date" means the date of this Indenture.

                  "Code" means the Internal Revenue Code of 1986, as amended.

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                  "Common Stock" means the shares of Common Stock of the Company
as it exists on the date of this Indenture or any other shares of Capital Stock
of the Company into which the Common Stock shall be reclassified or changed.

                  "Company" means Enron Corp., an Oregon corporation, until a
successor Person shall have become such pursuant to the applicable provisions of
this Indenture, and thereafter "Company" shall mean such successor Person and,
for purposes of any provision contained herein and required by the Trust
Indenture Act, each other obligor on the indenture securities.

                  "Consolidated Net Tangible Assets" means total assets less (a)
total current liabilities (excluding indebtedness due within 12 months) and (b)
goodwill, patents and trademarks, all as reflected in the Company's audited
consolidated balance sheet preceding the date of a determination under Section
4.06.

                  "Conversion Agent" means the Trustee or such other office or
agency designated by the Issuer where Securities may be presented for
conversion.

                  "Conversion Date" has the meaning specified in Section 11.02.

                  "Conversion Rate" has the meaning specified in Section 11.01.

                  "Corporate Trust Office" means the office of the Trustee
specified in Section 12.02.

                  "Default" means any event which is, or after notice or passage
of time or both would be, an Event of Default.

                  "Defaulted Interest" has the meaning specified in Section
10.04.

                  "Definitive Securities" has the meaning specified in Section
2.01.

                  "Depositary" means, with respect to the Securities issuable in
whole or in part in global form, the Person specified pursuant to Section 2.01
hereof as the initial Depositary with respect to the Securities, until a
successor shall have been appointed and become such pursuant to the applicable
provisions of this Indenture, and thereafter "Depositary" shall mean or include
such successor.

                  "Dollar" means a dollar or other equivalent unit in such coin
or currency of the United States as at the time shall be legal tender for the
payment of public and private debt.

                  "Euroclear" has the meaning specified in Section 2.01.

                  "Ex-Dividend Time" has the meaning specified in Section 11.01.

                  "Exchange Act" means the Securities Exchange Act of 1934, as
amended.

                  "Fundamental Change" has the meaning specified in Section
3.09.

                                       2
<PAGE>   8

                  "Fundamental Change Notice" has the meaning specified in
Section 3.09.

                  "Fundamental Change Notice Date" has the meaning specified in
Section 3.09.

                  "Fundamental Change Repurchase Date" has the meaning specified
in Section 3.09.

                  "Fundamental Change Repurchase Notice" has the meaning
specified in Section 3.09.

                  "Fundamental Change Repurchase Price" has the meaning
specified in Section 3.09.

                  "Funded Debt" as applied to any corporation means all
indebtedness incurred, created, assumed or guaranteed by such corporation, or
upon which it customarily pays interest charges, which matures, or is renewable
by such corporation to a date, more than one year after the date as of which
Funded Debt is being determined; provided, however, that the term "Funded Debt"
shall not include (i) indebtedness incurred in the ordinary course of business
representing borrowings, regardless of when payable, of such corporation from
time to time against, but not in excess of the face amount of, its installment
accounts receivable for the sale of appliances and equipment sold in the regular
course of business or (ii) advances for construction and security deposits
received by such corporation in the ordinary course of business.

                  "GAAP" means generally accepted accounting principles in the
United States of America as in effect from time to time, including those
principles set forth in (i) the opinions and pronouncements of the Accounting
Principles Board of the American Institute of Certified Public Accountants, (ii)
statements and pronouncements of the Financial Accounting Standards Board, (iii)
such other statements by such other entity as approved by a significant segment
of the accounting profession and (iv) the rules and regulations of the SEC
governing the inclusion of financial statements (including pro forma financial
statements) in periodic reports required to be filed pursuant to Section 13 of
the Exchange Act, including opinions and pronouncements in staff accounting
bulletins and similar written statements from the accounting staff of the SEC.
All computations based on GAAP contained in this Indenture shall be computed in
conformity with GAAP.

                  "Global Security" has the meaning specified in Section 2.01.

                  "Holder" or "Securityholder" means the Person in whose name a
Security is registered on the Registrar's books.

                  The term "indebtedness", as applied to the Company or any
Subsidiary, shall mean bonds, debentures, notes and other instruments
representing obligations created or assumed by any such corporation for the
repayment of money borrowed (other than unamortized debt discount or premium).
All indebtedness secured by a lien upon property owned by the Company or any
Subsidiary and upon which indebtedness any such corporation customarily pays
interest, although any such corporation has not assumed or become liable for the
payment of such indebtedness, shall for all purposes hereof be deemed to be
indebtedness of any such corporation. All indebtedness for money borrowed
incurred by other persons which is directly guaranteed as

                                       3
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to payment of principal by the Company or any Subsidiary shall for all purposes
hereof be deemed to be indebtedness of any such corporation, but no other
contingent obligation of any such corporation in respect of indebtedness
incurred by other persons shall for any purpose be deemed indebtedness of such
corporation. Indebtedness of the Company or any Subsidiary shall not include (i)
amounts which are payable only out of all or a portion of the oil, gas, natural
gas, helium, coal, metals, minerals, steam, timber or other natural resources
produced, derived or extracted from properties owned or developed by such
corporation; (ii) any amount representing capitalized lease obligations; (iii)
any indebtedness incurred to finance oil, gas natural gas, helium, coal, metal,
mineral, steam, timber, hydrocarbons, or geothermal or other natural resource or
synthetic fuel exploration or development, payable, with respect to principal
and interest, solely out of the proceeds of oil, gas, natural gas, helium, coal,
metals, minerals, steam, timber, hydrocarbons, or geothermal or other natural
resources or synthetic fuel to be produced, sold, and/or delivered by the
Company or any Subsidiary; (iv) indirect guarantees or other contingent
obligations in connection with the indebtedness of others, including agreements,
contingent or otherwise, with such other persons or with third persons with
respect to, or to permit or ensure the payment of, obligations of such other
persons, including, without limitation, agreements to purchase or repurchase
obligations of such other persons, agreements to advance or supply funds to or
to invest in such other persons, or agreements to pay for property, products, or
services of such other persons (whether or not conferred, delivered or
rendered), and any demand charge, throughput, take-or-pay, keep-well,
make-whole, cash deficiency, maintenance of working capital or earnings or
similar agreements; and (v) any guarantees with respect to lease or other
similar periodic payments to be made by other persons.

                  "Indenture" means this Indenture as amended or supplemented
from time to time and includes the terms of Securities established as
contemplated by Section 2.01.

                  "Initial Purchasers" means Salomon Smith Barney Inc., J.P.
Morgan Securities Inc., Deutsche Banc Alex. Brown Inc., Barclays Capital Inc.
and Banc of America Securities LLC.

                  "Interest Payment Date" has the meaning specified in Section
10.01.

                  "Issue Date" means the date the Securities are originally
issued or deemed issued as set forth on the face of the Security under this
Indenture.

                  "Issue Price" of any Security means, in connection with the
original issuance of such Security, the initial issue price as set forth on the
face of the Security.

                  "Issuer" means the party named as such in this Indenture until
a successor replaces it and, thereafter, means the successor and, for purposes
of any provision contained herein and required by the Trust Indenture Act, each
other obligor on the indenture securities.

                  "Issuer's Notice" has the meaning specified in Section 3.08.

                  "Issuer's Notice Date" has the meaning specified in Section
3.08.

                  "Market Price" has the meaning specified in Section 3.08.

                                       4
<PAGE>   10

                  "Maturity", when used with respect to any Security, means the
date on which the principal, Restated Principal Amount, Purchase Price or
Fundamental Change Repurchase Price of such Security becomes due and payable as
therein or herein provided, whether at the Stated Maturity, on a Redemption
Date, Purchase Date or Fundamental Change Repurchase Date, or by declaration of
acceleration or otherwise.

                  "Non-Global Purchasers" has the meaning specified in Section
2.01.

                  "Offering Memorandum" means the offering memorandum relating
to the Securities dated January 31, 2001.

                  "Officer" means the Chairman of the Board, the Chief Executive
Officer, the Chief Financial Officer, the President, any Vice President, the
Treasurer, an Assistant or Deputy Treasurer or the Secretary or an Assistant
Secretary of the Issuer.

                  "Officers' Certificate" means a certificate signed by two
Officers.

                  "Opinion of Counsel" means a written opinion from legal
counsel. The counsel may be an employee of or counsel to the Issuer or the
Trustee.

                  "Option Exercise Date" has the meaning specified in Section
10.01.

                  "Original Issue Discount" of any Security means the difference
between the Issue Price and the Principal Amount at Maturity of the Security as
set forth on the face of the Security, which shall accrue as set forth in the
form of Security.

                  "Person" means any individual, corporation, partnership,
limited liability company, joint venture, association, joint-stock company,
trust, unincorporated organization, government or any agency or political
subdivision thereof or any other entity.

                  "Principal Amount at Maturity" of a Security means the
Principal Amount at Maturity as set forth on the face of the Security.

                  "Principal Property" means any oil or gas pipeline, gas
processing plant or chemical plant located in the United States, except any such
property, pipeline or plant that in the opinion of the Board of Directors is not
of material importance to the total business conducted by the Company and its
Subsidiaries. "Principal Property" shall not include any oil or gas property or
the production or any proceeds of production from an oil or gas producing
property or the production or any proceeds of production of gas processing
plants or oil or gas or petroleum in any pipeline.

                  "Purchase Agreement" means the Purchase Agreement dated
January 31, 2001, among the Issuer and the Initial Purchasers.

                  "Purchase Date" has the meaning specified in Section 3.08.

                  "Purchase Notice" has the meaning specified in Section 3.08.

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<PAGE>   11

                  "Purchase Price" has the meaning specified in Section 3.08.

                  "QIBs" has the meaning specified in Section 2.01.

                  "Redemption Date" shall mean the date specified for redemption
of the Securities in accordance with the terms of the Securities and Article 3
hereof.

                  "Redemption Price" has the meaning specified in the
Securities.

                  "Registration Rights Agreement" means the Registration Rights
Agreement dated February 7, 2001, among the Issuer and the Initial Purchasers.

                  "Regular Record Date" has the meaning specified in Section
10.01.

                  "Regulation S" has the meaning specified in Section 2.01.

                  "Restated Principal Amount" has the meaning specified in
Section 10.01.

                  "Restricted Security" has the meaning specified in Section
2.15.

                  "Restricted Securities Legend" means the legend labeled as
such and that is set forth in Exhibit A hereto.

                  "Rights" has the meaning specified in Section 11.19.

                  "Rights Agreement" has the meaning specified in Section 11.19.

                  "Rule 144A" has the meaning specified in Section 2.01.

                  "Sale Price" has the meaning specified in Section 3.08.

                  "SEC" means the Securities and Exchange Commission.

                  "Securities" has the meaning specified in the second paragraph
of this Indenture.

                  "Securities Act" means the Securities Act of 1933, as amended.

                  "Securities Custodian" means the custodian with respect to a
Global Security (as appointed by the Depositary) or any successor thereto, who
shall initially be the Trustee.

                  "Shelf Registration" shall have the meaning set forth in the
Registration Rights Agreement.

                  "Special Record Date" has the meaning specified in Section
10.04.

                  "Stated Maturity," when used with respect to any Security,
means the date specified in such Security as the fixed date on which an amount
equal to the Principal Amount at Maturity of such Security is due and payable
or, if the Securities have been converted into semi-

                                       6
<PAGE>   12

annual coupon notes, the date specified in such Security as the fixed date on
which the Restated Principal Amount thereof or any installment of interest
thereon is due and payable.

                  "Subsidiary" of any Person means any corporation, association,
partnership or other business entity of which more than 50% of the total voting
power of shares of Capital Stock or other interests (including partnership
interests) entitled (without regard to the occurrence of any contingency) to
vote in the election of directors, managers or trustees thereof is at the time
owned or controlled, directly or indirectly, by (i) such Person, (ii) such
Person and one or more Subsidiaries of such Person or (iii) one or more
Subsidiaries of such Person; provided, however, for purposes of Sections 4.04
and 4.06 of this Indenture (including all defined terms used in such Sections),
"Subsidiary" means a corporation all of the voting shares (that is, shares
entitled to vote for the election of directors, but excluding shares entitled so
to vote only upon the happening of some contingency unless such contingency
shall have occurred) of which shall be owned by the Company or by one or more
Subsidiaries or by the Company and one or more Subsidiaries.

                  "Tax Event" means that the Issuer shall have received an
opinion from independent tax counsel experienced in such matters to the effect
that, on or after January 31, 2001, as a result of (a) any amendment to, or
change (including any announced prospective change) in, the laws, rules or any
regulations thereunder of the United States or any political subdivision or
taxing authority thereof or therein or (b) any amendment to, or change in, an
interpretation or application of such laws, rules or regulations by any
legislative body, court, governmental agency or regulatory authority, in each
case which amendment or change is enacted, promulgated, issued or announced or
which interpretation is issued or announced or which action is taken, on or
after January 31, 2001, there is more than an insubstantial risk that interest
(including Original Issue Discount) payable on the Securities either (i) would
not be deductible on a current accrual basis or (ii) would not be deductible
under any other method, in either case in whole or in part, by the Issuer (by
reason of deferral, disallowance, or otherwise) for United States Federal income
tax purposes.

                  "Tax Event Date" has the meaning specified in Section 10.01.

                  "Trust Indenture Act" means the Trust Indenture Act of 1939
(15 U.S.C. Sections 77aaa-77bb in effect on the Closing Date.

                  "Time of Determination" has the meaning specified in Section
11.01.

                  "Trustee" means the party named as such in this Indenture
until a successor replaces it and, thereafter, means the successor.

                  "Trust Officer" means any Vice President, Assistant Vice
President or any other officer or assistant officer of the Trustee assigned by
the Trustee to administer its corporate trust matters.

                  "Uniform Commercial Code" means the New York Uniform
Commercial Code as in effect from time to time.

                                       7
<PAGE>   13

                  SECTION 1.02. Other Definitions.

<TABLE>
<CAPTION>
                 TERM                                             DEFINED IN SECTION
<S>                                                                      <C>
                 "Acquired Entity"                                       4.04(l)
                 "Bankruptcy Law"                                        6.01
                 "Custodian"                                             6.01
                 "Event of Default"                                      6.01
                 "Extraordinary Cash Dividend"                          11.08
                 "Legal Holiday"                                        12.08
                 "Measurement Period"                                   11.08
                 "Notice of Default"                                     6.01
                 "Paying Agent"                                          2.06
                 "protected purchaser"                                   2.08
                 "Registrar"                                             2.06
                 "Relevant Cash Dividends"                              11.08
                 "Successor Company"                                     5.01(a)
                 "trading day"                                          11.01

</TABLE>

                  SECTION 1.03. Incorporation by Reference of Trust Indenture
Act. This Indenture is subject to the mandatory provisions of the Trust
Indenture Act, which are incorporated by reference in and made a part of this
Indenture. The following Trust Indenture Act terms have the following meanings:

                  "Commission" means the SEC.

                  "indenture securities" means the Securities.

                  "indenture security holder" means a Holder or Securityholder.

                  "indenture to be qualified" means this Indenture.

                  "indenture trustee" or "institutional trustee" means the
Trustee.

                  "obligor" on the indenture securities means the Issuer and any
other obligor on the indenture securities.

                  All other terms used in this Indenture that are defined by the
Trust Indenture Act, defined by Trust Indenture Act reference to another statute
or defined by SEC rule have the meanings assigned to them by such definitions.

                  SECTION 1.04. Rules of Construction.

Unless the context otherwise requires:

                  (1) a term has the meaning assigned to it;

                                       8
<PAGE>   14

                  (2) an accounting term not otherwise defined has the meaning
         assigned to it in accordance with GAAP;

                  (3) "or" is not exclusive;

                  (4) "including" means including without limitation;

                  (5) words in the singular include the plural and words in the
         plural include the singular; and

                  (6) the principal amount of any non-interest bearing or other
         discount security at any date shall be the principal amount thereof
         that would be shown on a balance sheet of the issuer dated such date
         prepared in accordance with GAAP.

                                   ARTICLE 2

                                 THE SECURITIES

                  SECTION 2.01. Form of Securities. The Securities and the
Trustee's certificate of authentication shall be substantially in the form of
Exhibit A which is hereby incorporated in and expressly made a part of this
Indenture.

                  The Securities offered and sold (i) in reliance on Regulation
S under the Securities Act ("Regulation S") or (ii) to "qualified institutional
buyers" as defined in Rule 144A ("QIBs") in reliance on Rule 144A under the
Securities Act ("Rule 144A"), each as provided in the Purchase Agreement, shall
be issued in the form of one or more permanent global securities in definitive,
fully registered form without interest coupons with the Global Securities Legend
and Restricted Securities Legend set forth in Exhibit A hereto (each, a "Global
Security"). Any Global Security shall be deposited on behalf of the purchasers
of the Securities represented thereby with the Trustee, as custodian for the
Depositary, and registered in the name of the Depositary or a nominee of the
Depositary for the accounts of participants in the Depositary (and, in the case
of Securities held in accordance with Regulation S, registered with the
Depositary for the accounts of designated agents holding on behalf of the
Euroclear System ("Euroclear") or Clearstream Banking, societe anonyme
("Clearstream")), duly executed by the Company and authenticated by the Trustee
as hereinafter provided. The aggregate principal amount of a Global Security may
from time to time be increased or decreased by adjustments made on the records
of the Trustee and the Depositary or its nominee as hereinafter provided.

                  Except as provided in Section 2.10 and 2.13, owners of
beneficial interests in Global Securities will not be entitled to receive
physical delivery of Securities in definitive form. Transferees of Securities
who are not QIBs and did not purchase Securities sold in reliance on Regulation
S under the Securities Act (referred to herein as the "Non-Global Purchasers")
will receive certificated Securities in definitive form bearing the Restricted
Securities Legend set forth in Exhibit A hereto ("Definitive Securities").
Definitive Securities will bear the Restricted Securities Legend set forth on
Exhibit A unless removed in accordance with Section 2.13(b).

                  SECTION 2.02. Title and Terms. The aggregate Principal Amount
at Maturity of Securities which may be authenticated and delivered under this
Indenture is limited to

                                       9
<PAGE>   15

$1,907,698,000 (subject to increase by up to $381,540,000 in the event the
Initial Purchasers exercise the over-allotment option under the Purchase
Agreement), except for replacement Securities authenticated and delivered upon
registration or transfer of, or in exchange for, or in lieu of, other Securities
pursuant to Section 2.08.

                  The Securities shall be known and designated as the "Zero
Coupon Convertible Senior Notes due 2021" of the Issuer with a Stated Maturity
on February 7, 2021.

                  The Issue Price and Original Issue Discount accrued on the
Securities shall be payable at (i) the office or agency of the Company in The
City of New York maintained for such purpose, which initially shall be the
principal corporate trust office of the Trustee in The City of New York, (ii)
the Corporate Trust Office and (iii) at any other office or agency maintained by
the Issuer for such purpose; provided, however, that at the option of the Issuer
payments may be made by wire transfer or by check mailed to the address of the
Person entitled thereto as such address shall appear in the Security Register.

                  The Securities shall not have the benefit of a sinking fund.

                  The Securities shall not be superior in right of payment to,
and shall rank pari passu with, all other unsubordinated indebtedness of the
Issuer.

                  SECTION 2.03. Denominations. The Securities shall be issuable
only in registered form without coupons and in denominations of $1,000 Principal
Amount at Maturity and any integral multiple of $1,000 above that amount.

                  SECTION 2.04. Forms Generally.The Securities may have such
letters, notations, numbers or other marks of identification and such legends or
endorsements placed thereon as may be required by law, securities exchange rule,
the Code and regulations thereunder, agreements to which the Issuer is subject,
if any, or usage (provided that any such notation legend or endorsement is in a
form acceptable to the Issuer). Each Security shall be dated the date of its
authentication.

                  The definitive Securities shall be printed, lithographed or
engraved on steel engraved borders or may be produced in any other manner, all
as determined by the Officers executing such Securities, as evidenced by their
execution thereof.

                  SECTION 2.05. Execution, Authentication and Delivery. One or
more Officers of the Issuer shall sign the Securities on behalf of the Issuer by
manual or facsimile signature. The Issuer's seal, if any, may, but need not, be
impressed, affixed, imprinted or reproduced on the Securities and, if it is,
then it may be in facsimile form.

                  If an Officer of the Issuer whose signature is on a Security
no longer holds that office at the time the Trustee authenticates the Security,
the Security shall be valid nevertheless.

                  A Security shall not be valid until an authorized signatory of
the Trustee manually signs the certificate of authentication on the Security.
The signature shall be conclusive evidence that the Security has been
authenticated under this Indenture.

                                       10
<PAGE>   16

                  The Trustee may appoint an authenticating agent reasonably
acceptable to the Issuer to authenticate the Securities. Any such appointment
shall be evidenced by an instrument signed by a Trust Officer, a copy of which
shall be furnished to the Issuer. Unless limited by the terms of such
appointment, an authenticating agent may authenticate Securities whenever the
Trustee may do so. Each reference in this Indenture to authentication by the
Trustee includes authentication by such agent. An authenticating agent has the
same rights as any Registrar, Paying Agent or agent for service of notices and
demands.

                  SECTION 2.06. Registrar and Paying Agent. The Issuer shall
maintain an office or agency where Securities may be presented for registration
of transfer or for exchange (the "Registrar") and an office or agency where
Securities may be presented for payment (the "Paying Agent"). The Registrar
shall keep a register of the Securities and of their transfer and exchange. The
Issuer may have one or more co-registrars and one or more additional paying
agents. The term "Paying Agent" includes any additional paying agent, and the
term "Registrar" includes any co-registrars. The Issuer initially appoint the
Trustee as (i) Registrar and Paying Agent in connection with the Securities and
(ii) the Securities Custodian with respect to the Global Securities.

                  The Issuer shall enter into an appropriate agency agreement
with any Registrar or Paying Agent not a party to this Indenture, which shall
incorporate the terms of the Trust Indenture Act. The agreement shall implement
the provisions of this Indenture that relate to such agent. The Issuer shall
notify the Trustee of the name and address of any such agent. If the Issuer
fails to maintain a Registrar or Paying Agent, the Trustee shall act as such and
shall be entitled to appropriate compensation therefor pursuant to Section 7.07.
The Issuer or any of its domestically organized Subsidiaries may act as Paying
Agent or Registrar.

                  The Issuer may remove any Registrar or Paying Agent upon
written notice to such Registrar or Paying Agent and to the Trustee; provided,
however, that no such removal shall become effective until (1) acceptance of an
appointment by a successor as evidenced by an appropriate agreement entered into
by the Issuer and such successor Registrar or Paying Agent, as the case may be,
and delivered to the Trustee or (2) notification to the Trustee that the Trustee
shall serve as Registrar or Paying Agent until the appointment of a successor in
accordance with clause (1) above. The Registrar or Paying Agent may resign at
any time upon written notice; provided, however, that the Trustee may resign as
Paying Agent or Registrar only if the Trustee also resigns as Trustee in
accordance with Section 7.08.

                  SECTION 2.07. Transfer and Exchange. The Securities shall be
issued in registered form and shall be transferable only upon the surrender of a
Security for registration of transfer and in compliance with this Indenture.
When a Security is presented to the Registrar with a request to register a
transfer, the Registrar shall register the transfer as requested if the
requirements of Section 8-401(a)(1) of the Uniform Commercial Code are met. When
Securities are presented to the Registrar with a request to exchange them for
Securities of other denominations and of a like aggregate Principal Amount at
Maturity and tenor, the Registrar shall make the exchange as requested if the
same requirements are met. To permit registration of transfers and exchanges,
the Issuer shall execute and the Trustee shall authenticate Securities at the
Registrar's request. The Issuer may require payment of a sum sufficient to pay
all taxes, assessments or other governmental charges in connection with any such
transfer or exchange

                                       11
<PAGE>   17

pursuant to this Section. The Issuer shall not be required to make and the
Registrar need not register transfers or exchanges of Securities selected for
redemption (except, in the case of Securities to be redeemed in part, the
portion thereof not to be redeemed) or any Securities for a period of 15 days
before a selection of Securities to be redeemed.

                  Prior to the due presentation for registration of transfer of
any Security, the Issuer, the Trustee, the Paying Agent and the Registrar may
deem and treat the Person in whose name a Security is registered as the absolute
owner of such Security for the purpose of receiving any payment on such Security
(including interest, if the Securities have been converted into semi-annual
coupon notes) and for all other purposes whatsoever, whether or not such
Security is overdue, and none of the Issuer, the Trustee, the Paying Agent or
the Registrar shall be affected by notice to the contrary.

                  Any Holder of a Global Security shall, by acceptance of such
Global Security, agree that transfers of beneficial interest in such Global
Security may be effected only through a book-entry system maintained by (i) the
Holder of such Global Security (or its agent) or (ii) any Holder of a beneficial
interest in such Global Security, and that ownership of a beneficial interest in
such Global Security shall be required to be reflected in a book entry.

                  All Securities issued upon any transfer or exchange pursuant
to the terms of this Indenture will evidence the same debt and will be entitled
to the same benefits under this Indenture as the Securities surrendered upon
such transfer or exchange.

                  SECTION 2.08. Replacement Securities. If a mutilated Security
is surrendered to the Registrar or if the Holder of a Security claims that the
Security has been lost, destroyed or wrongfully taken, the Issuer shall issue
and the Trustee shall authenticate a replacement Security if the requirements of
Section 8-405 of the Uniform Commercial Code are met, such that the Holder (i)
satisfies the Issuer or the Trustee within a reasonable time after such Holder
has notice of such loss, destruction or wrongful taking, and the Registrar does
not register a transfer prior to receiving such notification, (ii) requests the
Issuer or the Trustee to issue a new replacement Security, prior to the Security
being acquired by a protected purchaser as defined in Section 8-303 of the
Uniform Commercial Code (a "protected purchaser") and (iii) satisfies any other
reasonable requirements of the Trustee. If required by the Trustee or the
Issuer, such Holder shall furnish an indemnity bond sufficient in the judgment
of the Trustee to protect the Issuer, the Trustee, the Paying Agent and the
Registrar from any loss that any of them may suffer if a Security is replaced.
The Issuer and the Trustee may charge the Holder for the expenses they incur in
replacing a Security. In the event any such mutilated, lost, destroyed or
wrongfully taken Security has become or is about to become due and payable or
has been called for redemption in full, the Issuer in its discretion may pay
such Security instead of issuing a new Security in replacement thereof.

                  Every replacement Security is an additional obligation of the
Issuer.

                  The provisions of this Section 2.08 are exclusive and shall
preclude (to the extent lawful) all other rights and remedies with respect to
the replacement or payment of mutilated, lost, destroyed or wrongfully taken
Securities.

                                       12
<PAGE>   18

                  SECTION 2.09. Outstanding Securities. Securities outstanding
at any time are all Securities authenticated by the Trustee except for those
canceled by it, those delivered to it for cancellation and those described in
this Section as not outstanding. Subject to Section 12.06, a Security does not
cease to be outstanding because the Issuer or an Affiliate of the Issuer holds
the Security.

                  If a Security is replaced pursuant to Section 2.08, the
Security so replaced ceases to be outstanding unless and until the Trustee and
the Issuer receive proof satisfactory to them that the replaced Security is held
by a protected purchaser.

                  If the Paying Agent segregates and holds in trust, in
accordance with this Indenture, at Maturity, money or securities sufficient to
pay all amounts payable on that date with respect to the Securities (or portions
thereof) to be redeemed, purchased or repurchased or maturing, as the case may
be, then on and after that date, such Securities (or portions thereof) shall
cease to be outstanding and Original Issue Discount (or interest, if the
Securities have been converted into semi-annual coupon notes following the
occurrence of a Tax Event) on them shall cease to accrue.

                  SECTION 2.10. Temporary Securities; Exchange of Global
Security for Definitive Securities.

                  (a) In the event that Definitive Securities are to be issued
under the terms of this Indenture, until such Definitive Securities are ready
for delivery, the Issuer may prepare and the Trustee shall authenticate
temporary Securities. Temporary Securities shall be substantially in the form of
Definitive Securities but may have variations that the Issuer consider
appropriate for temporary Securities. Without unreasonable delay, the Issuer
shall prepare and the Trustee shall authenticate Definitive Securities and
deliver them in exchange for temporary Securities upon surrender of such
temporary Securities at the office or agency of the Issuer, without charge to
the Holder.

                  (b) Except for transfers made in accordance with Section
2.13(a), a Global Security deposited with the Depositary or with the Trustee as
custodian for the Depositary pursuant to Section 2.11 shall be transferred to
the beneficial owners thereof in the form of certificated Securities in
definitive form only if such transfer complies with Section 2.13 and (i) the
Depositary notifies the Issuer that it is unwilling or unable to continue as
Depositary for such Global Security or if at any time such Depositary ceases to
be a "clearing agency" registered under the Exchange Act and a successor
Depositary is not appointed by the Issuer within 90 days of such notice, or (ii)
the Issuer so elects.

                  (c) Any Global Security or interest thereon that is
transferable to the beneficial owners thereof in the form of certificated
Securities in definitive form shall, if held by the Depository, be surrendered
by the Depositary to the Trustee, without charge, and the Trustee shall
authenticate and deliver, upon such transfer of each portion of such Global
Security, an equal aggregate principal amount of Securities of authorized
denominations in the form of certificated Securities in definitive form. Any
portion of a Global Security transferred pursuant to this Section shall be
executed, authenticated and delivered only in denominations of $1,000 and any
integral multiple thereof and registered in such names as the Depositary shall
direct.

                                       13
<PAGE>   19

Any Securities in the form of certificated Securities in definitive form
delivered in exchange for an interest in the Global Security shall, except as
otherwise provided by Section 2.13(b), bear the Restricted Securities Legend set
forth in Exhibit A hereto.

                  (d) Prior to any transfer pursuant to Section 2.10(b), the
registered holder of a Global Security may grant proxies and otherwise authorize
any Person, including Agent Members and Persons that may hold interests through
Agent Members, to take any action which a holder is entitled to take under this
Indenture or the Securities.

                  The Issuer will make available to the Trustee a reasonable
supply of certificated Securities in definitive form.

                  SECTION 2.11. Book-entry Provisions for Global Securities.
This Section 2.11 shall apply only to a Global Security deposited with or on
behalf of the Depositary.

                  The Issuer shall execute and the Trustee shall, in accordance
with this Section 2.11 and the written order of the Issuer, authenticate and
deliver initially one or more Global Securities that (i) shall be registered in
the name of Cede & Co. or other nominee of such Depositary and (ii) shall be
delivered by the Trustee to such Depositary or pursuant to such Depositary's
instructions or held by the Trustee as custodian for the Depositary pursuant to
a FAST Balance Certificate Agreement between the Depositary and the Trustee.

                  Members of, or participants in, the Depositary ("Agent
Members") shall have no rights under this Indenture with respect to any Global
Security held on their behalf by the Depositary or by the Trustee as the
custodian of the Depositary or under such Global Security, and the Depositary
may be treated by the Issuer, the Trustee and any agent of the Issuer or the
Trustee as the absolute owner of such Global Security for all purposes
whatsoever. Notwithstanding the foregoing, nothing herein shall prevent the
Issuer, the Trustee or any agent of the Issuer or the Trustee from giving effect
to any written certification, proxy or other authorization furnished by the
Depositary or impair, as between the Depositary and its Agent Members, the
operation of customary practices of such Depositary governing the exercise of
the rights of a holder of a beneficial interest in any Global Security.

                  The provisions of the "Operating Procedures of the Euroclear
System" and "Terms and Conditions Governing Use of Euroclear" and the
"Management Regulations and Instructions to Participants" of Clearstream shall
be applicable to interests in any Global Securities that are held by
participants through Euroclear or Clearstream. The Trustee shall have no
obligation to notify holders of any such procedures or to monitor or enforce
compliance with the same.

                  SECTION 2.12. Cancellation. The Issuer at any time may deliver
Securities to the Trustee for cancellation. The Registrar and the Paying Agent
shall forward to the Trustee any Securities surrendered to them for registration
of transfer, exchange or payment. The Trustee and no one else shall cancel all
Securities surrendered for registration of transfer, exchange, payment,
purchase, repurchase, redemption, conversion (pursuant to Article 11 hereof) or
cancellation and deliver canceled Securities to the Issuer pursuant to written
direction by an Officer of the Issuer. In the absence of any such direction, the
Trustee may treat canceled

                                       14
<PAGE>   20

Securities in accordance with its document retention policies. The Issuer may
not issue new Securities to replace Securities they have redeemed, paid in full
or delivered to the Trustee for cancellation. The Trustee shall not authenticate
Securities in place of canceled Securities other than pursuant to the terms of
this Indenture.

                  SECTION 2.13. Special Transfer Provisions. (a) Notwithstanding
any provision to the contrary herein, so long as a Global Security remains
outstanding and is held by or on behalf of the Depositary, transfers of a Global
Security, in whole or in part, or of any beneficial interest therein, shall only
be made in accordance with Sections 2.10 and 2.11 and this Section 2.13(a);
provided, however, that beneficial interests in a Global Security may be
transferred to Persons who take delivery thereof in the form of a beneficial
interest in the Global Security in accordance with the transfer restrictions set
forth under the heading "Notice to Investors" in the Offering Memorandum and, if
applicable, in Exhibit C.

                  Except for transfers or exchanges made in accordance with
paragraphs (1) through (4) of this Section 2.13(a) and Section 2.10, transfers
of a Global Security shall be limited to transfers of such Global Security in
whole, but not in part, to nominees of the Depositary or to a successor of the
Depositary or such successor's nominee.

                  (1) Global Security to Definitive Security. If an owner of a
         beneficial interest in a Global Security deposited with the Depositary
         or with the Trustee as custodian for the Depositary wishes at any time
         to transfer its interest in such Global Security to a Person who is
         required to take delivery thereof in the form of a Definitive Security,
         such owner may, subject to the rules and procedures of Euroclear or
         Clearstream, if applicable, and the Depositary, cause the exchange of
         such interest for one or more Definitive Securities of any authorized
         denomination or denominations and of the same aggregate principal
         amount. Upon receipt by the Registrar of (A) instructions from
         Euroclear or Clearstream, if applicable, and the Depositary directing
         the Trustee to authenticate and deliver one or more Definitive
         Securities of the same aggregate principal amount as the beneficial
         interest in the Global Security to be exchanged, such instructions to
         contain the name or names of the designated transferee or transferees,
         the authorized denomination or denominations of the Definitive
         Securities to be so issued and appropriate delivery instructions, (B) a
         certificate substantially in the form of Exhibit B attached hereto
         given by the owner of such beneficial interest, (C) a certificate
         substantially in the form of Exhibit C attached hereto given by the
         person acquiring the Definitive Securities for which such interest is
         being exchanged, to the effect set forth therein, and (D) such other
         certifications or other information and, in the case of transfers
         pursuant to Rule 144 under the Securities Act, legal opinions as the
         Issuer may reasonably require to confirm that such transfer is being
         made pursuant to an exemption from, or in a transaction not subject to,
         the registration requirements of the Securities Act, then Euroclear or
         Clearstream, if applicable, or the Registrar, as the case may be, will
         instruct the Depositary to reduce or cause to be reduced such Global
         Security by the aggregate principal amount of the beneficial interest
         therein to be exchanged and to debit or cause to be debited from the
         account of the Person making such transfer the beneficial interest in
         the Global Security that is being transferred, and concurrently with
         such reduction and debit the Company shall execute, and the Trustee
         shall authenticate and deliver, one or more Definitive

                                       15
<PAGE>   21

         Securities of the same aggregate principal amount in accordance with
         the instructions referred to above.

