Document:

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                                                                     EXHIBIT 4.1

                                                                  EXECUTION COPY

                                    INDENTURE

                           HUMAN GENOME SCIENCES, INC.

                                       to

                              THE BANK OF NEW YORK

                                     Trustee

                 3 3/4% Convertible Subordinated Notes Due 2007

                           Dated as of March 10, 2000

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                                Table of Contents

                                                                            Page

                                    ARTICLE I

             Definitions and Other Provisions of General Application

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SECTION 1.01.           Definitions............................................................ 1
SECTION 1.02.           Compliance Certificates and Opinions................................... 9
SECTION 1.03.           Form of Documents Delivered to Trustee................................ 10
SECTION 1.04.           Acts of Holders: Record Dates ........................................ 10
SECTION 1.05.           Notices, etc., to Trustee and Company................................. 12
SECTION 1.06.           Notice to Holders: Waiver............................................. 12
SECTION 1.07.           Conflict with Trust Indenture Act..................................... 13
SECTION 1.08.           Effect of Headings and Table of Contents.............................. 13
SECTION 1.09.           Successors and Assigns................................................ 13
SECTION 1.10.           Severability Clause................................................... 13
SECTION 1.11.           Benefits of Indenture................................................. 13
SECTION 1.12.           Governing Law......................................................... 13
SECTION 1.13.           Legal Holidays........................................................ 13

                                   ARTICLE II

                                 Security Forms
                                 --------------

SECTION 2.01.           Forms Generally....................................................... 14
SECTION 2.02.           Form of Face of Security.............................................. 15
SECTION 2.03.           Form of Reverse of Security .......................................... 18
SECTION 2.04.           Form of Trustee's Certificate of Authentication....................... 22
SECTION 2.05.           Form of Conversion Notice............................................. 23
SECTION 2.06.           Form of Certification................................................. 24

                                   ARTICLE III

                                 The Securities
                                 --------------

SECTION 3.01.           Title and Terms....................................................... 25
SECTION 3.02.           Denominations......................................................... 25
SECTION 3.03.           Execution, Authentication, Delivery and Dating........................ 25
SECTION 3.04.           Global and Non-Global Securities...................................... 26
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SECTION 3.05.           Registration; Registration of Transfer and Exchange................... 27
SECTION 3.06.           Mutilated, Destroyed, Lost and Stolen Securities...................... 31
SECTION 3.07.           Payment of Interest; Interest Rights Preserved ....................... 31
SECTION 3.08.           Persons Deemed Owners................................................. 33
SECTION 3.09.           Cancellation.......................................................... 33
SECTION 3.10.           Computation of Interest............................................... 33

                                   ARTICLE IV

                           Satisfaction and Discharge
                           --------------------------

SECTION 4.01.           Satisfaction and Discharge of Indenture............................... 33
SECTION 4.02.           Application of Trust Money............................................ 34

                                    ARTICLE V

                                    Remedies
                                    --------

SECTION 5.01.           Events of Default..................................................... 35
SECTION 5.02.           Acceleration of Maturity; Rescission and Annulment.................... 36
SECTION 5.03.           Collection of Indebtedness and Suits for Enforcement
                                      by Trustee.............................................. 37
SECTION 5.04.           Trustee May File Proofs of Claim...................................... 38
SECTION 5.05.           Trustee May Enforce Claims Without Possession of
                                      Securities.............................................. 39
SECTION 5.06.           Application of Money Collected........................................ 39
SECTION 5.07.           Limitation on Suits................................................... 39
SECTION 5.08.           Unconditional Right of Holders to Receive Principal,
                                      Premium and Interest and To Convert..................... 40
SECTION 5.09.           Restoration of Rights and Remedies.................................... 40
SECTION 5.10.           Rights and Remedies Cumulative........................................ 40
SECTION 5.11.           Delay or Omission Not Waiver.......................................... 40
SECTION 5.12.           Control by Holders.................................................... 40
SECTION 5.13.           Waiver of Past Defaults............................................... 41
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SECTION 5.14.           Undertaking for Costs................................................. 41
SECTION 5.15.           Waiver of Usury, Stay or Extension Laws............................... 41

                                   ARTICLE VI

                                   The Trustee
                                   -----------

SECTION 6.01.           Certain Duties and Responsibilities................................... 42
SECTION 6.02.           Notice of Defaults.................................................... 43
SECTION 6.03.           Certain Rights of Trustee............................................. 43
SECTION 6.04.           Not Responsible for Recitals or Issuance of Securities................ 44
SECTION 6.05.           May Hold Securities................................................... 44
SECTION 6.06.           Money Held in Trust................................................... 44
SECTION 6.07.           Compensation and Reimbursement........................................ 44
SECTION 6.08.           Disqualification; Conflicting Interests............................... 45
SECTION 6.09.           Corporate Trustee Required; Eligibility............................... 45
SECTION 6.10.           Resignation and Removal; Appointment of Successor..................... 45
SECTION 6.11.           Acceptance of Appointment by Successor................................ 46
SECTION 6.12.           Merger, Conversion, Consolidation or Succession
                                      to Business .............................................47
SECTION 6.13.           Preferential Collection of Claims Against Company .....................47
SECTION 6.14.           Appointment of Authenticating Agent....................................47
SECTION 6.15.           Appointment of Co-Trustee..............................................48

                                   ARTICLE VII

                     Holders' Lists and Reports by Trustee and Company
                     -------------------------------------------------

SECTION 7.01.           Company to Furnish Trustee Names and Addresses
                                      of Holders ...............................................49
SECTION 7.02.           Preservation of Information; Communications to
                                      Holders...................................................49
SECTION 7.03.           Reports by Trustee .....................................................50
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SECTION 7.04.           Reports by Company......................................................50

                                  ARTICLE VIII

                     Consolidation, Merger, Conveyance, Transfer or Lease
                     ----------------------------------------------------

SECTION 8.01.           Company May Consolidate, etc., Only on Certain Terms.................... 50
SECTION 8.02.           Successor Substituted................................................... 51

                                   ARTICLE IX

                             Supplemental Indentures
                             -----------------------

SECTION 9.01.           Supplemental Indentures Without Consent of Holders...................... 51
SECTION 9.02.           Supplemental Indentures with Consent of Holders......................... 52
SECTION 9.03.           Execution of Supplemental Indentures.................................... 53
SECTION 9.04.           Effect of Supplemental Indentures....................................... 53
SECTION 9.05.           Conformity with Trust Indenture Act..................................... 53
SECTION 9.06.           Reference in Securities to Supplemental Indentures...................... 53

                                    ARTICLE X

                                    Covenants
                                    ---------

SECTION 10.01.          Payment of Principal, Premium and Interest.............................. 54
SECTION 10.02.          Maintenance of Office or Agency......................................... 54
SECTION 10.03.          Money for Security Payments To Be Held in Trust......................... 54
SECTION 10.04.          Statement by Officers as to Default..................................... 55
SECTION 10.05.          Existence............................................................... 56
SECTION 10.06.          Maintenance of Properties............................................... 56
SECTION 10.07.          Payment of Taxes and Other Claims....................................... 56
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SECTION 10.08.          Waiver of Certain Covenants......................................... 56
SECTION 10.09.          Delivery of Certain Information..................................... 56
SECTION 10.10.          Resale of Certain Securities; Reporting Issuer...................... 57
SECTION 10.11.          Registration Rights................................................. 57

                                   ARTICLE XI

                            Redemption of Securities
                            ------------------------

SECTION 11.01.          Right of Provisional Redemption..................................... 58
SECTION 11.02.          Right of Optional Redemption........................................ 59
SECTION 11.03.          Applicability of Article............................................ 59
SECTION 11.04.          Election to Redeem; Notice to Trustee............................... 59
SECTION 11.05.          Selection by Trustee of Securities to Be Redeemed................... 59
SECTION 11.06.          Notice of Redemption................................................ 60
SECTION 11.07.          Deposit of Redemption Price......................................... 60
SECTION 11.08.          Securities Payable on Redemption Date............................... 61
SECTION 11.09.          Securities Redeemed in Part......................................... 62
SECTION 11.10.          Conversion Arrangement on Call for Redemption....................... 62

                                   ARTICLE XII

                           Subordination of Securities
                           ---------------------------

SECTION 12.01.          Securities Subordinate to Senior Indebtedness....................... 63
SECTION 12.02.          Payment over of Proceeds upon Dissolution, Etc...................... 63
SECTION 12.03.          No Payment When Senior Indebtedness in Default...................... 64
SECTION 12.04.          Payment Permitted If No Default..................................... 64
SECTION 12.05.          Subrogation to Rights of Holders of Senior Indebtedness............. 64
SECTION 12.06.          Provisions Solely to Define Relative Rights ........................ 65
SECTION 12.07.          Trustee to Effectuate Subordination................................. 65
SECTION 12.08.          No Waiver of Subordination Provisions............................... 65
SECTION 12.09.          Notice to Trustee................................................... 66
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SECTION 12.10.          Reliance on Judicial Order or Certificate of
                        Liquidating Agent................................................... 67
SECTION 12.11.          Trustee Not Fiduciary for Holders of Senior Indebtedness............ 67
SECTION 12.12.          Rights of Trustee as Holder of Senior Indebtedness;
                        Preservation of Trustee's Rights.................................... 67
SECTION 12.13.          Article Applicable to Paying Agents................................. 67
SECTION 12.14.          Certain Conversions Deemed Payment.................................. 67

                                  ARTICLE XIII

                            Conversion of Securities
                            ------------------------

SECTION 13.01.          Conversion Privilege and Conversion Price......................... 68
SECTION 13.02.          Exercise of Conversion Privilege.................................. 69
SECTION 13.03.          Fractions of Shares............................................... 70
SECTION 13.04.          Adjustment of Conversion Price.................................... 70
SECTION 13.05.          Notice of Adjustments of Conversion Price......................... 75
SECTION 13.06.          Notice of Certain Corporate Action................................ 75
SECTION 13.07.          Company to Reserve Common Stock................................... 76
SECTION 13.08.          Taxes on Conversions.............................................. 76
SECTION 13.09.          Covenant as to Common Stock....................................... 76
SECTION 13.10.          Cancellation of Converted Securities.............................. 77
SECTION 13.11.          Provisions in Case of Reclassification, Consolidation,
                        Merger or Sale of Assets.......................................... 77

                                   ARTICLE XIV

                           Right to Require Repurchase
                           ---------------------------

SECTION 14.01.          Right to Require Repurchase....................................... 77
SECTION 14.02.          Notice, Method of Exercising Repurchase Right .................... 78
SECTION 14.03.          Deposit of Repurchase Price....................................... 78
SECTION 14.04.          Securities Not Repurchased on Repurchase Date..................... 78
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SECTION 14.05.          Securities Repurchased in Part.................................... 79
SECTION 14.06.          Certain Definitions............................................... 79

                                   ARTICLE XV

                       Defeasance and Covenant Defeasance
                       ----------------------------------

SECTION 15.01.          Company's Option to Effect Defeasance or Covenant
                          Defeasance...................................................... 80
SECTION 15.02.          Defeasance and Discharge.......................................... 80
SECTION 15.03.          Covenant Defeasance............................................... 81
SECTION 15.04.          Conditions to Defeasance or Covenant Defeasance................... 81
SECTION 15.05.          Deposited Money and U.S. Government Obligations
                          to Be Held in Trust; Other Miscellaneous Provisions............. 83

SECTION 15.06.          Reinstatement..................................................... 83

                                   ARTICLE XVI

                                    Immunity
                                    --------

SECTION 16.01.          Personal Immunity of Incorporators, Shareholders,
                          Directors and Officers ......................................... 84
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                    INDENTURE dated as of March 10, 2000, between HUMAN GENOME
               SCIENCES, INC., a corporation duly organized and existing under
               the laws of the State of Delaware (herein called the "Company"),
               having its principal office at 9410 Key West Avenue, Rockville,
               Maryland 20850-3338, and THE BANK OF NEW YORK, as Trustee (herein
               called the "Trustee").

         The Company has duly authorized the execution and delivery of this
Indenture to provide for the issuance of its 3 3/4% Convertible Subordinated
Notes due 2007 (herein called the "Securities"), to be issued as in this
Indenture provided.

         All things necessary to make the Securities, when executed by the
Company and authenticated and delivered hereunder and duly issued by the
Company, the valid obligations of the Company, and to make this Indenture a
valid agreement of the Company, in accordance with their and its terms, have
been done.