                  (2) Definitive Security to Definitive Security. If a holder of
         a Definitive Security wishes at any time to transfer such Definitive
         Security (or portion thereof) to a Person who is required to take
         delivery thereof in the form of a Definitive Security, such holder may,
         subject to the restrictions on transfer set forth herein and in such
         Definitive Security, cause the transfer of such Definitive Security (or
         any portion thereof in a principal a mount equal to an authorized
         denomination) to such transferee. Upon receipt by the Registrar of (A)
         such Definitive Security, duly endorsed as provided herein, (B)
         instructions from such holder directing the Trustee to authenticate and
         deliver one or more Definitive Securities of the same aggregate
         principal amount as the Definitive Security (or portion thereof) to be
         transferred, such instruction as to contain the name or names of the
         designated transferee or transferees, the authorized denomination or
         denominations of the Definitive Securities to be so issued and
         appropriate delivery instructions, (C) a certificate from the holder of
         the Definitive Security to be transferred in substantially the form of
         Exhibit B attached hereto, (D) a certificate substantially in the form
         of Exhibit C attached hereto given by the person acquiring the
         Definitive Securities (or portion thereof), to the effect set forth
         therein, and (E) such other certifications or other information and, in
         the case of transfers pursuant to Rule 144 under the Securities Act,
         legal opinions as the Issuer may reasonably require to confirm that
         such transfer is being made pursuant to an exemption from, or in a
         transaction not subject to, the registration requirements of the
         Securities Act, then the Registrar, shall cancel or cause to be
         canceled such Definitive Security and concurrently therewith, the
         Issuer shall execute, and the Trustee shall authenticate and deliver,
         one or more Definitive Securities in the appropriate aggregate
         principal amount, in accordance with the instructions referred to above
         and, if only a portion of a Definitive Security is transferred as
         aforesaid, concurrently therewith the Issuer shall execute and the
         Trustee shall authenticate and deliver to the transferor a Definitive
         Security in a principal amount equal to the principal amount which has
         not been transferred. A holder of a Definitive Security may at any time
         exchange such Definitive Security for one or more Definitive Securities
         of other authorized denominations and in the same aggregate principal
         amount and registered in the same name by delivering such Definitive
         Security, duly endorsed as provided herein, to the Trustee together
         with instructions directing the Trustee to authenticate and deliver one
         or more Definitive Securities in the same aggregate principal amount
         and registered in the same name as the Definitive Security to be
         exchanged, and the Registrar thereupon shall cancel or caused to be
         canceled such Definitive Security and concurrently therewith the Issuer
         shall execute and Trustee shall authenticate and deliver, one or more
         Definitive Securities in the same aggregate principal amount and
         registered in the same name as the Definitive Security being exchanged.

                  (3) Definitive Security to Global Security. If a holder of a
         Definitive Security wishes at any time to transfer such Definitive
         Security (or portion thereof) to a Person who is not required to take
         delivery thereof in the form of a Definitive Security, such holder
         shall, subject to the restrictions on transfer set forth herein and in
         such Definitive Security and the rules of the Depositary and Euroclear
         and Clearstream, as applicable, cause the exchange of such Definitive
         Security for a beneficial interest in the Global

                                       16
<PAGE>   22

         Security. Upon receipt by the Registrar of (A) such Definitive
         Security, duly endorsed as provided herein, (B) instructions from such
         holder directing the Trustee to increase the aggregate principal amount
         of the Global Security deposited with the Depository or with the
         Trustee as custodian for the Depository by the same aggregate Principal
         Amount at Maturity as the Definitive Security to be exchanged, such
         instructions to contain the name or names of a member of, or
         participant in, the Depository that is designated as the transferee,
         the account of such member or participant and other appropriate
         delivery instructions, (C) the assignment form on the back of the
         Definitive Security completed in fall (certifying in effect that such
         transfer complies with Rule 144A or Regulation S under the Securities
         Act or is otherwise being made to a Person who is not required to take
         delivery of the Securities in the form of a Definitive Security) and
         (D) such other certifications or other information and, in the case of
         transfers pursuant to Rule 144 under the Securities Act, legal opinions
         as the Issuer may reasonably require to confirm that such transfer is
         being made pursuant to an exemption from, or in transaction not subject
         to, the registration requirements of the Securities Act, then the
         Trustee shall cancel or cause to be canceled such Definitive Security
         and concurrently therewith shall increase the aggregate principal
         amount of the Global Security by the same aggregate principal amount as
         the Definitive Security canceled.

                  (4) Other Exchanges. In the event that a Global Security is
         exchanged for Securities in definitive registered form pursuant to
         Section 2.10 prior to the effectiveness of a Shelf Registration with
         respect to such Securities, such Securities may be exchanged only in
         accordance with such procedures as are substantially consistent with
         the provisions of clauses (2) and (3) above (including the
         certification requirements intended to ensure that such transfers
         comply with Rule 144A or Regulation S under the Securities Act, as the
         case may be) and such other procedures as may from time to time be
         adopted by the Issuer.

                  (b) Except in connection with a Shelf Registration
contemplated by and in accordance with the terms of the Registration Rights
Agreement, if Securities are issued upon the registration of transfer, exchange
or replacement of Securities bearing a Restricted Securities Legend, or if a
request is made to remove such a Restrictive Securities Legend on Securities,
the Securities so issued shall bear the Restricted Securities Legend, or a
Restricted Securities Legend shall not be removed, as the case may be, unless
there is delivered to the Issuer such satisfactory evidence, which, in the case
of a transfer made pursuant to Rule 144 under the Securities Act, may include an
opinion of counsel, as may be reasonably required by the Issuer, that neither
the legend nor the restrictions on transfer set forth therein are required to
ensure that transfers thereof comply with the provisions of Rule 144A, Rule 144
or Regulation S under the Securities Act or that such Securities are not
"restricted" within the meaning of Rule 144 under the Securities Act. Upon
provision to the Issuer of such satisfactory evidence, the Trustee, at the
written direction of the Issuer, shall authenticate and deliver Securities that
do not bear the legend. The Issuer shall not otherwise be entitled to require
the delivery of a legal opinion in connection with any transfer or exchange of
Securities.

                  (c) Neither the Trustee nor any Agent shall have any
responsibility for any actions taken or not taken by the Depositary.

                                       17
<PAGE>   23

                  (d) The Trustee shall have no obligation or duty to monitor,
determine or inquire as to compliance with any restrictions on transfer imposed
under this Indenture or under applicable law with respect to any transfer of any
interest in any Securities (including any transfers between or among
Depositary's participants or beneficial owners of interests in any Global
Security) other than to require delivery of such certificates and other
documentation as is expressly required by, and to do so if and when expressly
required by, the terms of this Indenture and to examine the same to determine
substantial compliance as to form with the express requirements hereof.

                  SECTION 2.14. CUSIP Numbers. The Issuer in issuing the
Securities may use "CUSIP" numbers (if then generally in use) and, if so, the
Trustee shall use "CUSIP" numbers in notices of redemption as a convenience to
Holders; provided, however, that any such notice may state that no
representation is made as to the correctness of such numbers either as printed
on the Securities or as contained in any notice of a redemption and that
reliance may be placed only on the other identification numbers printed on the
Securities and any such redemption shall not be affected by any defect in or
omission of such numbers.

                  SECTION 2.15. Legend on Restricted Securities. During the
period beginning on February 7, 2001 (or such later date on which any Securities
may be originally issued pursuant to the Initial Purchasers' exercise of the
over-allotment option under the Purchase Agreement) and ending on the date two
years from such date, any Security including any Security issued in exchange
therefor or in lieu thereof, shall be deemed a "Restricted Security" and shall
be subject to the restrictions on transfer provided in the legends set forth on
the face of the form of Security in Exhibit A; provided, however, that the term
"Restricted Security" shall not include any Securities as to which restrictions
have been terminated in accordance with the terms of this Indenture. All
Securities shall bear the applicable legends set forth on the face of the form
of Security in Exhibit A. Except as provided in Section 2.13, the Trustee shall
not issue any unlegended Security until it has received an Officers' Certificate
from the Issuer directing it to do so.

                                   ARTICLE 3

                                   REDEMPTION

                  SECTION 3.01. Notices to Trustee. Prior to February 7, 2004,
Securities shall not be redeemable. Beginning on February 7, 2004, the Issuer,
at its option, may elect to redeem Securities in accordance with the provisions
thereof and of this Indenture. If the Issuer elects to redeem Securities, it
shall notify the Trustee in writing of the Redemption Date, the Principal Amount
at Maturity of Securities to be redeemed and the Redemption Price.

                  The Issuer shall give each notice to the Trustee provided for
in this Section at least 45 days before the Redemption Date unless the Trustee
consents to a shorter period. Such notice shall be accompanied by an Officers'
Certificate from the Issuer to the effect that such redemption will comply with
the conditions herein. If fewer than all the Securities are to be redeemed, the
record date relating to such redemption shall be selected by the Issuer and
given to the Trustee, which record date shall be not fewer than 15 days after
the date of notice to the

                                       18
<PAGE>   24

Trustee. Any such notice may be canceled at any time prior to notice of such
redemption being mailed to any Holder and shall thereby be void and of no
effect.

                  SECTION 3.02. Selection of Securities To Be Redeemed. If fewer
than all the Securities held in definitive form are to be redeemed, the Trustee
shall select the Securities to be redeemed pro rata or by lot or by a method
that complies with applicable legal and securities exchange requirements, if
any, and that the Trustee in its sole discretion shall deem to be fair and
appropriate and in accordance with methods generally used at the time of
selection by fiduciaries in similar circumstances. The Trustee shall make the
selection at least 30 days but no more than 60 days before the Redemption Date
from outstanding Securities not previously called for redemption. Securities and
portions thereof that the Trustee selects shall be in Principal Amounts at
Maturity of $1,000 or integral multiples of $1,000. Provisions of this Indenture
that apply to Securities called for redemption also apply to portions of
Securities called for redemption. The Trustee shall promptly notify the Issuer
of the Securities or portions thereof to be redeemed.

                  If any Security selected for partial redemption is converted
in part before termination of the conversion right with respect to the portion
of the Security so selected, the converted portion of such Security shall be
deemed (so far as may be) to be the portion selected for redemption. Securities
which have been converted during a selection of Securities to be redeemed shall
be treated by the Trustee as outstanding for the purpose of such selection.

                  SECTION 3.03. Notice of Redemption. At least 30 days but not
more than 60 days before a Redemption Date of Securities, the Issuer shall mail
a notice of redemption by first-class mail to each Holder of Securities to be
redeemed at such Holder's registered address.

                  The notice shall identify the Securities to be redeemed and
shall state:

                  (1) the Redemption Date;

                  (2) the Redemption Price and the Conversion Rate;

                  (3) the name and address of the Paying Agent and Conversion
         Agent;

                  (4) that Securities called for redemption must be surrendered
         to the Paying Agent to collect the Redemption Price;

                  (5) that Securities called for redemption may be converted at
         any time before the close of business on the Business Day immediately
         preceding the Redemption Date;

                  (6) that Holders who want to convert Securities must satisfy
         the requirements set forth therein and in this Indenture;

                  (7) if fewer than all the outstanding Securities are to be
         redeemed, the certificate numbers and Principal Amounts at Maturity of
         the particular Securities to be redeemed;

                                       19
<PAGE>   25

                  (8) that, unless the Issuer defaults in making payment of such
         Redemption Price or the Paying Agent is prohibited from making such
         payment pursuant to the terms of this Indenture, Original Issue
         Discount on Securities (or portions thereof) called for redemption, or
         interest, if any, will cease to accrue on and after the Redemption
         Date;

                  (9) the CUSIP number, if any, printed on the Securities being
         redeemed;

                  (10) that no representation is made as to the correctness or
         accuracy of the CUSIP number, if any, listed in such notice or printed
         on the Securities; and

                  (11) the election of the Company (which, subject to the
         provisions of Article 11 hereof, shall be irrevocable) to deliver
         shares of Common Stock or to pay cash in lieu of delivery of such
         shares with respect to any Securities that may be converted after the
         mailing of such notice and prior to the Redemption Date.

                  At the Issuer's request, the Trustee shall give the notice of
redemption in the Issuer's name and at the Issuer's expense. In such event, the
Issuer shall provide the Trustee with the information required by this Section.

                  SECTION 3.04. Effect of Notice of Redemption. Once notice of
redemption is mailed, Securities called for redemption become due and payable on
the Redemption Date and at the Redemption Price stated in the notice except for
Securities which are converted in accordance with the terms of this Indenture.
Upon surrender to the Paying Agent, such Securities shall be paid at the
Redemption Price stated in the notice. Failure to give notice or any defect in
the notice to any Holder shall not affect the validity of the notice to any
other Holder.

                  SECTION 3.05. Deposit of Redemption Price. Prior to 11:00 a.m.
(New York City time) on the Redemption Date, the Issuer shall deposit with the
Paying Agent (or, if the Issuer or a Subsidiary of the Issuer is the Paying
Agent, shall segregate and hold in trust) money sufficient to pay the Redemption
Price of all Securities to be redeemed on that date other than Securities or
portions of Securities called for redemption that have been delivered by the
Issuer to the Trustee for cancellation or have been converted. The Paying Agent
shall as promptly as practicable return to the Issuer any money, not required
for that purpose because of conversion of Securities pursuant to Article 11. If
such money is then held by the Issuer in trust and is not required for such
purpose it shall be discharged from such trust. The Issuer at any time may
require a Paying Agent to pay all money held by it to the Trustee and to account
for any funds disbursed by the Paying Agent. Upon complying with this Section,
the Paying Agent shall have no further liability for the money delivered to the
Trustee.

                  SECTION 3.06. Securities Redeemed in Part. Upon surrender of a
Security that is redeemed in part, the Issuer shall execute and the Trustee
shall authenticate for the Holder (at the Issuer's expense) a new Security equal
in Principal Amount at Maturity to the unredeemed portion of the Security
surrendered.

                  SECTION 3.07. Conversion Arrangement on Call for Redemption.
In connection with any redemption of Securities, the Issuer may arrange for the
purchase and conversion of any Securities called for redemption by an agreement
with one or more investment

                                       20
<PAGE>   26

bankers or other purchasers to purchase such Securities by paying to the Trustee
in trust for the Securityholders, on or prior to 11:00 a.m. (New York City time)
on the Redemption Date, an amount that, together with any amounts deposited with
the Trustee by the Issuer for the redemption of such Securities, is not less
than the Redemption Price of such Securities. Notwithstanding anything to the
contrary contained in this Article 3, the obligation of the Issuer to pay the
Redemption Price of such Securities shall be deemed to be satisfied and
discharged to the extent such amount is so paid by such purchasers. If such an
agreement is entered into, any Securities not duly surrendered for conversion by
the Holders thereof may, at the option of the Issuer, be deemed, to the fullest
extent permitted by law, acquired by such purchasers from such Holders and
(notwithstanding anything to the contrary contained in Article 11) surrendered
by such purchasers for conversion, all as of immediately prior to the close of
business on the Business Day prior to the Redemption Date, subject to payment of
the above amount as aforesaid. The Trustee shall hold and pay to the Holders
whose Securities are selected for redemption any such amount paid to it for
purchase and conversion in the same manner as it would moneys deposited with it
by the Issuer for the redemption of Securities. Without the Trustee's prior
written consent, no arrangement between the Issuer and such purchasers for the
purchase and conversion of any Securities shall increase or otherwise affect any
of the powers, duties, responsibilities or obligations of the Trustee as set
forth in this Indenture, and the Issuer agrees to indemnify the Trustee from,
and hold it harmless against, any loss, liability or expense arising out of or
in connection with any such arrangement for the purchase and conversion of any
Securities between the Issuer and such purchasers, including the costs and
expenses incurred by the Trustee in the defense of any claim or liability
arising out of or in connection with the exercise or performance of any of its
powers, duties, responsibilities or obligations under this Indenture.

                  SECTION 3.08. Purchase of Securities at Option of the Holder.

                  (a) General. Securities shall be purchased by the Issuer
pursuant to the terms thereof as of February 7, 2004, February 7, 2009 and
February 7, 2014 (each, a "Purchase Date"), at the purchase price of $698.13 per
$1,000 of Principal Amount at Maturity as of February 7, 2004, $775.96 per
$1,000 of Principal Amount at Maturity as of February 7, 2009 and $862.46 per
$1,000 of Principal Amount at Maturity as of February 7, 2014 (each, a "Purchase
Price", as applicable), at the option of the Holder thereof, upon:

                  (1) delivery to the Paying Agent by the Holder of a written
         notice of purchase (a "Purchase Notice"), substantially in the form of
         Exhibit D hereto, at any time from the opening of business on the date
         that is at least 20 Business Days prior to a Purchase Date until the
         close of business on such Purchase Date stating:

                           (A) the certificate number of the Security which the
                  Holder will deliver to be purchased,

                           (B) the portion of the Principal Amount at Maturity
                  of the Security which the Holder will deliver to be purchased,
                  which portion must be in a Principal Amount at Maturity of
                  $1,000 or integral multiples thereof,

                                       21
<PAGE>   27

                           (C) that such Security shall be purchased as of the
                  Purchase Date pursuant to the terms and conditions specified
                  in the Securities and in this Indenture, and

                           (D) in the event the Issuer elects, pursuant to
                  Section 3.08(b), to pay the Purchase Price to be paid as of
                  such Purchase Date, in whole or in part, in shares of Common
                  Stock but such portion of the Purchase Price shall ultimately
                  be payable to such Holder entirely in cash because any of the
                  conditions to payment of the Purchase Price in Common Stock is
                  not satisfied prior to the close of business on such Purchase
                  Date, as set forth in Section 3.08(d), whether such Holder
                  elects (i) to withdraw such Purchase Notice as to some or all
                  of the Securities to which such Purchase Notice relates
                  (stating the Principal Amount at Maturity and certificate
                  numbers of the Securities as to which such withdrawal shall
                  relate), or (ii) to receive cash in respect of the entire
                  Purchase Price for all Securities (or portions thereof) to
                  which such Purchase Notice relates; and

                  (2) delivery of such Security to the Paying Agent for
         cancellation prior to, on or after the Purchase Date (together with all
         necessary endorsements) at the offices of the Paying Agent, such
         delivery being a condition to receipt by the Holder of the Purchase
         Price therefor; provided, however, that such Purchase Price shall be so
         paid pursuant to this Section 3.08 only if the Security so delivered to
         the Paying Agent shall conform in all respects to the description
         thereof in the related Purchase Notice.

                  If a Holder, in such Holder's Purchase Notice, fails to
indicate such Holder's choice with respect to the election set forth in clause
(D) of Section 3.08(a)(1), such Holder shall be deemed to have elected to
receive cash in respect of the Purchase Price for all Securities subject to such
Purchase Notice in the circumstances set forth in such clause (D).

                  The Issuer shall purchase from the Holder thereof, pursuant to
this Section 3.08, a portion of a Security if the Principal Amount at Maturity
of such portion is $1,000 or an integral multiple of $1,000 if so requested by
the Holder. Provisions of this Indenture that apply to the purchase of all of a
Security also apply to the purchase of such portion of such Security.

                  Any purchase by the Issuer contemplated pursuant to the
provisions of this Section 3.08 shall be consummated by the delivery of the
consideration to be received by the Holder promptly following the later of the
Purchase Date and the time of delivery of the Security.

                  Notwithstanding anything herein to the contrary, any Holder
delivering to the Paying Agent the Purchase Notice contemplated by this Section
3.08(a) shall have the right to withdraw such Purchase Notice at any time prior
to the close of business on the Purchase Date by delivery of a written notice of
withdrawal to the Paying Agent in accordance with Section 3.10.

                  The Paying Agent shall promptly notify the Issuer of the
receipt by it of any Purchase Notice or written notice of withdrawal thereof.

                  (b) Issuer's Right to Elect Manner of Payment of Purchase
Price. The Securities to be purchased pursuant to Section 3.08(a) on February 7,
2004 shall be paid for in cash only,

                                       22
<PAGE>   28

but the Securities to be purchased on the other two Purchase Dates may be paid
for, at the election of the Issuer, in cash or in Common Stock valued at the
Market Price, or in any combination of cash and Common Stock, subject to the
conditions set forth in Sections 3.08(c) and (d). The Issuer shall designate, in
the Issuer's Notice delivered pursuant to Section 3.08(e), whether the Issuer
will purchase the Securities for cash or Common Stock, or, if a combination
thereof, the percentages of the Purchase Price of Securities in respect of which
it will pay in cash or Common Stock; provided that the Issuer shall pay cash for
fractional interests in Common Stock. For purposes of determining the existence
of potential fractional interests, all Securities subject to purchase by the
Issuer held by a Holder shall be considered together (no matter how many
separate certificates are to be presented). Each Holder whose Securities are
purchased pursuant to this Section 3.08 shall receive the same percentage of
cash or Common Stock in payment of the Purchase Price for such Securities,
except (i) as provided in Section 3.08(d) with regard to the payment of cash in
lieu of fractional shares of Common Stock and (ii) in the event that the Issuer
is unable to purchase the Securities of a Holder or Holders for Common Stock
because any necessary qualifications or registrations of the Common Stock under
applicable state or foreign securities laws cannot be obtained, the Issuer may
purchase the Securities of such Holder or Holders for cash. The Issuer may not
change its election with respect to the consideration (or components or
percentages of components thereof) to be paid once the Issuer has given the
Issuer's Notice to Securityholders except pursuant to this Section 3.08(b) or
pursuant to Section 3.08(d) in the event of a failure to satisfy, prior to the
close of business on the Purchase Date, any condition to the payment of the
Purchase Price, in whole or in part, in Common Stock.

                  If the Issuer elects to pay all or part of the Purchase Price
in Common Stock, the portion of accrued Original Issue Discount (or interest if
the Issuer has exercised its option to convert the Securities into semi-annual
coupon notes) attributable to the period from the Issue Date (or, if the Issuer
has exercised the option to convert the Securities into semi-annual coupon
notes, the later of (x) the date of such exercise, and (y) the date on which
interest was last paid) through the Purchase Date with respect to the
surrendered Security shall not be cancelled, extinguished or forfeited, but
rather shall be deemed to be paid in full to the Holder thereof through the
delivery of the Common Stock (together with cash payment, if any, in lieu of
fractional shares) and cash, if any, in exchange for the Security being
purchased pursuant to the terms hereof; and such cash and the fair market value
of such shares of Common Stock (together with any such cash payment in lieu of
fractional shares) shall be treated as delivered pro rata, to the extent
thereof, first in exchange for Original Issue Discount (or interest, if the
Issuer has exercised its option to convert the Securities into semi-annual
coupon notes) accrued through the Purchase Date, and the balance, if any, of
such cash and the fair market value of such Common Stock (and any such cash
payment) shall be treated as delivered in exchange for the Issue Price of the
Security being purchased pursuant to the provisions hereof.

                  At least one Business Day before the Issuer's Notice Date (as
defined herein), the Company shall deliver an Officers' Certificate to the
Trustee specifying:

                  (i) the manner of payment to be made by the Issuer,

                  (ii) the information required by Section 3.08(e),

                                       23
<PAGE>   29

                  (iii) if the Issuer elects to pay the Purchase Price, or a
         specified percentage thereof, in Common Stock on the Purchase Date in
         2009 or 2014, that the conditions to such manner of payment set forth
         in Section 3.08(d) have been or will be complied with, and

                  (iv) whether the Issuer desires the Trustee to give the
         Issuer's Notice required by Section 3.08(e).

                  (c) Purchase with Cash. On the initial Purchase Date, the
Purchase Price of all Securities in respect of which a Purchase Notice pursuant
to Section 3.08(a) has been given shall be paid by the Issuer with cash equal to
the aggregate Purchase Price of such Securities. On each other Purchase Date, at
the option of the Issuer, the Purchase Price of Securities in respect of which a
Purchase Notice pursuant to Section 3.08(a) has been given, or a specified
percentage thereof, may be paid by the Issuer with cash equal to the aggregate
Purchase Price of such Securities.

                  (d) Payment by Issuance of Common Stock. On each Purchase Date
other than the initial one, at the option of the Issuer, the Purchase Price of
Securities in respect of which a Purchase Notice pursuant to Section 3.08(a) has
been given, or a specified percentage thereof, may be paid by the Company by the
issuance of a number of shares of Common Stock equal to the quotient obtained by
dividing (i) the amount of cash to which the Securityholders would have been
entitled had the Issuer elected to pay all or such specified percentage, as the
case may be, of the Purchase Price of such Securities in cash by (ii) the Market
Price of a share of Common Stock, subject to the next succeeding paragraph.

                  The Company may not issue a fractional share of Common Stock
in payment of the Purchase Price. Instead the Issuer shall pay cash for the
current market value of the fractional share. The current market value of a
fraction of a share shall be determined, to the nearest 1/1,000th of a share, by
multiplying the Market Price by such fraction and rounding the product to the
nearest whole cent. It is understood that if a Holder elects to have more than
one Security purchased, the number of shares of Common Stock shall be based on
the aggregate amount of Securities to be purchased.

                  The Issuer's right to exercise its election to purchase the
Securities pursuant to Section 3.08 through the issuance of shares of Common
Stock on the Purchase Date in 2009 or 2014 shall be conditioned upon:

                  (i) the Issuer's not having given its Issuer's Notice of an
         election to pay entirely in cash and its giving of timely Issuer's
         Notice of election to purchase all or a specified percentage of the
         Securities with Common Stock as provided herein;

                  (ii) the registration of the shares of Common Stock to be
         issued in respect of the payment of the Purchase Price under the
         Securities Act and the Exchange Act, in each case if required;

                  (iii) any necessary qualification or registration under
         applicable state securities laws or the availability of an exemption
         from such qualification and registration; and

                                       24
<PAGE>   30

                  (iv) the receipt by the Trustee of an Officers' Certificate
         and an Opinion of Counsel, each stating that (A) the terms of the
         issuance of the Common Stock are in conformity with this Indenture and
         (B) the shares of Common Stock to be issued by the Company in payment
         of the Purchase Price in respect of Securities have been duly
         authorized and, when issued and delivered pursuant to the terms of this
         Indenture in payment of the Purchase Price in respect of the
         Securities, will be validly issued, fully paid and non-assessable and,
         to the best of such counsel's knowledge, free from preemptive rights,
         and, in the case of such Officers' Certificate, stating that conditions
         (i), (ii) and (iii) above and the condition set forth in the second
         succeeding sentence have been satisfied and, in the case of such
         Opinion of Counsel, stating that conditions (ii) and (iii) above has
         been satisfied.

                  Such Officers' Certificate shall also set forth the number of
shares of Common Stock to be issued for each $1,000 Principal Amount at Maturity
of Securities and the Sale Price of a share of Common Stock on each trading day
during the period during which the Market Price is calculated. The Issuer may
pay the Purchase Price (or any portion thereof) in Common Stock only if the
information necessary to calculate the Market Price is published in a daily
newspaper of national circulation. If the foregoing conditions are not satisfied
with respect to a Holder or Holders prior to the close of business on the
Purchase Date and the Issuer has elected to purchase the Securities pursuant to
this Section 3.08 through the issuance of shares of Common Stock, the Issuer
shall pay the entire Purchase Price of the Securities of such Holder or Holders
in cash.

                  The "Market Price" means the average of the Sale Prices of the
Common Stock for the five trading day period ending on the third Business Day
(if the third Business Day prior to the applicable Purchase Date or Fundamental
Change Repurchase Date is a trading day, or if not, then on the last trading
day) prior to the applicable Purchase Date or Fundamental Change Repurchase
Date, appropriately adjusted to take into account the occurrence, during the
period commencing on the first of such trading days during such five trading day
period and ending on such Purchase Date or Fundamental Change Repurchase Date,
of any event described in Section 11.06, 11.07 or 11.08; subject, however, to
the conditions set forth in Sections 11.09 and 11.10.

                  The "Sale Price" of the Common Stock on any date means the
closing sale price per share (or, if no closing sale price is reported, the
average of the bid and ask prices or, if more than one in either case, the
average of the average bid and average ask prices) on such date as reported in
the composite transactions for the principal United States securities exchange
on which the Common Stock is traded or, if the Common Stock is not listed on a
United States national or regional securities exchange, as reported by the
Nasdaq System.

                  (e) Notice. The Issuer's notice of whether it intends to pay
the Purchase Price with cash or Common Stock or any combination thereof shall be
sent to the Holders (and to beneficial owners as required by applicable law) in
the manner provided herein (the "Issuer's Notice"). The Issuer's Notice shall be
sent to Holders (and to beneficial owners as required by applicable law) not
less than 20 Business Days prior to such Purchase Date (the "Issuer's Notice
Date"). The Issuer's Notice shall state the manner of payment and shall contain
the following information:

                                       25
<PAGE>   31

                  In the event the Issuer has elected to pay the Purchase Price
(or a specified percentage thereof) with Common Stock on the Purchase Date in
either 2009 or 2014, the Issuer's Notice shall:

                  (1) state that each Holder will receive Common Stock in
         respect of the specified percentage of the Purchase Price of the
         Securities held by such Holder (except any cash amount to be paid in
         lieu of fractional shares);

                  (2) state that the total number of shares of Common Stock to
         be issued to Holders will be equal to the quotient obtained by dividing
         (i) the amount of cash to which the Securityholders would have been
         entitled had the Issuer elected to pay all or such specified
         percentage, as the case may be, of the Purchase Price of such
         Securities in cash by (ii) the Market Price of a share of Common Stock;

                  (3) set forth the method of calculating the Market Price of
         the Common Stock; and

                  (4) state that because the Market Price of Common Stock will
         be determined prior to the Purchase Date, Holders will bear the market
         risk with respect to the value of the Common Stock to be received from
         the date such Market Price is determined to the Purchase Date.

                  In any case, each Issuer's Notice shall include a form of
Purchase Notice to be completed by a Securityholder and shall state:

                  (i) the Purchase Price and the Conversion Rate applicable on
         the Issuer's Notice Date;

                  (ii) the name and address of the Paying Agent and the
         Conversion Agent;

                  (iii) that Securities as to which a Purchase Notice has been
         given may be converted pursuant to Article 11 hereof only if the
         applicable Purchase Notice has been withdrawn in accordance with the
         terms of this Indenture;

                  (iv) that Securities must be surrendered to the Paying Agent
         for cancellation to collect payment;

                  (v) that the Purchase Price for any security as to which a
         Purchase Notice has been given and not withdrawn will be paid promptly
         following the later of the Purchase Date and the time of surrender of
         such Security as described in (iv);

                  (vi) the procedures the Holder must follow to exercise rights
         under Section 3.08 and a brief description of those rights;

                  (vii) briefly, the conversion rights of the Securities;

                                       26
<PAGE>   32

                  (viii) the procedures for withdrawing a Purchase Notice
         (including, without limitation, for a conditional withdrawal pursuant
         to the terms of Section 3.08(a)(1)(D) or Section 3.10);

                  (ix) that, unless the Issuer defaults in making payment of
         such Purchase Price, Original Issue Discount on Securities covered by
         any Purchase Notice, or interest, if any, will cease to accrue on and
         after the Purchase Date; and

                  (x) the CUSIP number of the Securities, if applicable.

                  At the Issuer's request, the Trustee shall give such Issuer's
Notice in the name of the Issuer and at the Issuer's expense; provided, however,
that, in all cases, the text of such Issuer's Notice shall be prepared by the
Issuer.

                  (f) Covenants of the Company. All shares of Common Stock
delivered upon purchase of the Securities shall be newly issued shares or
treasury shares, shall be duly authorized, validly issued, fully paid and
nonassessable, and shall be free from preemptive rights and free of any lien or
adverse claim.

                  The Company shall use its best efforts to list or cause to
have quoted any shares of Common Stock to be issued to purchase Securities on
each United States national securities exchange or automated over-the-counter
trading market in the United States on which the Common Stock is then listed or
quoted.

                  (g) Procedure upon Purchase. The Issuer shall deposit cash (in
respect of a cash purchase under Section 3.08(c) or for fractional interests, as
applicable) or shares of Common Stock, or a combination thereof, as applicable,
at the time and in the manner as provided in Section 3.11, sufficient to pay the
aggregate Purchase Price of all Securities to be purchased pursuant to this
Section 3.08. As soon as practicable after the Purchase Date, the Company shall
deliver to each Holder entitled to receive Common Stock through its stock
transfer agent, a certificate for the number of full shares of Common Stock
issuable in payment of the Purchase Price. The Person in whose name the
certificate for Common Stock is registered shall be treated as a holder of
record of shares of Common Stock on the Business Day following the Purchase
Date. Subject to Section 3.08(d), no payment or adjustment will be made for
dividends on any Common Stock delivered in payment of the Purchase Price the
record date for which occurred on or prior to the Purchase Date.

                  (h) Taxes. If a Holder of a Security is paid in Common Stock,
the Issuer shall pay any documentary, stamp or similar issue or transfer tax due
on such issue of shares of Common Stock. However, the Holder shall pay any such
tax which is due because the Holder requests the shares of Common Stock to be
issued in a name other than the Holder's name. The Paying Agent may refuse to
deliver the certificates representing the Common Stock being issued in a name
other than the Holder's name until the Paying Agent receives a sum that the
Issuer deems to be sufficient to pay any tax which will be due because the
shares of Common Stock are to be issued in a name other than the Holder's name.
Nothing herein shall preclude any income tax withholding required by law or
regulations.

                                       27
<PAGE>   33

                  SECTION 3.09. Repurchase of Securities at Option of the Holder
upon Fundamental Change.

                  (a) General. If prior to February 7, 2004 there shall have
occurred a Fundamental Change, Securities shall be purchased by the Issuer, at a
purchase price specified in the Securities (the "Fundamental Change Repurchase
Price"), as of a date that is not less than 60 days nor more than 90 days after
the occurrence of the Fundamental Change (the "Fundamental Change Repurchase
Date"), at the option of the Holder thereof, upon:

                  (1) delivery to the Paying Agent by the Holder of a written
         notice of purchase (a "Fundamental Change Repurchase Notice"),
         substantially in the form of Exhibit E hereto, at any time until the
         close of business on such Fundamental Change Repurchase Date stating:

                           (A) the certificate number of the Security which the
                  Holder will deliver to be purchased,

                           (B) the portion of the Principal Amount at Maturity
                  of the Security which the Holder will deliver to be purchased,
                  which portion must be in a Principal Amount at Maturity of
                  $1,000 or integral multiples thereof,

                           (C) that such Security shall be purchased as of the
                  Fundamental Change Repurchase Date pursuant to the terms and
                  conditions specified in the Securities and in this Indenture,
                  and

                           (D) in the event the Issuer elects, pursuant to
                  Section 3.09(b), to pay the Fundamental Change Repurchase
                  Price to be paid as of such Fundamental Change Repurchase
                  Date, in whole or in part, in shares of Common Stock but such
                  portion of the Fundamental Change Repurchase Price shall
                  ultimately be payable to such Holder entirely in cash because
                  any of the conditions to payment of the Fundamental Change
                  Repurchase Price in Common Stock is not satisfied prior to the
                  close of business on such Fundamental Change Repurchase Date,
                  as set forth in Section 3.09(d), whether such Holder elects
                  (i) to withdraw such Fundamental Change Repurchase Notice as
                  to some or all of the Securities to which such Fundamental
                  Change Repurchase Notice relates (stating the Principal Amount
                  at Maturity and certificate numbers of the Securities as to
                  which such withdrawal shall relate), or (ii) to receive cash
                  in respect of the entire Fundamental Change Repurchase Price
                  for all Securities (or portions thereof) to which such
                  Fundamental Change Repurchase Notice relates; and

                  (2) delivery of such Security to the Paying Agent for
         cancellation prior to, on or after the Fundamental Change Repurchase
         Date (together with all necessary endorsements) at the offices of the
         Paying Agent, such delivery being a condition to receipt by the Holder
         of the Fundamental Change Repurchase Price therefor; provided, however,
         that such Fundamental Change Repurchase Price shall be so paid pursuant
         to this Section 3.09 only if the Security so delivered to the Paying
         Agent shall conform in

                                       28
<PAGE>   34

         all respects to the description thereof in the related Fundamental
         Change Repurchase Notice.

                  If a Holder, in such Holder's Fundamental Change Repurchase
Notice, fails to indicate such Holder's choice with respect to the election set
forth in clause (D) of Section 3.09(a)(1), such Holder shall be deemed to have
elected to receive cash in respect of the Fundamental Change Repurchase Price
for all Securities subject to such Fundamental Change Repurchase Notice in the
circumstances set forth in such clause (D).

                  The Issuer shall purchase from the Holder thereof, pursuant to
this Section 3.09, a portion of a Security if the Principal Amount at Maturity
of such portion is $1,000 or an integral multiple of $1,000 if so requested by
the Holder. Provisions of this Indenture that apply to the purchase of all of a
Security also apply to the purchase of such portion of such Security.

                  Any purchase by the Issuer contemplated pursuant to the
provisions of this Section 3.09 shall be consummated by the delivery of the
consideration to be received by the Holder promptly following the later of the
Fundamental Change Repurchase Date and the time of delivery of the Security.

                  Notwithstanding anything herein to the contrary, any Holder
delivering to the Paying Agent the Fundamental Change Repurchase Notice
contemplated by this Section 3.09(a) shall have the right to withdraw such
Fundamental Change Repurchase Notice at any time prior to the close of business
on the Fundamental Change Repurchase Date by delivery of a written notice of
withdrawal to the Paying Agent in accordance with Section 3.10.

                  The Paying Agent shall promptly notify the Issuer of the
receipt by it of any Fundamental Change Repurchase Notice or written notice of
withdrawal thereof.

                  A "Fundamental Change" shall be deemed to have occurred at
such time as any of the following events shall occur:

                  (i) the Company consolidates or merges with or into another
         Person (other than a Subsidiary of the Company);

                  (ii) the Company sells, conveys, transfers or leases its
         properties and assets substantially as an entirety to any Person (other
         than a Subsidiary of the Company);

                  (iii) any Person (other than a Subsidiary of the Company)
         consolidates with or merges with or into the Company; or

                  (iv) the Common Stock is reclassified into, exchanged for or
         converted into the right to receive any other property or security,

provided, that none of these circumstances will be a Fundamental Change if at
least 50% of the aggregate fair market value (as determined by the Board of
Directors) of such property and securities received by holders of Common Stock
in respect of such Common Stock in such transaction, other than cash payments
for fractional shares, consists of shares of voting Common Stock of the
surviving Person that are, or upon issuance will be, traded on a United States

                                       29
<PAGE>   35

national securities exchange or approved for trading on an established automated
over-the-counter trading market in the United States. For the avoidance of
doubt, none of the events referred to in the preceding clauses (i)-(iv) shall
constitute a Fundamental Change if the outstanding Common Stock is not affected
thereby.

                  (b) Issuer's Right to Elect Manner of Payment of Fundamental
Change Repurchase Price. The Securities to be purchased pursuant to Section
3.09(a) may be paid for, at the election of the Issuer, in cash or in Common
Stock valued at the Market Price, or in any combination of cash and Common
Stock, subject to the conditions set forth in Sections 3.09(c) and (d). The
Issuer shall designate, in the Fundamental Change Notice delivered pursuant to
Section 3.09(e), whether the Issuer will purchase the Securities for cash or
Common Stock, or, if a combination thereof, the percentages of the Fundamental
Change Repurchase Price of Securities in respect of which it will pay in cash or
Common Stock; provided that the Issuer shall pay cash for fractional interests
in Common Stock. For purposes of determining the existence of potential
fractional interests, all Securities subject to purchase by the Issuer held by a
Holder shall be considered together (no matter how many separate certificates
are to be presented). Each Holder whose Securities are purchased pursuant to
this Section 3.09 shall receive the same percentage of cash or Common Stock in
payment of the Fundamental Change Repurchase Price for such Securities, except
(i) as provided in Section 3.09(d) with regard to the payment of cash in lieu of
fractional shares of Common Stock and (ii) in the event that the Issuer is
unable to purchase the Securities of a Holder or Holders for Common Stock
because any necessary qualifications or registrations of the Common Stock under
applicable state or foreign securities laws cannot be obtained, the Issuer may
purchase the Securities of such Holder or Holders for cash. The Issuer may not
change its election with respect to the consideration (or components or
percentages of components thereof) to be paid once the Issuer has given its
Fundamental Change Notice to Securityholders except pursuant to this Section
3.09(b) or pursuant to Section 3.09(d) in the event of a failure to satisfy,
prior to the close of business on the Fundamental Change Repurchase Date, any
condition to the payment of the Fundamental Change Repurchase Price, in whole or
in part, in Common Stock.

                  If the Issuer elects to pay all or part of the Fundamental
Change Repurchase Price in Common Stock, the portion of accrued Original Issue
Discount (or interest if the Issuer has exercised its option to convert the
Securities into semi-annual coupon notes) attributable to the period from the
Issue Date (or, if the Issuer has exercised the option to convert the Securities
into semi-annual coupon notes, the later of (x) the date of such exercise, and
(y) the date on which interest was last paid) through the Fundamental Change
Repurchase Date with respect to the surrendered Security shall not be cancelled,
extinguished or forfeited, but rather shall be deemed to be paid in full to the
Holder thereof through the delivery of the Common Stock (together with cash
payment, if any, in lieu of fractional shares) and cash, if any, in exchange for
the Security being purchased pursuant to the terms hereof; and such cash, if
any, and the fair market value of such shares of Common Stock (together with any
such cash payment in lieu of fractional shares) shall be treated as delivered
pro rata, to the extent thereof, first in exchange for Original Issue Discount
(or interest, if the Issuer has exercised its option to convert the Securities
into semi-annual coupon notes) accrued through the Fundamental Change Repurchase
Date, and the balance, if any, of such cash or the fair market value of such
Common Stock (and any such cash payment) shall be treated as delivered in
exchange for the Issue Price of the Security being purchased pursuant to the
provisions hereof.

                                       30
<PAGE>   36

                  At least one Business Day before the Fundamental Change Notice
Date (as defined below), the Company shall deliver an Officers' Certificate to
the Trustee specifying:

                  (i) the manner of payment selected by the Issuer,

                  (ii) the information required by Section 3.09(e),

                  (iii) if the Issuer elects to pay the Fundamental Change
         Repurchase Price, or a specified percentage thereof, in Common Stock,
         that the conditions to such manner of payment set forth in Section
         3.09(d) have been or will be complied with, and

                  (iv) whether the Issuer desires the Trustee to give the
         Fundamental Change Notice required by Section 3.09(e).

                  (c) Purchase with Cash. On each Fundamental Change Repurchase
Date, at the option of the Issuer, the Fundamental Change Repurchase Price of
Securities in respect of which a Fundamental Change Repurchase Notice pursuant
to Section 3.09(a) has been given, or a specified percentage thereof, may be
paid by the Issuer with cash equal to the aggregate Fundamental Change
Repurchase Price of such Securities.

                  (d) Payment by Issuance of Common Stock. On each Fundamental
Change Repurchase Date, at the option of the Issuer, the Fundamental Change
Repurchase Price of Securities in respect of which a Fundamental Change
Repurchase Notice pursuant to Section 3.09(a) has been given, or a specified
percentage thereof, may be paid by the Company by the issuance of a number of
shares of Common Stock equal to the quotient obtained by dividing (i) the amount
of cash to which the Securityholders would have been entitled had the Issuer
elected to pay all or such specified percentage, as the case may be, of the
Fundamental Change Repurchase Price of such Securities in cash by (ii) the
Market Price of a share of Common Stock, subject to the next succeeding
paragraph.

                  The Company may not issue a fractional share of Common Stock
in payment of the Fundamental Change Repurchase Price. Instead the Issuer shall
pay cash for the current market value of the fractional share. The current
market value of a fraction of a share shall be determined, to the nearest
1/1,000th of a share, by multiplying the Market Price by such fraction and
rounding the product to the nearest whole cent. It is understood that if a
Holder elects to have more than one Security purchased, the number of shares of
Common Stock shall be based on the aggregate amount of Securities to be
purchased.

                  The Issuer's right to exercise its election to purchase the
Securities pursuant to Section 3.09 through the issuance of shares of Common
Stock shall be conditioned upon:

                  (i) the Issuer's not having given a Fundamental Change Notice
         of an election to pay entirely in cash and its giving of timely
         Fundamental Change Notice of election to purchase all or a specified
         percentage of the Securities with Common Stock as provided herein;

                                       31
<PAGE>   37

                  (ii) the registration of the shares of Common Stock to be
         issued in respect of the payment of the Fundamental Change Repurchase
         Price under the Securities Act and the Exchange Act, in each case if
         required;

                  (iii) any necessary qualification or registration under
         applicable state securities laws or the availability of an exemption
         from such qualification and registration;

                  (iv) the receipt by the Trustee of an Officers' Certificate
         and an Opinion of Counsel, each stating that (A) the terms of the
         issuance of the Common Stock are in conformity with this Indenture and
         (B) the shares of Common Stock to be issued by the Company in payment
         of the Fundamental Change Repurchase Price in respect of Securities
         have been duly authorized and, when issued and delivered pursuant to
         the terms of this Indenture in payment of the Fundamental Change
         Repurchase Price in respect of the Securities, will be validly issued,
         fully paid and non-assessable and, to the best of such counsel's
         knowledge, free from preemptive rights, and, in the case of such
         Officers' Certificate, stating that conditions (i), (ii) and (iii)
         above and the condition set forth in the second succeeding sentence
         have been satisfied and, in the case of such Opinion of Counsel,
         stating that conditions (ii) and (iii) above has been satisfied; and

                  (v) the Common Stock being listed or quoted on a United States
         national securities exchange or traded on an established automated
         over-the-counter trading market in the United States.

                  Such Officers' Certificate shall also set forth the number of
shares of Common Stock to be issued for each $1,000 Principal Amount at Maturity
of Securities and the Sale Price of a share of Common Stock on each trading day
during the period during which the Market Price is calculated. The Issuer may
pay the Fundamental Change Repurchase Price (or any portion thereof) in Common
Stock only if the information necessary to calculate the Market Price is
published in a daily newspaper of national circulation. If the foregoing
conditions are not satisfied with respect to a Holder or Holders prior to the
close of business on the Fundamental Change Repurchase Date and the Issuer has
elected to purchase the Securities pursuant to this Section 3.09 through the
issuance of shares of Common Stock, the Issuer shall pay the entire Fundamental
Change Repurchase Price of the Securities of such Holder or Holders in cash.

                  (e) Notice of Fundamental Change and Issuer's Election. Within
30 days after the occurrence of a Fundamental Change, the Issuer shall mail
notice of Fundamental Change (the "Fundamental Change Notice") by first-class
mail to the Trustee and to each Holder (and to beneficial owners as required by
applicable law). The Fundamental Change Notice shall disclose the Issuer's
election to repurchase with cash or Common Stock or any combination thereof in
the manner provided herein. The Fundamental Change Notice shall be sent to
Holders (and to beneficial owners as required by applicable law) not less than
60 days prior to such Fundamental Change Repurchase Date (the "Fundamental
Change Notice Date"). The notice shall include a form of Fundamental Change
Repurchase Notice to be completed by the Securityholder and shall state:

                  (1) briefly, the events causing a Fundamental Change and the
         date of such Fundamental Change;

                                       32
<PAGE>   38

                  (2) the date by which the Fundamental Change Repurchase Notice
         pursuant to this Section 3.09 must be given;

                  (3) the Fundamental Change Repurchase Date;

                  (4) the Fundamental Change Repurchase Price;

                  (5) the name and address of the Paying Agent and the
         Conversion Agent;

                  (6) the Conversion Rate applicable on the Fundamental Change
         Notice Date;

                  (7) that Securities as to which a Fundamental Change
         Repurchase Notice has been given may be converted pursuant to Article
         11 hereof only if the Fundamental Change Repurchase Notice has been
         withdrawn in accordance with the terms of this Indenture;

                  (8) that Securities must be surrendered to the Paying Agent
         for cancellation to collect payment;

                  (9) that the Fundamental Change Repurchase Price for any
         Security as to which a Fundamental Change Repurchase Notice has been
         duly given and not withdrawn will be paid promptly following the later
         of the Fundamental Change Repurchase Date and the time of surrender of
         such Security as described in (8);

                  (10) briefly, the procedures the Holder must follow to
         exercise rights under this Section 3.09;

                  (11) briefly, the conversion rights of the Securities;

                  (12) the procedures for withdrawing a Fundamental Change
         Repurchase Notice (including, without limitation, for a conditional
         withdrawal pursuant to the terms of Section 3.09(a)(1)(D) or Section
         3.10);

                  (13) that, unless the Issuer defaults in making payment of
         such Fundamental Change Repurchase Price, Original Issue Discount on
         Securities covered by any Fundamental Change Repurchase Notice, or
         interest, if any, will cease to accrue on and after the Fundamental
         Change Repurchase Date; and

                  (14) the CUSIP number of the Securities, if applicable.

                  In the event the Issuer has elected to pay the Fundamental
Change Repurchase Price (or a specified percentage thereof) with Common Stock,
the Fundamental Change Notice also shall:

                  (1) state that each Holder will receive Common Stock in
         respect of the specified percentage of the Fundamental Change
         Repurchase Price of the Securities held by such Holder (except any cash
         amount to be paid in lieu of fractional shares);

                                       33
<PAGE>   39

                  (2) state that the total number of shares of Common Stock to
         be issued to Holders will be equal to the quotient obtained by dividing
         (i) the amount of cash to which the Securityholders would have been
         entitled had the Issuer elected to pay all or such specified
         percentage, as the case may be, of the Fundamental Change Repurchase
         Price of such Securities in cash by (ii) the Market Price of a share of
         Common Stock;

                  (3) set forth the method of calculating the Market Price of
         the Common Stock; and

                  (4) state that because the Market Price of Common Stock will
         be determined prior to the Fundamental Change Repurchase Date, Holders
         will bear the market risk with respect to the value of the Common Stock
         to be received from the date such Market Price is determined to the
         Fundamental Change Repurchase Date.

                  At the Issuer's request, the Trustee shall give such
Fundamental Change Notice in the name of the Issuer and at the Issuer's expense;
provided, however, that, in all cases, the text of such Fundamental Change
Notice shall be prepared by the Issuer.

                  (f) Covenants of the Company. All shares of Common Stock
delivered upon purchase of the Securities shall be newly issued shares or
treasury shares, shall be duly authorized, validly issued, fully paid and
nonassessable, and shall be free from preemptive rights and free of any lien or
adverse claim.

                  The Company shall use its best efforts to list or cause to
have quoted any shares of Common Stock to be issued to purchase Securities on
each United States national securities exchange or automated over-the-counter
trading market in the United States on which the Common Stock is then listed or
quoted.

                  (g) Procedure upon Purchase. The Issuer shall deposit cash (in
respect of a cash purchase under Section 3.09(c) or for fractional interests, as
applicable) or shares of Common Stock, or a combination thereof, as applicable,
at the time and in the manner as provided in Section 3.11, sufficient to pay the
aggregate Fundamental Change Repurchase Price of all Securities to be purchased
pursuant to this Section 3.09. As soon as practicable after the Fundamental
Change Repurchase Date, the Issuer shall deliver to each Holder entitled to
receive Common Stock through its stock transfer agent, a certificate for the
number of full shares of Common Stock issuable in payment of the Fundamental
Change Repurchase Price. The Person in whose name the certificate for Common
Stock is registered shall be treated as a holder of record of shares of Common
Stock on the Business Day following the Fundamental Change Repurchase Date.
Subject to Section 3.09(d), no payment or adjustment will be made for dividends
on any Common Stock delivered in payment of the Fundamental Change Repurchase
Price the record date for which occurred on or prior to the Fundamental Change
Repurchase Date.

                  (h) Taxes. If a Holder of a Security is paid in Common Stock,
the Issuer shall pay any documentary, stamp or similar issue or transfer tax due
on such issue of shares of Common Stock. However, the Holder shall pay any such
tax which is due because the Holder requests the shares of Common Stock to be
issued in a name other than the Holder's name. The Paying Agent

                                       34
<PAGE>   40

may refuse to deliver the certificates representing the Common Stock being
issued in a name other than the Holder's name until the Paying Agent receives a
sum that the Issuer deems to be sufficient to pay any tax which will be due
because the shares of Common Stock are to be issued in a name other than the
Holder's name. Nothing herein shall preclude any income tax withholding required
by law or regulations.

                  SECTION 3.10. Effect of Purchase Notice or Fundamental Change
Repurchase Notice. Upon receipt by the Paying Agent of the Purchase Notice or
Fundamental Change Repurchase Notice specified in Section 3.08(a) or Section
3.09(a), as applicable, the Holder of the Security in respect of which such
Purchase Notice or Fundamental Change Repurchase Notice, as the case may be, was
given shall (unless such Purchase Notice or Fundamental Change Repurchase Notice
is withdrawn as specified in the following two paragraphs) thereafter be
entitled to receive solely the Purchase Price or Fundamental Change Repurchase
Price, as the case may be, with respect to such Security. Such Purchase Price or
Fundamental Change Repurchase Price shall be paid to such Holder, subject to
receipts of funds and/or securities by the Paying Agent, promptly following the
later of (x) the Purchase Date or the Fundamental Change Repurchase Date, as the
case may be, with respect to such Security (provided the conditions in Section
3.08(a) or Section 3.09(a), as applicable, have been satisfied) and (y) the time
of delivery of such Security to the Paying Agent by the Holder thereof in the
manner required by Section 3.08(a) or Section 3.09(a), as applicable. Securities
in respect of which a Purchase Notice or Fundamental Change Repurchase Notice,
as the case may be, has been given by the Holder thereof may not be converted
pursuant to Article 11 hereof on or after the date of the delivery of such
Purchase Notice or Fundamental Change Repurchase Notice, as the case may be,
unless such Purchase Notice or Fundamental Change Repurchase Notice, as the case
may be, has first been validly withdrawn as specified in the following two
paragraphs.

                  A Purchase Notice or Fundamental Change Repurchase Notice, as
the case may be, may be withdrawn by means of a written notice of withdrawal
delivered to the office of the Paying Agent in accordance with the Purchase
Notice or Fundamental Change Repurchase Notice, as the case may be, at any time
prior to the close of business on the Purchase Date or the Fundamental Change
Repurchase Date, as the case may be, specifying:

                  (1) the certificate number of the Security in respect of which
         such notice of withdrawal is being submitted,

                  (2) the Principal Amount at Maturity of the Security with
         respect to which such notice of withdrawal is being submitted, and

                  (3) the Principal Amount at Maturity, if any, of such Security
         which remains subject to the original Purchase Notice or Fundamental
         Change Repurchase Notice, as the case may be, and which has been or
         will be delivered for purchase or repurchase by the Issuer.

                  A written notice of withdrawal of a Purchase Notice or
Fundamental Change Repurchase Notice may be in the form set forth in the
preceding paragraph or may be in the form of (i) a conditional withdrawal
contained in a Purchase Notice or Fundamental Change Repurchase Notice pursuant
to the terms of Section 3.08(a)(1)(D) or 3.09(a)(1)(D) or (ii) a

                                       35
<PAGE>   41

conditional withdrawal containing the information set forth in Section
3.08(a)(1)(D) or 3.09(a)(1)(D) and the preceding paragraph and contained in a
written notice of withdrawal delivered to the Paying Agent as set forth in the
preceding paragraph.

                  There shall be no purchase of any Securities pursuant to
Section 3.08 or 3.09 (other than through the issuance of Common Stock in payment
of the Purchase Price, including cash in lieu of fractional shares) if there has
occurred (prior to, on or after, as the case may be, the giving, by the Holders
of such Securities, of the required Purchase Notice or Fundamental Change
Repurchase Notice, as the case may be) and is continuing an Event of Default
(other than a default in the payment of the Purchase Price or Fundamental Change
Repurchase Price, as the case may be, with respect to such Securities). The
Paying Agent will promptly return to the respective Holders thereof any
Securities (x) with respect to which a Purchase Notice or Fundamental Change
Repurchase Notice, as the case may be, has been withdrawn in compliance with
this Indenture, or (y) held by it during the continuance of an Event of Default
(other than a default in the payment of the Purchase Price or Fundamental Change
Repurchase Price, as the case may be, with respect to such Securities) in which
case, upon such return, the Purchase Notice or Fundamental Change Repurchase
Notice with respect thereto shall be deemed to have been withdrawn.

                  SECTION 3.11. Deposit of Purchase Price or Fundamental Change
Repurchase Price. Prior to 11:00 a.m. (local time in The City of New York) on
the Business Day following the Purchase Date or the Fundamental Change
Repurchase Date, as the case may be, the Issuer shall deposit with the Trustee
or with the Paying Agent (or, if the Issuer or a Subsidiary of the Issuer is the
Paying Agent, shall segregate and hold in trust) an amount of money (in
immediately available funds if deposited on such Business Day) sufficient to pay
the cash portion of the aggregate Purchase Price or Fundamental Change
Repurchase Price, as the case may be, of all the Securities or portions thereof
which are to be purchased as of the Purchase Date or Fundamental Change
Repurchase Date, as the case may be, and shall instruct its stock transfer agent
to deliver the number of full shares of Common Stock issuable in payment of the
remaining portion of the aggregate Purchase Price or Fundamental Change
Repurchase Price, as the case may be. The Issuer shall promptly notify the
Trustee in writing of the amount of any deposits of cash or deliveries of Common
Stock made pursuant to this Section.

                  SECTION 3.12. Securities Purchased or Repurchased in Part. Any
Security which is to be purchased or repurchased only in part shall be
surrendered at the office of the Paying Agent (with, if the Issuer or the
Trustee so requires, due endorsement by, or a written instrument of transfer in
form satisfactory to the Issuer and the Trustee duly executed by, the Holder
thereof or such Holder's attorney duly authorized in writing) and the Issuer
shall execute and the Trustee shall authenticate and deliver to the Holder of
such Security, without service charge, a new Security or Securities, of any
authorized denomination as requested by such Holder in aggregate Principal
Amount at Maturity equal to, and in exchange for, the portion of the Principal
Amount at Maturity of the Security so surrendered which is not purchased.

                  SECTION 3.13. Covenant to Comply With Securities Laws Upon
Purchase or Repurchase of Securities. In connection with any offer to purchase
or repurchase or purchase or repurchase of Securities under Section 3.08 or 3.09
hereof (provided that such offer or purchase or repurchase constitutes an
"issuer tender offer" for purposes of Rule 13e-4 (which term, as

                                       36
<PAGE>   42

used herein, includes any successor provision thereto) under the Exchange Act at
the time of such offer or purchase), the Issuer shall (i) comply with Rule 13e-4
and Rule 14e-1 under the Exchange Act, (ii) file the related Schedule TO (or any
successor schedule, form or report) under the Exchange Act, and (iii) otherwise
comply with all Federal and state securities laws so as to permit the rights and
obligations under Sections 3.08 and 3.09 to be exercised in the time and in the
manner specified in Sections 3.08 and 3.09.

                  SECTION 3.14. Repayment to the Issuer. The Trustee and the
Paying Agent shall return to the Issuer any cash that remains unclaimed,
together with interest or dividends, if any, thereon, held by them for the
payment of the Purchase Price or Fundamental Change Repurchase Price, as the
case may be; provided, however, that to the extent that the aggregate amount of
cash deposited by the Issuer pursuant to Section 3.11 exceeds the cash portion
of the aggregate Purchase Price or Fundamental Change Repurchase Price, as the
case may be, of the Securities or portions thereof which the Issuer is obligated
to purchase as of the Purchase Date or Fundamental Change Repurchase Date, as
the case may be, then on the Business Day following the Purchase Date or
Fundamental Change Repurchase Date, as the case may be, the Trustee shall return
any such excess to the Issuer.

                                   ARTICLE 4

                                   COVENANTS

                  SECTION 4.01. Payment of Securities. The Issuer shall promptly
make all payments in respect of the Securities on the dates and in the manner
provided in the Securities and in this Indenture. Such payments shall be
considered made on the date due if on such date the Trustee or the Paying Agent
holds, in accordance with this Indenture, money sufficient to make all payments
with respect of the Securities then due and the Trustee or the Paying Agent, as
the case may be, is not prohibited from paying such money to the Securityholders
on that date pursuant to the terms of this Indenture.

                  SECTION 4.02. Financial Information; SEC Reports. At any time
the Company is not subject to either Section 13 or 15(d) of the Exchange Act,
the Company shall at the request of any Holder (or holders of Common Stock
issued upon conversion of the Securities) provide to such Holder (or holders of
such Common Stock) and any prospective purchaser designated by such Holders (or
holders of such Common Stock), as the case may be, such information, if any,
required by Rule 144A(d)(4) under the Securities Act. Further, the Company shall
file with the Trustee, within 15 days after it files the same with the SEC,
copies of its annual reports and of the information, documents and other reports
(or copies of such portions of any of the foregoing as the Commission may by
rules and regulations prescribe) which the Company is required to file with the
SEC pursuant to Section 13 or 15(d) of the Exchange Act. Delivery of such
reports, information and documents to the Trustee is for informational purposes
only and the Trustee's receipt of such shall not constitute constructive notice
of any information contained therein or determinable from information contained
therein, including the Issuer's compliance with any of its covenants hereunder
(as to which the Trustee is entitled to rely exclusively on Officers'
Certificates). The Issuer also shall comply with any other provisions of Trust
Indenture Act Section 314(a).

                                       37
<PAGE>   43

                  SECTION 4.03. Corporate Existence. The Issuer shall do or
cause to be done all things necessary to preserve and keep in full force and
effect its corporate existence, material rights (charter and statutory) and
material franchises (other than as contemplated by Section 5.01); provided,
however, that the Issuer shall not be required to preserve any such right or
franchise if the Board of Directors shall determine that the preservation of
such rights or franchises is no longer desirable in the conduct of the business
of the Issuer.

                  SECTION 4.04. Restrictions on Liens. Except as provided in
Section 4.06, so long as any of the Securities are outstanding, the Company
shall not pledge, mortgage or hypothecate, or permit to exist, and shall not
cause, suffer or permit any Subsidiary to pledge, mortgage or hypothecate, or
permit to exist, except in favor of the Company or any Subsidiary, any mortgage,
pledge or other lien upon, any Principal Property at any time owned by it, to
secure any indebtedness, without making effective provisions whereby the
Securities shall be equally and ratably secured with any and all such
indebtedness and with any other indebtedness similarly entitled to be equally
and ratably secured; provided, however, that this restriction shall not apply to
or prevent the creation or existence of:

                  (a) undetermined or inchoate liens and charges incidental to
         construction, maintenance, development or operation;

                  (b) the lien of taxes and assessments for the then current
         year;

                  (c) the lien of taxes and assessments not at the time
         delinquent;

                  (d) the lien of specified taxes and assessments which are
         delinquent but the validity of which is being contested at the time by
         the Company or such Subsidiary in good faith;

                  (e) the lien reserved in leases for rent and for compliance
         with the terms of the lease in the case of leasehold estates;

                  (f) any obligations or duties, affecting the property of the
         Company or such Subsidiary, to any municipality or public authority
         with respect to any franchise, grant, license, permit or similar
         arrangement;

                  (g) the liens of any judgments or attachments in an aggregate
         amount not in excess of $10,000,000, or the lien of any judgment or
         attachment the execution or enforcement of which has been stayed or
         which has been appealed and secured, if necessary, by the filing of an
         appeal bond;

                  (h) any mortgage, pledge, lien or encumbrance on any property
         held or used by the Company or a Subsidiary in connection with the
         exploration for, development of or production of oil, gas, natural gas
         (including liquefied gas and storage gas), other hydrocarbons, helium,
         coal, metals, minerals, steam, timber, geothermal or other natural
         resources or synthetic fuels, such properties to include, but not be
         limited to, the Company's or a Subsidiary's interest in any mineral fee
         interests, oil, gas or other mineral

                                       38
<PAGE>   44

         leases, royalty, overriding royalty or net profits interests,
         production payments and other similar interests, wellhead production
         equipment, tanks, field gathering lines, leasehold or field separation
         and processing facilities, compression facilities and other similar
         personal property and fixtures;

                  (i) any mortgage, pledge, lien or encumbrance on oil, gas,
         natural gas (including liquefied gas and storage gas), and other
         hydrocarbons, helium, coal, metals, minerals, steam, timber, geothermal
         or other natural resources or synthetic fuels produced or recovered
         from any property, an interest in which is owned or leased by the
         Company or a Subsidiary;

                  (j) mortgages, pledges, liens or encumbrances upon any
         property heretofore or hereafter acquired, created at the time of
         acquisition or within one year thereafter to secure all or a portion of
         the purchase price thereof, or existing thereon at the date of
         acquisition, whether or not assumed by the Company or a Subsidiary,
         provided that every such mortgage, pledge, lien or encumbrance shall
         apply only to the property so acquired and fixed improvements thereon;

                  (k) any extension, renewal or refunding, in whole or in part,
         of any mortgage, pledge, lien or encumbrance permitted by subparagraph
         (j) above, if limited to the same property or any portion thereof
         subject to, and securing not more than the amount secured by, the
         mortgage, pledge, lien or encumbrance extended, renewed or refunded;

                  (l) mortgages, pledges, liens or encumbrances upon any
         property heretofore or hereafter acquired by any corporation that is or
         becomes a Subsidiary after the date hereof ("Acquired Entity"),
         provided that every such mortgage, pledge, lien or encumbrance (1)
         shall either (A) exist prior to the time the Acquired Entity becomes a
         Subsidiary or (B) be created at the time the Acquired Entity becomes a
         Subsidiary or within one year thereafter to secure all or a portion of
         the acquisition price thereof and (2) shall only apply to those
         properties owned by the Acquired Entity at the time it becomes a
         Subsidiary or thereafter acquired by it from sources other than the
         Company or any other Subsidiary;

                  (m) the pledge of current assets, in the ordinary course of
         business, to secure current liabilities;

                  (n) mechanics' or materialmen's liens, any liens or charges
         arising by reason of pledges or deposits to secure payment of workmen's
         compensation or other insurance, good faith deposits in connection with
         tenders, leases of real estate, bids or contracts (other than contracts
         for the payment of money), deposits to secure duties or public or
         statutory obligations, deposits to secure, or in lieu of, surety, stay
         or appeal bonds, and deposits as security for the payment of taxes or
         assessments or similar charges;

                  (o) any lien arising by reason of deposits with, or the giving
         of any form of security to, any governmental agency or any body created
         or approved by law or governmental regulation for any purpose at any
         time in connection with the financing of

                                       39
<PAGE>   45

         the acquisition or construction of property as to be used in the
         business of the Company or a Subsidiary or as required by law or
         governmental regulation as a condition to the transaction of any
         business or the exercise of any privilege or license, or to enable the
         Company or a Subsidiary to maintain self-insurance or to participate in
         any funds established to cover any insurance risks or in connection
         with workmen's compensation, unemployment insurance, old age pensions
         or other social security, or to share in the privileges or benefits
         required for companies participating in such arrangements;

                  (p) any lien to secure indebtedness other than Funded Debt;

                  (q) any mortgage, pledge, lien or encumbrance of or upon any
         office equipment, data processing equipment (including, without
         limitation, computer and computer peripheral equipment), or
         transportation equipment (including, without limitation, motor
         vehicles, tractors, trailers, marine vessels, barges, towboats, rolling
         stock and aircraft);

                  (r) any mortgage, pledge, lien or encumbrance created or
         assumed by the Company or a Subsidiary in connection with the issuance
         of debt notes the interest on which is excludable from gross income of
         the holder of such security pursuant to the Code for the purpose of
         financing, in whole or in part, the acquisition or construction of
         property to be used by the Company or a Subsidiary; or

                  (s) the pledge or assignment of accounts receivable, or the
         pledge or assignment of conditional sales contracts or chattel
         mortgages and evidences of indebtedness secured thereby, received in
         connection with the sale by the Company or such Subsidiary or others of
         goods or merchandise to customers of the Company or such Subsidiary.

         In the case the Company or any Subsidiary shall propose to pledge,
mortgage or hypothecate any Principal Property at any time owned by it to secure
any indebtedness, other than as permitted by subdivisions (a) to (s), inclusive,
of this Section 4.04, the Company shall prior thereto give written notice
thereof to the Trustee, and the Company shall, or shall cause such Subsidiary
to, prior to or simultaneously with such pledge, mortgage or hypothecation, by
supplemental indenture executed to the Trustee (or to the extent legally
necessary to another trustee or additional or separate trustee), in form
satisfactory to the Trustee, effectively secure all the Securities equally and
ratably with such indebtedness.

                  SECTION 4.05. [Intentionally omitted]

                  SECTION 4.06. Exempted Indebtedness. Notwithstanding the
provisions of Section 4.04, the Company or a Subsidiary may issue, assume or
guarantee indebtedness secured by mortgage which would otherwise be subject to
the restrictions of Section 4.04 in an aggregate amount which, together with all
other indebtedness of the Company or a Subsidiary secured by a mortgage which
(if originally issued, assumed or guaranteed at such time) would otherwise be
subject to such restrictions (not including indebtedness permitted to be secured
under clauses (a) through (s) of Section 4.04), does not at the time exceed 10%
of the Consolidated Net Tangible

                                       40
<PAGE>   46

Assets of the Company, as shown on the audited consolidated financial statements
of the Company as of the end of the fiscal year preceding the date of
determination.

                  SECTION 4.07. Waiver of Certain Covenants. The Issuer may in
any particular instance, be excused from failing to comply with any term,
provision or condition set forth in Section 4.02 or 4.04, if before the time for
such compliance the Holders of at least a majority in Principal Amount at
Maturity of the outstanding Securities shall, by act of such Holders, either
waive such compliance in such instance or generally waive compliance with such
term, provision or condition but no such waiver shall extend to or affect such
term, provision or condition except to the extent so expressly waived, and,
until such waiver shall become effective, the obligations of the Issuer, and the
duties of the Trustee in respect of any such term, provision or condition shall
remain in full force and effect.

                  The Issuer may, but shall not be obligated to, fix a record
date for the purpose of determining the Persons entitled to waive compliance
with any covenant or condition hereunder. If a record date is fixed, the Holders
on such record date, or their duly designated proxies, and only such Persons,
shall be entitled to waive any such compliance, whether or not such Holders
remain Holders after such record date; provided that unless the Holders of at
least a majority in Principal Amount at Maturity of the outstanding Securities
affected shall have waived such compliance prior to the date which is 90 days
after such record date, any such waiver previously given shall automatically and
without further action by any Holder be canceled and of no further effect.

                  SECTION 4.08. Compliance Certificate. The Issuer shall deliver
to the Trustee within 120 days after the end of each fiscal year of the Issuer
an Officers' Certificate stating that in the course of the performance by the
signers of their duties as Officers of the Issuer they would normally have
knowledge of any Default and whether or not the signers know of any Default that
occurred during such period. If they do, the certificate shall describe the
Default, its status and what action the Issuer is taking or proposes to take
with respect thereto. The Issuer also shall comply with Trust Indenture Act
Section 314(a)(4).

                  SECTION 4.09. Further Instruments and Acts. The Issuer shall
execute and deliver to the Trustee such further instruments and do such further
acts as may be reasonably necessary or proper to carry out more effectively the
purpose of this Indenture.