                              W I T N E S S E T H :

         For and in consideration of the premises and the purchase of the
Securities by the Holders thereof, it is mutually agreed, for the equal and
proportionate benefit of all Holders of the Securities or of any series thereof,
as follows:

                                    ARTICLE I

         Definitions and Other Provisions of General Application

         SECTION 1.01. Definitions. For all purposes of this Indenture, except
as otherwise expressly provided or unless the context otherwise requires:

         1. The terms defined in this Article have the meanings assigned to them
in this Article and include the plural as well as the singular.

         2. All other terms used herein which are defined in the Trust Indenture
Act, either directly or by reference therein, have the meanings assigned to them
therein.

         3. All accounting terms not otherwise defined herein have the meanings
assigned to them in accordance with generally accepted accounting principles,
and,

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except as otherwise herein expressly provided, the term "generally accepted
accounting principles" with respect to any computation required or permitted
hereunder shall mean such accounting principles as are generally accepted at the
date of such computation.

         4. Unless the context otherwise requires, any reference to an "Article"
or a "Section" refers to an Article or Section, as the case may be, of this
Indenture.

         5. The words "herein", "hereof and "hereunder" and other words of
similar import refer to this Indenture as a whole and not to any particular
Article, Section or other subdivision.

         Certain terms used in Article XIV have the meanings specified therein.

         "Act", when used with respect to any Holder, has the meaning specified
in Section 1.04.

         "Additional Interest" has the meaning specified in Section 10.11.

         "Affiliate" of any specified Person means any other Person who
directly, or indirectly through one or more intermediaries, controls, is
controlled by, or is under common control with, such specified Person. For the
purposes of this definition, "control" when used with respect to any specified
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 Member" means any member of, or participant in, the Depositary.

         "Applicable Procedures" means, with respect to any transfer or
transaction involving a Global Security or beneficial interest therein, the
rules and procedures of the Depositary for such Security, in each case to the
extent applicable to such transaction and as in effect from time to time.

         "Authenticating Agent" means any Person authorized by the Trustee
pursuant to Section 6.14 to act on behalf of the Trustee to authenticate
Securities.

         "Beneficial Owner" has the meaning specified in Section 14.06.

         "Board of Directors" means either the board of directors of the Company
or any duly authorized committee of that board.

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                                                                               3

         "Board Resolution" means a copy of a resolution certified by the
Secretary or an Assistant Secretary of the Company to have been duly adopted by
the Board of Directors and to be in full force and effect on the date of such
certification, and delivered to the Trustee.

         "Business Day" means a day on which banking institutions are open for
business and carrying out transactions in Dollars at the relevant place of
payment.

         "Change in Control" has the meaning specified in Section 14.06.

         "Closing Price" on any Trading Day with respect to the per share price
of Common Stock means the last reported sales price regular way or, in case no
such reported sale takes place on such Trading Day, the average of the reported
closing bid and asked prices regular way, in either case on the New York Stock
Exchange or, if the Common Stock is not listed or admitted to trading on the New
York Stock Exchange, on the principal national securities exchange on which the
Common Stock is listed or admitted to trading, or, if not listed or admitted to
trading on any national securities exchange, on The Nasdaq Stock Market, Inc.
("Nasdaq") or, if the Common Stock is not listed or admitted to trading on any
national securities exchange or Nasdaq, the average of the closing bid and asked
prices in the over-the-counter market as furnished by any New York Stock
Exchange member firm that is selected from time to time by the Company for that
purpose and is reasonably acceptable to the Trustee.

         "Commencement Date" has the meaning specified in Section 13.04.

         "Commission" means the Securities and Exchange Commission, as from time
to time constituted, created under the Exchange Act, or, if at any time after
the execution of this instrument such Commission is not existing and performing
the duties now assigned to it under the Trust Indenture Act, then the body
performing such duties at such time.

         "Common Stock" includes any stock of any class of the Company which has
no preference in respect of dividends or of amounts payable in the event of any
voluntary or involuntary liquidation, dissolution or winding-up of the Company
and which is not subject to redemption by the Company. However, subject to the
provisions of Section 13.11, shares issuable on conversion of Securities shall
include only shares of the class designated as Common Stock of the Company at
the date of this instrument or

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                                                                               4

shares of any class or classes resulting from any reclassification or
reclassifications thereof and which have no preference in respect of dividends
or of amounts payable in the event of any voluntary or involuntary liquidation,
dissolution or winding-up of the Company and which are not subject to redemption
by the Company; provided that if at any time there shall be more than one such
resulting class, the shares of each such class then so issuable shall be
substantially in the proportion which the total number of shares of such class
resulting from all such reclassifications bears to the total number of shares of
all such classes resulting from all such reclassifications.

         "Company" means the Person named as the "Company" in the first
paragraph of this instrument until a successor Person shall have become such
pursuant to the applicable provisions of this Indenture, and thereafter
"Company" shall mean such successor Person.

         "Company Order" has the meaning specified in the definition of Company
Request in this Section 1.01.

         "Company Request" or "Company Order" means a written request or order
signed in the name of the Company by its Chairman of the Board, its Vice
Chairman of the Board, its President or a Vice President, and by its Treasurer,
an Assistant Treasurer, its Secretary or an Assistant Secretary, and delivered
to the Trustee.

         "Corporate Trust Office" means the principal office of the Trustee in
the city at which at any particular time its corporate trust business shall be
administered. As of the date hereof, the Corporate Trust Office of the Trustee
is located at 101 Barclay Street, Floor 21 West, New York, New York 10286.

         "Corporation" means a corporation, association, company, joint-stock
company or business trust.

         "Current Event" has the meaning specified in Section 13.04.

         "Defaulted Interest" has the meaning specified in Section 3.07.

         "Depositary" means, with respect to the Securities issued in whole or
in part in the form of one or more Global Securities, a clearing agency
registered under the Exchange Act that is designated to act as Depositary for
such Securities as contemplated by Section 2.01 (or any successor securities
clearing agency so registered).

         "Distribution Date" has the meaning specified in Section 13.04.

<PAGE>   14
                                                                               5

         "Dollar" or "U.S.$" 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 debts.

         "DTC" means The Depository Trust Company, a New York corporation.

         "Event of Default" has the meaning specified in Section 5.01.

         "ex date" has the meaning specified in Section 13.04.

         "Exchange Act" means the Securities Exchange Act of 1934 as it may be
amended from time to time, and any successor act thereto, and the rules and
regulations of the Commission promulgated thereunder.

         "Expiration Date" has the meaning specified in Section 1.04.

         "Expiration Time" has the meaning specified in Section 13.04.

         "Global Security" means a Security that is registered in the Security
Register in the name of a Depositary or a nominee thereof.

         "Group" has the meaning specified in Section 14.06.

         "Holder" means a Person in whose name a Security is registered in the
Security Register.

         "Indenture" means this instrument as originally executed or as it may
from time to time be supplemented or amended by one or more indentures
supplemental hereto entered into pursuant to the applicable provisions hereof,
including, for all purposes of this instrument and any such supplemental
indenture, the provisions of the Trust Indenture Act that are deemed to be a
part of and govern this instrument and any such supplemental indenture,
respectively.

         "Initial Purchaser" means Credit Suisse First Boston Corporation.

         "Interest Payment Date" means the Stated Maturity of an installment of
interest on the Securities.

         "Issue Date" means the date of first issuance of the Securities under
this

<PAGE>   15
                                                                               6

Indenture.

         "junior securities" has the meaning specified in Section 12.14.

         "Make-Whole Payment" has the meaning specified in Section 11.01.

         "Maturity", when used with respect to any Security, means the date on
which the principal of such Security or an installment of principal becomes due
and payable as therein or herein provided, whether at the Stated Maturity or by
declaration of acceleration, call for redemption, exercise of the repurchase
right or otherwise.

         "Nasdaq" has the meaning specified in the definition of Closing Price
in this Section 1.01.

         "Non-Recourse Obligation" means indebtedness or other obligation or
that portion of indebtedness or other obligation incurred by a Subsidiary (the
"Non-Recourse Subsidiary") with respect to the acquisition of assets not
previously owned by the Company or any Subsidiary or the financing of a project
involving the development or expansion of properties of the Company or any
Subsidiary (i) as to which neither the Company nor any of its Subsidiaries
(other than the Non-Recourse Subsidiary) (a) provides credit support (including
any undertaking, agreement or instrument that would constitute indebtedness),
(b) is directly or indirectly liable (as a guarantor or otherwise), or (c)
constitutes the lender; and (ii) no default with respect to which would permit
(upon notice, lapse of time or both) any holder of any other indebtedness of the
Company or any of its Subsidiaries to declare a default under such other
indebtedness or cause the payment thereof to be accelerated or payable prior to
its stated maturity; and (iii) as to which the lenders have been notified in
writing that they will not have any recourse to the stock or assets of the
Company or any Subsidiary other than the assets that were acquired with the
proceeds of such transaction or the project financed with the proceeds of such
transaction (and the proceeds thereof).

         "Non-Recourse Subsidiary" has the meaning specified in the definition
of Non-Recourse Obligation in this Section 1.01.

         "Notice of Default" means a written notice of the kind specified in
Section 5.01(4) or 5.01(5).

<PAGE>   16
                                                                               7

         "Officers' Certificate" means a certificate signed by any of the
Chairman of the Board, a Vice Chairman of the Board, the President or a Vice
President, and by any of the Treasurer, an Assistant Treasurer, the Secretary or
an Assistant Secretary, of the Company, and delivered to the Trustee. One of the
officers signing an Officers' Certificate given pursuant to Section 10.04 shall
be the principal executive, financial or accounting officer of the Company.

         "Opinion of Counsel" means a written opinion of counsel, who may be
counsel for the Company.

         "Optional Redemption" has the meaning specified in Section 11.02.

         "Other Event" has the meaning specified in Section 13.04.

         "Outstanding", when used with respect to Securities, means, as of the
date of determination, all Securities theretofore authenticated and delivered
under this Indenture, except:

         (i) Securities theretofore cancelled by the Trustee or delivered to the
     Trustee for cancellation;

     (ii) Securities for whose payment or redemption money in the necessary
     amount has been theretofore deposited with the Trustee or any Paying Agent
     (other than the Company) in trust or set aside and separated in trust by
     the Company (if the Company shall act as its own Paying Agent) for the
     Holders of such Securities; provided that, if such Securities are to be
     redeemed, notice of such redemption shall have been duly given pursuant to
     this Indenture or provision therefor satisfactory to the Trustee shall have
     been made;

     (iii) Securities which have been paid pursuant to Section 3.07 or in
     exchange for or in lieu of which other Securities have been authenticated
     and delivered pursuant to this Indenture, other than any such Securities in
     respect of which there shall have been presented to the Trustee proof
     satisfactory to it that such Securities are held by a bona fide purchaser
     in whose hands such Securities are valid obligations of the Company; and

<PAGE>   17
                                                                               8

         (iv) Securities which have been defeased pursuant to Section 15.02;

provided, however, that in determining whether the Holders of the requisite
principal amount of the Outstanding Securities have given, made or taken any
request, demand, authorization, direction, notice, consent, waiver or other
action hereunder as of any date, Securities owned by the Company or any other
obligor upon the Securities or any Affiliate of the Company or of such other
obligor shall be disregarded and deemed not to be Outstanding, except that, in
determining whether the Trustee shall be protected in relying upon any such
request, demand, authorization, direction, notice, consent, waiver or other
action, only Securities which a Responsible Officer of the Trustee knows to be
so owned shall be so disregarded. Securities so owned which have been pledged in
good faith may be regarded as Outstanding if the pledgee establishes to the
satisfaction of the Trustee the pledgee's right so to act with respect to such
Securities and that the pledgee is not the Company or any other obligor upon the
Securities or any Affiliate of the Company or of such other obligor.

              "Paying Agent" means any Person authorized by the Company to pay
the principal of and premium, if any (including the Make-Whole Payment, if any),
or interest on any Securities on behalf of the Company.

              "Person" means any individual, corporation, partnership, joint
venture, trust, unincorporated organization or government or any agency or
political subdivision thereof.

              "Predecessor Security" of any particular Security means every
previous Security evidencing all or a portion of the same debt as that evidenced
by such particular Security; and, for the purposes of this definition, any
Security authenticated and delivered under Section 3.06 in exchange for or in
lieu of a mutilated, destroyed, lost or stolen Security shall be deemed to
evidence the same debt as the mutilated, destroyed, lost or stolen Security.

              "Provisional Redemption" has the meaning specified in Section
11.01.

              "Provisional Redemption Date" has the meaning specified in
Section 11.01.

              "Purchased Shares" has the meaning specified in Section 13.04.