                  SECTION 4.10. Calculation of Original Issue Discount. The
Issuer shall file with the Trustee promptly at the end of each calendar year (i)
a written notice specifying the amount of Original Issue Discount (including
daily rates and accrual periods) accrued on the outstanding Securities as of the
end of such year and (ii) such other specific information relating to such
Original Issue Discount as may then be relevant under the Code.

                                       41
<PAGE>   47

                                   ARTICLE 5

                               SUCCESSOR COMPANIES

                  SECTION 5.01. Merger and Consolidation. The Issuer shall not
consolidate with or merge with or into, or convey, transfer or lease its assets
as, or substantially as, an entirety to, any Person, unless:

                  (i) the resulting, surviving or transferee Person (the
         "Successor Company") shall expressly assume, by a supplemental
         indenture, executed and delivered to the Trustee, in form satisfactory
         to the Trustee, all the obligations of the Issuer under the Securities
         and this Indenture;

                  (ii) immediately after giving effect to such transaction, no
         Event of Default shall have occurred and be continuing;

                  (iii) the Issuer shall have delivered to the Trustee an
         Officers' Certificate and an Opinion of Counsel, each stating that such
         consolidation, merger or transfer and such supplemental indenture (if
         any) comply with this Indenture; and

                  (iv) if, as a result of any such consolidation, merger or
         transfer, the Principal Property of the Issuer would become subject to
         a Lien which shall not be permitted by this Indenture, the Issuer or
         the Successor Company, as the case may be, shall take such steps as
         shall be necessary to secure the Securities equally and ratably with
         (or prior to) all Indebtedness secured thereby.

                  The Successor Company shall succeed to, and be substituted
for, and may exercise every right and power of, the Issuer under this Indenture,
but the predecessor Issuer in the case of a lease of all or substantially all of
its assets shall not be released from its obligations under the Securities and
this Indenture.

                                   ARTICLE 6

                              DEFAULTS AND REMEDIES

                  SECTION 6.01. Events of Default. An "Event of Default" with
respect to Notes occurs if:

                  (1) the Issuer defaults in any payment of the Principal Amount
         at Maturity (or, if the Securities have been converted to semi-annual
         coupon notes following a Tax Event, the Restated Principal Amount),
         Redemption Price, Purchase Price or Fundamental Change Repurchase Price
         on any Security when it becomes due and payable;

                  (2) the Issuer defaults in the payment of interest on any
         Security, if the Issuer has exercised its option following a Tax Event
         to convert the Securities into semi-annual coupon notes, when such
         interest becomes due and payable, and such default continues for a
         period of 30 days;

                                       42
<PAGE>   48

                  (3) the Issuer defaults in the payment of liquidated damages
         required to be made on any Security pursuant to the Registration Rights
         Agreement, and such default continues for a period of 30 days;

                  (4) the Issuer fails to comply with any of its covenants or
         agreements contained in the Securities or this Indenture (other than
         those referred to in (1), (2) or (3) above) and such failure continues
         for 60 days after the notice specified below;

                  (5) the Issuer pursuant to or within the meaning of any
         Bankruptcy Law:

                           (A) commences a voluntary case;

                           (B) consents to the entry of an order for relief
                  against it in an involuntary case;

                           (C) consents to the appointment of a Custodian of it
                  or for any substantial part of its property; or

                           (D) makes a general assignment for the benefit of its
                  creditors or takes any comparable action under any foreign
                  laws relating to insolvency; or

                  (6) a court of competent jurisdiction enters an order or
         decree under any Bankruptcy Law that:

                           (A) is for relief against the Issuer or in an
                  involuntary case;

                           (B) appoints a Custodian of the Issuer or for any
                  substantial part of its property; or

                           (C) orders the winding up or liquidation of the
                  Issuer or any similar relief is granted under any foreign laws
                  and the order or decree remains unstayed and in effect for 60
                  days.

                  The foregoing shall constitute Events of Default whatever the
reason for any such Event of Default and whether it is voluntary or involuntary
or is effected by operation of law or pursuant to any judgment, decree or order
of any court or any order, rule or regulation of any administrative or
governmental body.

                  The term "Bankruptcy Law" means Title 11, United States Code,
or any similar Federal or state law for the relief of debtors. The term
"Custodian" means any receiver, trustee, assignee, liquidator, custodian or
similar official under any Bankruptcy Law.

                  A Default under clause (4) above is not an Event of Default
until the Trustee or the Holders of at least 25% in Principal Amount at Maturity
of the outstanding Securities notify the Issuer of the Default and the Issuer
does not cure such Default within the time specified in clause (4) after receipt
of such notice. Such notice must specify the Default, demand that it be remedied
and state that such notice is a "Notice of Default."

                                       43
<PAGE>   49

                  SECTION 6.02. Acceleration. If an Event of Default with
respect to any Securities at the time outstanding (other than an Event of
Default specified in Section 6.01(5) or (6) with respect to the Issuer) occurs
and is continuing, the Trustee or the Holders of at least 25% in Principal
Amount at Maturity of the outstanding Securities by notice to the Issuer, may
declare the Issue Price (or, if the Securities have been converted into
semi-annual coupon notes, the Restated Principal Amount) of and accrued Original
Issue Discount (or, if the Securities have been converted into semi-annual
coupon notes, accrued but unpaid interest) to the date of declaration on all the
Securities to be immediately due and payable. Upon such a declaration, such
Issue Price (or, if the Securities have been converted into semi-annual coupon
notes, the Restated Principal Amount) and Original Issue Discount (or, if the
Securities have been converted into semi-annual coupon notes, accrued but unpaid
interest) shall be due and payable immediately. If an Event of Default specified
in Section 6.01(5) or (6) occurs, the Issue Price (or, if the Securities have
been converted into semi-annual coupon notes, the Restated Principal Amount) of
and accrued Original Issue Discount (or, if the Securities have been converted
into semi-annual coupon notes, accrued but unpaid interest) to the occurrence of
such event on all the Securities shall ipso facto become and be immediately due
and payable without any declaration or other act on the part of the Trustee or
any Holder. The Holders of a majority in Principal Amount at Maturity of the
Securities by notice to the Trustee may rescind an acceleration and its
consequences if the rescission would not conflict with any judgment or decree
and if all existing Events of Default have been cured or waived except
nonpayment of the Issue Price (or, if the Securities have been converted into
semi-annual coupon notes, the Restated Principal Amount) or Original Issue
Discount (or, if the Securities have been converted into semi-annual coupon
notes, accrued but unpaid interest) that has become due solely because of
acceleration. No such rescission shall affect any subsequent Default or impair
any right consequent thereto.

                  SECTION 6.03. Other Remedies. If an Event of Default occurs
and is continuing, the Trustee may pursue any available remedy to collect the
payment of the Issue Price (or, if the Securities have been converted into
semi-annual coupon notes, the Restated Principal Amount) of or accrued Original
Issue Discount (or, if the Securities have been converted into semi-annual
coupon notes, accrued but unpaid interest) on the Securities or to enforce the
performance of any provision of the Securities or this Indenture.

                  The Trustee may institute and maintain a suit or legal
proceeding even if it does not possess any of the Securities or does not produce
any of them in the proceeding. A delay or omission by the Trustee or any
Securityholder in exercising any right or remedy accruing upon an Event of
Default shall not impair the right or remedy or constitute a waiver of or
acquiescence in the Event of Default. No remedy is exclusive of any other
remedy. All available remedies are cumulative.

                  SECTION 6.04. Waiver of Past Defaults. The Holders of a
majority in Principal Amount at Maturity of the Securities by notice to the
Trustee may waive an existing Default and its consequences except (i) a Default
in the payment of the Issue Price (or, if the Securities have been converted
into semi-annual coupon notes, the Restated Principal Amount) of, accrued
Original Issue Discount (or, if the Securities have been converted into
semi-annual coupon notes, accrued but unpaid interest) on, or liquidated damages
with respect to, a Security, (ii) a Default arising from the failure to purchase
or repurchase any Security when required pursuant to the terms of this
Indenture, (iii) a Default arising from the failure to comply with the
provisions of

                                       44
<PAGE>   50

Article 11, or (iv) a Default in respect of a provision that under Section 9.02
cannot be amended without the consent of each Securityholder affected. When a
Default is waived, it is deemed cured, but no such waiver shall extend to any
subsequent or other Default or impair any consequent right.

                  SECTION 6.05. Control by Majority. The Holders of a majority
in Principal Amount at Maturity of the outstanding Securities may direct the
time, method and place of conducting any proceeding for any remedy available to
the Trustee or of exercising any trust or power conferred on the Trustee.
However, the Trustee may refuse to follow any direction that conflicts with law
or this Indenture or, subject to Section 7.01, that the Trustee determines is
unduly prejudicial to the rights of any other Holder or that would subject the
Trustee to personal liability, unless the Trustee is offered indemnity
reasonably satisfactory to it.

                  SECTION 6.06. Limitation on Suits. Except as provided in
Section 6.07, no Holder of a Security may pursue any remedy with respect to this
Indenture or the Securities unless:

                  (1) the Holder previously gave the Trustee written notice
         stating that an Event of Default is continuing;

                  (2) the Holders of at least 25%, in Principal Amount at
         Maturity of the outstanding Securities make a written request to the
         Trustee to pursue the remedy;

                  (3) such Holder or Holders offer to the Trustee reasonable
         security or indemnity satisfactory to the Trustee against any loss,
         liability or expense;

                  (4) the Trustee does not comply with the request within 60
         days after receipt of the request and the offer of security or
         indemnity; and

                  (5) the Holders of a majority in Principal Amount at Maturity
         of the outstanding Securities do not give the Trustee a direction
         inconsistent with the request during such 60-day period.

                  A Securityholder may not use this Indenture to prejudice the
rights of another Securityholder or to obtain a preference or priority over
another Securityholder.

                  SECTION 6.07. Rights of Holders to Receive Payment.
Notwithstanding any other provision of this Indenture, the right of any Holder
to receive payment of Issue Price (or, if the Securities have been converted
into semi-annual coupon notes, the Restated Principal Amount) of and liquidated
damages and accrued Original Issue Discount (or, if the Securities have been
converted into semi-annual coupon notes, accrued but unpaid interest) on the
Securities held by such Holder, on or after their Maturity, or to bring suit for
the enforcement of any such payment on or after their Maturity or the right to
convert such Securities as provided herein, shall not be impaired or affected
without the consent of such Holder.

                  SECTION 6.08. Collection Suit by Trustee. If an Event of
Default specified in Section 6.01 (1) or (2) occurs and is continuing, the
Trustee may recover judgment in its own

                                       45
<PAGE>   51

name and as trustee of an express trust against the Issuer for the whole amount
then due and owing (together with interest on any unpaid interest to the extent
lawful) and the amounts provided for in Section 7.07.

                  SECTION 6.09. Trustee May File Proofs of Claim. The Trustee
may file such proofs of claim and other papers or documents as may be necessary
or advisable in order to have the claims of the Trustee and the Securityholders
allowed in any judicial proceedings relative to any Issuer or any of its
Subsidiaries, their creditors or their property and, unless prohibited by law or
applicable regulations, may vote on behalf of the Holders in any election of a
trustee in bankruptcy or other Person performing similar functions, and any
Custodian in any such judicial proceeding is hereby authorized by each Holder to
make payments to the Trustee and, in the event that the Trustee shall consent to
the making of such payments directly to the Holders, to pay to the Trustee any
amount due it for the reasonable compensation, expenses, disbursements and
advances of the Trustee, its agents and its counsel, and any other amounts due
the Trustee under Section 7.07.

                  SECTION 6.10. Priorities. If the Trustee collects any money or
property pursuant to this Article 6, it shall pay out the money or property in
the following order:

                  FIRST: to the Trustee for amounts due under Section 7.07;

                  SECOND: to Securityholders for amounts due and unpaid on the
Securities for the Issue Price and accrued Original Issue Discount (or, if the
Securities have been converted to semi-annual coupon notes following a Tax
Event, the Restated Principal Amount and accrued interest), ratably, without
preference or priority of any kind, according to the amounts due and payable on
the Securities for the Issue Price and accrued Original Issue Discount (or, if
the Securities have been converted to semi-annual coupon notes following a Tax
Event, the Restated Principal Amount and accrued interest); and

                  THIRD: to the Issuer.

                  The Trustee may fix a record date and payment date for any
payment to Securityholders pursuant to this Section. At least 15 days before
such record date, the Trustee shall mail to each Securityholder and the Issuer a
notice that states the record date, the payment date and amount to be paid.

                  SECTION 6.11. Undertaking for Costs. In any suit for the
enforcement of any right or remedy under this Indenture or in any suit against
the Trustee for any action taken or omitted by it as Trustee, a court in its
discretion may require the filing, by any party litigant in the suit, of an
undertaking to pay the costs of the suit, and the court in its discretion may
assess reasonable costs, including reasonable attorneys' fees, against any party
litigant in the suit, having due regard to the merits and good faith of the
claims or defenses made by the party litigant. This Section does not apply to a
suit by the Trustee, a suit by a Holder pursuant to Section 6.07 or a suit by
Holders of more than 10% in Principal Amount at Maturity of the Securities.

                                       46
<PAGE>   52

                  SECTION 6.12. Waiver of Stay or Extension Laws. The Issuer (to
the extent it may lawfully do so) shall not at any time insist upon, plead, or
in any manner whatsoever claim or take the benefit or advantage of, any stay or
extension law, wherever enacted, now or at any time hereafter in force, which
may affect the covenants or the performance of this Indenture; and the Issuer
(to the extent that it may lawfully do so) hereby expressly waives all benefit
or advantage of any such law, and shall not hinder, delay or impede the
execution of any power herein granted to the Trustee, but shall suffer and
permit the execution of every such power as though no such law had been enacted.

                                    ARTICLE 7

                                     TRUSTEE

                  SECTION 7.01. Duties of Trustee. (a) If an Event of Default
has occurred and is continuing, the Trustee shall exercise the rights and powers
vested in it by this Indenture and use the same degree of care and skill in its
exercise thereof as a prudent person would exercise or use under the
circumstances in the conduct of such person's own affairs.

                  (b) Except during the continuance of an Event of Default:

                  (1) the Trustee undertakes to perform such duties and only
         such duties as are specifically set forth in this Indenture and no
         implied covenants or obligations shall be read into this Indenture
         against the Trustee; and

                  (2) in the absence of bad faith on its part, the Trustee may
         conclusively rely, as to the truth of the statements and the
         correctness of the opinions expressed therein, upon certificates or
         opinions furnished to the Trustee and conforming to the requirements of
         this Indenture. However, the Trustee shall examine the certificates and
         opinions to determine whether or, not they conform to the requirements
         of this Indenture (but need not confirm or investigate the accuracy of
         mathematical calculations or other facts stated therein.

                  (c) The Trustee may not be relieved from liability for its own
grossly negligent action, its own grossly negligent failure to act or its own
willful misconduct, except that:

                  (1) this paragraph does not limit the effect of paragraph (b)
         of this Section;

                  (2) the Trustee shall not be liable for any error of judgment
         made in good faith by a Trust Officer unless it is proved that the
         Trustee was grossly negligent in ascertaining the pertinent facts; and

                  (3) the Trustee shall not be liable with respect to any action
         it takes or omits to take in good faith in accordance with a direction
         received by it pursuant to Section 6.05.

                  (d) Every provision of this Indenture that in any way relates
to the Trustee is subject to paragraphs (a), (b), (c) and (g) of this Section.

                                       47
<PAGE>   53

                  (e) The Trustee shall not be liable for interest on any money
received by it except as the Trustee may agree in writing with the Issuer.

                  (f) Money held in trust by the Trustee need not be segregated
from funds except to the extent required by law.

                  (g) No provision of this Indenture shall require the Trustee
to expend or risk its own funds or otherwise incur financial liability in the
performance of any of its duties hereunder or in the exercise of any of its
rights or powers.

                  (h) Every provision of this Indenture relating to the conduct
or affecting the liability of or affording protection to the Trustee shall be
subject to the provisions of this Section and to the provisions of the Trust
Indenture Act.

                  SECTION 7.02. Rights of Trustee. (a) The Trustee may
conclusively rely on any document believed by it to be genuine and to have been
signed or presented by the proper person. The Trustee need not investigate any
fact or matter stated in the document.

                  (b) Before the Trustee acts or refrains from acting, it may
require an Officers' Certificate or an Opinion of Counsel. The Trustee shall not
be liable for any action it takes or omits to take in good, faith in reliance on
the Officers' Certificate or Opinion of Counsel.

                  (c) The Trustee may act through agents or attorneys and shall
not be responsible for the misconduct or negligence of any agent or attorney
appointed with due care.

                  (d) The Trustee shall not be liable for any action it takes or
omits to take in good faith which it believes to be authorized or within its
rights or powers; provided, however, that the Trustee's conduct does not
constitute willful misconduct or gross negligence.

                  (e) The Trustee may consult with counsel, and the advice or
opinion of counsel with respect to legal matters relating to this Indenture and
the Securities, shall be full and complete authorization and protection from
liability in respect to any action taken, omitted or suffered by it hereunder in
good faith and in accordance with the advice or opinion of such counsel.

                  (f) The Trustee shall not be bound to make any investigation
into the facts or matters stated in any resolution, certificate, statement,
instrument, opinion, report, notice, request, consent, order, approval, bond,
debenture, note or other paper or document.

                  (g) The Trustee shall not be deemed to have notice of any
Default or Event of Default, except Events of Default under Section 6.01(1) or
(2), unless a Trust Officer of the Trustee has actual knowledge thereof or
unless written notice of any event which is in fact such a default is received
by the Trustee at the Corporate Trust Office of the Trustee, and such notice
references the Securities and this Indenture.

                  (h) The rights, privileges, protections, immunities and
benefits given to the Trustee, including, without limitation, its right to be
indemnified, are extended to and shall be

                                       48
<PAGE>   54

enforceable by, the Trustee in each of its capacities hereunder, and to each
agent, custodian and other Person employed to act hereunder.

                  SECTION 7.03. Individual Rights of Trustee. The Trustee in its
commercial banking or any other capacity may become the owner or pledgee of
Securities and may otherwise deal with the Issuer or its Affiliates with the
same rights it would have if it were not Trustee. Any Paying Agent, Registrar or
co-paying agent may do the same with like rights. However, the Trustee must
comply with Sections 7.10 and 7.11.

                  SECTION 7.04. Trustee's Disclaimer. The Trustee shall not be
responsible for and makes no representation as to the validity or adequacy of
this Indenture or the Securities, it shall not be accountable for the Issuer's
use of the proceeds from the Securities, and it shall not be responsible for any
statement in this Indenture, in the Securities, or in any document executed in
connection with the sale of the Securities, other than those set forth in the
Trustee's certificate of authentication.

                  SECTION 7.05. Notice of Defaults. If a Default occurs and is
continuing and if it is actually known to a Trust Officer of the Trustee, the
Trustee shall mail to each Securityholder notice of the Default within 90 days
after it occurs. Except in the case of a Default in payment of the Issue Price
(or, if the Securities have been converted into semi-annual coupon notes, the
Restated Principal Amount) of or accrued Original Issue Discount (or, if the
Securities have been converted into semi-annual coupon notes, accrued interest)
on any Security (including payments pursuant to the mandatory purchase or
repurchase provisions of such Security, if any), the Trustee may withhold the
notice if and so long as a committee of its Trust Officers in good faith
determines that withholding the notice is in the interests of Securityholders.

                  SECTION 7.06. Reports by Trustee to Holder. As promptly as
practicable after each February 28 beginning with the February 28 following the
Closing Date, and in any event prior to April 30 in each year, the Trustee shall
mail to each Securityholder a brief report dated as of such February that
complies with Section 313(a) of the Trust Indenture Act. The Trustee shall also
comply with Section 313(b) of the Trust Indenture Act.

                  A copy of each report at the time of its mailing to
Securityholders shall be filed with the SEC and each stock exchange (if any) on
which the Securities are listed. The Issuer agrees to notify promptly the
Trustee whenever the Securities become listed on any stock exchange and of any
delisting thereof.

                  SECTION 7.07. Compensation and Indemnity. The Issuer shall pay
to the Trustee from time to time such compensation for its services as the
Issuer and the Trustee shall from time to time agree in writing. The Trustee's
compensation shall not be limited by any law on compensation of a trustee of an
express trust. The Issuer shall reimburse the Trustee upon request for all
reasonable out-of-pocket expenses incurred or made by it, including costs of
collection, in addition to the compensation for its services. Such expenses
shall include the reasonable compensation and expenses, disbursements and
advances of the Trustee's agents, counsel, accountants and experts. The Issuer
shall indemnify the Trustee against any and all loss, liability or expense
(including reasonable attorneys' fees) incurred by or in connection with

                                       49
<PAGE>   55

the administration of this trust and the performance of its duties hereunder.
The Trustee shall notify the Issuer of any claim for which it may seek indemnity
promptly upon obtaining actual knowledge thereof, provided, however, that any
failure so to notify the Issuer shall not relieve the Issuer of its indemnity
obligations hereunder. The Issuer need not reimburse any expense or indemnify
against any loss, liability or expense incurred by an indemnified party through
such party's own willful misconduct, gross negligence or bad faith.

                  To secure the Issuer's payment obligations in this Section,
the Trustee shall have a lien prior to the Securities on all money or property
held or collected by the Trustee other than money or property held in trust to
make any payment on particular Securities.

                  The Issuer's payment obligations pursuant to this Section
shall survive the satisfaction or discharge of this Indenture, any rejection or
termination of this Indenture under any bankruptcy law or the resignation or
removal of the Trustee. When the Trustee incurs expenses after the occurrence of
a Default specified in Section 6.01(5) or (6), the expenses are intended to
constitute expenses of administration under the Bankruptcy Law.

                  SECTION 7.08. Replacement of Trustee. The Trustee may resign
at any time with respect to the Securities by so notifying the Issuer. The
Holders of a majority in Principal Amount at Maturity of the Securities may
remove the Trustee and may appoint a successor Trustee. The Issuer shall remove
the Trustee if:

                  (1) the Trustee fails to comply with Section 7.10;

                  (2) the Trustee is adjudged bankrupt or insolvent;

                  (3) a receiver or other public officer takes charge of the
         Trustee or its property; or

                  (4) the Trustee otherwise becomes incapable of acting.

                  If the Trustee resigns, is removed by the Issuer or by the
Holders of a majority in Principal Amount at Maturity of the Securities and such
Holders do not reasonably promptly appoint a successor Trustee or if a vacancy
exists in the office of Trustee for any reason (the Trustee in such event being
referred to herein as the retiring Trustee), the Issuer shall promptly appoint a
successor Trustee.

                  A successor Trustee shall deliver a written acceptance of its
appointment to the retiring Trustee and to the Issuer. Thereupon the resignation
or removal of the retiring Trustee shall become effective, and the successor
Trustee shall have all the rights, powers and duties of the Trustee under this
Indenture. The successor Trustee shall mail a notice of its succession to
Securityholders. The retiring Trustee shall promptly transfer all property held
by it as Trustee to the successor Trustee, subject to the lien provided for in
Section 7.07.

                  If a successor Trustee does not take office within 30 days
after the retiring Trustee resigns or is removed, the retiring Trustee or the
Holders of 10% in Principal Amount at Maturity of the Securities may petition
any court of competent jurisdiction for the appointment of a successor Trustee.

                                       50
<PAGE>   56

                  If the Trustee fails to comply with Section 7.10, any
Securityholder may petition any court of competent jurisdiction for the removal
of the Trustee and the appointment of a successor Trustee.

                  Notwithstanding the replacement of the Trustee pursuant to
this Section 7.08, the Issuer's obligations under Section 7.07 shall continue
for the benefit of the retiring Trustee.

                  SECTION 7.09. Successor Trustee by Merger. If the Trustee
consolidates with, merges or converts into, or transfers all or substantially
all its corporate-trust business or assets to, another corporation or banking
association, the resulting, surviving or transferee corporation without any
further act shall be the successor Trustee. As promptly as practicable
thereafter, the Trustee shall notify the Issuer of such succession.

                  In case at the time such successor or successors by merger,
conversion or consolidation to the Trustee shall succeed to the trusts created
by this Indenture any of the Securities shall have been authenticated but not
delivered, any such successor to the Trustee may adopt the certificate of
authentication of any predecessor trustee, and deliver such Securities so
authenticated; and if at that time any of the Securities shall not have been
authenticated, any such successor to the Trustee may authenticate such
Securities either in the name of any predecessor hereunder or in the name of the
successor to the Trustee; and in all such cases such certificates shall have the
full force which it is anywhere in the Securities or in this Indenture provided
that the certificate of the Trustee shall have.

                  SECTION 7.10. Eligibility; Disqualification. The Trustee shall
at all times satisfy the requirements of Trust Indenture Act Section 310(a). The
Trustee shall have a combined capital and surplus of at least $100,000,000 as
set forth in its most recent published annual report of condition. The Trustee
shall comply with Trust Indenture Act Section 310(b); provided, however, that
there shall be excluded from the operation of Trust Indenture Act Section
310(b)(1) any indenture or indentures under which other securities or
certificates of interest or participation in other securities of the Issuer are
outstanding if the requirements for such exclusion set forth in Trust Indenture
Act Section 310(b)(1) are met.

                  SECTION 7.11. Preferential Collection of Claims Against
Issuer. The Trustee shall comply with Trust Indenture Act Section 311(a),
excluding any creditor relationship listed in Trust Indenture Act Section
311(b). A Trustee who has resigned or has been removed shall be subject to Trust
Indenture Act Section 311(a) to the extent indicated.

                                   ARTICLE 8

                             DISCHARGE OF INDENTURE

                  SECTION 8.01. Discharge of Liability on Securities. This
Indenture shall cease to be of further effect, and the Trustee, on demand of and
at the expense of the Issuer, shall execute proper instruments acknowledging
satisfaction and discharge of this Indenture, when

                                       51
<PAGE>   57

                  (a) either

                  (1) all Securities theretofore authenticated and delivered
         (other than (A) Securities which have been destroyed, lost or stolen
         and which have been replaced or paid as provided in Section 2.08 and
         (B) Securities for whose payment money has theretofore been deposited
         with the Trustee in trust or segregated and held in trust by the Issuer
         and thereafter repaid to the Issuer or otherwise discharged from such
         trust as provided in Section 10.02) have been delivered to the Trustee
         for cancellation; or

                  (2) all such Securities not theretofore delivered to the
         Trustee for cancellation have become due and payable, whether at Stated
         Maturity or upon any Redemption Date, Fundamental Change Repurchase
         Date, Purchase Date or Conversion Date, and the Issuer has deposited or
         caused to be deposited with the Trustee, the Paying Agent or the
         Conversion Agent, as applicable, as trust funds in trust for the
         purpose an amount of money or securities sufficient to pay and
         discharge the entire Indebtedness evidenced by such Securities not
         theretofore delivered to the Trustee for cancellation;

                  (b) the Issuer has paid or caused to be paid all other sums
payable hereunder by the Issuer; and

                  (c) the Issuer has delivered to the Trustee an Officers'
Certificate and an Opinion of Counsel, each stating that all conditions
precedent herein provided for relating to the satisfaction and discharge of this
Indenture have been complied with.

                  Notwithstanding clauses (a) and (b) above, the Issuer's
obligations in Sections 2.04, 2.05, 2.06, 2.07, 2.08, 2.09, 7.07, 7.08, 10.2
and, if money or securities shall have been deposited with the Trustee pursuant
to subclause (2) of clause (a) of this Section 8.01, shall survive until the
Securities have been paid in full. Thereafter, the Issuer's obligations in
Section 7.07 shall survive.

                  SECTION 8.02. Application of Trust Money. The Trustee shall
hold in trust all money deposited with it pursuant to Section 8.01. It shall
apply the deposited money through the Paying Agent and in accordance with this
Indenture to the payment to the Persons entitled thereto.

                  SECTION 8.03. Repayment to Issuer. Subject to any applicable
abandoned property law, the Trustee and the Paying Agent shall pay to the Issuer
upon written request any money or securities held by them that remains unclaimed
for two years, and, thereafter, Securityholders entitled to the money or
securities must look to the Issuer for payment as general creditors.

                                   ARTICLE 9

                                   AMENDMENTS

                  SECTION 9.01. Without Consent of Holders. The Issuer and the
Trustee may amend this Indenture or the Securities without notice to or consent
of any Securityholder:

                                       52
<PAGE>   58

                  (1) to cure any ambiguity or correct or supplement any
         defective or inconsistent provision contained in this Indenture or make
         any other changes in the provisions of this Indenture which the Issuer
         and the Trustee may deem necessary or desirable provided such amendment
         does not materially and adversely affect the legal rights under the
         Indenture of the Securityholders;

                  (2) to comply with Article 5;

                  (3) to provide for uncertificated Securities in addition to or
         in place of certificated Securities; provided, however, that the
         uncertificated Securities are issued in registered form for purposes of
         Section 163(f) of the Code or in a manner such that the uncertificated
         Securities are described in Section 163(f)(2)(B) of the Code;

                  (4) to add guarantees or co-obligors with respect to the
         Securities or to secure the Securities;

                  (5) to increase the Conversion Rate;

                  (6) to add to the covenants of the Issuer for the benefit of
         the Holders or to surrender any right or power herein conferred upon
         the Issuer;

                  (7) to comply with any requirements of the SEC in connection
         with qualifying, or maintaining the qualification of, this Indenture
         under the Trust Indenture Act; or

                  (8) to make any changes that would provide the Securityholders
         with any additional rights or benefits or that do not adversely affect
         the legal rights under this Indenture of any such Securityholder.

                  SECTION 9.02. With Consent of Holders. The Issuer and the
Trustee may amend this Indenture or the Securities without notice to any
Securityholder but with the written consent of the Holders of at least a
majority in Principal Amount at Maturity of the Securities then outstanding
(including consents obtained in connection with a tender offer or exchange for
the Securities). However, without the consent of each Securityholder affected,
an amendment may not:

                  (1) make any change in the manner or rate of accrual in
         connection with Original Issue Discount, reduce the yield to maturity
         referred to in the Securities, reduce the rate of interest referred to
         in Section 10.01 upon the occurrence of a Tax Event, or extend the time
         for payment of Original Issue Discount or interest, if any, on any
         Security;

                  (2) reduce the Principal Amount at Maturity, Restated
         Principal Amount or the Issue Price of or extend the Stated Maturity of
         any Security;

                  (3) reduce the Redemption Price, Purchase Price or Fundamental
         Change Repurchase Price of any Security;

                                       53
<PAGE>   59

                  (4) make any Security payable in money or securities other
         than that stated in the Security;

                  (5) make any change that adversely affects the right to
         convert any Security;

                  (6) make any change that adversely affects the right to
         require the Issuer to repurchase or purchase the Securities in
         accordance with the terms thereof and this Indenture;

                  (7) reduce the percentage in Principal Amount at Maturity of
         the outstanding Securities, the consent of whose Holders is required
         for any such amendment, or the consent of whose Holders is required for
         any waiver (of compliance with certain provisions of this Indenture or
         certain defaults hereunder and their consequences) provided for in this
         Indenture; or

                  (8) make any change in Section 6.04 or 6.07 or the second
         sentence of this Section 9.02.

                  It shall not be necessary for the consent of the Holders under
this Section to approve the particular form of any proposed amendment, but it
shall be sufficient if such consent approves the substance thereof. After an
amendment under this Section becomes effective, the Issuer shall mail to all
affected Securityholders a notice briefly describing such amendment. The failure
to give such notice to all such Securityholders, or any defect therein, shall
not impair or affect the validity of an amendment under this Section.

                  SECTION 9.03. Compliance with Trust Indenture Act. Every
amendment to this Indenture or the Securities shall comply with the Trust
Indenture Act as then in effect.

                  SECTION 9.04. Revocation and Effect of Consents and Waivers. A
consent to an amendment or a waiver by a Holder of a Security shall bind the
Holder and every subsequent Holder of that Security or portion of the Security
that evidences the same debt as the consenting Holder's Security, even if
notation of the consent or waiver is not made on the Security. However, any such
Holder or subsequent Holder may revoke the consent or waiver as to such Holder's
Security or portion of the Security if the Trustee receives the notice of
revocation before the date the amendment or waiver becomes effective. After an
amendment or waiver becomes effective, it shall bind every Securityholder. An
amendment or waiver becomes effective once both (i) the requisite number of
consents have been received by the Issuer or the Trustee and (ii) such amendment
or waiver has been executed by the Issuer and the Trustee.

                  The Issuer may, but shall not be obligated to, fix a record
date for the purpose of determining the Securityholders entitled to give their
consent or take any other action described above or required or permitted to be
taken pursuant to this Indenture. If a record date is fixed, then
notwithstanding the immediately preceding paragraph, those Persons who were
Securityholders at such record date (or their duly designated proxies), and only
those Persons, shall be entitled to give such consent or to revoke any consent
previously given or to take any such action, whether or not such Persons
continue to be Holders after such record date. No such consent shall be valid or
effective for more than 120 days after such record date.

                                       54
<PAGE>   60

                  SECTION 9.05. Notation on or Exchange of Securities. If an
amendment changes the terms of a Security, the Trustee may require the Holder of
the Security to deliver it to the Trustee. The Trustee may place an appropriate
notation on the Security regarding the changed terms and return it to the
Holder. Alternatively, if the Issuer or the Trustee so determines, the Issuer in
exchange for the Security shall issue and the Trustee shall authenticate a new
Security that reflects the changed terms. Failure to make the appropriate
notation or to issue a new Security shall not affect the validity of such
amendment.

                  SECTION 9.06. Trustee To Sign Amendments. The Trustee shall
sign any amendment authorized pursuant to this Article 9 if the amendment does
not adversely affect the rights, duties, liabilities or immunities of the
Trustee. If it does, the Trustee may but need not sign it. In signing such
amendment the Trustee shall be entitled to receive indemnity satisfactory to it
and to receive, and (subject to Section 7.01) shall be fully protected in
relying upon, an Officers' Certificate and an Opinion of Counsel stating that
such amendment is authorized or permitted by this Indenture and that such
amendment is the legal, valid and binding obligation of the Issuer, enforceable
against it in accordance with its terms, subject to customary exceptions, and
complies with the provisions hereof (including Section 9.03).

                                   ARTICLE 10

                          SPECIAL TAX EVENT CONVERSION

                  SECTION 10.01. Optional Conversion to Semi-annual Coupon Note
Upon Tax Event. From and after (i) the date (the "Tax Event Date") of the
occurrence of a Tax Event and (ii) the date the Issuer exercises its option set
forth in this Section 10.01, whichever is later (the "Option Exercise Date"), at
the option of the Issuer, interest in lieu of future Original Issue Discount
shall accrue at the rate of 2.125% per annum on a restated principal amount per
$1,000 original Principal Amount at Maturity (the "Restated Principal Amount")
equal to the Issue Price plus Original Issue Discount accrued to the Option
Exercise Date and shall be payable semi-annually on February 7 and August 7 of
each year (each an "Interest Payment Date") to holders of record at the close of
business on January 23 and July 23 (each a "Regular Record Date") immediately
preceding such Interest Payment Date. Interest will be computed on the basis of
a 360-day year comprised of twelve 30-day months and will accrue from the most
recent date on which interest has been paid or, if no interest has been paid,
from the Option Exercise Date. Within 15 days of its exercise of the option set
forth in this Section 10.01, the Issuer shall deliver a written notice of the
Option Exercise Date by facsimile and first-class mail to the Trustee and by
first-class mail to the Holders of the Securities. From and after the Option
Exercise Date, (i) the Issuer shall be obligated to pay at Stated Maturity, in
lieu of the Principal Amount at Maturity of a Security, the Restated Principal
Amount thereof and (ii) "Issue Price and accrued Original Issue Discount,"
"Issue Price plus Original Issue Discount" or similar words, as used herein,
shall mean Restated Principal Amount plus accrued and unpaid interest with
respect to any Security. Securities authenticated and delivered after the Option
Exercise Date may, and shall if required by the Trustee, bear a notation in a
form approved by the Trustee as to the conversion of the Securities to
semi-annual coupon notes.

                  In the event the Issuer exercises its option pursuant to this
Section 10.01 to have interest in lieu of Original Issue Discount accrue on the
Security following a Tax Event, the

                                       55
<PAGE>   61

Holder shall be entitled on conversion into Common Stock to receive the same
number of shares of Common Stock such Holder would have received if the Issuer
had not exercised such option. If the Issuer exercises such option, Securities
surrendered for conversion during the period from the close of business on any
Regular Record Date next preceding any Interest Payment Date to the opening of
business on such Interest Payment Date (except Securities to be redeemed on a
date within such period) must be accompanied by payment of an amount equal to
the interest thereon that the registered Holder is entitled to receive. Except
where Securities surrendered for conversion must be accompanied by payment as
described above, no interest on converted Securities shall be payable by the
Issuer on any Interest Payment Date subsequent to the date of conversion.

                  SECTION 10.02. Paying Agent To Hold Money in Trust. Prior to
11 a.m. (New York City time) on the Interest Payment Date, the Issuer shall
deposit with the Paying Agent (or if the Issuer or a Subsidiary of the Issuer is
acting as Paying Agent, segregate and hold in trust for the benefit of the
Persons entitled thereto) a sum sufficient to pay interest when due. The Issuer
shall require each Paying Agent (other than the Trustee) to agree in writing
that the Paying Agent shall hold in trust for the benefit of Securityholders or
the Trustee all money held by the Paying Agent for the payment of principal or
interest on the Securities and shall notify the Trustee of any default by the
Issuer in making any such payment. If the Issuer or a Subsidiary of the Issuer
acts as Paying Agent, it shall segregate the money held by it as Paying Agent
and hold it as a separate trust fund. The Issuer at any time may require a
Paying Agent to pay all money held by it to the Trustee and to account for any
funds disbursed by the Paying Agent. Upon complying with this Section, the
Paying Agent shall have no further liability for the money delivered to the
Trustee.

                  SECTION 10.03. Securityholder Lists. The Trustee shall
preserve in as current a form as is reasonably practicable the most recent list
available to it of the names and addresses of Securityholders. If the Trustee is
not the Registrar, the Issuer shall furnish, or cause the Registrar to furnish,
to the Trustee, in writing at least five Business Days before each Interest
Payment Date and at such other times as the Trustee may request in writing, a
list in such form and as of such date as the Trustee may reasonably require of
the names and addresses of Securityholders.

                  SECTION 10.04. Payment of Interest; Interest Rights Preserved.
(a) Interest on any Security that is payable, and is punctually paid or duly
provided for, on any Interest Payment Date shall be paid to the Person in whose
name that Security is registered at the close of business on the Regular Record
Date for such interest at the office or agency of the Issuer maintained for such
purpose. Each installment of interest on any Security shall be paid in same-day
funds by transfer to an account maintained by the Holder located inside the
United States, provided that with respect to any Holder, such Holder shall have
furnished to the Paying Agent all required wire payment instructions no later
than the related Regular Record Date, or if no such instructions have been
furnished, by check payable to such Holder. In the case of a Global Security,
interest payable on any Interest Payment Date will be paid to the Depositary,
with respect to that portion of such Global Security held for its account by
Cede & Co. for the purpose of permitting such party to credit the interest
received by it in respect of such Global Security to the accounts of the
beneficial owners thereof.

                                       56
<PAGE>   62

                  (b) Except as otherwise specified with respect to the
Securities, any interest on any Security that is payable, but is not punctually
paid or duly provided for, within 30 days following any Interest Payment Date
(herein called "Defaulted Interest", which term shall include any accrued and
unpaid interest that has accrued on such defaulted amount in accordance with the
paragraph of the Securities captioned "Interest"), shall forthwith cease to be
payable to the registered Holder thereof on the relevant Regular Record Date by
virtue of having been such Holder, and such Defaulted Interest may be paid by
the Issuer, at its election in each case, as provided in clause (1) or (2)
below:

                  (1) The Issuer may elect to make payment of any Defaulted
         Interest to the Persons in whose names the Securities are registered at
         the close of business on a date (the "Special Record Date") for the
         payment of such Defaulted Interest, which shall be fixed in the
         following manner. The Issuer shall notify the Trustee in writing of the
         amount of Defaulted Interest proposed to be paid on each Security and
         the date of the proposed payment (which shall not be less than 20 days
         after such notice is received by the Trustee), and at the same time the
         Issuer shall deposit with the Trustee an amount of money equal to the
         aggregate amount proposed to be paid in respect of such Defaulted
         Interest or shall make arrangements satisfactory to the Trustee for
         such deposit on or prior to the date of the proposed payment, such
         money when deposited to be held in trust for the benefit of the Persons
         entitled to such Defaulted Interest as in this clause provided.
         Thereupon the Trustee shall fix a Special Record Date for the payment
         of such Defaulted Interest which shall be not more than 15 days and not
         less than 10 days prior to the date of the proposed payment and not
         less than 10 days after the receipt by the Trustee of the notice of the
         proposed payment. The Trustee shall promptly notify the Issuer of such
         Special Record Date and, in the name and at the expense of the Issuer,
         shall cause notice of the proposed payment of such Defaulted Interest
         and the Special Record Date therefor to be mailed, first-class postage
         prepaid, to each Holder of Securities at his address as it appears on
         the list of Securityholders maintained pursuant to this Indenture not
         less than 10 days prior to such Special Record Date. Notice of the
         proposed payment of such Defaulted Interest and the Special Record Date
         therefor having been mailed as aforesaid, such Defaulted Interest shall
         be paid to the Persons in whose names the Securities are registered at
         the close of business on such Special Record Date and shall no longer
         be payable pursuant to the following clause (2).

                  (2) The Issuer may make payment of any Defaulted Interest on
         the Securities in any other lawful manner not inconsistent with the
         requirements of any securities exchange on which such Securities may be
         listed, and upon such notice as may be required by such exchange, if,
         after notice given by the Issuer to the Trustee of the proposed payment
         pursuant to this clause, such manner of payment shall be deemed
         practicable by the Trustee.

                  Subject to the foregoing provisions, each Security delivered
under this Indenture upon registration of transfer of or in exchange for or in
lieu of any other Security shall carry the rights to interest accrued and
unpaid, and to accrue, which were carried by such other Security.

                                       57
<PAGE>   63

                                   ARTICLE 11

                                   CONVERSION

                  SECTION 11.01. Conversion Privilege. Except as provided in
this Article 11, a Holder of a Security may convert such Security into Common
Stock at any time during the period stated in the Securities. The number of
shares of Common Stock issuable upon conversion of a Security per $1,000 of
Principal Amount at Maturity thereof (the "Conversion Rate") shall be that set
forth in the Securities, subject to adjustment as herein set forth.

               The Holders' right to convert Securities into shares of Common
Stock is subject to the condition that, if the Sale Price on the Conversion Date
is (a) less than 100% of the Accreted Conversion Price in effect on such date,
then a Holder electing to exercise its right to convert its Securities on such
date shall receive, in lieu of Common Stock, cash in an amount equal to 95% of
the product of the Conversion Rate in effect on such date and such Sale Price or
(b) greater than or equal to 100% of the Accreted Conversion Price in effect on
such date but less than 110% of such Accreted Conversion Price, then a Holder
electing to exercise its right to convert its Securities on such date shall
receive, in lieu of Common Stock, cash in an amount equal to the sum of the
Issue Price plus Original Issue Discount (or, if the Issuer has exercised its
option to convert the Securities to semi-annual coupon notes following the
occurrence of a Tax Event, the Restated Principal Amount plus unpaid interest
thereon) accrued to the Conversion Date; provided, however, that this provision
shall not apply with respect to any Securities that have been called for
redemption pursuant to Section 3.03 nor shall it be subject to the proviso set
forth in the next succeeding paragraph.

               The Holders' right to convert Securities into shares of Common
Stock is also subject to the Company's right to elect to instead pay such Holder
the amount of cash set forth in the next succeeding sentence, in lieu of
delivering such shares of Common Stock; provided, however, that if an Event of
Default (other than a default in a cash payment upon conversion of the
Securities) shall have occurred and be continuing, the Company shall deliver
shares of Common Stock (and cash in lieu of fractional shares of Common Stock)
in accordance with this Article 11, whether or not the Company has delivered a
notice pursuant to Section 3.03 or 11.02 hereof to the effect that the
Securities would be paid in cash. The amount of cash to be paid pursuant to
Section 11.02 hereof for each $1,000 of Principal Amount of a Security upon
conversion shall be equal to the average Sale Price of the Common Stock for the
five consecutive trading days immediately following (i) the date of the
Company's notice of its election to deliver cash upon conversion, if the Company
shall not have given a notice of redemption pursuant to Section 3.03, or (ii)
the Conversion Date, in the case of a conversion following such a notice of
redemption specifying an intent to deliver cash upon conversion, in either case
multiplied by the Conversion Rate in effect on such Conversion Date. The Company
shall not pay cash in lieu of delivering shares of Common Stock upon the
conversion of any Security pursuant to the terms of this Article 11 (other than
cash in lieu of fractional shares pursuant to Section 11.03 hereof) if there has
occurred (prior to, on or after, as the case may be, the Conversion Date or the
date on which the Company delivers its notice of whether such Security shall be
converted into shares of Common Stock or cash pursuant to Section 11.02 hereof)
and is continuing an Event of Default (other than a default in a cash payment
upon conversion of such Securities).

                                       58
<PAGE>   64

                  A Holder may convert a portion of the Principal Amount at
Maturity of a Security if the portion is $1,000 or an integral multiple of
$1,000. Provisions of this Indenture that apply to conversion of all of a
Security also apply to conversion of a portion of a Security.

                  "Average Quoted Price" means the average of the Sale Prices of
the Common Stock for the shorter of

                  (i) 30 consecutive trading days ending on the last full
         trading day prior to the Time of Determination with respect to the
         rights, warrants or options or distribution in respect of which the
         Average Quoted Price is being calculated, or

                  (ii) the period (x) commencing on the date next succeeding the
         first public announcement of (a) the issuance of rights, warrants or
         options or (b) the distribution, in each case, in respect of which the
         Average Quoted Price is being calculated and (y) proceeding through the
         last full trading day prior to the Time of Determination with respect
         to the rights, warrants or options or distribution in respect of which
         the Average Quoted Price is being calculated (excluding days within
         such period, if any, which are not trading days), or

                  (iii) the period, if any, (x) commencing on the date next
         succeeding the Ex-Dividend Time with respect to the next preceding (a)
         issuance of rights, warrants or options or (b) distribution, in each
         case, for which an adjustment is required by the provisions of Section
         11.06(4), 11.07 or 11.08 and (y) proceeding through the last full
         trading day prior to the Time of Determination with respect to the
         rights, warrants or options or distribution in respect of which the
         Average Quoted Price is being calculated (excluding days within such
         period, if any, which are not trading days).

                  In the event that the Ex-Dividend Time (or in the case of a
subdivision, combination or reclassification, the effective date with respect
thereto), with respect to a dividend, subdivision, combination or
reclassification to which Section 11.06(1), (2), (3) or (5) applies, occurs
during the period applicable for calculating "Average Quoted Price" pursuant to
the definition in the preceding sentence, "Average Quoted Price" shall be
calculated for such period in a manner determined by the Board of Directors to
reflect the impact of such dividend, subdivision, combination or
reclassification on the Sale Price of the Common Stock during such period.

                  "Time of Determination" means the time and date of the earlier
of (i) the determination of stockholders entitled to receive rights, warrants or
options or a distribution, in each case, to which Section 11.07 or 11.08 applies
and (ii) the time ("Ex-Dividend Time") immediately prior to the commencement of
"ex-dividend" trading for such rights, warrants or options or distribution on
the New York Stock Exchange or such other national or regional exchange or
market on which the Common Stock is then listed or quoted.

                  The term "trading day" means a day during which trading in
securities generally occurs on the New York Stock Exchange or, if the applicable
security is not listed on the New York Stock Exchange, on the Nasdaq National
Market, or if the applicable security is not quoted on the Nasdaq National
Market, on the principal other national or regional securities exchange

                                       59
<PAGE>   65

on which the applicable security is then listed or, if the applicable security
is not listed on a national or regional securities exchange, on the principal
other market on which the applicable security is then traded.

                  SECTION 11.02. Conversion Procedure. To convert a Security a
Holder must satisfy the requirements set forth in the Securities. The date on
which the Holder satisfies all those requirements is the conversion date (the
"Conversion Date"). Within two Business Days following the Conversion Date, the
Company shall deliver to the Holder, through the Conversion Agent, written
notice of whether such Security shall be converted into shares of Common Stock
or paid in cash, unless the Company shall have delivered such notice previously
pursuant to Section 3.03 hereof. If the Company shall have notified the Holder
that all of such Security shall be converted into shares of Common Stock, the
Company shall deliver to the Holder through the Conversion Agent no later than
the fifth Business Day following the Conversion Date a certificate for the
number of full shares of Common Stock issuable upon the conversion and cash in
lieu of any fractional share determined pursuant to Section 11.03 hereof. Except
as provided in the proviso in the third paragraph of Section 11.01 hereof, if
the Company shall have notified the Holder that all or a portion of such
Security shall be paid in cash, the Company shall deliver to the Holder
surrendering such Security the amount of cash payable with respect to such
Security no later than the tenth Business Day following such Conversion Date,
together with a certificate for the number of full shares of Common Stock
issuable upon the conversion and cash in lieu of any fractional share determined
pursuant to Section 11.03 hereof. Except as provided in the proviso in the third
paragraph of Section 11.01 hereof, the Company may not change its election with
respect to the consideration to be delivered upon conversion of a Security once
the Company has notified the Holder in accordance with this paragraph. If shares
of Common Stock are delivered as consideration, then the Person in whose name
the certificate representing such shares is registered shall be treated as a
stockholder of record on and after the Conversion Date; provided, however, that
no surrender of a Security on any date when the stock transfer books of the
Company shall be closed shall be effective to constitute the Person or Persons
entitled to receive the shares of Common Stock upon such conversion as the
record holder or holders of such shares of Common Stock on such date, but such
surrender shall be effective to constitute the Person or Persons entitled to
receive such shares of Common Stock as the record holder or holders thereof for
all purposes at the close of business on the next succeeding day on which such
stock transfer books are open; such conversion shall be at the Conversion Rate
in effect on the date that such Security shall have been surrendered for
conversion, as if the stock transfer books of the Company had not been closed.
Upon conversion of a Security, such Person shall no longer be a Holder of such
Security and such Security shall be cancelled and no longer Outstanding.

                  No payment or adjustment will be made for dividends on, or
other distributions with respect to, any Common Stock except as provided in this
Article 11. On conversion of a Security, that portion of accrued Original Issue
Discount (or interest, if the Issuer has exercised its option provided for in
Section 10.01) attributable to the period from the Issue Date (or, if the Issuer
has exercised the option provided for in Section 10.01, the later of (x) the
date of such exercise and (y) the date on which interest was last paid) through
the Conversion Date with respect to the converted Security shall not be
cancelled, extinguished or forfeited, but rather shall be deemed to be paid in
full to the Holder thereof through delivery of the Common Stock (together with
the cash payment, if any, in lieu of fractional shares) and cash, if any, in
exchange

                                       60
<PAGE>   66

for the Security being converted pursuant to the provisions hereof; and such
cash, if any, and the fair market value of such shares of Common Stock (together
with any such cash payment in lieu of fractional shares) shall be treated as
delivered pro rata, to the extent thereof, first in exchange for Original Issue
Discount (or interest, if the Issuer has exercised its option provided for in
Section 10.01) accrued through the Conversion Date, and the balance, if any, of
such cash and the fair market value of such Common Stock (and any such cash
payment) shall be treated as delivered in exchange for the Issue Price of the
Security being converted pursuant to the provisions hereof.

                  If the Holder converts more than one Security at the same
time, the number of shares of Common Stock issuable or cash paid upon the
conversion shall be based on the total Principal Amount at Maturity of the
Securities converted.

                  If the last day on which a Security may be converted is a
Legal Holiday in a place where the Conversion Agent is located, the Security may
be surrendered to such Conversion Agent on the next succeeding day that is not a
Legal Holiday.

                  Upon surrender of a Security that is converted in part, the
Issuer shall execute, and the Trustee shall authenticate and deliver to the
Holder, a new Security in an authorized denomination equal in Principal Amount
at Maturity to the unconverted portion of the Security surrendered.

                  SECTION 11.03. Fractional Shares. The Company will not issue a
fractional share of Common Stock upon conversion of a Security. Instead, the
Issuer will deliver cash for the current market value of the fractional share.
The current market value of a fractional share shall be determined, to the
nearest 1/1,000th of a share, by multiplying the last reported sale price
(determined as set forth in the definition of Market Price) on the last trading
day prior to the Conversion Date by the fractional amount and rounding the
product to the nearest whole cent.

                  SECTION 11.04. Taxes on Conversion. If a Holder converts a
Security, the Issuer shall pay any documentary, stamp or similar issue or
transfer tax due on the issue of shares of Common Stock upon the conversion.
However, the Holder shall pay any such tax which is due because the Holder
requests the shares to be issued in a name other than the Holder's name. The
Conversion Agent may refuse to deliver the certificates representing the Common
Stock being issued in a name other than the Holder's name until the Conversion
Agent receives a sum that the Issuer deems to be sufficient to pay any tax which
will be due because the shares are to be issued in a name other than the
Holder's name. Nothing herein shall preclude any tax withholding required by law
or regulations.

                  SECTION 11.05. Company to Provide Stock. The Company shall,
prior to issuance of any Securities under this Article 11, and from time to time
as may be necessary, reserve out of its authorized but unissued or treasury
Common Stock a sufficient number of shares of Common Stock to permit the
conversion of the Securities.

                                       61
<PAGE>   67

                  All shares of Common Stock delivered upon conversion of the
Securities shall be newly issued shares or treasury shares, shall be duly and
validly issued and fully paid and nonassessable, and shall be free from
preemptive rights and free of any lien or adverse claim.

                  The Company shall endeavor promptly to comply with all federal
and state securities laws regulating the offer and delivery of shares of Common
Stock upon conversion of Securities, if any, including the addition of any and
all restrictive legends that are required to appear on the face of the Common
Stock, and shall list or cause to have quoted such shares of Common Stock on
each United States national securities exchange or in the automated
over-the-counter market in the United States on which the Common Stock is then
listed or quoted.

                  SECTION 11.06. Adjustment for Change In Capital Stock. If,
after the Issue Date of the Securities, the Company:

                  (1) pays a dividend or makes a distribution on its Common
         Stock in shares of its Common Stock;

                  (2) subdivides its outstanding shares of Common Stock into a
         greater number of shares;

                  (3) combines its outstanding shares of Common Stock into a
         smaller number of shares;

                  (4) pays a dividend or makes a distribution on its Common
         Stock in shares of its Capital Stock (other than Common Stock or
         rights, warrants or options for its Capital Stock); or

                  (5) issues by reclassification of its Common Stock any shares
         of its Capital Stock (other than rights, warrants or options for its
         Capital Stock),

then the Conversion Rate in effect immediately prior to such action shall be
adjusted so that the Holder of a Security thereafter converted may receive the
number of shares of Capital Stock of the Company which such Holder would have
owned immediately following such action if such Holder had converted the
Security into Common Stock immediately prior to such action.

                  The adjustment shall become effective immediately after the
record date in the case of a dividend or distribution and immediately after the
effective date in the case of a subdivision, combination or reclassification.

                  If after an adjustment a Holder of a Security upon conversion
of such Security may receive shares of two or more classes of Capital Stock of
the Company, the Conversion Rate shall thereafter be subject to adjustment upon
the occurrence of an action taken with respect to any such class of Capital
Stock as is contemplated by this Article 11 with respect to the Common Stock, on
terms comparable to those applicable to Common Stock in this Article 11.

                  SECTION 11.07. Adjustment for Rights Issue. If after the Issue
Date of the Securities, the Company distributes any rights, warrants or options
to all holders of its Common Stock entitling them, for a period expiring within
60 days after the record date for such

                                       62
<PAGE>   68

distribution, to subscribe for or purchase shares of Common Stock at a price per
share less than the Sale Price as of the Time of Determination, the Conversion
Rate shall be adjusted, subject to the provisions of the last paragraph of this
Section 11.07, in accordance with the formula

                                      R x (O + N)
                                R' = -------------
                                    (O + (N x P)/M)

where:

                  R' = the adjusted Conversion Rate.

                  R = the current Conversion Rate.

                  O = the number of shares of Common Stock outstanding on the
record date for the distribution to which this Section 11.07 is being applied.

                  N = the number of additional shares of Common Stock offered
pursuant to the distribution.

                  P = the offering price per share of the additional shares.

                  M = the Average Quoted Price, minus, in the case of (i) a
distribution to which Section 11.06(4) applies or (ii) a distribution to which
Section 11.08 applies, for which, in each case, (x) the record date shall occur
on or before the record date for the distribution to which this Section 11.07
applies and (y) the Ex-Dividend Time shall occur on or after the date of the
Time of Determination for the distribution to which this Section 11.07 applies,
the fair market value (on the record date for the distribution to which this
Section 11.07 applies) of the

                  (1) Capital Stock of the Company distributed in respect of
         each share of Common Stock in such Section 11.06(4) distribution and

                  (2) assets of the Company or debt securities or any rights,
         warrants or options to purchase securities of the Company distributed
         in respect of each share of Common Stock in such Section 11.08
         distribution.

                  The Board of Directors shall determine fair market values for
the purposes of this Section 11.07.

                  The adjustment shall become effective immediately after the
record date for the determination of shareholders entitled to receive the
rights, warrants or options to which this Section 11.07 applies. If all of the
shares of Common Stock subject to such rights, warrants or options have not been
issued when such rights, warrants or options expire, then the Conversion Rate
shall promptly be readjusted to the Conversion Rate which would then be in
effect had the adjustment upon the issuance of such rights, warrants or options
been made on the basis of the actual number of shares of Common Stock issued
upon the exercise of such rights, warrants or options.

                                       63
<PAGE>   69

                  No adjustment shall be made under this Section 11.07 if the
application of the formula stated above in this Section 11.07 would result in a
value of R' that is equal to or less than the value of R.

                  SECTION 11.08. Adjustment for Other Distributions. If, after
the Issue Date of the Securities, the Company distributes to all holders of its
Common Stock any of its assets, or debt securities or any rights, warrants or
options to purchase securities of the Company (including securities or cash, but
excluding (x) distributions of Capital Stock referred to in Section 11.06 and
distributions of rights, warrants or options referred to in Section 11.07 and
(y) cash dividends or other cash distributions that are paid out of consolidated
current net earnings or earnings retained in the business as shown on the books
of the Company unless such cash dividends or other cash distributions are
Extraordinary Cash Dividends) the Conversion Rate shall be adjusted, subject to
the provisions of the last paragraph of this Section 11.08, in accordance with
the formula:
                                    R x M
                               R' = -----
                                    M - F

where:

                  R' = the adjusted Conversion Rate.

                  R = the current Conversion Rate.

                  M = the Average Quoted Price, minus, in the case of a
distribution to which Section 11.06(4) applies, for which (i) the record date
shall occur on or before the record date for the distribution to which this
Section 11.08 applies and (ii) the Ex-Dividend Time shall occur on or after the
date of the Time of Determination for the distribution to which this Section
11.08 applies, the fair market value (on the record date for the distribution to
which this Section 11.08 applies) of any Capital Stock of the Company
distributed in respect of each share of Common Stock in such Section 11.06(4)
distribution.

                  F = the fair market value (on the record date for the
distribution to which this Section 11.08 applies) of the assets, securities,
rights, warrants or options to be distributed in respect of each share of Common
Stock in the distribution to which this Section 11.08 is being applied
(including, in the case of cash dividends or other cash distributions giving
rise to an adjustment, all such cash distributed concurrently).

                  The Board of Directors shall determine fair market values for
the purposes of this Section 11.08.

                  The adjustment shall become effective immediately after the
record date for the determination of shareholders entitled to receive the
distribution to which this Section 11.08 applies.

                  For purposes of this Section 11.08, the term "Extraordinary
Cash Dividend" shall mean any cash dividend with respect to the Common Stock the
amount of which, together with the aggregate amount of cash dividends on the
Common Stock to be aggregated with such cash

                                       64
<PAGE>   70

dividend in accordance with the provisions of this paragraph, exceeds the
threshold percentage set forth in item (i) below. For purposes of item (i)
below, the "Measurement Period" with respect to a cash dividend on the Common
Stock shall mean the 365 consecutive day period ending on the date prior to the
Ex-Dividend Time with respect to such cash dividend, and the "Relevant Cash
Dividends" with respect to a cash dividend on the Common Stock shall mean the
cash dividends on the Common Stock with Ex-Dividend Times occurring in the
Measurement Period.

                  (i) If, upon the date prior to the Ex-Dividend Time with
         respect a cash dividend on the Common Stock, the aggregate amount of
         such cash dividend together with the amounts of all Relevant Cash
         Dividends equals or exceeds on a per share basis 15% of the Sale Price
         of the Common Stock on the last trading day preceding the date of
         declaration by the Board of Directors of the cash dividend with respect
         to which this provision is being applied, then such cash dividend
         together with all Relevant Cash Dividends, shall be deemed to be an
         Extraordinary Cash Dividend and for purposes of applying the formula
         set forth above in this Section 11.08, the value of "F" shall be equal
         to (y) the aggregate amount of such cash dividend together with the
         amount of all Relevant Cash Dividends, minus (z) the aggregate amount
         of all Relevant Cash Dividends for which a prior adjustment in the
         Conversion Rate was previously made under this Section 11.08.

         In making the determinations required by item (i) above, the amount of
         cash dividends paid on a per share basis and the amount of any Relevant
         Cash Dividends specified in item (i) above, shall be appropriately
         adjusted to reflect the occurrence during such period of any event
         described in Section 11.06.

                  In the event that, with respect to any distribution to which
this Section 11.08 would otherwise apply, the difference "M-F" as defined in the
above formula is less than $1.00 or "F" is equal to or greater than "M", then
the adjustment provided by this Section 11.08 shall not be made and in lieu
thereof the provisions of Section 11.14 shall apply to such distribution.

                  SECTION 11.09. When Adjustment May Be Deferred. No adjustment
in the Conversion Rate need be made unless the adjustment would require an
increase or decrease of at least 1% in the Conversion Rate. Any adjustments that
are not made shall be carried forward and taken into account in any subsequent
adjustment.

                  All calculations under this Article 11 shall be made to the
nearest cent or to the nearest 1/1,000th of a share, as the case may be.

                  SECTION 11.10. When No Adjustment Required. No adjustment need
be made for a transaction referred to in Section 11.06, 11.07, 11.08 or 11.14 if
Securityholders are to participate in the transaction on a basis and with notice
that the Board of Directors determines to be fair and appropriate in light of
the basis and notice on which holders of Common Stock participate in the
transaction. Such participation by Securityholders may include participation
upon conversion provided that an adjustment shall be made at such time as the
Securityholders are no longer entitled to participate.

                                       65
<PAGE>   71

                  No adjustment need be made for rights to purchase Common Stock
pursuant to a Company plan for reinvestment of dividends or interest.

                  No adjustment need be made for a change in the par value or no
par value of the Common Stock.

                  To the extent the Securities become convertible pursuant to
this Article 11 into cash, no adjustment need be made thereafter as to the cash.
Interest will not accrue on the cash.

                  SECTION 11.11. Notice of Adjustment. Whenever the Conversion
Rate is adjusted, the Issuer shall promptly mail to Securityholders by
first-class mail a notice of the adjustment. The Issuer shall file with the
Trustee and the Conversion Agent such notice and a certificate from the
Company's independent public accountants briefly stating the facts requiring the
adjustment and the manner of computing it. The certificate shall be conclusive
evidence that the adjustment is correct. Neither the Trustee nor any Conversion
Agent shall be under any duty or responsibility with respect to any such
certificate except to exhibit the same to any Holder desiring inspection
thereof.

                  SECTION 11.12. Voluntary Increase. The Issuer from time to
time may increase the Conversion Rate by any amount for any period of time.
Whenever the Conversion Rate is increased, the Issuer shall mail to
Securityholders by first-class mail and file with the Trustee and the Conversion
Agent a notice of the increase. The Issuer shall mail the notice at least 15
days before the date the increased Conversion Rate takes effect. The notice
shall state the increased Conversion Rate and the period it will be in effect.

                  A voluntary increase of the Conversion Rate does not change or
adjust the Conversion Rate otherwise in effect for purposes of Section 11.06,
11.07 or 11.08.

                  SECTION 11.13. Notice of Certain Transactions. If:

                  (1) the Company takes any action that would require an
         adjustment in the Conversion Rate pursuant to Section 11.06, 11.07 or
         11.08 (unless no adjustment is to occur pursuant to Section 11.10); or

                  (2) there is a liquidation or dissolution of the Company;

then the Issuer shall mail to Securityholders by first-class mail and file with
the Trustee and the Conversion Agent a notice stating the proposed record date
for a dividend or distribution or the proposed effective date of a subdivision,
combination, reclassification, consolidation, merger, binding share exchange,
transfer, liquidation or dissolution. The Issuer shall file and mail the notice
at least 15 days before such date. Failure to file or mail the notice or any
defect in it shall not affect the validity of the transaction.

                  SECTION 11.14. Reorganization of Company; Special
Distributions. If the Company is a party to a transaction subject to Section
5.01 (other than a sale of the assets of the Company as, or substantially as, an
entity in a transaction in which the holders of Common Stock immediately prior
to such transaction do not receive securities, cash or other assets of the

                                       66
<PAGE>   72

Company or any other Person) or a merger or binding share exchange which
reclassifies or changes its outstanding Common Stock, the Person obligated to
deliver securities, cash or other assets upon conversion of Securities shall
enter into a supplemental indenture. If the issuer of securities deliverable
upon conversion of Securities is an Affiliate of the Successor Company, that
issuer shall join in the supplemental indenture.

                  The supplemental indenture shall provide that the Holder of a
Security may convert it into the kind and amount of securities, cash or other
assets which such Holder would have received immediately after the
consolidation, merger, binding share exchange or transfer if such Holder had
converted the Security into Common Stock immediately before the effective date
of the transaction, assuming (to the extent applicable) that such Holder (i) was
not a constituent Person or an Affiliate of a constituent Person to such
transaction; (ii) made no election with respect thereto; and (iii) was treated
alike with the plurality of non-electing Holders. The supplemental indenture
shall provide for adjustments which shall be as nearly equivalent as may be
practical to the adjustments provided for in this Article 11. The Successor
Company shall mail to Securityholders a notice briefly describing the
supplemental indenture.

                  If this Section 11.14 applies, neither Section 11.06 nor
Section 11.07 applies.

                  If the Company makes a distribution to all holders of its
Common Stock of any of its assets, or debt securities or any rights, warrants or
options to purchase securities of the Company that, but for the provisions of
the last paragraph of Section 11.08, would otherwise result in an adjustment in
the Conversion Rate pursuant to the provisions of Section 11.08, then, from and
after the record date for determining the holders of Common Stock entitled to
receive the distribution, a Holder of a Security that converts such Security in
accordance with the provisions of this Indenture shall upon such conversion be
entitled to receive, in addition to the shares of Common Stock into which the
Security is convertible, the kind and amount of securities, cash or other assets
comprising the distribution that such Holder would have received if such Holder
had converted the Security into Common Stock immediately prior to the record
date for determining the holders of Common Stock entitled to receive the
distribution.

                  SECTION 11.15. Company Determination Final. Any determination
that the Company or the Board of Directors must make pursuant to Section 11.03,
11.06, 11.07, 11.08, 11.09, 11.10, 11.14 or 11.17 is conclusive in the absence
of manifest error.

                  SECTION 11.16. Trustee's Adjustment Disclaimer. The Trustee
has no duty to determine when an adjustment under this Article 11 should be
made, how it should be made or what it should be. The Trustee has no duty to
determine whether a supplemental indenture under Section 11.14 need be entered
into or whether any provisions of any supplemental indenture are correct. The
Trustee shall not be accountable for and makes no representation as to the
validity or value of any securities or assets issued upon conversion of
Securities. The Trustee shall not be responsible for the Issuer's failure to
comply with this Article 11. Each Conversion Agent shall have the same
protection under this Section 11.16 as the Trustee.

                  SECTION 11.17. Simultaneous Adjustments. In the event that
this Article 11 requires adjustments to the Conversion Rate under more than one
of Sections 11.06(4), 11.07 or 11.08, and the record dates for the distributions
giving rise to such adjustments shall occur on the

                                       67
<PAGE>   73

same date, then such adjustments shall be made by applying, first, the
provisions of Section 11.06, second, the provisions of Section 11.08 and, third,
the provisions of Section 11.07.

                  SECTION 11.18. Successive Adjustments. After an adjustment to
the Conversion Rate under this Article 11, any subsequent event requiring an
adjustment under this Article 11 shall cause an adjustment to the Conversion
Rate as so adjusted.

                  SECTION 11.19. Rights Issued in Respect of Common Stock Issued
Upon Conversion. Each share of Common Stock issued upon conversion of Securities
pursuant to this Article 11 shall be entitled to receive the appropriate number
of common stock or preferred stock purchase rights, as the case may be (the
"Rights"), if any, and the certificates representing the Common Stock issued
upon such conversion shall bear such legends, if any, in each case as may be
provided by the terms of any shareholder rights agreement adopted by the
Company, as the same may be amended from time to time (in each case, a "Rights
Agreement"). Provided that such Rights Agreement requires that each share of
Common Stock issued upon conversion of Securities at any time prior to the
distribution of separate certificates representing the Rights be entitled to
receive such Rights, then, notwithstanding anything else to the contrary in this
Article 11, there shall not be any adjustment to the Conversion Rate as a result
of the issuance of Rights, the distribution of separate certificates
representing the Rights, the exercise or redemption of such Rights in accordance
with any such Rights Agreement, or the termination or invalidation of such
Rights.

                  SECTION 11.20. Restriction on Common Stock Issued Upon
Conversion. Shares of Common Stock to be issued upon conversion of Securities
prior to the effectiveness of a Shelf Registration shall be physically delivered
in certificated form to the holders converting such Securities and the
certificate representing such shares of Common Stock shall bear will bear a
legend substantially to the following effect:

                  "These Securities have not been registered under the
                  Securities Act of 1933. Further offers or sales of these
                  Securities are subject to certain restrictions, as set forth
                  in the Offering Memorandum dated January 31, 2001 relating to
                  these Securities."

unless removed in accordance with Section 11.20(b).

                  (a) If (i) shares of Common Stock to be issued upon conversion
of a Security prior to the effectiveness of a Shelf Registration are to be
registered in a name other than that of the holder of such Security or (ii)
shares of Common Stock represented by a certificate bearing the above legend are
transferred subsequently by such holder, then, unless the Shelf Registration has
become effective and such shares are being transferred pursuant to the Shelf
Registration, the holder must deliver to the transfer agent for the Common Stock
a certificate in substantially the form of Exhibit F as to compliance with the
restrictions on transfer applicable to such shares of Common Stock and neither
the transfer agent nor the registrar for the Common Stock shall be required to
register any transfer of such Common Stock not so accompanied by a properly
completed certificate.