              "Qualified Institutional Buyer" means a "qualified institutional
buyer" as defined in Rule 144A.

<PAGE>   18
                                                                               9

              "Redemption Date", when used with respect to any Security to be
redeemed, means the date fixed for such redemption by or pursuant to this
Indenture.

              "Redemption Notice Date" has the meaning specified in Section
11.01.

              "Redemption Price", when used with respect to any Security to be
redeemed, means the price at which it is to be redeemed as set forth in the
Securities.

              "Reference Date" has the meaning specified in Section 13.04.

              "Registration Default" has the meaning specified in Section 10.11.

              "Registration Rights Agreement" has the meaning specified in
Section 10.11.

              "Regular Record Date" for the interest payable on any Interest
Payment Date means March 1 or September 1 (whether or not a Business Day), as
the case may be, next preceding such Interest Payment Date.

              "Repurchase Date" has the meaning specified in Section 14.01.

              "Repurchase Price" has the meaning specified in Section 14.01.

              "Responsible Officer", when used with respect to the Trustee,
means any officer in the corporate trust department of the Trustee to whom any
matter has been referred because of such officer's knowledge and familiarity
with the particular subject.

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

              "Restricted Security" means a Security required to bear the
restricted securities legend set forth in Section 2.02.

              "Rule 144A" means Rule 144A under the Securities Act (or any
successor provision), as it may be amended from time to time.

              "Rule 144A Information" has the meaning specified in Section
10.09.

<PAGE>   19
                                                                              10

              "Securities" has the meaning stated in the first recital of this
Indenture and more particularly means any Securities authenticated and delivered
under this Indenture and "Security" means one of such Securities.

              "Securities Act" means the Securities Act of 1933 as it may be
amended from time to time, and any successor act thereto, and the rules and
regulations of the Commission promulgated thereunder.

              "Security Register" has the meaning specified in Section 3.05.

              "Security Registration" has the meaning specified in Section 3.05.

              "Senior Indebtedness" means the principal of and premium, if any,
and interest on all indebtedness of the Company for money borrowed, other than
the Securities, whether outstanding on the date of execution of the Indenture or
thereafter created, incurred, guaranteed or assumed, except such indebtedness
that by the terms of the instrument or instruments by which such indebtedness
was created or incurred expressly provides that it (i) is junior in right of
payment to the Securities or any other indebtedness of the Company for borrowed
money or (ii) ranks pari passu in right of payment to the Securities. The term
"indebtedness for money borrowed" when used with respect to the Company is
defined to mean (i) any obligation of, or any obligation guaranteed by, the
Company for the repayment of borrowed money, whether or not evidenced by bonds,
debentures, notes or other written instruments, (ii) all obligations of the
Company with respect to interest rate hedging agreements to hedge interest rates
relating to Senior Indebtedness of the Company, (iii) any deferred payment
obligation of, or any such obligation guaranteed by, the Company for the payment
of the purchase price of property or assets evidenced by a note or similar
instrument, and (iv) any obligation of, or any such obligation guaranteed by,
the Company for the payment of rent or other amounts under a lease of property
or assets which obligation is required to be classified and accounted for as a
capitalized lease on the balance sheet of the Company under generally accepted
accounting principles.

              "Shelf Registration Statement" has the meaning specified in
Section 10.11.

              "Special Record Date" for the payment of any Defaulted Interest
means a date fixed by the Trustee pursuant to Section 3.07.

              "Stated Maturity", when used with respect to any Security or any
installment of principal thereof or interest thereon, means the date specified
in such

<PAGE>   20
                                                                              11

Security as the fixed date on which the principal of such Security or such
installment of principal or interest is due and payable.

              "Subsidiary" means a corporation more than 50% of the outstanding
voting stock of which is owned, directly or indirectly, by the Company or by one
or more other Subsidiaries, or by the Company and one or more other
Subsidiaries. For the purposes of this definition, "voting stock" means stock
which ordinarily has voting power for the election of directors, whether at all
times or only so long as no senior class of stock has such voting power by
reason of any contingency.

              "Surrendered Securities" has the meaning specified in Section
2.06.

              "Trading Day" means each Monday, Tuesday, Wednesday, Thursday and
Friday, other than any day on which securities are not traded on the applicable
securities exchange or in the applicable securities market.

              "Transfer Restricted Securities" has the meaning specified in the
Registration Rights Agreement.

              "Trust Indenture Act" means the Trust Indenture Act of 1939 as in
force at the date as of which this instrument was executed and the rules and
regulations thereunder; provided, however, that in the event the Trust Indenture
Act of 1939 or such rules and regulations are amended after such date, "Trust
Indenture Act" means, to the extent required by any such amendment, the Trust
Indenture Act of 1939 and such rules and regulations as so amended.

              "Trustee" means the Person named as the "Trustee" in the first
paragraph of this instrument until a successor Trustee shall have become such
pursuant to the applicable provisions of this Indenture, and thereafter
"Trustee" shall mean such successor Trustee.

              "United States" means the United States of America (including the
States thereof and the District of Columbia), its territories, its possessions
and other areas subject to its jurisdiction.

              "U.S. Government Obligation" has the meaning specified in Section
15.04.

              "Vice President", when used with respect to the Company or the
Trustee,

<PAGE>   21
                                                                              12

means any vice president, whether or not designated by a number or a word or
words added before or after the title "vice president".

              SECTION 1.02. Compliance Certificates and Opinions. Upon any
application or request by the Company to the Trustee to take any action under
any provision of this Indenture, the Company shall furnish to the Trustee an
Officers' Certificate, if to be given by an officer of the Company, or an
Opinion of Counsel, if to be given by counsel, stating that all conditions
precedent, if any, provided for in this Indenture relating to the proposed
action have been complied with.

              Every certificate or opinion with respect to compliance with a
condition or covenant provided for in this Indenture shall include:

              (a) a statement that each individual signing such certificate or
         opinion has read such covenant or condition and the definitions herein
         relating thereto;

              (b) 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;

              (c) a statement that, in the opinion of each 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

              (d) a statement as to whether, in the opinion of each such
         individual, such condition or covenant has been complied with.

              SECTION 1.03. Form of Documents Delivered to Trustee. In any case
where several matters are required to be certified by, or covered by an opinion
of, any specified Person, it is not necessary that all such matters be certified
by, or covered by the opinion of, only one such Person, or that they be so
certified or covered by only one document, but one such Person may certify or
give an opinion with respect to some matters and one or more other such Persons
as to other matters, and any such Person may certify or give an opinion as to
such matters in one or several documents.

              Any certificate or opinion of an officer of the Company may be
based, insofar as it relates to legal matters, upon a certificate or opinion of,
or representations by, counsel, unless such officer knows, or in the exercise of
reasonable care should know, that the certificate or opinion or representations
with respect to the matters upon which his certificate or opinion is based are
erroneous. Any such certificate or Opinion of

<PAGE>   22
                                                                              13

Counsel may be based, insofar as it relates to factual matters, upon a
certificate or opinion of, or representations by, an officer or officers of the
Company stating that the information with respect to such factual matters is in
the possession of the Company, unless such counsel knows, or in the exercise of
reasonable care should know, that the certificate or opinion or representations
with respect to such matters are erroneous.

              Where any Person is required to make, give or execute two or more
applications, requests, consents, certificates, statements, opinions or other
instruments under this Indenture, they may, but need not, be consolidated and
form one instrument.

              SECTION 1.04. Acts of Holders; Record Dates. Any request, demand,
authorization, direction, notice, consent, waiver or other action provided or
permitted by this Indenture to be given or taken by Holders may be embodied in
and evidenced by one or more instruments of substantially similar tenor signed
by such Holders in person or by an agent duly appointed in writing; and, except
as herein otherwise expressly provided, such action shall become effective when
such instrument or instruments are delivered to the Trustee and, where it is
hereby expressly required, to the Company. Such instrument or instruments (and
the action embodied therein and evidenced thereby) are herein sometimes referred
to as the "Act" of the Holders signing such instrument or instruments. Proof of
execution of any such instrument or of a writing appointing any such agent shall
be sufficient for any purpose of this Indenture and (subject to Section 6.01)
conclusive in favor of the Trustee and the Company, if made in the manner
provided in this Section 1.04.

              The fact and date of the execution by any Person of any such
instrument or writing may be proved by the affidavit of a witness of such
execution or by a certificate of a notary public or other officer authorized by
law to take acknowledgments of deeds, certifying that the individual signing
such instrument or writing acknowledged to him the execution thereof. Where such
execution is by a signer acting in a capacity other than his individual
capacity, such certificate or affidavit shall also constitute sufficient proof
of his authority. The fact and date of the execution of any such instrument or
writing, or the authority of the Person executing the same, may also be proved
in any other manner which the Trustee deems sufficient.

              The ownership of Securities shall be proved by the Security
Register.

              Any request, demand, authorization, direction, notice, consent,
waiver or other Act of the Holder of any Security shall bind every future Holder
of the same

<PAGE>   23
                                                                              14

Security and the Holder of every Security issued upon the registration of
transfer thereof or in exchange therefor or in lieu thereof in respect of
anything done, omitted or suffered to be done by the Trustee or the Company in
reliance thereon, whether or not notation of such action is made upon such
Security.

              The Company may set any day as a record date for the purpose of
determining the Holders of Outstanding Securities entitled to give or take any
request, demand, authorization, direction, notice, consent, waiver or other
action provided or permitted by this Indenture to be given or taken by Holders
of Securities; provided that the Company may not set a record date for, and the
provisions of this paragraph shall not apply with respect to, the giving or
making of any notice, declaration, request or direction referred to in the next
paragraph. If any record date is set pursuant to this paragraph, the Holders of
Outstanding Securities on such record date, and no other Holders, shall be
entitled to take the relevant action, whether or not such Holders remain Holders
after such record date; provided that no such action shall be effective
hereunder unless taken on or prior to the applicable Expiration Date by Holders
of the requisite principal amount of Outstanding Securities on such record date;
and provided further, that for the purpose of determining whether Holders of the
requisite principal amount of such Securities have taken such action, no
Security shall be deemed to have been Outstanding on such record date unless it
is also Outstanding on the date such action is to become effective. Nothing in
this paragraph shall prevent the Company from setting a new record date for any
action for which a record date has previously been set pursuant to this
paragraph (whereupon the record date previously set shall automatically and with
no action by any Person be cancelled and of no effect), nor shall anything in
this paragraph be construed to render ineffective any action taken by Holders of
the requisite principal amount of Outstanding Securities on the date such action
is taken. Promptly after any record date is set pursuant to this paragraph, the
Company, at its own expense, shall cause notice of such record date, the
proposed action by Holders and the applicable Expiration Date to be given to the
Trustee in writing and to each Holder of Securities in the manner set forth in
Section 1.06.

              The Trustee may set any day as a record date for the purpose of
determining the Holders of Outstanding Securities entitled to join in the giving
or making of (i) any Notice of Default, (ii) any declaration of acceleration
referred to in Section 5.02, (iii) any request to institute proceedings referred
to in Section 5.07(2), or (iv) any direction referred to in Section 5.12. If any
record date is set pursuant to this paragraph, the Holders of Outstanding
Securities on such record date, and no other Holders, shall be entitled to join
in such notice, declaration, request or direction, whether or not such Holders
remain Holders after such record date; provided that no such action shall be
effective hereunder unless taken on or prior to the applicable Expiration Date
by

<PAGE>   24
                                                                              15

Holders of the requisite principal amount of Outstanding Securities on such
record date; and provided, further, that for the purpose of determining whether
Holders of the requisite principal amount of such Securities have taken such
action, no Security shall be deemed to have been Outstanding on such record date
unless it is also Outstanding on the date such action is to become effective.
Nothing in this paragraph shall be construed to prevent the Trustee from setting
a new record date for any action (whereupon the record date previously set shall
automatically and without any action by any Person be cancelled and of no
effect), nor shall anything in this paragraph be construed to render ineffective
any action taken by Holders of the requisite principal amount of Outstanding
Securities on the date such action is taken. Promptly after any record date is
set pursuant to this paragraph, the Trustee, at the Company's expense, shall
cause notice of such record date, the proposed action by Holders and the
applicable Expiration Date to be given to the Company in writing and to each
Holder of Securities in the manner set forth in Section 1.06.

              With respect to any record date set pursuant to this Section, the
party hereto that sets such record date may designate any day as the "Expiration
Date" and from time to time may change the Expiration Date to any earlier or
later day; provided that no such change shall be effective unless notice of the
proposed new Expiration Date is given to the other party hereto in writing, and
to each Holder of Securities in the manner set forth in Section 1.06, on or
before the existing Expiration Date. Notwithstanding the foregoing, no
Expiration Date shall be later than the 180th day after the applicable record
date and, if an Expiration Date is not designated with respect to any record
date set pursuant to this Section, the party hereto that set such record date
shall be deemed to have designated the 180th day after such record date as the
Expiration Date with respect thereto.

              Without limiting the foregoing, a Holder entitled hereunder to
take any action hereunder with regard to any particular Security may do so with
regard to all or any part of the principal amount of such Security or by one or
more duly appointed agents, each of which may do so pursuant to such appointment
with regard to all or any part of such principal amount.

              SECTION 1.05. Notices, etc. to Trustee and Company. Any request,
demand, authorization, direction, notice, consent, waiver or Act of Holders or
other document provided or permitted by this Indenture to be made upon, given or
furnished to, or filed with,

              (1) the Trustee by any Holder or by the Company shall be
sufficiently given if made, given, furnished or filed in writing to or with the
Trustee at its Corporate

<PAGE>   25
                                                                              16

Trust Office, Attention: Corporate Trust Administration, or at any other address
previously furnished in writing to the Company by the Trustee, or

              (2) the Company by the Trustee or by any Holder shall be
sufficiently given (unless otherwise herein expressly provided) if in writing
and mailed, first-class postage prepaid, to the Company, addressed to it at the
address of its principal office specified in the first paragraph of this
instrument or at any other address previously furnished in writing to the
Trustee by the Company.

              SECTION 1.06. Notice to Holders; Waiver. Where this Indenture
provides for notice to Holders of any event, such notice shall be sufficiently
given (unless otherwise herein expressly provided) if in writing and mailed,
first-class postage prepaid, to each Holder affected by such event, at his
address as it appears in the Security Register, not later than the latest date
(if any), and not earlier than the earliest date (if any), prescribed for the
giving of such notice. In any case where notice to Holders is given by mail,
neither the failure to mail such notice, nor any defect in any notice so mailed,
to any particular Holder shall affect the sufficiency of such notice with
respect to other Holders. Where this Indenture provides for notice in any
manner, such notice may be waived in writing by the Person entitled to receive
such notice, either before or after the event, and such waiver shall be the
equivalent of such notice. Waivers of notice by Holders shall be filed with the
Trustee, but such filing shall not be a condition precedent to the validity of
any action taken in reliance upon such waiver.

              In case by reason of the suspension of regular mail service or by
reason of any other cause it shall be impracticable to give such notice by mail,
then such notification as shall be made with the approval of the Trustee shall
constitute a sufficient notification for every purpose hereunder.

              SECTION 1.07. Conflict with Trust Indenture Act. If any provision
hereof limits, qualifies or conflicts with a provision of the Trust Indenture
Act which is required under such Act to be a part of and govern this Indenture,
the latter provision shall control. If any provision of this Indenture modifies
or excludes any provision of the Trust Indenture Act which may be so modified or
excluded, the latter provision shall be deemed to apply to this Indenture as so
modified or to be excluded, as the case may be. To the extent a Security
conflicts with a provision in the Indenture, the Indenture governs.

              SECTION 1.08. Effect of Headings and Table of Contents. The
Article

<PAGE>   26
                                                                              17

and Section headings herein and the Table of Contents are for convenience only
and shall not affect the construction hereof.

              SECTION 1.09. Successors and Assigns. All covenants and agreements
in this Indenture by the Company shall bind its successors and assigns, whether
so expressed or not.

              SECTION 1.10. Severability Clause. In case any provision in this
Indenture or in the Securities shall be invalid, illegal or unenforceable, the
validity, legality and enforceability of the remaining provisions shall not in
any way be affected or impaired thereby.

              SECTION 1.11. Benefits of Indenture. Nothing in this Indenture or
in the Securities, express or implied, shall give to any Person, other than the
parties hereto and their successors hereunder, the holders of Senior
Indebtedness and the Holders of Securities, any benefit or any legal or
equitable right, remedy or claim under this Indenture.

              SECTION 1.12. Governing Law. THIS INDENTURE AND THE SECURITIES
SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAW OF THE STATE OF
NEW YORK WITHOUT REGARD TO CONFLICT OF LAWS PRINCIPLES.

              SECTION 1.13. Legal Holidays. In any case where any Interest
Payment Date, Redemption Date, Repurchase Date or Stated Maturity of any
Security or the last date on which a Holder has the right to convert his
Securities shall not be a Business Day then (notwithstanding any other provision
of this Indenture or of the Securities) payment of interest or principal and
premium, if any (including the Make-Whole Payment, if any), or conversion of the
Securities need not be made on such date, but may be made on the next succeeding
Business Day with the same force and effect as if made on the Interest Payment
Date, Redemption Date, Repurchase Date or at the Stated Maturity, or on such
last day for conversion; provided that no interest shall accrue for the period
from and after such Interest Payment Date, Redemption Date, Repurchase Date or
Stated Maturity, as the case may be.

                                   ARTICLE II

                                 Security Forms

<PAGE>   27
                                                                              18

              SECTION 2.01. Forms Generally. The Securities, the conversion
notice and the Trustee's certificates of authentication shall be in
substantially the forms set forth in this Article, with such appropriate
insertions, omissions, substitutions and other variations as are required or
permitted by this Indenture, and may have such letters, numbers or other marks
of identification and such legends or endorsements placed thereon as may be
required to comply with the rules of any securities exchange or Depositary
therefor or as may, consistently herewith, be determined by the officers
executing such Securities, as evidenced by their execution of the Securities.

              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 of such Securities.

              In certain cases described elsewhere herein, the legends set forth
in the first four paragraphs of Section 2.02 may be omitted from Securities
issued hereunder.

              Upon their original issuance, Securities offered and sold in
reliance on Rule 144A as provided in the Purchase Agreement, shall be issued in
the form of a single Global Security in definitive, fully registered form
without interest coupons, substantially in the form of Security set forth in
Sections 2.02 and 2.03, with such applicable legends as are provided for in
Section 2.02, except as otherwise permitted herein. Such Global Security shall
be registered in the name of DTC, as Depositary, or its nominee, duly executed
by the Company and authenticated by the Trustee as hereinafter provided, and
deposited with the Trustee, as custodian for DTC, for credit by DTC to the
respective accounts of beneficial owners of the Securities represented thereby
(or such other accounts as they may direct). Such Global Security, together with
its Successor Securities which are Global Securities, are collectively herein
called the "Restricted Global Security".

              Except as provided in this Section 2.01 or Section 3.05, owners of
beneficial interests in Global Securities will not be entitled to receive
physical delivery of certificated Securities. Upon transfer of definitive
Securities to a Qualified Institutional Buyer, such definitive Securities will,
unless the Restricted Global Security has previously been exchanged, be
exchanged for an interest in the Restricted Global Security pursuant to the
provisions of Section 3.05.

              Neither the Company nor the Trustee shall have any responsibility
for any defect in the CUSIP number that appears on any Security, check, advice
of payment or redemption or repurchase notice, and any such document may contain
a statement to the effect that CUSIP numbers have been assigned by an
independent service for

<PAGE>   28
                                                                              19

convenience of reference and that neither the Company nor the Trustee shall be
liable for any inaccuracy in such numbers.

              SECTION 2.02. Form of Face of Security.

              [INCLUDE IF SECURITY IS A RESTRICTED SECURITY OR A DEFINITIVE
SECURITY OTHER THAN A RESTRICTED GLOBAL SECURITY:

              THIS SECURITY (OR ITS PREDECESSOR) WAS ORIGINALLY ISSUED IN A
TRANSACTION EXEMPT FROM REGISTRATION UNDER THE UNITED STATES SECURITIES ACT OF
1933 (THE "SECURITIES ACT"), AND THIS SECURITY AND THE COMMON STOCK ISSUABLE
UPON THE CONVERSION THEREOF MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED IN
THE ABSENCE OF SUCH REGISTRATION OR IN A TRANSACTION EXEMPT FROM, OR NOT SUBJECT
TO, THE SECURITIES ACT. EACH PURCHASER OF THIS SECURITY IS HEREBY NOTIFIED THAT
THE SELLER OF THIS SECURITY, AND THE COMMON STOCK ISSUABLE UPON THE CONVERSION
THEREOF, MAY BE RELYING ON THE EXEMPTION FROM THE PROVISIONS OF SECTION 5 OF THE
SECURITIES ACT PROVIDED BY RULE 144A THEREUNDER.

              THE HOLDER OF THIS SECURITY AGREES FOR THE BENEFIT OF THE COMPANY
THAT (A) THIS SECURITY AND THE COMMON STOCK ISSUABLE UPON THE CONVERSION THEREOF
MAY BE OFFERED, RESOLD, PLEDGED OR OTHERWISE TRANSFERRED, ONLY (I) TO A PERSON
WHOM THE SELLER REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL BUYER (AS
DEFINED IN RULE 144A UNDER THE SECURITIES ACT) IN A TRANSACTION MEETING THE
REQUIREMENTS OF RULE 144A, (II) PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER
THE SECURITIES ACT PROVIDED BY RULE 144 THEREUNDER (IF AVAILABLE) OR (III)
PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT, IN
EACH OF CASES (I) THROUGH (III) IN ACCORDANCE WITH ANY APPLICABLE SECURITIES
LAWS OF ANY STATE OF THE UNITED STATES, AND (B) THE HOLDER WILL, AND EACH
SUBSEQUENT HOLDER IS REQUIRED TO, NOTIFY ANY PURCHASER OF THIS SECURITY AND ANY
SHARES OF COMMON STOCK ISSUABLE UPON THE CONVERSION THEREOF OF THE RESALE
RESTRICTIONS REFERRED TO IN (A) ABOVE.]

<PAGE>   29
                                                                              20

              [INCLUDE IF SECURITY IS A RESTRICTED GLOBAL SECURITY:

              THE SECURITIES EVIDENCED BY THIS GLOBAL SECURITY (OR ITS
PREDECESSOR) WERE ORIGINALLY ISSUED IN A TRANSACTION EXEMPT FROM REGISTRATION
UNDER THE UNITED STATES SECURITIES ACT OF 1933 (THE "SECURITIES ACT"), AND SUCH
SECURITIES AND THE COMMON STOCK ISSUABLE UPON THE CONVERSION THEREOF MAY NOT BE
OFFERED, SOLD OR OTHERWISE TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR IN
A TRANSACTION EXEMPT FROM, OR NOT SUBJECT TO, THE SECURITIES ACT. EACH PURCHASER
OF ANY BENEFICIAL INTEREST IN THE SECURITIES IS HEREBY NOTIFIED THAT THE SELLER
OF SUCH BENEFICIAL INTEREST MAY BE RELYING ON THE EXEMPTION FROM THE PROVISIONS
OF SECTION 5 OF THE SECURITIES ACT PROVIDED BY RULE 144A THEREUNDER.

              EACH BENEFICIAL OWNER OF AN INTEREST IN ANY OF THE SECURITIES
EVIDENCED BY THIS GLOBAL SECURITY (INCLUDING ANY PARTICIPANT IN THE DEPOSITARY
HOLDING THE GLOBAL SECURITY THAT IS SHOWN AS HOLDING SUCH AN INTEREST ON THE
RECORDS OF SUCH DEPOSITARY AND EACH BENEFICIAL OWNER THAT HOLDS THROUGH SUCH
PARTICIPANT) AGREES FOR THE BENEFIT OF THE COMPANY THAT (A) ANY BENEFICIAL
INTEREST IN THE SECURITIES AND THE COMMON STOCK ISSUABLE UPON THE CONVERSION
THEREOF MAY BE OFFERED, RESOLD, PLEDGED OR OTHERWISE TRANSFERRED, ONLY (I) TO A
PERSON WHOM THE SELLER REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL BUYER
(AS DEFINED IN RULE 144A UNDER THE SECURITIES ACT) IN A TRANSACTION MEETING THE
REQUIREMENTS OF RULE 144A, (II) PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER
THE SECURITIES ACT PROVIDED BY RULE 144 THEREUNDER (IF AVAILABLE) OR (III)
PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT, IN
EACH OF CASES (I) THROUGH (III) IN ACCORDANCE WITH ANY APPLICABLE SECURITIES
LAWS OF ANY STATE OF THE UNITED STATES, AND (B) THE BENEFICIAL OWNER WILL, AND
EACH SUBSEQUENT BENEFICIAL OWNER OF THIS SECURITY OR ANY SHARES OF COMMON STOCK
ISSUABLE UPON CONVERSION THEREOF IS REQUIRED TO, NOTIFY ANY PURCHASER OF ANY
BENEFICIAL INTEREST IN THE SECURITIES AND ANY SHARES OF COMMON STOCK ISSUABLE
UPON CONVERSION THEREOF FROM IT OF THE RESALE RESTRICTIONS REFERRED TO IN (A)
ABOVE.]