                                       68
<PAGE>   74

                  (b) Except in connection with a Shelf Registration, if
certificates representing shares of Common Stock are issued upon the
registration of transfer, exchange or replacement of any other certificate
representing shares of Common Stock bearing the above legend, or if a request is
made to remove such legend from certificates representing shares of Common
Stock, the certificates so issued shall bear the above legend, or the above
legend shall not be removed, as the case may be, unless there is delivered to
the Company such satisfactory evidence, which, in the case of a transfer made
pursuant to Rule 144 under the Securities Act, may include an opinion of
counsel, as may be reasonably required by the Company, that neither the legend
nor the restrictions on transfer set forth therein are required to ensure that
transfers thereof comply with the provisions of Rule 144A, Rule 144 or
Regulation S under the Securities Act or that such shares of Common Stock are
securities that are not "restricted" within the meaning of Rule 144 under the
Securities Act. Upon provision to the Company of such reasonably satisfactory
evidence, the Company shall cause the transfer agent for the Common Stock to
countersign and deliver certificates representing shares of Common Stock that do
not bear the legend.

                                   ARTICLE 12

                                  MISCELLANEOUS

                  SECTION 12.01. Trust Indenture Act Controls. If any provision
of this Indenture limits, qualifies or conflicts with another provision which is
required to be included in this Indenture by the Trust Indenture Act, the
required provision shall control.

                  SECTION 12.02. Notices. Any notice or communication shall be
in writing and delivered in person or mailed by first-class mail (registered or
certified, return receipt requested), telecopier or overnight air courier
guaranteeing next day delivery), addressed as follows:

                  If to the Issuer:

                  Enron Corp.
                  1400 Smith Street
                  Houston, Texas 77002
                  Telecopy No.:  (713) 646-4990
                  Attention:  Treasurer

                  If to the Trustee:

                  For payment, registration of transfer and exchange of the
                  Securities:

                  The Chase Manhattan Bank
                  2001 Bryan Street, 9th Floor
                  Dallas, Texas 75201
                  Telephone:  (214) 672-5125 or (800) 275-2048
                  Telecopy No.:  (214) 672-5873

                                       69
<PAGE>   75

                  For all other communications relating to the Securities:

                  The Chase Manhattan Bank
                  Institutional Trust Services
                  600 Travis Street, Suite 1150
                  Houston, Texas 77002
                  Telephone:  (713) 216-6877
                  Telecopy No.:  (713) 577-5200

                  The Issuer or the Trustee by notice to the other may designate
additional or different addresses for subsequent notices or communications.
Notices to the Trustee shall be effective only upon receipt.

                  Any notice or communication mailed to a Securityholder shall
be mailed to the Securityholder at the Securityholder's address as it appears on
the registration books of the Registrar and shall be sufficiently given if so
mailed within the time prescribed.

                  Failure to mail a notice or communication to a Securityholder
or any defect in it shall not affect its sufficiency with respect to other
Securityholders. If a notice or communication is given in the manner provided
above, it is duly given, whether or not the addressee receives it.

                  SECTION 12.03. Communication by Holders with Other Holders.
Securityholders may communicate pursuant to Trust Indenture Act Section 312(b)
with other Securityholders with respect to their rights under this Indenture or
the Securities. The Issuer, the Trustee, the Registrar and anyone else shall
have the protection of Trust Indenture Act Section 312(c).

                  SECTION 12.04. Certificate and Opinion as to Conditions
Precedent. Upon any request or application by the Issuer to the Trustee to take
or refrain from taking any action under this Indenture, the Issuer shall furnish
to the Trustee:

                  (1) an Officers' Certificate of the Issuer in form and
         substance reasonably satisfactory to the Trustee stating that, in the
         opinion of the signers, all conditions precedent, if any, provided for
         in this Indenture relating to the proposed action have been complied
         with; and

                  (2) an Opinion of Counsel in form and substance reasonably
         satisfactory to the Trustee stating that, in the opinion of such
         counsel, all such conditions precedent have been complied with.

                  SECTION 12.05. Statements Required in Certificate or Opinion.
Each certificate or opinion with respect to compliance with a covenant or
condition provided for in this Indenture shall include:

                  (1) a statement that the individual making such certificate or
         opinion has read such covenant or condition;

                                       70
<PAGE>   76

                  (2) a brief statement as to the nature and scope of the
         examination or investigation upon which the statements or opinions
         contained in such certificate or opinion are based;

                  (3) a statement that, in the opinion of such individual, he
         has made such examination or investigation as is necessary to enable
         him to express an informed opinion as to whether or not such covenant
         or condition has been complied with; and

                  (4) a statement as to whether or not, in the opinion of such
         individual, such covenant or condition has been complied with.

                  SECTION 12.06. When Securities Disregarded. In determining
whether the Holders of the required Principal Amount at Maturity of Securities
have concurred in any direction, waiver or consent, Securities owned by the
Issuer, or by any Person directly or indirectly controlling or controlled by or
under direct or indirect common control with the Issuer, shall be disregarded
and deemed not to be outstanding, except that, for the purpose of determining
whether the Trustee shall be protected in relying on any such direction, waiver
or consent, only Securities which the Trustee knows are so owned shall be so
disregarded. Subject to the foregoing, only Securities outstanding at the time
shall be considered in any such determination.

                  SECTION 12.07. Rules by Trustee, Paying Agent and Registrar.
The Trustee may make reasonable rules for action by or a meeting of
Securityholders. The Registrar and the Paying Agent may make reasonable rules
for their functions.

                  SECTION 12.08. Legal Holidays. A "Legal Holiday" is a
Saturday, Sunday or other day on which banking institutions in either the State
of Texas or the State of New York are authorized or required by law to close. If
a payment date is a Legal Holiday, payment shall be made on the next succeeding
day that is not a Legal Holiday, and no interest shall accrue for the
intervening period. If a regular record date is a Legal Holiday, the record date
shall not be affected.

                  SECTION 12.09. Governing Law. THIS INDENTURE AND THE
SECURITIES SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF
THE STATE OF NEW YORK.

                  SECTION 12.10. No Recourse Against Others. A director,
officer, employee or stockholder, as such, of the Issuer shall not have any
liability for any obligations of the Issuer under the Securities or this
Indenture or for any claim based on, in respect of or by reason of such
obligations or their creation. By accepting a Security, each Securityholder
shall waive and release all such liability. The waiver and release shall be part
of the consideration for the issuance of the Securities.

                  SECTION 12.11. Successors. All agreements of the Issuer in
this Indenture and the Securities shall bind its successors. All agreements of
the Trustee in this Indenture shall bind its successors.

                                       71
<PAGE>   77

                  SECTION 12.12. Multiple Originals. The parties may sign any
number of copies of this Indenture. Each signed copy shall be an original, but
all of them together represent the same agreement. One signed copy of the
Indenture is enough to prove this Indenture.

                  SECTION 12.13. Table of Contents; Headings. The table of
contents, cross-reference sheet and headings of the Articles and Sections of
this Indenture have been inserted for convenience of reference only, are not
intended to be considered a part hereof and shall not modify or restrict any of
the terms or provisions hereof.

                  SECTION 12.14. Severability. If any provision in this
Indenture is deemed unenforceable, it shall not affect the validity or
enforceability of any other provision set forth herein, or of the Indenture as a
whole.

                     [Rest of page intentionally left blank]

                                       72
<PAGE>   78

                  IN WITNESS WHEREOF, the parties have caused this Indenture to
be duly executed as of the date first written above.

                                               ENRON CORP.

                                               By:
                                                  ------------------------------
                                                  Name:
                                                  Title:

                                               THE CHASE MANHATTAN BANK, as
                                                  Trustee

                                               By:
                                                  ------------------------------
                                                  Name:
                                                  Title:

                                       73
<PAGE>   79

                                    EXHIBIT A

                           [FORM OF FACE OF SECURITY]

         FOR PURPOSES OF SECTIONS 1273 AND 1275 OF THE INTERNAL REVENUE CODE,
THE ISSUE PRICE AND AMOUNT OF ORIGINAL ISSUE DISCOUNT WITH RESPECT TO EACH
$1,000 OF PRINCIPAL AMOUNT AT MATURITY OF THIS SECURITY ARE $655.24 AND $344.76,
RESPECTIVELY, THE ISSUE DATE IS FEBRUARY 7, 2001 AND THE YIELD TO MATURITY IS
2.125%.

         [INCLUDE IF SECURITY IS A RESTRICTED SECURITY - THESE SECURITIES HAVE
NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933. FURTHER OFFERS OR SALES OF
THESE SECURITIES ARE SUBJECT TO CERTAIN RESTRICTIONS, AS SET FORTH IN THE
OFFERING MEMORANDUM DATED JANUARY 31, 2001 RELATING TO THESE SECURITIES.

         THE HOLDER OF THIS SECURITY IS SUBJECT TO, AND ENTITLED TO THE BENEFITS
OF, A REGISTRATION RIGHTS AGREEMENT, DATED AS OF FEBRUARY 7, 2001, ENTERED INTO
BY THE ISSUER FOR THE BENEFIT OF CERTAIN HOLDERS FROM TIME TO TIME OF
SECURITIES.]

         [INCLUDE IF SECURITY IS A GLOBAL SECURITY -- THIS SECURITY IS A GLOBAL
SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS
REGISTERED IN THE NAME OF A DEPOSITARY OR A NOMINEE THEREOF. THIS SECURITY MAY
NOT BE EXCHANGED IN WHOLE OR IN PART FOR A SECURITY REGISTERED, AND NO TRANSFER
OF THIS SECURITY IN WHOLE OR IN PART MAY BE REGISTERED, IN THE NAME OF ANY
PERSON OTHER THAN SUCH DEPOSITARY OR A NOMINEE THEREOF, EXCEPT IN THE LIMITED
CIRCUMSTANCES DESCRIBED IN THE INDENTURE.

         UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF
THE DEPOSITORY TRUST COMPANY ("DTC"), A NEW YORK CORPORATION, TO THE ISSUER OR
ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE
ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS
REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO
CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY OR TO ANY PERSON IS WRONGFUL IN AS MUCH AS THE REGISTERED OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.]

                                      A-1
<PAGE>   80

                                   ENRON CORP.

                  ZERO COUPON CONVERTIBLE SENIOR NOTE DUE 2021

<TABLE>
<S>                                                   <C>
CUSIP No. 293561 CC 8                                  $___________ Principal Amount at
                                                       Maturity

Issue Date: February 7, 2001                           Original Issue Discount: $344.76
Issue Price: $655.24                                   (for each $1,000 Principal Amount at Maturity)
(for each $1,000 Principal Amount at Maturity)
</TABLE>

         Enron Corp., an Oregon corporation (herein called the "Issuer" or the
"Company", which term includes any successor Person under the Indenture
hereinafter referred to), for value received, hereby promises to pay to
_____________, or registered assigns, the Principal Amount at Maturity set forth
above [INCLUDE IF SECURITY IS A GLOBAL SECURITY -- (which amount may from time
to time be increased or decreased by adjustments made on the records of the
Trustee, as custodian for the Depositary, in accordance with the rules and
procedures of the Depositary)] on February 7, 2021.

         This Security shall not bear interest except as specified on the other
side of this Security. Original Issue Discount will accrue as specified on the
other side of this Security. This Security is convertible as specified on the
other side of this Security.

         Reference is hereby made to the further provisions of this Security set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

         Unless the certificate of authentication hereon has been executed by
the Trustee referred to on the reverse hereof by manual signature, this Security
shall not be entitled to any benefit under the Indenture or be valid or
obligatory for any purpose.

         IN WITNESS WHEREOF, the Issuer has caused this instrument to be duly
executed.

                                              ENRON CORP.

                                              By:
                                                 -------------------------------
                                                 Name:
                                                      --------------------------
                                                 Title:
                                                       -------------------------

                                      A-2
<PAGE>   81

                     TRUSTEE'S CERTIFICATE OF AUTHENTICATION

THE CHASE MANHATTAN BANK, as Trustee, certifies that this is one of the
Securities referred to in the Indenture.

By:
   ---------------------------------------------
   Authorized Signatory

Date of authentication:

                                      A-3
<PAGE>   82

                       [FORM OF REVERSE SIDE OF SECURITY]

         This Security is one of a duly authorized issue of Securities of the
Issuer designated as its Zero Coupon Convertible Senior Notes due 2021, limited
in aggregate Principal Amount at Maturity to $1,907,698,000 (subject to increase
by up to $381,540,000 in the event the Initial Purchasers exercise the
over-allotment option granted to them in the Purchase Agreement) (herein called
the "Securities"), issued and to be issued under an Indenture, dated as of
February 7, 2001 (herein called the "Indenture"), between the Issuer and The
Chase Manhattan Bank, as Trustee (herein called the "Trustee", which term
includes any successor trustee under the Indenture), to which Indenture and all
indentures supplemental thereto reference is hereby made for a statement of the
respective rights, limitations of rights, duties and immunities thereunder of
the Issuer, the Trustee and the Holders of the Securities and of the terms upon
which the Securities are, and are to be, authenticated and delivered.

         Interest - This Security shall not bear interest, except as specified
herein. If the Principal Amount hereof or any portion of such Principal Amount
is not paid when due (whether upon acceleration pursuant to Section 6.02 of the
Indenture, upon the date set for payment of the Redemption Price, upon the date
set for payment of a Purchase Price or Fundamental Change Repurchase Price or
upon the Stated Maturity of this Security), then in each such case the overdue
amount shall bear interest at the rate of 2.125% per annum, compounded
semiannually (to the extent that the payment of such interest shall be legally
enforceable), which interest shall accrue from the date such overdue amount was
due to the date payment of such amount, including interest thereon, has been
made or duly provided for. All such interest shall be payable on demand. The
accrual of such interest on overdue amounts shall be in lieu of, and not in
addition to, the continued accrual of Original Issue Discount. Original Issue
Discount (the difference between the Issue Price and the Principal Amount at
Maturity of the Security), in the period during which a Security remains
outstanding, shall accrue at 2.125% per annum, on a semi-annual bond equivalent
basis using a 360-day year composed of twelve 30-day months, from the Issue Date
of this Security. Original Issue Discount shall cease to accrue on the earlier
of (a) the date on which the Principal Amount hereof or any portion of such
Principal Amount becomes due and payable and (b) any Redemption Date, Conversion
Date, Fundamental Change Repurchase Date, Purchase Date or other date on which
such Original Issue Discount (or, if such Securities have been converted to
semi-annual coupon notes following the occurrence of a Tax Event, interest
thereon) shall cease to accrue in accordance with Section 2.09 of the Indenture.

         Method of Payment - Holders must surrender Securities to the Paying
Agent to collect all payments in respect of the Securities, except for
liquidated damages payable pursuant to the Registration Rights Agreement and, if
such Securities have been converted to semi-annual coupon notes following the
occurrence of a Tax Event, interest thereon. The Company will pay cash amounts
in money of the United States that at the time of payment is legal tender for
payment of public and private debts.

         Redemption at the Option of the Issuer - No sinking fund is provided
for the Securities. The Securities are redeemable as a whole, or from time to
time in part, at any time at the option of the Issuer at a Redemption Price
equal to the Issue Price plus the accrued Original Issue Discount to the
Redemption Date, provided that the Securities are not redeemable prior to
February 7, 2004.

                                      A-4
<PAGE>   83

         The table below shows Redemption Prices of a Security per $1,000
Principal Amount at Maturity on the dates shown below and at Stated Maturity,
which prices equal the Issue Price plus accrued Original Issue Discount
calculated to each such date. The Redemption Price of a Security redeemed
between such dates shall include an additional amount reflecting the additional
Original Issue Discount accrued since the next preceding date in the table.

<TABLE>
<CAPTION>
                ------------------------------------------------------------------------------------------------
                                                                   ACCRUED ORIGINAL           REDEMPTION
                                                   ISSUE            ISSUE DISCOUNT               PRICE
                         DATE                   PRICE(1)             AT 2.125%(2)              (1) + (2)
                ------------------------------------------------------------------------------------------------
<S>              <C>                         <C>                    <C>                       <C>
                   February 7, 2004              $655.24                  $42.90                 $698.13
                   February 7, 2005               655.24                   57.81                  713.05
                   February 7, 2006               655.24                   73.04                  728.28
                   February 7, 2007               655.24                   88.60                  743.84
                   February 7, 2008               655.24                  104.49                  759.73
                   February 7, 2009               655.24                  120.72                  775.96
                   February 7, 2010               655.24                  137.30                  792.54
                   February 7, 2011               655.24                  154.23                  809.47
                   February 7, 2012               655.24                  171.52                  826.76
                   February 7, 2013               655.24                  189.18                  844.42
                   February 7, 2014               655.24                  207.22                  862.46
                   February 7, 2015               655.24                  225.65                  880.89
                   February 7, 2016               655.24                  244.47                  899.70
                   February 7, 2017               655.24                  263.69                  918.92
                   February 7, 2018               655.24                  283.32                  938.56
                   February 7, 2019               655.24                  303.37                  958.61
                   February 7, 2020               655.24                  323.85                  979.08
                  At Stated Maturity              655.24                  344.76                1,000.00
</TABLE>

         If converted to a semi-annual coupon note following the occurrence of a
Tax Event, this Security will be redeemable at the Restated Principal Amount
plus accrued and unpaid interest from the later of the date of such conversion
and the date on which interest was last paid through the Redemption Date; but in
no event will this Security be redeemable before February 7, 2004.

                                      A-5
<PAGE>   84

         Purchase By the Issuer at the Option of the Holder - Subject to the
terms and conditions of the Indenture, the Issuer shall become obligated to
purchase, at the option of the Holder, the Securities held by such Holder on the
following Purchase Dates and at the following Purchase Prices per $1,000
Principal Amount at Maturity, upon delivery of a Purchase Notice containing the
information set forth in the Indenture, at any time from the opening of business
on the date that is 20 Business Days prior to such Purchase Date until the close
of business on such Purchase Date and upon delivery of the Securities to the
Paying Agent by the Holder as set forth in the Indenture.

<TABLE>
<CAPTION>
        Purchase Date                  Purchase Price
        -------------                  --------------
<S>                                    <C>
        February 7, 2004                    $698.13
        February 7, 2009                    $775.96
        February 7, 2014                    $862.46
</TABLE>

         The Purchase Price (equal to the Issue Price plus accrued Original
Issue Discount to the Purchase Date) will be paid in cash on February 7, 2004,
but on the later two Purchase Dates it may be paid, at the option of the Issuer,
in cash or by the issuance and delivery of shares of Common Stock of the Company
valued at the Market Price, or in any combination thereof.

         If prior to a Purchase Date this Security has been converted to a
semi-annual coupon note following the occurrence of a Tax Event, the Purchase
Price will be equal to the Restated Principal Amount plus accrued and unpaid
interest from the later of the date of such conversion and the date on which
interest was last paid to the Purchase Date.

         At the option of the Holder and subject to the terms and conditions of
the Indenture, the Issuer shall become obligated to repurchase the Securities if
a Fundamental Change occurs at any time prior to February 7, 2004 for a
Fundamental Change Repurchase Price equal to the Issue Price plus accrued
Original Issue Discount to the Fundamental Change Repurchase Date, which
Fundamental Change Repurchase Price shall be paid in cash or, at the option of
the Issuer, in Common Stock of the Company, as long as it is then listed on a
United States national securities exchange or traded on an established automated
over-the-counter trading market in the United States, or any combination
thereof. The fair market value of the Common Stock for such purpose shall be the
Market Price (as defined in the Indenture) of the Common Stock. If prior to a
Fundamental Change Repurchase Date this Security has been converted to a
semi-annual coupon note following the occurrence of a Tax Event, the Fundamental
Change Repurchase Price shall be equal to the Restated Principal Amount plus
accrued and unpaid interest from the later of the date of such conversion and
the date on which interest was last paid to the Fundamental Change Repurchase
Date.

         Holders have the right to withdraw any Purchase Notice or Fundamental
Change Repurchase Notice, as the case may be, by delivering to the Paying Agent
a written notice of withdrawal in accordance with the provisions of the
Indenture.

                                      A-6
<PAGE>   85

         If cash and/or securities sufficient to pay the Purchase Price or
Fundamental Change Repurchase Price, as the case may be, of all Securities or
portions thereof to be purchased as of the Purchase Date or the Fundamental
Change Repurchase Date, as the case may be, are deposited with the Paying Agent
on the Business Day following the Purchase Date or the Fundamental Change
Repurchase Date, as the case may be, Original Issue Discount or, if the
Securities have been converted to semi-annual coupon notes following the
occurrence of a Tax Event, interest, will cease to accrue on such Securities (or
portions thereof) immediately after such Purchase Date or Fundamental Change
Repurchase Date, as the case may be, and the Holder thereof shall have no other
rights as such (other than the right to receive the Purchase Price or
Fundamental Change Repurchase Price, as the case may be, upon surrender of such
Security).

         If the Issuer elects to pay all or part of the Purchase Price or the
Fundamental Change Repurchase Price in Common Stock, the portion of accrued
Original Issue Discount (or interest if the Issuer has exercised the option to
convert the Securities into semi-annual coupon notes as provided for herein),
attributable to the period from the Issue Date (or, if the Issuer has exercised
its option to convert the Securities into semi-annual coupon notes, the later of
(x) the date of such exercise, and (y) the date on which interest was last paid)
through the Purchase Date or the Fundamental Change Repurchase Date, as the case
may be, with respect to the surrendered Security shall not be cancelled,
extinguished or forfeited, but rather shall be deemed to be paid in full to the
Holder thereof through the delivery of the Common Stock (together with cash
payment, if any, in lieu of fractional shares) and cash, if any, in exchange for
the Security being purchased pursuant to the terms hereof; and such cash, if
any, and the fair market value of such shares of Common Stock (together with any
such cash payment in lieu of fractional shares) shall be treated as delivered
pro rata, to the extent thereof, first in exchange for Original Issue Discount
(or interest, if the Issuer has exercised its option to convert the Securities
into semi-annual coupon notes) accrued through the Purchase Date (or the
Fundamental Change Repurchase Date, as the case may be), and the balance, if
any, of such cash and the fair market value of such Common Stock (and any such
cash payment) shall be treated as delivered in exchange for the Issue Price of
the Security being purchased pursuant to the provisions hereof.

         Conversion - Except as described hereinafter, a Holder of a Security
may convert it into Common Stock at any time on or after the 90th day following
the Issue Date and before the close of business on February 7, 2021. If the Sale
Price on the Conversion Date is (a) less than 100% of the Accreted Conversion
Price, then a Holder electing to exercise its right to convert its Securities on
that date shall receive, in lieu of Common Stock, cash in an amount equal to 95%
of the product of the Conversion Rate and such Sale Price or (b) greater than or
equal to 100% of the Accreted Conversion Price but less than 110% of the
Accreted Conversion Price, then a Holder electing to exercise its right to
convert its Securities on that date shall receive, in lieu of Common Stock, cash
in an amount equal to the sum of the Issue Price plus Original Issue Discount
(or, if the Issuer has exercised its option to convert the Securities to
semi-annual coupon notes following the occurrence of a Tax Event, the Restated
Principal Amount plus unpaid interest thereon) accrued to the Conversion Date;
provided, however, that this provision shall not apply with respect to any
Securities that have been called for redemption pursuant to Section 3.03 of the
Indenture nor shall it be subject to the condition set forth in the second
succeeding paragraph. Further, if the Security is called for redemption, the
Holder may convert it at any time before the close of business on the Business
Day immediately preceding the

                                      A-7
<PAGE>   86

Redemption Date. A Security in respect of which a Holder has delivered a
Purchase Notice or Fundamental Change Repurchase Notice exercising the option of
such Holder to require the Issuer to purchase such Security may be converted
only if such Purchase Notice or Fundamental Change Repurchase Notice is
withdrawn in accordance with the terms of the Indenture.

         A Holder's right to convert Securities into shares of Common Stock is
also subject to the Company's right to elect to instead pay such Holder the
amount of cash set forth in the next succeeding sentence in lieu of delivering
all or part of such shares of Common Stock; provided, however, that if such
payment of cash is not permitted pursuant to the provisions of the Indenture,
the Company shall deliver shares of Common Stock (and cash in lieu of fractional
shares of Common Stock) in accordance with Article 11 of the Indenture, whether
or not the Company has delivered a notice pursuant to Section 11.02 of the
Indenture to the effect that the Securities will be paid in cash. The amount of
cash to be paid for each $1,000 Principal Amount of a Security shall be equal to
the average Sale Price of a share of Common Stock for the five consecutive
trading days immediately following (i) the date of the Company's notice of its
election to deliver cash upon conversion, if the Company shall not have given a
notice of redemption pursuant to Section 3.03 of the Indenture, or (ii) the
Conversion Date, in the case of a conversion following such a notice of
redemption specifying an intent to deliver cash upon conversion, in either case
multiplied by the Conversion Rate in effect on such Conversion Date. If the
Issuer shall elect to make such payment wholly in shares of Common Stock, then
such shares shall be delivered through the Conversion Agent to Holders
surrendering Securities no later than the fifth Business Day following the
Conversion Date. If, however, the Company shall elect to make any portion of
such payment in cash, then the payment, including any delivery of Common Stock,
shall be made to Holders surrendering Securities no later than the tenth
Business Day following the Conversion Date.

         The Company shall not pay cash in lieu of delivering all or part of
such shares of Common Stock upon the conversion of any Security pursuant to the
terms of Article 11 of the Indenture (other than cash in lieu of fractional
shares) if there has occurred (prior to, on or after, as the case may be, the
Conversion Date or the date on which the Company delivers its notice of whether
each Security shall be converted into shares of Common Stock or cash) and is
continuing an Event of Default (other than a default in such payment on such
Securities).

         The initial Conversion Rate is 5.7565 shares of Common Stock per $1,000
Principal Amount at Maturity, subject to adjustment in certain events described
in the Indenture. The Issuer will deliver cash or a check in lieu of any
fractional share of Common Stock.

         In the event the Issuer exercises its option pursuant to Section 10.01
of the Indenture to have interest in lieu of Original Issue Discount accrue on
the Security following a Tax Event, the Holder will be entitled on conversion
into Common Stock to receive the same number of shares of Common Stock such
Holder would have received if the Issuer had not exercised such option. If the
Issuer exercises such option, Securities surrendered for conversion during the
period from the close of business on any Regular Record Date next preceding any
Interest Payment Date to the opening of business on such Interest Payment Date
(except Securities to be redeemed on a date within such period) must be
accompanied by payment of an amount equal to the interest thereon that the
registered Holder is entitled to receive. Except where Securities surrendered
for conversion must be accompanied by payment as described above, no interest on
converted

                                      A-8
<PAGE>   87

Securities shall be payable by the Issuer on any Interest Payment Date
subsequent to the date of conversion.

         To convert a Security, a Holder must (1) complete and manually sign the
conversion notice below (or complete and manually sign a facsimile of such
notice) and deliver such notice to the Conversion Agent, (2) surrender the
Security to the Conversion Agent for cancellation, (3) furnish appropriate
endorsements and transfer documents if required by the Conversion Agent, the
Issuer or the Trustee and (4) pay any transfer or similar tax, if required.

         A Holder may convert a portion of a Security if the Principal Amount at
Maturity of such portion is $1,000 or an integral multiple of $1,000. No payment
or adjustment will be made for dividends on the Common Stock except as provided
in the Indenture. On conversion of a Security, that portion of accrued Original
Issue Discount (or interest if the Issuer has exercised its option provided for
below in "Tax Event") attributable to the period from the Issue Date (or, if the
Issuer has exercised the option referred to below in "Tax Event", the later of
(x) the date of such exercise and (y) the date on which interest was last paid)
through the Conversion Date with respect to the converted Security shall not be
cancelled, extinguished or forfeited, but rather shall be deemed to be paid in
full to the Holder thereof through the delivery of the Common Stock (together
with the cash payment, if any, in lieu of fractional shares) and cash, if any,
in exchange for the Security being converted pursuant to the terms hereof; and
such cash, if any, and the fair market value of such shares of Common Stock
(together with any such cash payment in lieu of fractional shares) shall be
treated as delivered pro rata, to the extent thereof, first in exchange for
Original Issue Discount (or interest, if the Issuer has exercised its option
provided for below in "Tax Event") accrued through the Conversion Date, and the
balance, if any, of such cash and the fair market value of such Common Stock
(and any such cash payment) shall be treated as delivered in exchange for the
Issue Price of the Security being converted pursuant to the provisions hereof.

         The Conversion Rate will be adjusted for dividends or distributions on
Common Stock payable in Common Stock or other Capital Stock; subdivisions,
combinations or certain reclassifications of Common Stock; distributions to all
holders of Common Stock of certain rights to purchase Common Stock for a period
expiring within 60 days at less than the Sale Price at the Time of
Determination; and distributions to such holders of assets or debt securities of
the Company or certain rights to purchase securities of the Company (excluding
certain cash dividends or distributions). However, no adjustment need be made if
Securityholders may participate in the transaction or in certain other cases.
The Issuer from time to time may voluntarily increase the Conversion Rate.

         If the Company is a party to a consolidation, merger or binding share
exchange or a transfer of its assets as, or substantially as, an entirety, or
upon certain distributions described in the Indenture, the right to convert a
Security into Common Stock may be changed into a right to convert it into
securities, cash or other assets of the Company or another Person.

         Tax Event - From and after (1) the date (the "Tax Event Date") of the
occurrence of a Tax Event and (2) the date the Issuer exercises such option,
whichever is later (the "Option Exercise Date"), at the option of the Issuer,
interest in lieu of future Original Issue Discount shall accrue at the rate of
2.125% per annum on a principal amount per Security (the "Restated Principal

                                       A-9
<PAGE>   88

Amount") equal to the Issue Price plus Original Issue Discount accrued to the
Option Exercise Date and shall be payable semi-annually on February 7 and August
7 of each year (each an "Interest Payment Date") to holders of record at the
close of business on January 23 or July 23 (each a "Regular Record Date")
immediately preceding such Interest Payment Date. Interest will be computed on
the basis of a 360-day year comprised of twelve 30-day months and will accrue
from the most recent date to which interest has been paid or, if no interest has
been paid, from the Option Exercise Date.

                  Interest on any Security that is payable, and is punctually
paid or duly provided for, on any Interest Payment Date shall be paid to the
Person in whose name that Security is registered at the close of business on the
Regular Record Date for such interest at the office or agency of the Company
maintained for such purpose. Each installment of interest on any Security shall
be paid in same-day funds by transfer to an account maintained by the payee
located inside the United States, provided that with respect to any Holder, such
Holder shall have furnished to the Paying Agent all required wire payment
instructions no later than the related Regular Record Date, or if no such
instructions have been furnished, by check payable to such Holder.

                  Except as otherwise specified with respect to the Securities,
any Defaulted Interest on any Security shall forthwith cease to be payable to
the registered Holder thereof on the relevant Regular Record Date by virtue of
having been such Holder, and such Defaulted Interest may be paid by the Issuer
as provided for in Section 10.04(b) of the Indenture.

         [INCLUDE IF SECURITY IS A GLOBAL SECURITY -- In the event of a deposit
or withdrawal of an interest in this Security, including an exchange, transfer,
repurchase or conversion of this Security in part only, the Trustee, as
custodian of the Depositary, shall make an adjustment on its records to reflect
such deposit or withdrawal in accordance with the rules and procedures of the
Depositary.]

         [INCLUDE IF SECURITY IS A RESTRICTED SECURITY -- Subject to certain
limitations in the Indenture, at any time when the Issuer is not subject to
Section 13 or 15(d) of the United States Securities Exchange Act of 1934, as
amended, upon the request of a Holder of a Restricted Security, the Issuer shall
promptly furnish or cause to be furnished Rule 144A Information (as defined
below) to such Holder of Restricted Securities, or to a prospective purchaser of
any such security designated by any such Holder, to the extent required to
permit compliance by any such Holder with Rule 144A under the Securities Act of
1933, as amended (the "Securities Act"). "Rule 144A Information" shall be such
information as is specified pursuant to Rule 144A(d)(4) under the Securities Act
(or any successor provision thereto).]

         If an Event of Default shall occur and be continuing, the Issue Price
plus the Original Issue Discount or, if the Securities have been converted to
semi-annual coupon notes following the occurrence of a Tax Event, the Restated
Principal Amount plus interest, accrued on all the Securities may be declared
due and payable in the manner and with the effect provided in the Indenture.

         The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Issuer and the rights of the

                                      A-10
<PAGE>   89

Holders of the Securities under the Indenture at any time by the Issuer and the
Trustee with the consent of the Holders of not less than a majority in aggregate
Principal Amount at Maturity of the outstanding Securities. The Indenture also
contains provisions permitting the Holders of specified percentages in aggregate
Principal Amount at Maturity of the outstanding Securities, on behalf of the
Holders of all the Securities, to waive compliance by the Issuer with certain
provisions of the Indenture and certain past defaults under the Indenture and
their consequences. Any such consent or waiver by the Holder of this Security
shall be conclusive and binding upon such Holder and upon all future Holders of
this Security and of any Security issued upon the registration of transfer
hereof or in exchange herefor or in lieu hereof, whether or not notation of such
consent or waiver is made upon this Security.

         As provided in and subject to the provisions of the Indenture, the
Holder of this Security shall not have the right to institute any proceeding
with respect to the Indenture or for the appointment of a receiver or trustee or
for any other remedy thereunder, unless such Holder shall have previously given
the Trustee written notice of a continuing Event of Default with respect to the
Securities, the Holders of not less than 25% in Principal Amount at Maturity of
the outstanding Securities shall have made written request to the Trustee to
institute proceedings in respect of such Event of Default as Trustee and offered
the Trustee reasonable indemnity, and the Trustee shall not have received from
the Holders of a majority in Principal Amount at Maturity of outstanding
Securities a direction inconsistent with such request, and shall have failed to
institute any such proceeding, for 60 days after receipt of such notice, request
and offer of indemnity. The foregoing shall not apply to any suit instituted by
the Holder of this Security for the enforcement of any payment hereon on or
after the respective due dates expressed herein.

         No reference herein to the Indenture and no provision of this Security
or of the Indenture shall alter or impair the obligation of the Issuer, which is
absolute and unconditional, to pay the Principal Amount at Maturity, Restated
Principal Amount, Purchase Price or Fundamental Change Repurchase Price of,
accrued Original Issue Discount or interest, if any, on, and liquidated damages
on this Security at the times, place and rate, and in the coin or currency,
prescribed in the Indenture.

         As provided in the Indenture and subject to certain limitations therein
set forth, the transfer of this Security is registrable in the Security
Register, upon surrender of this Security for registration of transfer at the
office or agency of the Company established pursuant to the Indenture, duly
endorsed by, or accompanied by a written instrument of transfer in form
satisfactory to the Issuer and the Registrar duly executed by, the Holder hereof
or his attorney duly authorized in writing, and thereupon one or more new
Securities, of authorized denominations and for the same aggregate Principal
Amount at Maturity, will be issued to the designated transferee or transferees.

         The Securities are issuable only in registered form without coupons in
denominations of $1,000 Principal Amount at Maturity and any integral multiple
of $1,000 above that amount. As provided in the Indenture and subject to certain
limitations therein set forth, Securities are exchangeable for a like aggregate
Principal Amount at Maturity of Securities of a different authorized
denomination, as requested by the Holder surrendering the same.

                                      A-11
<PAGE>   90

         No service charge shall be made for any such registration of transfer
or exchange, but the Issuer may require payment of a sum sufficient to cover any
tax or other governmental charge payable in connection therewith.

         Prior to due presentment of this Security for registration of transfer,
the Issuer, the Trustee and any agent of the Issuer or the Trustee may treat the
Person in whose name this Security is registered as the owner hereof for all
purposes, whether or not this Security be overdue, and neither the Issuer, the
Trustee nor any such agent shall be affected by notice to the contrary.

         All terms used in this Security which are defined in the Indenture
shall have the meanings assigned to them in the Indenture.

                                      A-12
<PAGE>   91

                                 ASSIGNMENT FORM

         If you want to assign this Security, fill in the form below and have
your signature guaranteed:

         I or we assign and transfer this Security to:

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

(Print or type name, address and zip code and social security or tax ID number
of assignee)

         and irrevocably appoint _____________________________________ agent to
transfer this Security on the books of the Issuer. The agent may substitute
another to act for him.

<TABLE>
<S>                                                <C>
        Date:                                      Signed:
              ------------------------------              ----------------------------
</TABLE>

         (Sign exactly as your name appears on the other side of this Security)

         Signature Guarantee:
                             ---------------------------------

         In connection with any transfer of this Security occurring prior to the
date of the declaration by the Commission of the effectiveness of a registration
statement under the Securities Act of 1933, as amended (the "Securities Act"),
covering resales of this Security (which effectiveness shall not have been
suspended or terminated at the date of the transfer):

                                   [Check One]

         (1) [ ]   to the Issuer or a subsidiary of the Issuer; or

         (2) [ ]  pursuant to and in compliance with Rule 144A under the
                  Securities Act; or

         (3) [ ]  outside the United States to a "foreign person" in compliance
                  with Rule 904 of Regulation S under the Securities Act; or

         (4) [ ]  pursuant to the exemption from registration provided by Rule
                  144 under the Securities Act, or

         (5) [ ]  pursuant to an effective registration statement under the
                  Securities Act; or

         (6) [ ]  pursuant to another available exemption from the registration
                  requirements of the Securities Act.

         Unless one of the boxes is checked, the Trustee will refuse to register
any of the Securities evidenced by this certificate in the name of any Person
other than the registered Holder thereof, provided that if box (3), (4) or (6)
is checked, the Issuer may require, prior to

                                      A-13
<PAGE>   92

registering any such transfer of the Securities, in its sole discretion, such
legal opinions, certifications (including an investment letter in the case of
box (3)) and other information as the Issuer may reasonably request to confirm
that such transfer is being made pursuant to an exemption from, or in a
transaction not subject to, the registration requirements of the Securities Act.

         If none of the foregoing boxes is checked, the Trustee or Registrar
shall not be obligated to register this Security in the name of any Person other
than the Holder hereof unless and until the conditions to any such transfer of
registration set forth herein and in Section 3.10 of the Indenture shall have
been satisfied.

<TABLE>
<S>                                                   <C>
        Date:                                         Signed:
              ------------------------------                 -----------------------------
</TABLE>

         (Sign exactly as your name appears on the other side of this Security)

         Signature Guarantee:
                             --------------------------------

              TO BE COMPLETED BY PURCHASER IF (2) ABOVE IS CHECKED

         The undersigned represents and warrants that it is purchasing this
Security for its own account or an account with respect to which it exercises
sole investment discretion and that it and any such account is a "qualified
institutional buyer" within the meaning of Rule 144A under the Securities Act
and is aware that the sale to it is being made in reliance on Rule 144A and
acknowledges that it has received such information regarding the Issuer as the
undersigned has requested pursuant to Rule 144A or has determined not to request
such information and that it is aware that the transferor is relying upon the
undersigned's foregoing representations in order to claim the exemption from
registration provided by Rule 144A.

<TABLE>
<S>                                                    <C>
        Date:                                         Signed:
              ------------------------------                 -----------------------------
</TABLE>

         NOTICE: To be executed by an executive officer.

                                      A-14
<PAGE>   93

                            FORM OF CONVERSION NOTICE

         If you want to convert this Security into Common Stock of the Company,
check the box: [ ]

         To convert only part of this Security, state the Principal Amount at
Maturity to be converted (which must be $1,000 or an integral multiple of
$1,000):

         $----------------------------------

         If you want the stock certificate made out in another person's name,
fill in the form below:

--------------------------------------------------------------------------------
             (Insert other person's social security or tax ID no.)

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
            (Print or type other person's name, address and zip code)

<TABLE>
<S>                                                  <C>
        Date:                                        Signed:
              ------------------------------                 -----------------------------
</TABLE>

         (Sign exactly as your name appears on the other side of this Security)

         Signature Guarantee:
                             --------------------------------

                                      A-15
<PAGE>   94

                                    EXHIBIT B

                   [FORM OF TRANSFER CERTIFICATE FOR TRANSFER
                   FROM GLOBAL SECURITY OR DEFINITIVE SECURITY
                             TO DEFINITIVE SECURITY]

                  (Transfers pursuant to Section 2.13(a)(1) or
                      Section 2.13(a)(2) of the Indenture)

                                                             ------------, -----

The Chase Manhattan Bank, as Registrar
600 Travis Street, Suite 1150
Houston, Texas 77002
Attn: Institutional Trust Services

Re:      Transfer of  $________ Principal Amount at Maturity of
         Zero Coupon Convertible Senior Notes due 2021
         (the "Securities") of Enron Corp. (the "Issuer")

         Reference is hereby made to the Indenture dated as of February 7, 2001
(the "Indenture") between the Issuer and The Chase Manhattan Bank, as Trustee.
Capitalized terms used but not defined herein shall have the meanings given them
in the Indenture.

         This letter relates to U.S. $_________ aggregate principal amount of
Securities which are held [in the form of a [Definitive] [Global Security (CUSIP
No. _____________ )]* in the name of [name of transferor] (the "Transferor") to
effect the transfer of Securities.

         In connection with such request, and in respect of such Securities, the
Transferor does hereby certify that such Securities are being transferred in
accordance with (i) the transfer restrictions set forth in the Securities and
the Indenture and (ii) to a transferee that the Transferor reasonably believes
is an institutional "accredited investor" (as defined in Rule 501 (a)(1), (2),
(3) or (7) of Regulation D under the U.S. Securities Act of 1933, as amended)
(an "Institutional Accredited Investor") which is acquiring such Securities for
its own account or for one or more accounts, each of which is an Institutional
Accredited Investor, over which it exercises sole investment discretion and
(iii) in accordance with applicable securities laws of any state of the United
States.

----------
* Insert, if appropriate.

                                       B-1
<PAGE>   95

                                                [Name of Transferor],

                                                By:
                                                   -----------------------------
                                                Name:
                                                     ---------------------------
                                                Title:
                                                      --------------------------
                                                Dated:
                                                      --------------------------

                                       B-2
<PAGE>   96

                                    EXHIBIT C

    [FORM OF NON-DISTRIBUTION LETTER FOR INSTITUTIONAL ACCREDITED INVESTORS]

                   (Transfers pursuant to Section 2.13(a)(1)
                    or Section 2.13(a)(2) of the Indenture)

                                                           ----------------, ---

The Chase Manhattan Bank, as Registrar
600 Travis Street, Suite 1150
Houston, Texas 77002
Attn:  Institutional Trust Services

Enron Corp.
1400 Smith Street
Houston, Texas 77002

Re:  Purchase of $________ Principal Amount at Maturity of Zero Coupon
     Convertible Senior Notes due 2021 (together with the Common Stock
     issuable upon conversion thereof, the "Securities") of Enron Corp.
     (the "Issuer")(1)

Ladies and Gentlemen:

                  In connection with our purchase of the Securities we confirm
that:

                  1. We understand that the Securities are not being and will
not be registered under the Securities Act of 1933, as amended (the "Securities
Act"), and are being sold to us in a transaction that is exempt from the
registration requirements of the Securities Act.

                  2. We acknowledge that (a) neither the Issuer, nor the Initial
Purchasers (as defined in the Offering Memorandum dated January 31, 2001
relating to the Securities (the "Offering Memorandum")) nor any person acting on
behalf of the Issuer or the Initial Purchasers has made any representation to us
with respect to the Issuer or the offer or sale of any Securities; and (b) any
information we desire concerning the Issuer and the Securities or any other
matter relevant to our decision to purchase the Securities (including a copy of
the Offering Memorandum) is or has been made available to us.

                  3. We have such knowledge and experience in financial and
business matters as to be capable of evaluating the merits and risks of an
investment in the Securities, and we are (or

----------
1 Each U.S. purchaser, or account for which each U.S. purchaser is acting,
should purchase at least $250,000 Principal Amount at Maturity of Securities.

                                      C-1
<PAGE>   97

any account for which we are purchasing under paragraph 4 below is) an
institutional "accredited investor" (within the meaning of Rule 501(a)(1), (2),
(3) or (7) of Regulation D under the Securities Act) able to bear the economic
risk of investment in the Securities.

                  4. We are acquiring the Securities for our own account (or for
accounts as to which we exercise sole investment discretion and have authority
to make, and do make, the statements contained in this letter) and not with a
view to any distribution of the Securities, subject, nevertheless, to the
understanding that the disposition of our property will at all times be and
remain within our control.

                  5. We understand that (a) the Securities will be in registered
form only and that any certificates delivered to us in respect of the Securities
will bear a legend substantially to the following effect:

                  "These Securities have not been registered under the
                  Securities Act of 1933. Further offers or sales of these
                  Securities are subject to certain restrictions, as set forth
                  in the Offering Memorandum dated January 31, 2001 relating to
                  these Securities."

                  and (b) the Issuer has agreed to reissue such certificates
without the foregoing legend only in the event of a disposition of the
Securities in accordance with the provisions of paragraph 6 below (provided, in
the case of a disposition of the Securities in accordance with paragraph 6(f)
below, that the legal opinion referred to in such paragraph so permits), or at
our request at such time as we would be permitted to dispose of them in
accordance with paragraph 6(a) below.

                  6. We agree that in the event that at some future time we wish
to dispose of any of the Securities, we will not do so unless such disposition
is made in accordance with any applicable securities laws of any state of the
United States and:

                  (a) the Securities are sold in compliance with Rule 144(k)
         under the Securities Act; or

                  (b) the Securities are sold in compliance with Rule 144A under
         the Securities Act; or

                  (c) the Securities are sold in compliance with Rule 904 of
         Regulation S under the Securities Act; or

                  (d) the Securities are sold pursuant to an effective
         registration statement under the Securities Act; or

                  (e) the Securities are sold to the Issuer or an affiliate (as
         defined in Rule 501(b) of Regulation D) of the Issuer; or

                                      C-2
<PAGE>   98

                  (f) the Securities are disposed of in any other transaction
         that does not require registration under the Securities Act, and we
         theretofore have furnished to the Issuer or its designee an opinion of
         counsel experienced in securities law matters to such effect or such
         other documentation as the Issuer or its designee may reasonably
         request.

                                                 Very truly yours,

                                                 By
                                                   ----------------------
                                                    (Authorized Officer)

                                       C-3
<PAGE>   99

                                    EXHIBIT D

                            [FORM OF PURCHASE NOTICE]

                                                           ----------------, ---

The Chase Manhattan Bank, as Registrar
600 Travis Street, Suite 1150
Houston, Texas 77002
Attn:    Institutional Trust Services

Enron Corp.
1400 Smith Street
Houston, Texas 77002

Re:      Purchase of  $________ Principal Amount at Maturity of
         Zero Coupon Convertible Senior Notes due 2021
         (the "Securities") of Enron Corp. (the "Issuer")

         Certificate No(s). of Securities: _____________________________

         This is a Purchase Notice as defined in Section 3.08(a) of the
Indenture dated as of February 7, 2001 (the "Indenture") between the Issuer and
The Chase Manhattan Bank, as Trustee. Terms used but not defined herein shall
have the meanings ascribed to them in the Indenture.

         I intend to deliver the following aggregate Principal Amount at
Maturity of Securities for purchase by the Issuer pursuant to Section 3.08(a) of
the Indenture (in multiples of $1,000):
$
---------------------------------

         I hereby agree that the Securities will be purchased as of the Purchase
Date pursuant to the terms and conditions thereof and of the Indenture.

         In the event that the Company elects, pursuant to Section 3.08(b) of
the Indenture, to pay the Purchase Price, in whole or in part, in shares of
Common Stock but such portion of the Purchase Price is ultimately payable
entirely in cash because any of the conditions to payment of the Purchase Price
in Common Stock is not satisfied prior to the close of business on the Purchase
Date, I elect (check one):

         [ ]  (1) to withdraw this Purchase Notice as to all of the Securities
         to which it relates;

         [ ]  (2) to withdraw this Purchase Notice as to $___________________
         Principal Amount at Maturity of Securities (Certificate No(s).
         ____________________); or

                                       D-1
<PAGE>   100

         [ ] (3) to receive cash in respect of the entire Purchase Price for
         all Securities or portions thereof to which this Purchase Notice
         relates.

                                                Signed:
                                                       -------------------------

                                      D-2
<PAGE>   101

                                    EXHIBIT E

                 [FORM OF FUNDAMENTAL CHANGE REPURCHASE NOTICE]

                                                           ----------------, ---

The Chase Manhattan Bank, as Registrar
600 Travis Street, Suite 1150
Houston, Texas 77002
Attn:    Institutional Trust Services

Enron Corp.
1400 Smith Street
Houston, Texas 77002

Re:      Purchase of  $________ Principal Amount at Maturity of
         Zero Coupon Convertible Senior Notes due 2021
         (the "Securities") of Enron Corp. (the "Issuer")

         Certificate No(s). of Securities: _____________________________

         This is a Fundamental Change Repurchase Notice as defined in Section
3.09 of the Indenture dated as of February 7, 2001 (the "Indenture") between the
Issuer and The Chase Manhattan Bank, as Trustee. Terms used but not defined
herein shall have the meanings ascribed to them in the Indenture.

         I intend to deliver the following aggregate Principal Amount at
Maturity of Securities for purchase by the Company pursuant to Section 3.09 of
the Indenture (in multiples of $1,000):
$
---------------------------------

         I hereby agree that the Securities will be purchased as of the
Fundamental Change Repurchase Date pursuant to the terms and conditions thereof
and of the Indenture.

         In the event that the Company elects, pursuant to Section 3.09(b) of
the Indenture, to pay the Fundamental Change Repurchase Price, in whole or in
part, in shares of Common Stock but such portion of the Fundamental Change
Repurchase Price is ultimately payable entirely in cash because any of the
conditions to payment of the Fundamental Change Repurchase Price in Common Stock
is not satisfied prior to the close of business on the Fundamental Change
Repurchase Date, I elect (check one):

         [ ] (1) to withdraw this Fundamental Change Repurchase Notice as to
         all of the Securities to which it relates;

                                      E-1
<PAGE>   102

         [ ] (2) to withdraw this Fundamental Change Repurchase Notice as to
         $___________________ Principal Amount at Maturity of Securities
         (Certificate No(s). ____________________); or

         [ ] (3) to receive cash in respect of the entire Fundamental Change
         Repurchase Price for all Securities or portions thereof to which this
         Fundamental Change Repurchase Notice relates.

                                            Signed:
                                                   -----------------------------

                                      E-2
<PAGE>   103

                                    EXHIBIT F

                   [FORM OF TRANSFER CERTIFICATE FOR TRANSFER
                           OF RESTRICTED COMMON STOCK]

            (Transfers pursuant to Section 11.20(c) of the Indenture)

[NAME AND ADDRESS OF COMMON STOCK TRANSFER AGENT]

The Chase Manhattan Bank, as Registrar
600 Travis Street, Suite 1150
Houston, Texas 77002
Attn:    Institutional Trust Services

Re:      Common Stock of Enron Corp. (the "Company")

         Reference is hereby made to the Indenture dated as of February 7, 2001
(the "Indenture") between the Company and The Chase Manhattan Bank, as Trustee.
Capitalized terms used but not defined herein shall have the meanings given them
in the Indenture.

         This letter relates to shares of Common Stock represented by the
accompanying certificate(s) that were issued upon conversion of Securities and
which are held in the name of [name of transferor] (the "Transferor") to effect
the transfer of such Common Stock.

         In connection with the transfer of such shares of Common Stock, the
undersigned confirms that such shares of Common Stock are being transferred:

         CHECK ONE BOX BELOW

         (1) [ ]  to the Company; or

         (2) [ ]  pursuant to and in compliance with Regulation S under the
                  Securities Act of 1933; or

         (3) [ ]  to an institutional "accredited investor" (as defined in Rule
                  501(a)(1), (2), (3) or (7) under the Securities Act of 1933)
                  that has furnished to the transfer agent a signed letter
                  containing certain representations and agreements (the form of
                  which letter can be obtained from the Company or transfer
                  agent); or

         (4) [ ]  pursuant to an exemption from registration under the
                  Securities Act of 1933 provided by Rule 144 thereunder.

         Unless one of the boxes is checked, the transfer agent will refuse to
register any of the Common Stock evidenced by this certificate in the name of
any person other than the registered holder thereof; provided, however, that if
box (2), (3) or (4) is checked, the transfer agent may

                                       F-1
<PAGE>   104

require, prior to registering any such transfer of the Common Stock such
certifications and other information, and if box (4) is checked such legal
opinions, as the Company reasonably requests in writing, by delivery to the
transfer agent of a standing letter of instruction, to confirm that such
transfer is being made pursuant to an exemption from, or in a transaction not
subject to, the registration requirements of the Securities Act of 1933.

                                               [Name of Transferor],

                                               By
                                                 -------------------------------
                                               Name:
                                                    ----------------------------
                                               Title:
                                                     ---------------------------

Dated:

                                       F-2<PAGE>   1
                                                                   EXHIBIT 4.03

                                   ENRON CORP.

                                 $1,907,698,000

                  Zero Coupon Convertible Senior Notes due 2021

                          REGISTRATION RIGHTS AGREEMENT

                                February 7, 2001

<PAGE>   2

                                TABLE OF CONTENTS
<TABLE>
<CAPTION>

                                                                                                               PAGE
                                                                                                               ----
<S>                                                                                                              <C>
1.  Certain Definitions...........................................................................................3
2.  Registration Under the Securities Act.........................................................................6
3.  Registration Procedures.......................................................................................9
4.  Holder's Obligations.........................................................................................14
5.  Registration Expenses........................................................................................14
6.  Representations and Warranties...............................................................................15
7.  Indemnification..............................................................................................17
8.  Rule 144.....................................................................................................19
9.  Miscellaneous................................................................................................20
</TABLE>

                                      -2-
<PAGE>   3

                                   ENRON CORP.

                  Zero Coupon Convertible Senior Notes due 2021

                          Registration Rights Agreement

                                                              New York, New York
                                                                February 7, 2001

Salomon Smith Barney Inc.
J.P. Morgan Securities Inc.
Deutsche Banc Alex. Brown Inc.
Banc of America Securities LLC
Barclays Capital Inc.
c/o Salomon Smith Barney Inc.
388 Greenwich Street
New York, New York  10013

Ladies and Gentlemen:

                  Enron Corp., an Oregon corporation (the "Issuer"), proposes to
issue and sell to the several purchasers (the "Initial Purchasers"),
$1,907,698,000 principal amount at maturity of its Zero Coupon Convertible
Senior Notes due 2021 (the "Firm Notes"), upon the terms set forth in a purchase
agreement, dated January 31, 2001 (the "Purchase Agreement"), relating to the
initial placement of the Firm Notes and the grant from the Issuer to the Initial
Purchasers of an option to purchase up to $381,540,000 additional principal
amount at maturity of such notes to cover over-allotments, if any (together with
the Firm Notes, the "Notes"). The Notes are to be issued under an indenture (the
"Indenture"), dated as of even date herewith, between the Issuer and The Chase
Manhattan Bank, as trustee (the "Trustee"). To induce the Initial Purchasers to
enter into the Purchase Agreement, the Issuer agreed in the Purchase Agreement
to enter into this registration rights agreement (this "Agreement"), with the
Initial Purchasers, under which the Issuer agrees with the Initial Purchasers
for their benefit and the benefit of the holders from time to time of the Notes
or the shares of common stock of the Issuer issuable upon conversion of the
Notes (including, without limitation, the Initial Purchasers) (each a "Holder"
and, together, the "Holders"), as follows:

         1. Certain Definitions. The following terms, when used in this
Agreement, shall have the meanings indicated:

                  (a) "Applicable Conversion Price" shall mean, as of any date
         of determination, the Applicable Principal Amount as of such date of
         determination divided by the Conversion Rate in effect as of such date
         of determination or, if no Notes are then outstanding, the Conversion
         Rate that would be in effect were Notes then outstanding.

                  (b) "Applicable Principal Amount" shall mean, as of any date
         of determination, with respect to each $1,000 principal amount at
         maturity of Notes outstanding, (i) the sum of the Issue Price (as
         defined in the Indenture) of such Notes ($655.24) plus accrued Original
         Issue Discount (as defined in the Indenture) with respect

                                      -3-
<PAGE>   4

         to such Notes through such date of determination or, if no Notes are
         then outstanding, such sum calculated as if Notes were then
         outstanding, or (ii) if the Notes have been converted to semiannual
         coupon notes upon a Tax Event (as defined in the Indenture) pursuant to
         Section 10 of the Indenture, the Restated Principal Amount (as defined
         in the Indenture).

                  (c) "Business Day" shall mean any day other than a Saturday, a
         Sunday or a legal holiday or a day on which banking institutions or
         trust companies are authorized or obligated by law to close either in
         the State of New York or the State of Texas.

                  (d) "Closing Date" shall mean February 7, 2001, the original
         date of issuance of the Notes.

                  (e) "Commission" shall mean the Securities and Exchange
         Commission.

                  (f) "Common Stock" shall mean the Issuer's common stock.

                  (g) "Conversion Rate" shall have the meaning indicated in the
         Indenture.

                  (h) "Damages Payment Date" shall have the meaning set forth in
         Section 2(f).

                  (i) "Deferral Notice" shall have the meaning indicated in
         Section 3(g).

                  (j) "Deferral Period" shall have the meaning indicated in
         Section 3(g).

                  (k) "Effective Time" shall mean the time and date as of which
         the Commission declares the Shelf Registration effective or as of which
         the Shelf Registration otherwise becomes effective.

                  (l) "Exchange Act" shall mean the Securities Exchange Act of
         1934, as amended, and the rules and regulations of the Commission
         promulgated thereunder.

                  (m) "Firm Notes" shall have the meaning indicated in the
         introductory paragraph.

                  (n) "Holder" and "Holders" shall have the meanings indicated
         in the introductory paragraph.

                  (o) "Indenture" shall have the meaning indicated in the
         introductory paragraph.

                  (p) "Initial Purchasers" shall have the meaning indicated in
         the introductory paragraph.

                  (q) "Issuer" shall have the meaning indicated in the
         introductory paragraph.

                  (r) "Material Event" shall have the meaning indicated in
         Section 3(b)(vi).

                  (s) "Notes" shall have the meaning indicated in the
         introductory paragraph.

                                      -4-
<PAGE>   5

                  (t) "Notice and Questionnaire" shall mean a written notice
         delivered to the Issuer containing substantially the information called
         for by the Selling Security Holder Notice and Questionnaire attached as
         Annex A to the Offering Memorandum.

                  (u) "Notice Holder" shall mean, on any date, any Holder that
         has delivered a Notice and Questionnaire to the Issuer on or prior to
         such date.

                  (v) "Offering Memorandum" shall mean the offering memorandum,
         dated January 31, 2001, as amended or supplemented, of the Issuer
         relating to the Notes including any and all annexes thereto and any
         information incorporated by reference therein.

                  (w) "Participant" shall have the meaning indicated in Section
         7(a).

                  (x) "Person" shall mean a corporation, limited liability
         company, association, partnership (whether general or limited),
         organization, business, individual, government or political subdivision
         thereof or governmental agency.

                  (y) "Prospectus" shall mean the prospectus included in any
         Shelf Registration, as amended or supplemented by any amendment or
         prospectus supplement, including post-effective amendments, and all
         materials incorporated by reference or explicitly deemed to be
         incorporated by reference in such Prospectus.

                  (z) "Purchase Agreement" shall have the meaning indicated in
         the introductory paragraph.

                  (aa) "Registrable Securities" shall mean the Securities until
         such time as: (i) in the circumstances contemplated by Section 2(a), a
         registration statement registering such Securities under the Securities
         Act has been declared or becomes effective and such Securities have
         been sold or otherwise transferred by the Holder thereof pursuant to
         such effective registration statement; (ii) such Securities are sold
         pursuant to Rule 144 under circumstances in which any legend borne by
         such Securities relating to restrictions on transferability thereof,
         under the Securities Act or otherwise, is removed or such Securities
         are eligible to be sold pursuant to paragraph (k) of Rule 144; or (iii)
         such Securities shall cease to be outstanding.

                  (bb) "Registration Default" shall have the meaning indicated
         in Section 2(c).

                  (cc) "Registration Default Damages" shall have the meaning
         indicated in Section 2(c).

                  (dd) "Registration Expenses" shall have the meaning indicated
         in Section 5.

                  (ee) "Resale Period" shall mean the period beginning on the
         date the Shelf Registration becomes effective and ending on the
         Termination Date.

                  (ff) "Restricted Holder" shall mean (i) a Holder that is an
         affiliate of the Issuer within the meaning of Rule 405 or (ii) a
         broker-dealer who receives Securities for its own

                                      -5-
<PAGE>   6

         account but did not acquire the Securities as a result of market-making
         activities or other trading activities.

                  (gg) "Rule 144," "Rule 144(k)," "Rule 405" and "Rule 415"
         shall mean, in each case, such rule promulgated under the Securities
         Act.

                  (hh) "Securities" shall mean, collectively, the Notes and the
         Shares.

                  (ii) "Securities Act" shall mean the Securities Act of 1933,
         as amended, and the rules and regulations of the Commission promulgated
         thereunder.

                  (jj) "Shares" shall mean the shares of Common Stock into which
         the Notes are convertible or that have been issued upon any conversion
         from Notes into Common Stock.

                  (kk) "Shelf Registration" shall have the meaning indicated in
         Section 2(a)

                  (ll) "Termination Date" shall have the meaning indicated in
         Section 2(a).

                  (mm) "Trustee" shall have the meaning indicated in the
         introductory paragraph.

                  (nn) "Trust Indenture Act" shall mean the Trust Indenture Act
         of 1939, as amended and the rules and regulations of the Commission
         promulgated thereunder.

         Unless the context otherwise requires, any reference herein to a
"Section" or "clause" refers to a Section or clause, as the case may be, of this
Agreement, and the words "herein," "hereof" and "hereunder" and other words of
similar import refer to this Agreement as a whole and not to any particular
Section or other subdivision. Unless the context otherwise requires, any
reference to a statute, act, rule or regulation refers to the same (including
any successor statute, act, rule or regulation thereto) as it may be amended
from time to time.

         2. Registration Under the Securities Act.

                  (a) The Issuer agrees to use commercially reasonable efforts
         to file with the Commission under the Securities Act as promptly as
         practicable but in any event on or prior to the 120th day after the
         Closing Date one or more "shelf" registration statements (collectively,
         the "Shelf Registration") on an appropriate form providing for the
         registration of, and the sale on a continuous or delayed basis by the
         Holders of, all of the Registrable Securities, pursuant to Rule 415
         under the Securities Act. The Issuer agrees to use commercially
         reasonable efforts to cause the Shelf Registration to become or be
         declared effective under the Securities Act no later than 180 days
         after the Closing Date and to keep such Shelf Registration continuously
         effective for a period ending on the earliest of (i) the time when all
         the Securities registered under the Shelf Registration can be sold by
         Persons who are not affiliates of the Issuer pursuant to Rule 144(k),
         (ii) the second anniversary of the Closing Date, (iii) the date on
         which all Securities registered under the Shelf Registration are
         disposed of in accordance therewith, and (iv) the date upon which there
         are no longer any Registrable Securities outstanding (the earliest date
         on which any such event occurs being the "Termination Date"). The
         Issuer agrees to give

                                      -6-
<PAGE>   7

         notice to the Holders of all of the Registrable Securities of the
         filing and effectiveness of the Shelf Registration. The Issuer further
         agrees to supplement or make amendments to the Shelf Registration, as
         and when required by the rules, regulations or instructions applicable
         to the registration form used for such Shelf Registration or by the
         Securities Act and the Issuer agrees to furnish to the Notice Holders
         of the Registrable Securities copies of any such supplement or
         amendment prior to its being used or promptly following its filing with
         the Commission.

                  (b) Each Holder of Registrable Securities agrees that if such
         Holder wishes to sell Registrable Securities pursuant to a Shelf
         Registration and related Prospectus, it will do so only in accordance
         with this Section 2(b) and Section 3(g). Each Holder of Registrable
         Securities wishing to sell Registrable Securities pursuant to a Shelf
         Registration and related Prospectus agrees to deliver a Notice and
         Questionnaire to the Issuer at least three (3) Business Days prior to
         any intended distribution of Registrable Securities under the Shelf
         Registration. From and after the Effective Time, the Issuer shall, as
         promptly as is practicable after the date a Notice and Questionnaire is
         delivered, and in any event within five (5) Business Days after such
         date, (i) if required by applicable law, file with the Commission a
         post-effective amendment to the Shelf Registration or prepare and, if
         required by applicable law, file a supplement to the related Prospectus
         or a supplement or amendment to any document incorporated therein by
         reference or file any other required document so that such Notice
         Holder is named as a selling security Holder in the Shelf Registration
         and the related Prospectus and so that such Notice Holder is permitted
         to deliver such Prospectus to purchasers of the Registrable Securities
         in accordance with applicable law and, if the Issuer shall file a
         post-effective amendment to the Shelf Registration, use commercially
         reasonable efforts to cause such post-effective amendment to be
         declared effective under the Securities Act as promptly as is
         practicable; (ii) provide such Holder copies of any documents filed
         pursuant to Section 2(b)(i); and (iii) notify such Holder as promptly
         as practicable after the effectiveness under the Securities Act of any
         post-effective amendment filed pursuant to Section 2(b)(i); provided,
         that if such Notice and Questionnaire is delivered during a Deferral
         Period, the Issuer shall so inform the Notice Holder and shall take the
         actions set forth in clauses (i), (ii) and (iii) above upon expiration
         of the Deferral Period in accordance with Section 3(g). Notwithstanding
         anything contained herein to the contrary, the Issuer shall be under no
         obligation to name any Holder that is not a Notice Holder as a selling
         security Holder in any Shelf Registration or related Prospectus;
         provided, however, that any Holder that becomes a Notice Holder
         pursuant to the provisions of Section 2(b) (whether or not such Holder
         was a Notice Holder at the time the Shelf Registration was declared
         effective) shall be named as a selling security Holder in the Shelf
         Registration or related Prospectus in accordance with the requirements
         of this Section 2(b).

                  (c) If any of the following events (any such event a
         "Registration Default") shall occur, then the Issuer shall pay
         liquidated damages (the "Registration Default Damages") to the Holders
         in respect of the Registrable Securities as follows:

                           (i) if the Shelf Registration is not filed with the
                  Commission on or prior to the 120th day following the Closing
                  Date, then commencing on the 121st

                                      -7-
<PAGE>   8

                  day after the Closing Date, Registration Default Damages shall
                  accrue on the Applicable Principal Amount of any outstanding
                  Notes that are Registrable Securities and the Applicable
                  Conversion Price of any outstanding Shares that are
                  Registrable Securities at a rate of 0.25% per annum for the
                  first 120 days from and including such 121st day and 0.5% per
                  annum thereafter; or

                           (ii) if the Shelf Registration is filed but not
                  declared effective by the Commission on or prior to the 180th
                  day following the Closing Date, then commencing on the 181st
                  day after the Closing Date, Registration Default Damages shall
                  accrue on the Applicable Principal Amount of any outstanding
                  Notes that are Registrable Securities and the Applicable
                  Conversion Price of any outstanding Shares that are
                  Registrable Securities at a rate of 0.25% per annum for the
                  first 120 days from and including such 181st day and 0.5% per
                  annum thereafter; or

                           (iii) if the Shelf Registration has been declared
                  effective but such Shelf Registration ceases to be effective
                  (other than pursuant to Section 3(g) hereof) at any time prior
                  to the Termination Date, then commencing on the day such Shelf
                  Registration ceases to be effective, Registration Default
                  Damages shall accrue on the Applicable Principal Amount of any
                  outstanding Notes that are Registrable Securities and the
                  Applicable Conversion Price of any outstanding Shares that are
                  Registrable Securities at a rate of 0.25% per annum for the
                  first 120 days from and including such date on which the Shelf
                  Registration ceases to be effective and 0.5% per annum
                  thereafter; or

                           (iv) if the aggregate duration of Deferral Periods in
                  any period exceeds the number of days permitted in respect of
                  such period pursuant to Section 3(g) hereof, then commencing
                  on the day the aggregate duration of Deferral Periods in any
                  period exceeds the number of days permitted in respect of such
                  period, Registration Default Damages shall accrue on the
                  Applicable Principal Amount of any outstanding Notes that are
                  Registrable Securities and the Applicable Conversion Price of
                  any outstanding Shares that are Registrable Securities at a
                  rate of 0.25% per annum for the first 120 days from and
                  including such date and 0.5% per annum thereafter;

         provided, however, that (1) upon the filing of the Shelf Registration
         (in the case of clause (i) above), (2) upon the effectiveness of the
         Shelf Registration (in the case of clause (ii) above), (3) upon the
         effectiveness of the Shelf Registration which had ceased to remain
         effective (in the case of clause (iii) above), (4) upon the termination
         of the Deferral Period that caused the limit on the aggregate duration
         of Deferral Periods in a period set forth in Section 3(g) to be
         exceeded (in the case of clause (iv) above) or (5) upon the Termination
         Date, Registration Default Damages on all Securities shall cease to
         accrue. It is understood and agreed that, notwithstanding any provision
         to the contrary, so long as any Registrable Security is then capable of
         being sold under an effective Shelf Registration Statement, no
         Registration Default Damages shall accrue on such Registrable Security.
         Registration Default Damages shall constitute the sole monetary damages
         with respect to any matters covered in this Section 2(c).

                                      -8-
<PAGE>   9

                  (d) Any reference herein to a registration statement shall be
         deemed to include any document incorporated therein by reference as of
         the applicable Effective Time and any reference herein to any
         post-effective amendment to a registration statement shall be deemed to
         include any document incorporated therein by reference as of a time
         after such Effective Time.

                  (e) Notwithstanding any other provision of this Agreement, any
         Holder of Registrable Securities who does not comply with the
         provisions of Section 3(d), if applicable, shall not be entitled to
         receive Registration Default Damages unless and until such Holder
         complies with the provisions of Section 3(d), as applicable.

                  (f) Any amounts of Registration Default Damages due pursuant
         to Section 2(c) will be payable in cash semi-annually on each February
         7 and August 7 (each a "Damages Payment Date"), commencing with the
         first such date occurring after any such Registration Default Damages
         commences to accrue, to Holders of record on the January 23 or July 23
         next preceding such Damages Payment Date with respect to Notes that are
         Registrable Securities or with respect to outstanding Shares that are
         Registrable Securities. The amount of Registration Default Damages for
         Registrable Securities will be determined on the basis of a 360-day
         year comprised of twelve 30-day months.

         3. Registration Procedures. The following provisions shall apply to
registration statements filed pursuant to Section 2:

                  (a) At the Effective Time of the Shelf Registration, the
         Issuer shall qualify the Indenture under the Trust Indenture Act.