<PAGE>   30
                                                                              21

              [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, A NEW YORK CORPORATION ("DTC"),
NEW YORK, NEW YORK, TO THE COMPANY 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 BECAUSE THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.]

                           Human Genome Sciences, Inc.

                 3 3/4% Convertible Subordinated Notes due 2007

                                                   No. ____  U. S. $ __________

[IF RESTRICTED GLOBAL SECURITY - CUSIP No. [  ]]
[IF DEFINITIVE SECURITY - CUSIP No. [ ]]

              Human Genome Sciences, Inc., a corporation duly organized and
existing under the laws of the State of Delaware (herein called the "Company",
which term includes any successor Person under the Indenture hereinafter
referred to), for value

<PAGE>   31
                                                                              22

received, hereby promises to pay to ________, or registered assigns, the
principal sum of ______ United States Dollars (U.S.$________ ) on March 15,
20007, and to pay interest thereon from March 10, 2000, or from the most recent
Interest Payment Date to which interest has been paid or duly provided for,
semi-annually on March 15 and September 15 in each year, commencing September
15, 2000, at the rate of 3 3/4% per annum, until the principal hereof is paid or
made available for payment. The interest so payable, and punctually paid or duly
provided for, on any Interest Payment Date will, as provided in such Indenture,
be paid to the Person in whose name this Security (or one or more Predecessor
Securities) is registered at the close of business on the Regular Record Date
for such interest, which shall be March 1 or September 1 (whether or not a
Business Day), as the case may be, next preceding such Interest Payment Date.
Any such interest not so punctually paid or duly provided for will forthwith
cease to be payable to the Holder on such Regular Record Date and may either be
paid to the Person in whose name this Security (or one or more Predecessor
Securities) is registered at the close of business on a Special Record Date for
the payment of such Defaulted Interest to be fixed by the Trustee, notice
whereof shall be given to Holders of Securities not less than 10 days prior to
such Special Record Date, or be paid at any time in any other lawful manner not
inconsistent with the requirements of any securities exchange on which the
Securities may be listed, and upon such notice as may be required by such
exchange, all as more fully provided in said Indenture.

              Payment of the principal of, premium, if any (including the
Make-Whole Payment, if any), and interest (including payment of any Additional
Interest) on this Security will be made at the Corporate Trust Office, in such
coin or currency of the United States of America as at the time of payment is
legal tender for payment of public and private debts by a U.S. Dollar check
drawn on an account maintained with a bank in the Borough of Manhattan, The City
of New York; provided, however, that upon written application by the Holder to
the Security Registrar setting forth wire instructions not later than 15 days
prior to the relevant payment date (in the case of payment of principal) or not
later than the relevant Record Date (in the case of payment of interest), such
Holder may receive payment by wire transfer of Dollars to a U.S. Dollar account
(such transfers to be made only to Holders of an aggregate principal amount in
excess of U.S.$2,000,000) maintained by the payee with a bank in the United
States or in Europe and designated by the payee to the Security Registrar.

              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

<PAGE>   32
                                                                              23

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 Company has caused this instrument to be
duly executed.

                                      HUMAN GENOME SCIENCES, INC.

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

              SECTION 2.03. Form of Reverse of Security. This Security is one of
a duly authorized issue of Securities of the Company designated as its 3 3/4%
Convertible Subordinated Notes due 2007 (herein called the "Securities"),
limited in aggregate principal amount to U.S.$300,000,000 (subject to increase
as provided in the Indenture herein defined up to an additional U.S.$50,000,000
aggregate principal amount), issued and to be issued under an Indenture, dated
as of March 10, 2000 (herein called the "Indenture"), between the Company and
The Bank of New York, as Trustee for the Holders of Securities issued under said
Indenture (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 Company, the
Trustee, the holders of Senior Indebtedness and the Holders of the Securities
and of the terms upon which the Securities are, and are to be, authenticated and
delivered.

              Subject to and upon compliance with the provisions of the
Indenture, the Holder of this Security is entitled, at his option, at any time
on or before the close of business on the Business Day immediately preceding
March 15, 2007, or in case this Security or a portion hereof is called for
redemption, then in respect of this Security or such portion hereof until and
including, but (unless the Company defaults in making the payment due upon
redemption or repurchase) not after, the close of business on the Business Day
immediately preceding the Redemption Date or Repurchase Date, as the
<PAGE>   33
                                                                              24

case may be, to convert this Security (or any portion of the principal amount
hereof which is U.S.$1,000 or an integral multiple thereof), at the principal
amount hereof, or of such portion, into fully paid and non-assessable shares of
Common Stock of the Company at a conversion price equal to U.S.$219.00 aggregate
principal amount of Securities for each share of Common Stock (or at the current
adjusted conversion price if an adjustment has been made as provided in Article
XIII of the Indenture) by surrender of this Security, duly endorsed or assigned
to the Company or in blank, to the Company at its office or agency in the
Borough of Manhattan, The City of New York, accompanied by the conversion notice
hereon executed by the Holder hereof evidencing such Holder's election to
convert this Security, or if less than the entire principal amount hereof is to
be converted, the portion hereof to be converted, and, in case such surrender
shall be made during the period from the close of business on any Regular Record
Date to the opening of business on the corresponding Interest Payment Date
(unless this Security or the portion hereof being converted has been called for
redemption on a Redemption Date within such period between and including such
Regular Record Date and such Interest Payment Date), also accompanied by payment
in funds acceptable to the Company of an amount equal to the interest payable on
such Interest Payment Date on the principal amount of this Security then being
converted. Subject to the aforesaid requirement for payment of interest and, in
the case of a conversion after the close of business on any Regular Record Date
and on or before the corresponding Interest Payment Date, to the right of the
Holder of this Security (or any Predecessor Security) of record at such Regular
Record Date to receive an installment of interest (even if the Security has been
called for redemption on a Redemption Date within such period), no payment or
adjustment is to be made on conversion for interest accrued hereon or for
dividends on the Common Stock issued on conversion. No fractions of shares or
scrip representing fractions of shares will be issued on conversion, but instead
of any fractional interest the Company shall pay a cash adjustment or round up
to the next higher whole share as provided in Article XIII of the Indenture. The
conversion price is subject to adjustment as provided in Article XIII of the
Indenture. In addition, the Indenture provides that in case of certain
reclassifications, consolidations, mergers, sales or transfers of assets or
other transactions pursuant to which the Common Stock is converted into the
right to receive other securities, cash or other property, the Indenture shall
be amended, without the consent of any Holders of Securities, so that this
Security, if then outstanding, will be convertible thereafter, during the period
this Security shall be convertible as specified above, only into the kind and
amount of securities, cash and other property receivable upon the transaction by
a holder of the number of shares of Common Stock into which this Security might
have been converted immediately prior to such transaction (assuming

<PAGE>   34
                                                                              25

such holder of Common Stock failed to exercise any rights of election and
received per share the kind and amount received per share by a plurality of
non-electing shares).

              The Company will furnish to any Holder, upon request and without
charge, copies of the Certificate of Incorporation and By-laws of the Company
then in effect. Any such request may be addressed to the Company.

              The Securities may be provisionally redeemed by the Company, in
whole or in part, at any time prior to March 21, 2003, at a Redemption Price
equal to $1,000 per Security to be redeemed plus accrued and unpaid interest, if
any, to the Redemption Date if (i) the closing price of the Common Stock shall
have exceeded 150% of the conversion price then in effect for at least 20
Trading Days in any consecutive 30-Trading Day period ending on the Trading Day
prior to the date of mailing of the notice of Provisional Redemption, which date
shall be no more than 60 nor less than 20 days prior to the Redemption Date and
(ii) the Shelf Registration Statement is effective and available for use and is
expected to remain effective and available for use for the 30 days immediately
following the Redemption Date. Upon any such Provisional Redemption, the Company
shall make an additional Make-Whole Payment, at the Company's option, in (A)
cash or (B) if the conditions set forth in the next paragraph are met, shares of
Common Stock with respect to the Securities called for redemption to Holders on
the date of mailing of the notice of Provisional Redemption in an amount equal
to $112.50 per $1,000 Security, less the amount of any interest actually paid on
such Security prior to such date, except that the Make-Whole Payment for any
Securities converted into Common Stock pursuant to the terms hereof after the
Redemption Notice Date and prior to the Provisional Redemption Date shall not be
reduced by any accrued and unpaid interest. The Company shall make the
Make-Whole Payment on all Securities called for Provisional Redemption,
including any Securities converted after the date of mailing of the notice of
Provisional Redemption and prior to the Redemption Date.

              The Company has the option to make the Make-Whole Payment in
shares of Common Stock if a shelf registration statement with respect to such
shares of Common Stock is effective and available for use and is expected to
remain effective and available for use for the 30 days immediately following the
Redemption Date; provided that such a shelf registration statement shall not be
required for shares of Common Stock used to make the Make-Whole Payment to the
extent such shares of Common Stock are freely tradeable and the Company delivers
to the Holders an opinion of its counsel that as of the Provisional Redemption
Date such shares of Common Stock are freely tradeable. If the

<PAGE>   35
                                                                              26

Company elects to make the Make-Whole Payment in shares of Common Stock, the
number of shares of Common Stock due to make such payments is determined by
dividing the amount of such Make-Whole Payment by the market price of the Common
Stock (valued at 97% of the average of the closing bid prices of the Common
Stock for the five Trading Days ending on the Trading Day prior to the
Redemption Date) with fractional shares to be paid in cash.

              The Securities are subject to redemption at the option of the
Company upon not less than 20 days' or more than 60 days' notice by mail, as a
whole or from time to time in part, at any time on or after March 21, 2003
through March 15, 2004 at 101.88% of the principal amount, and thereafter, at
the following Redemption Prices (expressed as percentages of the principal
amount), if redeemed during the 12-month period beginning on March 16 of the
years indicated,

<TABLE>
<CAPTION>
                                                          Redemption
          Year                                               Price
          ----                                               -----
<S>                                                        <C>
          2004                                              101.25%
          -----------------------------------------
          2005                                              100.63%
          -----------------------------------------
          2006                                              100.00%
          -----------------------------------------
</TABLE>

and thereafter at a Redemption Price equal to 100% of the principal amount,
together in the case of any such redemption with accrued interest to (but not
including) the Redemption Date, but interest installments whose Stated Maturity
is on or prior to such Redemption Date will be payable to the Holders of such
Securities, or one or more Predecessor Securities, of record at the close of
business on the relevant Record Dates referred to on the face hereof, all as
provided in the Indenture.

              In certain circumstances involving a Change in Control, each
Holder shall have the right to require the Company to redeem all or part of its
Securities at a repurchase price equal to 100% of the principal amount thereof,
together with accrued and unpaid interest through the Repurchase Date.

              The Securities do not have the benefit of any sinking fund.

              In the event of redemption, conversion or repurchase of this
Security in part only, a new Security or Securities for the unredeemed,
unconverted or unrepurchased portion hereof will be issued in the name of the
Holder hereof upon the cancellation

<PAGE>   36
                                                                              27

hereof.

              Subject to certain limitations in the Indenture, at any time when
the Company is not subject to Section 13 or 15(d) of the United States
Securities Exchange Act of 1934, upon the request of a Holder or the holder of
shares of Common Stock issued upon conversion thereof, the Company will promptly
furnish or cause to be furnished Rule 144A Information (as defined below) to
such Holder or such holder of shares of Common Stock issued upon conversion, or
to a prospective purchaser of any such security designated by any such Holder or
holder of shares of Common Stock, as the case may be, to the extent required to
permit compliance by such Holder or holder of shares of Common Stock with Rule
144A under the United States Securities Act of 1933 (the "Securities Act"), in
connection with the resale of any such security. "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 this Security is a Transfer Restricted Security, then the
Holder of this Security [IF THIS SECURITY IS A GLOBAL SECURITY, THEN INSERT-
(including any Person that has a beneficial interest in this Security)] and the
Common Stock issuable upon conversion thereof is entitled to the benefits of a
Registration Rights Agreement, dated as of March 10, 2000 (the "Registration
Rights Agreement") executed by the Company. If a Registration Default occurs (as
defined in the Registration Rights Agreement and in the Indenture), Additional
Interest will accrue on this Security from and including the day following such
Registration Default to but excluding the day on which such Registration Default
has been cured. Additional Interest will be paid semi-annually in arrears, with
the first semi-annual payment due on the first Interest Payment Date in respect
of the Securities following the date on which such Additional Interest begins to
accrue, and will accrue at a rate per annum equal to an additional one-half of
one percent (0.50%) of the principal amount of the Securities.