                  (b) The Issuer shall, with respect to any such registration
         statement:

                           (i) prepare and file with the Commission a
                  registration statement with respect to the Shelf Registration
                  on any form which may be utilized by the Issuer and which
                  shall permit the disposition of the Registrable Securities in
                  accordance with the intended method or methods thereof, as
                  specified in writing by the Holders of the Registrable
                  Securities, and use commercially reasonable efforts to cause
                  such registration statement to become effective in accordance
                  with Section 2(a) above;

                           (ii) prepare and file with the Commission such
                  amendments and supplements to such registration statement and
                  the Prospectus included therein as may be necessary to effect
                  and maintain the effectiveness of such registration statement
                  for the period specified in Section 2(a), and as may be
                  required by the applicable rules and regulations of the
                  Commission and the instructions applicable to the form of such
                  registration statement and as may be necessary to permit the
                  Holders of the Registrable Securities to deliver the
                  Prospectus to purchasers of such Securities, and furnish to
                  the Notice Holders of the Registrable Securities copies of any
                  such supplement or amendment simultaneously with or prior to
                  its being used or filed with the Commission;

                                      -9-
<PAGE>   10

                           (iii) comply, as to all matters within the Issuer's
                  control, with the provisions of the Securities Act with
                  respect to the disposition of all of the Registrable
                  Securities covered by such registration statement in
                  accordance with the intended methods of disposition by the
                  Holders thereof provided for in such registration statement;

                           (iv) provide to any of (A) the Notice Holders, (B)
                  the underwriters (which term, for purposes of this Agreement,
                  shall include a Person deemed to be an underwriter within the
                  meaning of Section 2(11) of the Securities Act), if any,
                  thereof, (C) the sales or placement agent, if any, therefor,
                  (D) counsel for such underwriters or agent and (E) not more
                  than one counsel for all the Holders of such Registrable
                  Securities who so request of the Issuer in writing the
                  opportunity to participate in the preparation of such
                  registration statement, each Prospectus included therein or
                  filed with the Commission and each amendment or supplement
                  thereto;

                           (v) for a reasonable period prior to the filing of
                  such registration statement, and throughout the Resale Period,
                  make available at reasonable times at the Issuer's principal
                  place of business or such other reasonable place for
                  inspection by the Persons referred to in Section 3(b)(iv), who
                  shall certify to the Issuer that they have or are acting on
                  behalf of a Holder who has a current intention to sell
                  Registrable Securities pursuant to the Shelf Registration,
                  such financial and other information and books and records of
                  the Issuer, and cause the officers, employees, counsel and
                  independent certified public accountants of the Issuer to
                  respond to such inquiries, as shall be reasonably necessary,
                  in the judgment of the respective counsel referred to in such
                  Section, to conduct a reasonable investigation within the
                  meaning of Section 11 of the Securities Act; provided,
                  however, that each such party shall be required to maintain in
                  confidence and not to disclose to any other Person or
                  otherwise use or take advantage of any information or records
                  reasonably designated by the Issuer in writing as being
                  confidential, until such time as (A) such information becomes
                  a matter of public record (whether by virtue of its inclusion
                  in such registration statement or otherwise), (B) such Person
                  shall be required so to disclose such information pursuant to
                  a subpoena or order of any court or other governmental agency
                  or body having jurisdiction over the matter (subject to the
                  requirements of such order, and only after such Person shall
                  have given the Issuer prompt prior written notice of such
                  requirement and the opportunity to contest the same or seek an
                  appropriate protective order), or (C) subject to Section 3(g),
                  such information is required to be set forth in such
                  registration statement or the Prospectus included therein or
                  in an amendment to such registration statement or an amendment
                  or supplement to such Prospectus in order that such
                  registration statement, Prospectus, amendment or supplement,
                  as the case may be, does not contain an untrue statement of a
                  material fact or omit to state therein a material fact
                  required to be stated therein or necessary to make the
                  statements therein not misleading, and the Issuer may require
                  each such Person to execute a written agreement to comply with
                  the above confidentiality requirements;

                                      -10-
<PAGE>   11

                           (vi) promptly notify Holders of Registrable
                  Securities included in such registration statement, the sales
                  or placement agent, if any, therefor and the managing
                  underwriter or underwriters, if any, thereof named in the
                  Shelf Registration or a supplement thereto, and confirm such
                  notice in writing, (A) when such registration statement or the
                  Prospectus included therein or any Prospectus amendment or
                  supplement or post-effective amendment has been filed, and,
                  with respect to such registration statement or any
                  post-effective amendment, when the same has become effective,
                  (B) of the issuance by the Commission of any stop order
                  suspending the effectiveness of such registration statement or
                  the initiation or written threat of any proceedings for that
                  purpose, (C) of the receipt by the Issuer of any notification
                  with respect to the suspension of the qualification of the
                  Registrable Securities for sale in any jurisdiction or the
                  initiation or written threat of any proceeding for such
                  purpose, (D) of the occurrence of (but not the nature of or
                  details concerning) any event or the existence of any fact (a
                  "Material Event") as a result of which any Shelf Registration
                  shall contain any untrue statement of a material fact or omit
                  to state any material fact required to be stated therein or
                  necessary to make the statements therein not misleading, or
                  any Prospectus shall contain any untrue statement of a
                  material fact or omit to state any material fact required to
                  be stated therein or necessary to make the statements therein,
                  in the light of the circumstances under which they were made,
                  not misleading, (E) of the determination by the Issuer that a
                  post-effective amendment to a Shelf Registration will be filed
                  with the Commission, which notice may, at the discretion of
                  the Issuer (or as required pursuant to Section 3(g)), state
                  that it constitutes a Deferral Notice, in which event the
                  provisions of Section 3(g) shall apply or (F) at any time when
                  a Prospectus is required to be delivered under the Securities
                  Act, that such registration statement, Prospectus, Prospectus
                  amendment or supplement or post-effective amendment does not
                  conform in all material respects to the applicable
                  requirements of the Securities Act and the Trust Indenture
                  Act;

                           (vii) use commercially reasonable efforts to obtain
                  the withdrawal of any order suspending the effectiveness of
                  such registration statement or any post-effective amendment
                  thereto at the earliest practicable date;

                           (viii) if requested by any managing underwriter or
                  underwriters, any placement or sales agent or any Holder of
                  Registrable Securities included in the Shelf Registration,
                  promptly incorporate in a Prospectus supplement or
                  post-effective amendment such information as is required by
                  the applicable rules and regulations of the Commission
                  relating to the terms of the sale of such Registrable
                  Securities, including information with respect to the
                  principal amount at maturity or number of Registrable
                  Securities being sold by such Holder or agent or to any
                  underwriters, the name and description of such Holder, agent
                  or underwriter, the offering price of such Registrable
                  Securities and any discount, commission or other compensation
                  payable in respect thereof, the purchase price being paid
                  therefor by such underwriters and with respect to any other
                  terms of the offering of the Registrable Securities to be sold
                  by such Holder or agent or to such underwriters; and make all
                  required filings of such Prospectus supplement or

                                      -11-
<PAGE>   12

                  post-effective amendment promptly after notification of the
                  matters to be incorporated in such Prospectus supplement or
                  post-effective amendment;

                           (ix) furnish to each Holder of Registrable Securities
                  included in the Shelf Registration, each placement or sales
                  agent, if any, therefor, each underwriter, if any, thereof and
                  the respective counsel referred to in Section 3(b)(iv) one
                  conformed copy of such registration statement and each such
                  amendment or supplement thereto (in each case including all
                  exhibits thereto) and such number of copies of the Prospectus
                  included in such registration statement (including each
                  preliminary Prospectus and any summary Prospectus) as such
                  Person shall reasonably request, in each case in conformity in
                  all material respects with the applicable requirements of the
                  Securities Act and the Trust Indenture Act; and the Issuer
                  hereby consents (except during such periods that a Deferral
                  Notice is outstanding and has not been revoked) to the use of
                  such Prospectus (including any such preliminary or summary
                  Prospectus) and any amendment or supplement thereto by each
                  such Holder and by any such agent and underwriter, in each
                  case in the form most recently provided to such Person by the
                  Issuer in connection with the offering and sale of the
                  Registrable Securities covered by the Prospectus (including
                  any such preliminary or summary Prospectus) or any supplement
                  or amendment thereto; and

                           (x) use its commercially reasonable efforts to (A)
                  register or qualify, to the extent required by law, the
                  Registrable Securities to be included in such registration
                  statement under such securities laws or blue sky laws of such
                  United States jurisdictions as any Holder of such Registrable
                  Securities included in the Shelf Registration and each
                  placement or sales agent, if any, therefor and underwriter, if
                  any, thereof shall reasonably request, and (B) keep such
                  registrations or qualifications in effect and comply with such
                  laws so as to permit the continuance of offers, sales and
                  dealings therein in such jurisdictions during the period the
                  Shelf Registration is required to remain effective under
                  Section 2(a) and for so long as may be necessary to enable any
                  such Holder, agent or underwriter to complete its distribution
                  of Securities pursuant to such registration statement but in
                  any event not later than the date through which the Issuer is
                  required to keep the Shelf Registration effective pursuant to
                  Section 2(a); provided, however, that the Issuer shall not be
                  required for any such purpose to (1) qualify as a foreign
                  corporation in any jurisdiction wherein it would not otherwise
                  be required to qualify but for the requirements of this
                  Section 3(b)(x), (2) consent to general service of process in
                  any such jurisdiction, or (3) make any changes to its
                  certificate of incorporation or by-laws or any agreement
                  between it and its stockholders.

         In case any of the foregoing obligations is dependent upon information
         provided or to be provided by a party other than the Issuer, such
         obligation shall be subject to the provision of such information by
         such party; provided that the Issuer shall use commercially reasonable
         efforts to obtain the necessary information from any party responsible
         for providing such information.

                                      -12-
<PAGE>   13

                  (c) Each Holder of Registrable Securities agrees that upon
         receipt of any notice from the Issuer, pursuant to Section 3(b)(vi)(D),
         such Holder shall forthwith discontinue (and cause any placement or
         sales agent or underwriters acting on their behalf to discontinue) the
         disposition of Registrable Securities pursuant to the registration
         statement applicable to such Registrable Securities until such Holder
         (i) shall have received copies of such amended or supplemented
         Prospectus and, if so directed by the Issuer, such Holder shall deliver
         to the Issuer (at the Issuer's expense) all copies, other than
         permanent file copies, then in such Holder's possession of the
         Prospectus covering such Registrable Securities at the time of receipt
         of such notice or (ii) shall have received notice from the Issuer that
         the disposition of Registrable Securities pursuant to the Shelf
         Registration may continue.

                  (d) The Issuer may require each Holder of Registrable
         Securities as to which any registration pursuant to Section 2(a) is
         being effected to furnish to the Issuer such information regarding such
         Holder and such Holder's intended method of distribution of such
         Registrable Securities as the Issuer may from time to time reasonably
         request in writing, but only to the extent that such information is
         required in order to comply with the Securities Act or other applicable
         federal or state securities or blue sky laws. Each such Holder agrees
         to notify the Issuer as promptly as practicable of any inaccuracy or
         change in information previously furnished by such Holder to the Issuer
         or of the occurrence of any event in either case as a result of which
         any Prospectus relating to such registration contains or would contain
         an untrue statement of a material fact regarding such Holder or such
         Holder's intended method of disposition of such Registrable Securities
         or omits to state any material fact regarding such Holder or such
         Holder's intended method of disposition of such Registrable Securities
         required to be stated therein or necessary to make the statements
         therein not misleading, and promptly to furnish to the Issuer any
         additional information required to correct and update any previously
         furnished information or required so that such Prospectus shall not
         contain, with respect to such Holder or the disposition of such
         Registrable Securities, an untrue statement of a material fact or omit
         to state a material fact required to be stated therein or necessary to
         make the statements therein not misleading.

                  (e) Until the expiration of two years after the Closing Date,
         the Issuer will not, and will not permit any of its "affiliates" (as
         defined in Rule 144) to, resell any of the Notes that have been
         reacquired by any of them except pursuant to an effective registration
         statement under the Securities Act.

                  (f) Subject to Section 3(g), upon the occurrence of a Material
         Event, the Issuer shall as promptly as practicable prepare and file a
         post-effective amendment to the Shelf Registration or a supplement to
         the related Prospectus or any document incorporated therein by
         reference or file any other required document that would be
         incorporated by reference into such Shelf Registration and Prospectus
         so that such Shelf Registration does not contain any untrue statement
         of a material fact or omit to state any material fact required to be
         stated therein or necessary to make the statements therein not
         misleading, and such Prospectus does not contain any untrue statement
         of a material fact or omit to state any material fact required to be
         stated therein or necessary to make the statements therein, in the
         light of the circumstances under which they were made, not

                                      -13-
<PAGE>   14

         misleading, as thereafter delivered to the purchasers of the
         Registrable Securities being sold thereunder, and, in the case of a
         post-effective amendment to a Shelf Registration, use commercially
         reasonable efforts to cause it to be declared effective as promptly as
         is reasonably practicable. The Issuer shall prepare and furnish to each
         such Holder, to each placement or sales agent, if any, and to each such
         underwriter, if any, a reasonable number of copies of any such
         Prospectus supplemented or amended so that, as thereafter delivered to
         purchasers of Registrable Securities, such Prospectus shall conform in
         all material respects to the applicable requirements of the Securities
         Act and the Trust Indenture Act.

                  (g) Upon the occurrence or existence of any pending corporate
         development or any other Material Event that, in the sole judgment of
         the Issuer, makes it appropriate to suspend the availability of the
         Shelf Registration and the related Prospectus, the Issuer shall give
         notice (without notice of the nature or details of such events) to the
         Notice Holders that the availability of the Shelf Registration is
         suspended (a "Deferral Notice") and, upon receipt of any Deferral
         Notice, each Notice Holder agrees not to sell any Registrable
         Securities pursuant to the Shelf Registration until such Notice
         Holder's receipt of copies of the supplemented or amended Prospectus
         provided for in clause (f) above, or until it is advised in writing by
         the Issuer that the Prospectus may be used, and has received copies of
         any additional or supplemental filings that are incorporated or deemed
         incorporated by reference in such Prospectus. The period during which
         the availability of the Shelf Registration and any Prospectus is
         suspended (the "Deferral Period") shall, without the Issuer incurring
         any obligation to pay Registration Default Damages pursuant to Section
         2(c), not exceed sixty (60) days in any three (3) month period or
         ninety (90) days in any twelve (12) month period. The Issuer's
         obligations under Sections 3(b) and 3(f) shall be suspended during any
         Deferral Period.

         4. Holder's Obligations. Each Holder agrees, by acquisition of the
Registrable Securities, that no Holder of Registrable Securities shall be
entitled to sell any of such Registrable Securities pursuant to a Shelf
Registration or to receive a Prospectus relating thereto, unless such Holder has
furnished the Issuer with a Notice and Questionnaire as required pursuant to
Section 2(b) hereof (including the information required to be included in such
Notice and Questionnaire) and the information set forth in the next sentence.
Each Notice Holder agrees promptly to furnish to the Issuer all information
required to be disclosed in order to make the information previously furnished
to the Issuer by such Notice Holder not misleading and any other information
regarding such Notice Holder and the distribution of such Registrable Securities
as may be required to be disclosed in the Shelf Registration under applicable
law or pursuant to SEC comments. Each Holder further agrees not to sell any
Registrable Securities pursuant to the Shelf Registration without delivering, or
causing to be delivered, a Prospectus to the purchaser thereof and, following
the Termination Date, to notify the Issuer, within 10 business days of request,
of the amount of Registrable Securities sold pursuant to the Shelf Registration
and, in the absence of a response, the Issuer may assume that all of the
Holder's Registrable Securities were so sold. Each Holder specifically agrees
that no underwritten offerings of Registrable Securities may be effected without
the Issuer's prior agreement.

         5. Registration Expenses. The Issuer agrees to bear and to pay or cause
to be paid promptly upon request being made therefor all expenses incident to
the Issuer's performance of

                                      -14-
<PAGE>   15

or compliance with this Agreement, including (a) all Commission and any NASD
registration and filing fees and expenses, (b) all fees and expenses in
connection with the qualification of the Securities for offering and sale under
the state securities and blue sky laws referred to in Section 3(b)(x) hereof,
including reasonable fees and disbursements of one counsel (selected as set
forth in clause (j) below) for the placement or sales agent or underwriters, if
any, in connection with such qualifications, (c) all expenses relating to the
preparation, printing, distribution and reproduction of each registration
statement required to be filed hereunder, each Prospectus included therein or
prepared for distribution pursuant hereto, each amendment or supplement to the
foregoing, the certificates representing the Securities and all other documents
relating hereto, (d) all costs and expenses relating to qualifying the
Securities with The Depository Trust Company and to admitting the Securities for
trading in the PORTAL market, (e) fees and expenses of the Trustee under the
Indenture, and of any paying agent, escrow agent or custodian, and of the
registrar and transfer agent for the Shares issued upon conversion of the Notes,
as well as the reasonable fees and expenses of counsel therefor, (f) internal
expenses (including all salaries and expenses of the Issuer's officers and
employees performing legal or accounting duties), (g) fees, disbursements and
expenses of counsel and independent certified public accountants of the Issuer
(including the expenses of any opinions or "cold comfort" letters required by or
incident to such performance and compliance), (h) fees and expenses of listing
the Shares on all exchanges where the Common Stock is listed, (i) fees charged
by rating agencies to rate the Notes, and (j) reasonable fees, disbursements and
expenses of one counsel for the Holders of Registrable Securities retained in
connection with the Shelf Registration (which shall initially be Bracewell &
Patterson, L.L.P., but which may, with the written consent of the Initial
Purchasers, be another nationally recognized law firm experienced in securities
matters designated by the Issuer (unless reasonably objected to by Holders of at
least a majority in aggregate Applicable Principal Amount and Applicable
Conversion Price of the Registrable Securities being registered)), and fees,
expenses and disbursements of any other Persons, including special experts,
retained by the Issuer in connection with such registration (collectively, the
"Registration Expenses"). To the extent that any Registration Expenses are
incurred, assumed or paid by any Holder of Registrable Securities or any
placement or sales agent therefor or underwriter hereof, the Issuer shall
reimburse such Person for the full amount of the Registration Expenses so
incurred, assumed or paid promptly after receipt of a documented request
therefor. Notwithstanding the foregoing, the Holders of the Registrable
Securities being registered shall pay all agency fees and commissions and
underwriting discounts and commissions attributable to the sale of such
Registrable Securities and the fees and disbursements of any counsel or other
advisors or experts retained by such Holders (severally or jointly), other than
the counsel and experts specifically referred to above.

         6. Representations and Warranties. The Issuer represents and warrants
to, and agrees with, the Initial Purchasers and each of the Holders from time to
time of Registrable Securities that:

                  (a) Each registration statement covering Registrable
         Securities and each Prospectus (including any preliminary or summary
         Prospectus) contained therein or furnished pursuant to Section 3(c)
         hereof and any further amendments or supplements to any such
         registration statement or Prospectus, when it becomes effective or is
         filed with the Commission, as the case may be, and, in the case of an
         underwritten offering of Registrable Securities, at the time of the
         closing under the underwriting agreement

                                      -15-
<PAGE>   16

         relating thereto, will conform in all material respects to the
         applicable requirements of the Securities Act and the Trust Indenture
         Act and will not contain an untrue statement of a material fact or omit
         to state a material fact required to be stated therein or necessary to
         make the statements therein not misleading; and at all times subsequent
         to the Effective Time when a Prospectus would be required to be
         delivered under the Securities Act, other than from (i) such time as a
         notice has been given to Holders of Registrable Securities pursuant to
         Section 3(b)(vi)(D) or Section 3(g) hereof until (ii) such time as the
         Issuer furnishes an amended or supplemented Prospectus pursuant to
         Section 3(f) hereof or such time as the Issuer provides notice that
         offers and sales pursuant to the Shelf Registration may continue, the
         Shelf Registration, and each Prospectus (including any summary
         Prospectus) contained therein or furnished pursuant to Section 3(b)
         hereof, as then amended or supplemented, will conform in all material
         respects to the applicable requirements of the Securities Act and the
         Trust Indenture Act; provided, however, that this representation and
         warranty shall not apply to any statements or omissions made in
         reliance upon and in conformity with information furnished in writing
         to the Issuer by or on behalf of a Holder of Registrable Securities
         expressly for use therein.

                  (b) Any documents incorporated by reference in any Prospectus
         referred to in Section 6(a) hereof, when they become or became
         effective or are or were filed with the Commission, as the case may be,
         will conform or conformed in all material respects to the requirements
         of the Securities Act or the Exchange Act, as applicable, and none of
         such documents will contain or contained an untrue statement of a
         material fact or will omit or omitted to state a material fact required
         to be stated therein or necessary to make the statements therein not
         misleading, provided, however, that this representation and warranty
         shall not apply to any statements or omissions made in reliance upon
         and in conformity with information furnished in writing to the Issuer
         by a Holder of Registrable Securities expressly for use therein.

                  (c) The compliance by the Issuer with all of the provisions of
         this Agreement and the consummation of the transactions herein
         contemplated will not contravene any provision of applicable law or the
         certificate of incorporation or by-laws of the Issuer or, except to the
         extent that any such contravention would not have a material adverse
         effect on the Issuer and its subsidiaries, taken as a whole, any
         indenture or instrument relating to indebtedness for money borrowed or
         any agreement to which the Issuer is a party or any order, rule,
         regulation or decree of any court or governmental agency or authority
         located in the United States having jurisdiction over the Issuer or any
         property of the Issuer; and, to the best knowledge of the Issuer, no
         consent, authorization or order of, or filing or registration with, any
         court or governmental agency or authority is required for the
         consummation by the Issuer of the transactions contemplated by this
         Agreement, except the registration under the Securities Act
         contemplated hereby, qualification of the Indenture under the Trust
         Indenture Act and such consents, approvals, authorizations,
         registrations or qualifications as may be required under State
         securities or blue sky laws.

                  (d) This Agreement has been duly authorized, executed and
         delivered by the Issuer.

                                      -16-
<PAGE>   17

         7. Indemnification.

                  (a) Indemnification by the Issuer. In connection with the
         Shelf Registration, the Issuer shall, and hereby agrees to, indemnify
         and hold harmless each of the Holders of Registrable Securities
         included in such Shelf Registration, and each Person who is named in
         such Shelf Registration or a supplement thereto as an underwriter in
         any offering or sale of such Registrable Securities, such Person's
         partners, principals, directors and officers and each Person who
         controls any such Person (each, a "Participant") against any losses,
         claims, damages or liabilities, joint or several, to which such
         Participant may become subject under the Securities Act, the Exchange
         Act or other federal or state statutory law or regulation, at common
         law or otherwise, insofar as such losses, claims, damages or
         liabilities (or actions in respect thereof) arise out of or are based
         upon an untrue statement or alleged untrue statement of a material fact
         contained in any registration statement under which such Registrable
         Securities were registered under the Securities Act, or any
         preliminary, final or summary Prospectus contained therein or furnished
         by the Issuer to any such Participant, or any amendment or supplement
         thereto, or arise out of or are based upon the omission or alleged
         omission to state therein a material fact required to be stated therein
         or necessary to make the statements therein not misleading and the
         Issuer shall, and hereby agrees to, reimburse each such Participant for
         any legal or other expenses reasonably incurred by it in connection
         with investigating or defending any such loss, claim, damage, liability
         or action; provided, however, that the Issuer shall not be liable to
         any such Person in any such case to the extent that any such loss,
         claim, damage or liability arises out of or is based upon an untrue
         statement or alleged untrue statement or omission or alleged omission
         made in such registration statement, or preliminary, final or summary
         Prospectus, or amendment or supplement thereto, in reliance upon and in
         conformity with written information furnished to the Issuer by such
         Participant expressly for use therein; provided, further, that this
         indemnity agreement shall not apply to any loss, liability, claim,
         damage or expense arising from (i) an offer or sale of Registrable
         Securities occurring during a Deferral Period, if Notice Holders
         received a Deferral Notice, or (ii) the Participant's failure to
         deliver at or prior to the written confirmation of sale, the most
         recent Prospectus, as amended or supplemented, and such Prospectus, as
         amended or supplemented, would have corrected such untrue statement or
         alleged untrue statement of a material fact. This indemnity agreement
         will be in addition to any liability which the Issuer may otherwise
         have.

                  (b) Indemnification by Participants. Each Participant,
         severally and not jointly, agrees to indemnify and hold harmless the
         Issuer, each of the Issuer's directors and officers and each Person who
         controls the Issuer within the meaning of either the Securities Act or
         the Exchange Act, to the same extent as the foregoing indemnity from
         the Issuer, but only with reference to written information furnished to
         the Issuer by or on behalf of such Participant specifically for use in
         any registration statement, or any preliminary or final or summary
         Prospectus contained therein or any amendment or supplement thereto.
         This indemnity agreement will be acknowledged by each Participant that
         is not an Initial Purchaser in such Participant's Notice and
         Questionnaire and will be in addition to any liability which any such
         Person may otherwise have.

                  (c) Promptly after receipt by an indemnified party under
         Section 7(a) or (b) of notice of the commencement of any action, such
         indemnified party will, if a claim in respect thereof is to be made
         against the indemnifying party under such subsection, notify

                                      -17-
<PAGE>   18

         the indemnifying party in writing of the commencement thereof; but the
         omission so to notify the indemnifying party will not relieve the
         indemnifying party from any liability which it may have to any
         indemnified party otherwise than under Section 7(a) or (b). In case any
         such action is brought against any indemnified party, and it notifies
         the indemnifying party of the commencement thereof, the indemnifying
         party will be entitled to participate therein, and to the extent that
         it may elect by written notice delivered to the indemnified party
         promptly after receiving the aforesaid notice from such indemnified
         party, to assume the defense thereof; provided that, if the defendants
         in any such action include both the indemnified party and the
         indemnifying party and representation of both parties by the same
         counsel would be inappropriate due to actual or potential conflicting
         interests between them, the indemnified party or parties shall have the
         right to select separate counsel to participate in the defense of such
         action on behalf of such indemnified party or parties. Upon receipt of
         notice from the indemnifying party to such indemnified party of its
         election so to assume the defense of such action, the indemnifying
         party will not be liable to such indemnified party under Section 7(a)
         or (b) for any legal or other expenses subsequently incurred by such
         indemnified party (other than reasonable costs of investigation) in
         connection with the defense thereof unless (i) the indemnified party
         shall have employed separate counsel in connection with the assertion
         of legal defenses in accordance with the proviso to the immediately
         preceding sentence (it being understood, however, that the indemnifying
         party shall not be liable for the expenses of more than one separate
         national counsel, approved by the indemnifying party, representing the
         indemnified parties who are parties to such action), (ii) the
         indemnifying party shall not have employed counsel satisfactory to the
         indemnified party to represent the indemnified party within a
         reasonable time after notice of commencement of the action or (iii) the
         indemnifying party has authorized the employment of counsel for the
         indemnified party at the expense of the indemnifying party; and except
         that, if clause (i) or (iii) is applicable, such liability shall be
         only in respect of the counsel referred to in such clause (i) or (iii).

         No indemnifying party shall, without the prior written consent of the
         indemnified party, effect any settlement of any pending or threatened
         action in respect of which any indemnified party is or could have been
         a party and indemnity could have been sought hereunder by such
         indemnified party unless such settlement includes an unconditional
         release of such indemnified party from all liability on any claims that
         are the subject matter of such action. No indemnifying party shall be
         liable for any settlement effected without its consent.

                  (d) Contribution. Each party hereto agrees that, if for any
         reason the indemnification provisions contemplated by Section 7(a) or
         Section 7(b) are unavailable to or insufficient to hold harmless an
         indemnified party in respect of any losses, claims, damages or
         liabilities (or actions in respect thereof) referred to therein, then
         each indemnifying party shall contribute to the amount paid or payable
         by such indemnified party as a result of such losses, claims, damages
         or liabilities (or actions in respect thereof) in such proportion as is
         appropriate to reflect the relative fault of the indemnifying party and
         the indemnified party in connection with the statements or omissions
         which resulted in such losses, claims, damages or liabilities (or
         actions in respect thereof), as well as any other relevant equitable
         considerations. The relative fault

                                      -18-
<PAGE>   19

         of such indemnifying party and indemnified party shall be determined by
         reference to, among other things, whether the untrue or alleged untrue
         statement of a material fact or omission or alleged omission to state a
         material fact relates to information supplied by such indemnifying
         party or by such indemnified party, and the parties' relative intent,
         knowledge, access to information and opportunity to correct or prevent
         such statement or omission. The parties hereto agree that it would not
         be just and equitable if contributions pursuant to this Section 7(d)
         were determined by pro rata allocation (even if the Participants were
         treated as one entity for such purpose) or by any other method of
         allocation which does not take account of the equitable considerations
         referred to in this Section 7(d). The amount paid or payable by an
         indemnified party as a result of the losses, claims, damages, or
         liabilities (or actions in respect thereof) referred to above shall be
         deemed to include any legal or other fees or expenses reasonably
         incurred by such indemnified party in connection with investigating or
         defending any such action or claim. Notwithstanding the provisions of
         this Section 7(d), no Participant shall be required to contribute any
         amount in excess of the amount by which the dollar amount of the
         proceeds received by such Participant from the sale of any Registrable
         Securities exceeds the amount of any damages which such Participant has
         otherwise been required to pay by reason of such untrue or alleged
         untrue statement or omission or alleged omission, and no underwriter
         shall be required to contribute any amount in excess of the amount by
         which the total price at which the Registrable Securities underwritten
         by it and distributed to the public were offered to the public exceeds
         the amount of any damages which such underwriter has otherwise been
         required to pay by reason of such untrue or alleged untrue statement or
         omission or alleged omission. No Person guilty of fraudulent
         misrepresentation (within the meaning of Section 11(f) of the
         Securities Act) shall be entitled to contribution from any Person who
         was not guilty of such fraudulent misrepresentation. The Participants'
         obligations in this Section 7(d) to contribute shall be several in
         proportion to the aggregate principal amount at maturity or number of
         Registrable Securities registered or underwritten, as the case may be,
         by them and not joint.

                  (e) The obligations of the Issuer under this Section 7 shall
         be, in addition to any liability which the Issuer may otherwise have
         and shall extend, upon the same terms and conditions, to each officer,
         director, principal and partner of each Participant and each Person, if
         any, who controls any Participant within the meaning of the Securities
         Act or the Exchange Act; and the obligations of the Participants
         contemplated by this Section 7 shall be in addition to any liability
         which the respective Participants may otherwise have and shall extend,
         upon the same terms and conditions, to each officer and director of the
         Issuer (including any Person who, with such Person's consent, is named
         in any registration statement as about to become a director of the
         Issuer), and to each Person, if any, who controls the Issuer within the
         meaning of the Securities Act or the Exchange Act.

         8. Rule 144. The Issuer covenants to the Holders of Registrable
Securities that, until the Termination Date, the Issuer shall use commercially
reasonable efforts to timely file the reports required to be filed by it under
the Exchange Act referred to in subparagraph (c)(1) of Rule 144 adopted by the
Commission under the Securities Act. Upon the request of any Holder of
Registrable Securities in connection with that Holder's sale pursuant to Rule
144, the Issuer shall

                                      -19-
<PAGE>   20

deliver to such Holder a written statement as to whether it has complied with
such requirements. If the Issuer ever ceases to be subject to the reporting
requirements of the Exchange Act, it will deliver to the Holders and prospective
purchasers the information required to be delivered pursuant to Rule 144A(d)(4)
under the Securities Act.

         9. Miscellaneous.

                  (a) Notices. All notices, requests, claims, demands, waivers
         and other communications hereunder shall be in writing and effective
         only on receipt, and if sent to the Issuer, will be mailed, delivered
         or telefaxed to 1400 Smith Street, Houston, Texas, 77002, Attention:
         Ben Glisan, Managing Director and Treasurer, Facsimile No. (713)
         646-4990, if to an Initial Purchaser, to it at the address for the
         Initial Purchasers set forth in the Purchase Agreement; and if to a
         Holder, will be mailed, delivered to telefaxed to the address of such
         Holder set forth in the security register, a Notice and Questionnaire
         or other records of the Issuer or to such other address as the Issuer
         or any such Holder may have furnished to the other in writing in
         accordance herewith, except that notices of change of address shall be
         effective only upon receipt.

                  (b) Parties in Interest. All the terms and provisions of this
         Agreement shall be binding upon, shall inure to the benefit of and
         shall be enforceable by the respective successors and assigns of the
         parties hereto. In the event that any transferee of any Holder of
         Registrable Securities shall acquire Registrable Securities, in any
         manner, whether by gift, bequest, purchase, operation of law or
         otherwise, such transferee shall, without any further writing or action
         of any kind, be deemed a party hereto for all purposes and such
         Registrable Securities shall be held subject to all of the terms of
         this Agreement, and by taking and holding such Registrable Securities
         such transferee shall be entitled to receive the benefits of, and be
         conclusively deemed to have agreed to be bound by and to perform, all
         of the applicable terms and provisions of this Agreement.

                  (c) Survival. The respective agreements, representations,
         warranties, indemnities and other statements of the Issuer or its
         officers and directors and of the Holders set forth or made pursuant to
         this Agreement shall remain in full force and effect regardless of any
         investigation (or statement as to the results thereof) made by or on
         behalf of any Holder, the Issuer, any agent or underwriter or any
         director, principal, partner, officer, or any controlling Person of any
         of the foregoing, and shall survive delivery of and payment for the
         Securities pursuant to the Purchase Agreement and the transfer and
         registration of the Securities pursuant to this Agreement. However,
         this Agreement shall terminate and be of no force or effect after the
         Termination Date, except with respect to any obligations under Sections
         2(c), 5 or 7 hereof that relate to events occurring prior to the
         Termination Date.

                  (d) Applicable Law. This Agreement will be governed by and
         construed in accordance with the laws of the Sate of New York
         applicable to contracts made and to be performed within the Sate of New
         York.

                  (e) Headings. The section headings used herein are inserted
         for convenience only and shall not affect the construction hereof.

                                      -20-
<PAGE>   21

                  (f) Entire Agreement; Amendments. This Agreement and the other
         writings referred to herein (including the Purchase Agreement and the
         Indenture) or delivered pursuant hereto which form a part hereof
         contain the entire understanding of the parties with respect to its
         subject matter. This Agreement and the Purchase Agreement supersede all
         prior agreements and understandings between the parties with respect to
         subject matter. This Agreement may be amended and the observance of any
         term of this Agreement may be waived (either generally or in a
         particular instance and either retroactively or prospectively) only by
         a written instrument duly executed by the Issuer and the Holders of at
         least a majority of the Shares constituting Registrable Securities at
         the time outstanding (with Holders of Notes deemed to be the Holders,
         for the purposes of this Section, of the number of outstanding Shares
         into which such Notes are or would be convertible or exchangeable as of
         the date on which such consent is requested). Each Holder of any
         Registrable Securities at the time or thereafter outstanding shall be
         bound by any amendment or waiver effected pursuant to this Section
         9(f), whether or not any notice, writing or marking indicating such
         amendment or waiver appears on such Registrable Securities or is
         delivered to such Holder.

                  (g) Inspection. For so long as this Agreement shall be in
         effect, this Agreement and a complete list of the names and addresses
         of all the Holders of Registrable Securities shall be made available
         for inspection and copying on any business day by any Holder of
         Registrable Securities for proper purposes only (which shall include
         any purpose related to the rights of the Holders of Registrable
         Securities under the Securities, the Indenture and this Agreement) at
         the offices of the Issuer at the address thereof set forth in Section
         9(a) above, or at the office of the Trustee under the Indenture.

                  (h) Counterparts. This Agreement may be executed by one or
         more counterparts, each of which shall constitute an original and all
         of which together shall constitute one and the same instrument.

                                      -21-
<PAGE>   22

         Agreed to and accepted as of the date referred to above.

                                          Very truly yours,

                                          ENRON CORP.

                                          By
                                            ------------------------------------
                                            Name:
                                            Title:

                                      -22-
<PAGE>   23

The foregoing Agreement is hereby confirmed and
accepted as of the date first above written.

SALOMON SMITH BARNEY INC.
J.P. MORGAN SECURITIES INC.
DEUTSCHE BANC ALEX. BROWN INC.
BANC OF AMERICA SECURITIES LLC
BARCLAYS CAPITAL INC.

By:  Salomon Smith Barney Inc.

By
  ----------------------------
   Name:
   Title:

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