              Whenever in this Security there is a reference, in any context, to
the payment of the principal of, premium, if any (including the Make-Whole
Payment, if any), or interest on, or in respect of, any Security, such mention
shall be deemed to include mention of the payment of Additional Interest payable
as described in the preceding paragraph to the extent that, in such context,
Additional Interest is, was or would be payable in respect of such Security and
express mention of the payment of Additional Interest (if applicable) in any
provisions of this Security shall not be construed as excluding Additional
Interest in those provisions of this Security where such express mention is not
made.

              The indebtedness evidenced by this Security is, to the extent
provided in the Indenture, subordinate and subject in right of payment to the
prior payment in full of

<PAGE>   37
                                                                              28

all Senior Indebtedness, and this Security is issued subject to the provisions
of the Indenture with respect thereto. Each Holder of this Security, by
accepting the same, (a) agrees to and shall be bound by such provisions, (b)
authorizes and directs the Trustee on his behalf to take such action as may be
necessary or appropriate to effectuate the subordination so provided and (c)
appoints the Trustee his attorney-in-fact for any and all such purposes.

              If an Event of Default shall occur and be continuing, the
principal of all the Securities may be declared due and payable in the manner
and with the effect provided in Article V of the Indenture.

              The Indenture permits, with certain exceptions as therein
provided, the amendment thereof and the modification of the rights and
obligations of the Company and the rights of the Holders of the Securities under
the Indenture at any time by the Company and the Trustee with the consent of the
Holders of a majority in aggregate principal amount of the Securities at the
time Outstanding. The Indenture also contains provisions permitting the Holders
of a majority in aggregate principal amount of the Securities at the time
Outstanding, on behalf of the Holders of all the Securities, to waive compliance
by the Company 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.

              No reference herein to the Indenture and no provision of this
Security or of the Indenture shall alter or impair the obligation of the
Company, which is absolute and unconditional, to pay the principal of, premium
on, if any (including the Make- Whole Payment, if any), and interest on
(including Additional Interest) this Security at the times, place and rate, and
in the coin or currency, herein prescribed or to convert this Security as
provided 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
Corporate Trust Office duly endorsed by, or accompanied by a written instrument
of transfer in form satisfactory to the Company and the Security Registrar duly
executed by, the Holder hereof or his attorney duly authorized

<PAGE>   38
                                                                              29

in writing, and thereupon one or more new Securities, of authorized
denominations and for the same aggregate principal amount, will be issued to the
designated transferee or transferees.

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

              No service charge shall be made for any such registration of
transfer or exchange, but the Company 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 Company, the Trustee and any agent of the Company or the Trustee
may treat the Person in whose name this Security is registered as the owner
hereof for all purposes, whether or not payment of or on this Security is
overdue, and neither the Company, the Trustee nor any such agent shall be
affected by notice to the contrary.

              Interest on this Security shall be computed on the basis of a
360-day year of twelve 30-day months.

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

              THE INDENTURE AND THIS SECURITY SHALL BE GOVERNED BY AND CONSTRUED
IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO CONFLICT
OF LAWS PRINCIPLES.

              SECTION 2.04. Form of Trustee's Certificate of Authentication.

              This is one of the Securities referred to in the within-mentioned
Indenture.

Dated:                                         The Bank of New York, as Trustee

                                                                             By

                                                           Authorized Signatory

<PAGE>   39
                                                                              30

              SECTION 2.05. Form of Conversion Notice.

                            CONVERSION NOTICE

To:  Human Genome Sciences, Inc.

              The undersigned Holder of this Security hereby irrevocably
exercises the option to convert this Security, or the portion hereof (which is
U.S.$1,000 or an integral multiple thereof) below designated, at any time
following the date of original issuance thereof, into shares of Common Stock in
accordance with the terms of the Indenture referred to in this Security, and
directs that the shares issuable and deliverable upon conversion, together with
any check in payment for a fractional share and any Security representing any
unconverted principal amount hereof, be issued and delivered to the registered
owner hereof unless a different name has been provided below. If shares or any
portion of this Security not converted are to be issued in the name of a person
other than the undersigned, the undersigned will pay all transfer taxes payable
with respect thereto and is delivering herewith a certificate in proper form
certifying that the applicable restrictions on transfer have been complied with.
Any amount required to be paid by the undersigned on account of interest
accompanies this Security.

              The Applicant hereby agrees that, promptly after request of the
Company, he or it will furnish such proof in support of this certification as
the Company or the Security Registrar for the Common Stock may, from time to
time, request.

Dated:

                                                             Signature*

                                                             Signature Guaranty

If shares or Securities are to be               Principal amount to be converted
registered in the name of a Person              (if less than all):
other than the Holder, please print             $           ,000
such Person's name and address:*

<PAGE>   40
                                                                              31

                 Name                                   Social Security or
                                                 Taxpayer Identification Number
            Street Address

        City, State and Zip Code

* Signature(s) must be guaranteed by an eligible guarantor institution (banks,
stock brokers, savings and loan associations and credit unions with membership
in an approved signature guarantee medallion program) pursuant to Securities and
Exchange Commission Rule 17Ad-15 if shares of Common Stock are to be delivered,
or unconverted Securities are to be issued, other than to and in the name of the
registered owner.

              SECTION 2.06. Form of Certification. Whenever any certification is
required to be given to evidence compliance with certain restrictions relating
to transfers of Restricted Securities contemplated by Section 3.05(b)(iv),
Section 3.05(c) or Section 13.02, such certification shall be provided
substantially in the form of the following certificate, with only such changes
as shall be approved by the Company and the Initial Purchaser.

                              TRANSFER CERTIFICATE

              The undersigned Holder hereby certifies with respect to U.S.$____
principal amount of the above-captioned securities presented or surrendered on
the date hereof (the "Surrendered Securities") for registration of transfer, or
for exchange or conversion where the securities issuable upon such exchange or
conversion are to be registered in a name other than that of the undersigned
Holder (each such transaction being a "transfer"), that such transfer complies
with the restrictive legend set forth on the face of the Surrendered Securities
for the reason checked below:

                            The transfer of the Surrendered Securities complies
                            with Rule 144 under the U.S. Securities Act of 1933
                            (the "Securities Act"); or

                            The transfer of the Surrendered Securities complies
                            with

<PAGE>   41
                                                                              32

                            Rule 144A under the Securities Act; or

                            The transfer of the Surrendered Securities is
                            pursuant to an effective registration statement
                            under the Securities Act, the prospectus delivery
                            requirements under the Securities Act have been
                            satisfied with respect to such transfer, the
                            undersigned Holder is named as a "Selling
                            Securityholder" in the prospectus relating to such
                            registration statement, or in amendments or
                            supplements thereto, and the aggregate principal
                            amount of Surrendered Securities transferred are all
                            or a portion of the securities listed in such
                            prospectus opposite the undersigned's name.

Dated:                              *
*       To be dated the date of surrender.

                                                                Signature

                                                        (If the registered owner
                                                        is a corporation,
                                                        partnership or
                                                        fiduciary, the title of
                                                        the Person signing on
                                                        behalf of such
                                                        registered owner must be
                                                        stated.)

                                   ARTICLE III

                                 The Securities

              SECTION 3.01. Title and Terms. The aggregate principal amount of
Securities which may be authenticated and delivered under this Indenture is
limited to (a) U.S.$300,000,000 plus (b) such aggregate principal amount (which
may not exceed U.S.$50,000,000 principal amount) of Securities as may be
purchased by the Initial Purchaser pursuant to the Initial Purchaser's option
pursuant to the Purchase Agreement dated March 6, 2000, between the Company and
the Initial Purchaser, except for Securities authenticated and delivered upon
registration of transfer of, or in exchange for, or in lieu of, other Securities
pursuant to Sections 3.04, 3.05, 3.06, 9.06, 11.09, 13.02 or

<PAGE>   42
                                                                              33

14.05 and except for Securities which, pursuant to Section 3.03, are deemed
never to have been authenticated and delivered hereunder.

              The Stated Maturity of the Securities shall be March 15, 2007, and
they shall bear interest at the rate of 3 3/4% per annum, payable semi-annually
on March 15 and September 15, commencing September 15, 2000, until the principal
thereof is paid or made available for payment.

              Payment of the principal of, premium, if any (including the
Make-Whole Payment, if any), and interest (including payment of any Additional
Interest) on this Security will be made at the Corporate Trust Office, in such
coin or currency of the United States of America as at the time of payment is
legal tender for payment of public and private debts by a U.S. Dollar check
drawn on an account maintained with a bank in the Borough of Manhattan, The City
of New York; provided, however, that upon written application by the Holder to
the Security Registrar setting forth wire instructions not later than 15 days
prior to the relevant payment date (in the case of payment of principal) or not
later than the relevant Record Date (in the case of payment of interest), such
Holder may receive payment by wire transfer of Dollars to a U.S. Dollar account
(such transfers to be made only to Holders of an aggregate principal amount in
excess of U.S.$2,000,000) maintained by the payee with a bank in the United
States or in Europe and designated by the payee to the Security Registrar.

              The Securities shall be redeemable by the Company as provided in
Article XI.

              The Securities shall be subordinated in right of payment to the
prior payment in full of Senior Indebtedness as provided in Article XII.

              The Securities shall be convertible as provided in Article XIII.

              The Securities shall be subject to purchase by the Company at the
option of the Holder as provided in Article XIV.

              SECTION 3.02. Denominations. The Securities shall be issuable only
in registered form without coupons and only in denominations of U.S.$1,000 and
any integral multiple thereof.

              SECTION 3.03. Execution, Authentication, Delivery and Dating. The

<PAGE>   43
                                                                              34

Securities shall be executed on behalf of the Company by any of its Chairman of
the Board, its Vice Chairman of the Board, its President or one of its Vice
Presidents. The signature of any of these officers on the Securities may be
manual or facsimile.

              Securities bearing the manual or facsimile signatures of
individuals who were at any time the proper officers of the Company shall bind
the Company, notwithstanding that such individuals or any of them have ceased to
hold such offices prior to the authentication and delivery of such Securities or
did not hold such offices at the date of such Securities.

              At any time and from time to time after the execution and delivery
of this Indenture, the Company may deliver Securities of any series executed by
the Company to the Trustee for authentication, together with a Company Order for
the authentication and delivery of such Securities; and the Trustee in
accordance with such Company Order shall authenticate and deliver such
Securities as in this Indenture provided and not otherwise.

              Each Security shall be dated the date of its authentication.

              No Security shall be entitled to any benefit under this Indenture
or be valid or obligatory for any purpose unless there appears on such Security
a certificate of authentication substantially in the form provided for herein
executed by the Trustee by manual signature, and such certificate upon any
Security shall be conclusive evidence, and the only evidence, that such Security
has been duly authenticated and delivered hereunder.

              SECTION 3.04. Global and Non-Global Securities. (a) Global
Securities. (i) Each Global Security authenticated under this Indenture shall be
registered in the name of the Depositary designated by the Company for such
Global Security or a nominee thereof and delivered to such Depositary or a
nominee thereof or custodian therefor, and each such Global Security shall
constitute a single Security for all purposes of this Indenture.

              (ii) Notwithstanding any other provision in this Indenture, no
Global Security may be exchanged in whole or in part for Securities registered,
and no transfer of a Global Security in whole or in part may be registered, in
the name of any Person other than the Depositary for such Global Security or a
nominee thereof unless (A) such Depositary (1) has notified the Company that it
is unwilling or unable to continue as Depositary for such Global Security or (2)
has ceased to be a clearing agency registered as such under the Exchange Act or
announces an intention permanently to cease business

<PAGE>   44
                                                                              35

or does in fact do so, (B) there shall have occurred and be continuing an Event
of Default with respect to such Global Security, or (C) the Company in its
discretion at any time determines not to have all the Securities represented by
a Global Security. Any Global Security exchanged pursuant to clause (i) above
shall be so exchanged in whole and not in part and any Global Security exchanged
pursuant to clause (ii) or (iii) above may be exchanged in whole or from time to
time in part as directed by the Depositary. Any Security issued in exchange for
a Global Security or any portion thereof shall be a Global Security; provided
that any such Security so issued that is registered in the name of a Person
other than the Depositary or a nominee thereof shall not be a Global Security.

              (iii) If any Global Security is to be exchanged for other
Securities or cancelled in whole, it shall be surrendered by or on behalf of the
Depositary or its nominee to the Trustee, as Security Registrar, for exchange or
cancellation as provided in this Article III. If any Global Security is to be
exchanged for other Securities or cancelled in part, or if another Security is
to be exchanged in whole or in part for a beneficial interest in any Global
Security, in each case, as provided in Section 3.05, then either (i) such Global
Security shall be so surrendered for exchange or cancellation as provided in
this Article III or (ii) the principal amount thereof shall be reduced or
increased by an amount equal to the portion thereof to be so exchanged or
cancelled, or equal to the principal amount of such other Security to be so
exchanged for a beneficial interest therein, as the case may be, by means of an
appropriate adjustment made on the records of the Trustee, as Security
Registrar, whereupon the Trustee, in accordance with the Applicable Procedures,
shall instruct the Depositary or its authorized representative to make a
corresponding adjustment to its records. Upon any such surrender or adjustment
of a Global Security, the Trustee shall, subject to Section 3.05(c) and as
otherwise provided in this Article III, authenticate and deliver any Securities
issuable in exchange for such Global Security (or any portion thereof) to or
upon the order of, and registered in such names as may be directed by, the
Depositary or its authorized representative. Upon the request of the Trustee in
connection with the occurrence of any of the events specified in the preceding
paragraph, the Company shall promptly make available to the Trustee a reasonable
supply of Securities that are not in the form of Global Securities. The Trustee
shall be entitled to rely upon any order, direction or request of the Depositary
or its authorized representative which is given or made pursuant to this Article
III if such order, direction or request is given or made in accordance with the
Applicable Procedures.

              (iv) Every Security authenticated and delivered upon registration
of transfer of, or in exchange for or in lieu of, a Global Security or any
portion thereof,

<PAGE>   45
                                                                              36

whether pursuant to this Article III or otherwise, shall be authenticated and
delivered in the form of, and shall be, a Global Security, unless such Security
is registered in the name of a Person other than the Depositary for such Global
Security or a nominee thereof, in which case such Security shall be
authenticated and delivered in definitive, fully registered form, without
interest coupons.

              (v) The Depositary or its nominee, as registered owner of a Global
Security, shall be the Holder of such Global Security for all purposes under the
Indenture and the Securities, and owners of beneficial interests in a Global
Security shall hold such interests pursuant to the Applicable Procedures.
Accordingly, any such owner's beneficial interest in a Global Security will be
shown only on, and the transfer of such interest shall be effected only through,
records maintained by the Depositary or its nominee or its Agent Members and
such owners of beneficial interests in a Global Security will not be considered
the owners or holders thereof. Notwithstanding the foregoing, nothing herein
shall prevent the Company, the Trustee or any agent of the Company or the
Trustee from giving effect to any written certification, proxy or other
authorization furnished by the Depositary or such nominee, as the case may be,
or impair, as between the Depositary, its Agent Members and any other person on
whose behalf an Agent Member may act, the operation of customary practices of
such Persons governing the exercise of the rights of a holder of any Security.

              SECTION 3.05. Registration; Registration of Transfer and Exchange.
(a) The Company shall cause to be kept at the Corporate Trust Office of the
Trustee a register (the register maintained in such office and in any other
office or agency designated pursuant to Section 10.02 being herein sometimes
collectively referred to as the "Security Register") in which, subject to such
reasonable regulations as it may prescribe, the Company shall provide for the
registration of Securities and of transfers and exchanges thereof. The Trustee
is hereby appointed "Security Registrar" for the purpose of registering
Securities and transfers and exchanges thereof as herein provided. Upon
surrender for registration of transfer or exchange of any Security at an office
or agency of the Company designated pursuant to Section 10.02 for such purpose,
accompanied by a written instrument of transfer or exchange in the form provided
by the Company, the Company shall execute, and the Trustee shall authenticate
and deliver, in the name of the designated transferee or transferees, one or
more new Securities of any authorized denominations and of a like aggregate
principal amount.

              (b) Notwithstanding any other provisions of this Indenture or the
Securities, transfers and exchanges of Securities and beneficial interests in a
Global Security of the kinds specified in this Section 3.05(b) shall be made
only in accordance with this Section 3.05(b).

<PAGE>   46
                                                                              37

              (i) Transfer of Global Security. Other than as set forth in
Section 3.04(a), a Global Security may not be transferred, in whole or in part,
to any Person other than the Depositary or a nominee thereof, and no such
transfer to any such other Person may be registered; provided that this Section
3.05(b)(i) shall not prohibit any transfer of a Security that is issued in
exchange for a Global Security but is not itself a Global Security. No transfer
of a Security to any Person shall be effective under this Indenture or the
Securities unless and until such Security has been registered in the name of
such Person. Nothing in this Section 3.05(b)(i) shall prohibit or render
ineffective any transfer of a beneficial interest in a Global Security effected
in accordance with the other provisions of this Section 3.05(b).

(ii) Transfer of Beneficial Interests in the Global Security. Transfer of
beneficial interests in the Global Security shall be effected through the
Depositary, in accordance with this Indenture (including applicable restrictions
on transfer set forth herein, if any) and the procedures of the Depositary
therefor, if applicable.

(iii) Other Exchanges. In the event that a Global Security or any portion
thereof is exchanged for Securities other than Global Securities, such other
Securities may in turn be exchanged (on transfer or otherwise) for Securities
that are not Global Securities or for beneficial interests in a Global Security
(if any is then outstanding) only in accordance with such procedures, which
shall be substantially consistent with the provisions of this Section 3.05(b)
(including the certification requirements set forth on the reverse of the
Security intended to insure that transfers of beneficial interests in a Global
Security comply with Rule 144A or Rule 144 under the Securities Act, as the case
may be) and any Applicable Procedures, as may be from time to time adopted by
the Company and the Trustee.

(iv) Transfer and Exchange of Definitive Securities. When definitive Securities
are presented to the Security Registrar with a request:

                            (A) to register the transfer of such definitive
              Securities; or

                            (B) to exchange such definitive Securities for an
              equal principal amount of definitive Securities of other
              authorized denominations, the Security Registrar shall register
              the transfer or make the exchange as requested if its reasonable
              requirements for such transaction are met; provided, however, that
              the definitive Securities surrendered for transfer or exchange:

<PAGE>   47
                                                                              38

                            (x) shall be duly endorsed or accompanied by a
              written instrument of transfer in form reasonably satisfactory to
              the Company and the Security Registrar, duly executed by the
              Holder thereof or his attorney duly authorized in writing; and

                            (y) are being transferred or exchanged pursuant to
              an effective registration statement under the Securities Act,
              pursuant to Section 3.05(b)(v), or pursuant to clause (1), (2) or
              (3) below, and are accompanied by the following additional
              information and documents, as applicable:

                                   (1) if such definitive Securities are being
                            delivered to the Security Registrar by a Holder for
                            registration in the name of such Holder, without
                            transfer, a certification from such Holder to that
                            effect (in the form set forth in Section 2.06); or

                                   (2) if such definitive Securities are being
                            transferred to the Company, a certification to that
                            effect (in the form set forth in Section 2.06); or

                                   (3) if such definitive Securities are
                            being transferred pursuant to an exemption from
                            registration in accordance with Rule 144, (i) a
                            certification to that effect (in the form set forth
                            in Section 2.06) and (ii) if the Company or Security
                            Registrar so requests, an opinion of counsel or
                            other evidence reasonably satisfactory to them as to
                            the compliance with the restrictions set forth in
                            the legend set forth in Section 2.02.

                        (v) Restrictions on Transfer of a Definitive Security
        for a Beneficial Interest in a Global Security. A definitive Security
        may not be exchanged for a beneficial interest in a Global Security
        except upon satisfaction of the requirements set forth below. Upon
        receipt by the Trustee of a definitive Security, duly endorsed or
        accompanied by appropriate instruments of transfer, in form satisfactory
        to the Trustee, together with:

                                    (A) certification in the form set forth on
                        the reverse of the Security

<PAGE>   48
                                                                              39

              that such definitive Security is being transferred to a Qualified
              Institutional Buyer in accordance with Rule 144A; and

                            (B) written instructions directing the Trustee to
              make, or to direct the Securities Registrar to make, an adjustment
              on its books and records with respect to such Global Security to
              reflect an increase in the aggregate principal amount of the
              Securities represented by the Global Security, such instructions
              to contain information regarding the Depositary account to be
              credited with such increase,

          then the Trustee shall cancel such definitive Security and cause, or
          direct the Securities Registrar to cause, in accordance with the
          standing instructions and procedures existing between the Depositary
          and the Securities Registrar, the aggregate principal amount of
          Securities represented by the Global Security to be increased by the
          aggregate principal amount of the definitive Security to be exchanged
          and shall credit or cause to be credited to the account of the Person
          specified in such instructions a beneficial interest in the Global
          Security equal to the principal amount of the definitive Security so
          cancelled. If no Global Securities are then outstanding, the Company
          shall issue and the Trustee shall authenticate, upon written order of
          the Company in the form of an Officers' Certificate, a new Global
          Security in the appropriate principal amount.

              (c) Subject to the succeeding paragraph, every Security shall be
subject to the restrictions on transfer provided in the legends required by
Section 2.02 to be applied to such Security. Whenever any Security is presented
or surrendered for registration of transfer or for exchange for a Security
registered in a name other than that of the Holder, such Security must be
accompanied by a certificate in substantially the form set forth in Section
2.06, dated the date of such surrender and signed by the Holder of such
Security, as to compliance with such restrictions on transfer. The Security
Registrar shall not be required to accept for such registration of transfer or
exchange any Security not so accompanied by a properly completed certificate.

               (d) The restrictions imposed by the legend set forth in the first
or second bracketed legend, as the case may be, of Section 2.02 upon the
transferability of any Security shall cease and terminate when such Security has
been sold pursuant to an effective registration statement under the Securities
Act, transferred in compliance with Rule 144 under the Securities Act (or any
successor provision thereto), or after the second anniversary of the original
issuance date of the Security (or such earlier date after which the Security may
be freely transferred without registration under the Securities Act or without
being subject to transfer restrictions pursuant to the Securities Act, as may be

<PAGE>   49
                                                                              40

provided in Rule 144(k) under the Securities Act (or any successor provision
thereto) or otherwise). Any Security as to which such restrictions on transfer
shall have expired in accordance with their terms or shall have terminated may,
upon surrender of such Security for exchange to the Security Registrar in
accordance with the provisions of this Section 3.05 (accompanied, in the event
that such restrictions on transfer have terminated by reason of a transfer in
compliance with Rule 144 or any successor provision, by an opinion of counsel
having substantial experience in practice under the Securities Act and otherwise
reasonably acceptable to the Company, addressed to the Company and in form
acceptable to the Company, to the effect that the transfer of such Security has
been made in compliance with Rule 144 or such successor provision), be exchanged
for a new Security, of like tenor and aggregate principal amount, which shall
not bear the restrictive legend set forth in the first paragraph of Section
2.02. The Company shall inform the Trustee of the effective date of any
registration statement registering the Securities under the Securities Act. The
Trustee shall not be liable for any action taken or omitted to be taken by it in
good faith in accordance with the aforementioned opinion of counsel or notice of
an effective registration statement.

              (e) As used in the preceding two paragraphs (c) and (d) of this
Section 3.05, the term "transfer" encompasses any sale, pledge, transfer,
hypothecation or other disposition of any Security.

              (f) No service charge shall be made for any registration of
transfer or exchange of Securities, but the Company may require payment of a sum
sufficient to cover any tax or other governmental charge that may be imposed in
connection with any registration of transfer or exchange of Securities, other
than exchanges pursuant to Section 3.04, 9.06, 11.09, 13.02 or 14.05 not
involving any transfer.

              (g) The Company shall not be required (i) to issue, register the
transfer of or exchange any Security during a period beginning at the opening of
business 15 days before the day of the mailing of a notice of redemption of
Securities selected for redemption under Section 11.05 and ending at the close
of business on the day of such mailing, or (ii) to register the transfer of or
exchange any Security so selected for redemption in whole or in part, except the
unredeemed portion of any Security being redeemed in part.

              SECTION 3.06. Mutilated, Destroyed, Lost and Stolen Securities. If
any mutilated Security is surrendered to the Trustee, the Company shall execute
and the

<PAGE>   50
                                                                              41

Trustee shall authenticate and deliver in exchange therefor a new
Security of like tenor and principal amount and bearing a number not
contemporaneously outstanding.

              If there shall be delivered to the Company and the Trustee (i)
evidence to their satisfaction of the destruction, loss or theft of any Security
and (ii) such security or indemnity as may be required by them to save each of
them and any agent of either of them harmless, then, in the absence of notice to
the Company or the Trustee that such Security has been acquired by a bona fide
purchaser, the Company shall execute and the Trustee shall authenticate and
deliver, in lieu of any such destroyed, lost or stolen Security, a new Security
of like tenor and principal amount and bearing a number not contemporaneously
outstanding.

              In case any such mutilated, destroyed, lost or stolen Security has
become or is about to become due and payable, the Company in its discretion, but
subject to any conversion rights, may, instead of issuing a new Security, pay
such Security.

              Upon the issuance, authentication and delivery by the Trustee of
any new Security under this Section 3.06, the Company may require the payment of
a sum sufficient to cover any tax or other governmental charge that may be
imposed in relation thereto and any other expenses (including the fees and
expenses of the Trustee) connected therewith.

              Every new Security issued, authenticated and delivered by the
Trustee pursuant to this Section 3.06 in lieu of any destroyed, lost or stolen
Security shall constitute an original additional contractual obligation of the
Company, whether or not the destroyed, lost or stolen Security shall be at any
time enforceable by anyone, and shall be entitled to all the benefits of this
Indenture equally and proportionately with any and all other Securities duly
issued hereunder.

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

              SECTION 3.07. Payment of Interest; Interest Rights Preserved.
Interest on any Security which 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 (or one or more Predecessor Securities) is registered at the
close of business on the Regular Record Date for payment of such interest.

              If the Company shall be required by law to deduct any taxes from
any sum

<PAGE>   51
                                                                              42

of interest payable hereunder to a Holder, (i) the Company shall make such
deductions and shall pay the full amount deducted to the relevant taxing
authority in accordance with applicable law and (ii) the amount of such
deduction shall be treated for purposes hereof as a payment of interest.

              Any interest on any Security which is payable, but is not
punctually paid or duly provided for, on any Interest Payment Date (herein
called "Defaulted Interest") shall forthwith cease to be payable to the Holder
on the relevant Regular Record Date by virtue of having been such Holder, and
such Defaulted Interest may be paid by the Company, at its election in each
case, as provided in clause (1) or (2) below:

              (1) The Company may elect to make payment of any Defaulted
     Interest to the Persons in whose names the Securities (or their respective
     Predecessor Securities) are registered at the close of business on a
     Special Record Date for the payment of such Defaulted Interest, which shall
     be fixed in the following manner. The Company 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, and at the same time the
     Company 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
     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 (1) 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 Company of such Special Record Date and, in the name and at the expense
     of the Company, 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 at his address as it appears in
     the Security Register, 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 so mailed, such Defaulted Interest
     shall be paid to the Persons in whose names the Securities (or their
     respective Predecessor 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).

<PAGE>   52
                                                                              43

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

              Subject to the foregoing provisions of this Section, 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.

              In the case of any Security which is converted after any Regular
Record Date and on or prior to the corresponding Interest Payment Date, interest
on such Security whose Stated Maturity is on such Interest Payment Date shall be
deemed to continue to accrue and shall be payable on such Interest Payment Date
notwithstanding such conversion and notwithstanding that such Security may have
been called for redemption on a Redemption Date within such period, and such
interest (whether or not punctually paid or duly provided for) shall be paid to
the Person in whose name that Security (or one or more Predecessor Securities)
is registered at the close of business on such Regular Record Date. Except as
otherwise expressly provided in the immediately preceding sentence, in the case
of any Security which is converted, interest whose Stated Maturity is after the
date of conversion of such Security shall not be payable.

              SECTION 3.08. Persons Deemed Owners. Prior to due presentment of a
Security for registration of transfer, the Company, the Trustee and any agent of
the Company or the Trustee may treat the Person in whose name such Security is
registered as the owner of such Security for the purpose of receiving payment of
principal of, premium, if any (including the Make-Whole Payment, if any), and
(subject to Section 3.07) interest on such Security and for all other purposes
whatsoever, whether or not such Security be overdue, and neither the Company,
the Trustee nor any agent of the Company or the Trustee shall be affected by
notice to the contrary.

              SECTION 3.09. Cancellation. All Securities surrendered for
payment, redemption, repurchase, registration of transfer or exchange or
conversion shall, if surrendered to any Person other than the Trustee, be
delivered to the Trustee and shall be promptly cancelled by it. The Company may
at any time deliver to the Trustee for cancellation any Securities previously
authenticated and delivered hereunder which the Company may have acquired in any
manner whatsoever, and all Securities so delivered shall be promptly cancelled
by the Trustee. No Securities shall be authenticated in lieu of

<PAGE>   53
                                                                              44

or in exchange for any Securities cancelled as provided in this Section, except
as expressly permitted by this Indenture. All cancelled Securities held by the
Trustee shall be disposed of as directed by a Company Order; provided however,
the Trustee shall not be required to destroy such cancelled Securities..

              SECTION 3.10. Computation of Interest. Interest on the Securities
shall be computed on the basis of a 360-day year of twelve 30-day months.

                                   ARTICLE IV

                           Satisfaction and Discharge

              SECTION 4.01. Satisfaction and Discharge of Indenture. This
Indenture shall upon Company request cease to be of further effect (except as to
any surviving rights of conversion, registration of transfer or exchange of
Securities herein expressly provided for), and the Trustee, at the expense of
the Company, shall execute proper instruments acknowledging satisfaction and
discharge of this Indenture, when

              (1) either

                            (A) all Securities theretofore authenticated and
              delivered (other than (i) Securities which have been destroyed,
              lost or stolen and which have been replaced or paid as provided in
              Section 3.06 and (ii) Securities for whose payment money has
              theretofore been deposited in trust or segregated and held in
              trust by the Company and thereafter repaid to the Company or
              discharged from such trust, as provided in Section 10.03) have
              been delivered to the Trustee for cancellation;

                            (B) all such Securities not theretofore delivered to
              the Trustee for cancellation

              (i) have become due and payable, or

              (ii) will become due and payable at their Stated Maturity within
     one year, or

              (iii) are to be called for redemption within one year under
     arrangements satisfactory to the Trustee for the giving of notice of
     redemption by the Trustee in the name, and at the expense, of the Company,

<PAGE>   54
                                                                              45

and the Company, in the case of (i), (ii) or (iii) above, has deposited or
caused to be deposited irrevocably with the Trustee as trust funds in trust for
the benefit of Holders of Outstanding Securities in an amount sufficient to pay
and discharge the entire indebtedness on such Securities not theretofore
delivered to the Trustee for cancellation, for principal and premium, if any
(including the Make-Whole Payment, if any), and interest to the date of such
deposit (in the case of Securities which have become due and payable) or to the
Stated Maturity or Redemption Date, as the case may be;

              (2) the Company has paid or caused to be paid all other sums
     payable hereunder by the Company;

              (3) the Company 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; and

              (4) no Event of Default which, with notice or lapse of time, or
     both, would become an Event of Default with respect to the Securities shall
     have occurred and be continuing on the date of such deposit.

Notwithstanding the satisfaction and discharge of this Indenture, the
obligations of the Company to the Trustee under Section 6.07, the obligations of
the Company to any Authenticating Agent under Section 6.14 and, if money shall
have been deposited with the Trustee pursuant to subclause (B) of clause (1) of
this Section, the obligations of the Trustee under Section 4.02 and the last
paragraph of Section 10.03 shall survive.

              SECTION 4.02. Application of Trust Money. Subject to the
provisions of the last paragraph of Section 10.03, all money deposited with the
Trustee pursuant to Section 4.01 shall be held in trust and applied by it, in
accordance with the provisions of the Securities and this Indenture, to the
payment, either directly or through any Paying Agent (including the Company
acting as its own Paying Agent) as the Trustee may determine, to the Persons
entitled thereto, of the principal and premium, if any (including the Make-Whole
Payment, if any), and interest for whose payment such money has been deposited
with the Trustee. All moneys deposited with the Trustee pursuant to Section 4.01
(and held by it or any Paying Agent) for the payment of Securities subsequently
converted shall be returned to the Company upon Company Request.

<PAGE>   55
                                                                              46

                                    ARTICLE V

                                    Remedies

              SECTION 5.01. Events of Default. "Event of Default", wherever used
herein, means any one of the following events (whatever the reason for such
Event of Default and whether it shall be occasioned by the provisions of Article
XII or be voluntary or involuntary or be 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):

              (1) default in the payment of any interest (including Additional
     Interest) upon any Security when it becomes due and payable, and
     continuance of such default for a period of 30 days (whether or not such
     payment is prohibited by the provisions of Article XII); or

              (2) default in the payment of the principal of or premium, if any
     (including the Make-Whole Payment, if any), on any Security at its Maturity
     (whether or not such payment is prohibited by the provisions of Article
     XII); or

              (3) failure by the Company to provide the notice of a Change in
     Control in accordance with Section 14.02 or notice of a Change in Control
     or default in the payment of the Repurchase Price in respect of any
     Security on the Repurchase Date therefor (whether or not such payment is
     prohibited by the provisions of Article XII); or

              (4) default in the performance, or breach, of any covenant or
     warranty of the Company in this Indenture (other than a covenant or
     warranty a default in whose performance or whose breach is elsewhere in
     this Section specifically dealt with), and continuance of such default or
     breach for a period of 60 days after there has been given, by registered or
     certified mail, to the Company by the Trustee or to the Company and the
     Trustee by the Holders of at least 25% in principal amount of the
     Outstanding Securities a written notice specifying such default or breach
     and requiring it to be remedied and stating that such notice is a "Notice
     of Default" hereunder: or

               (5) a default under any bonds, debentures, notes or other
     evidences of indebtedness for money borrowed by the Company or a Subsidiary
     or under any

<PAGE>   56
                                                                              47

     mortgages, indentures or instruments under which there may be issued or by
     which there may be secured or evidenced any indebtedness for money borrowed
     by the Company or a Subsidiary, whether such indebtedness now exists or
     shall hereafter be created, other than under a Non-Recourse Obligation,
     which indebtedness, individually or in the aggregate, has a principal
     amount outstanding in excess of U.S.$10,000,000, which default shall
     constitute a failure to pay any portion of the principal of such
     indebtedness when due and payable after the expiration of any applicable
     grace or cure period with respect thereto or shall have resulted in such
     indebtedness becoming or being declared due and payable prior to the date
     on which it would otherwise have become due and payable, without such
     indebtedness having been discharged, or such acceleration having been
     rescinded or annulled, within a period of 10 days after there shall have
     been given, by registered or certified mail, to the Company by the Trustee
     or to the Company and the Trustee by the Holders of at least 25% in
     principal amount of the Outstanding Securities a written notice specifying
     such default and requiring the Company to cause such indebtedness to be
     discharged or cause such acceleration to be rescinded or annulled and
     stating that such notice is a "Notice of Default" hereunder; or

               (6) the entry by a court having jurisdiction in the premises of
     (A) a decree or order for relief in respect of the Company or a Subsidiary
     in an involuntary case or proceeding under any applicable Federal or State
     bankruptcy, insolvency, reorganization or other similar law or (B) a decree
     or order adjudging the Company or a Subsidiary bankrupt or insolvent, or
     approving as properly filed a petition seeking reorganization, arrangement,
     adjustment or composition of or in respect of the Company or a Subsidiary
     under any applicable Federal or State law, or appointing a custodian,
     receiver, liquidator, assignee, trustee, sequestrator or other similar
     official of the Company or a Subsidiary or of any substantial part of their
     respective properties, or ordering the winding up or liquidation of the
     affairs of the Company or a Subsidiary, and the continuance of any such
     decree or order for relief or any such other decree or order unstayed and
     in effect for a period of 60 consecutive days; or

               (7) the commencement by the Company or a Subsidiary of a
     voluntary case or proceeding under any applicable Federal or State
     bankruptcy, insolvency, reorganization or other similar law or of any other
     case or proceeding to be adjudicated a bankrupt or insolvent, or the
     consent by either the Company or a Subsidiary to the entry of a decree or
     order for relief in respect of the Company or a Subsidiary in an
     involuntary case or proceeding under any applicable Federal or State
     bankruptcy, insolvency, reorganization or other similar law or to the
     commencement of any bankruptcy or insolvency case or proceeding against
     either

<PAGE>   57
                                                                              48

     the Company or a Subsidiary, or the filing by either the Company or a
     Subsidiary of a petition or answer or consent seeking reorganization or
     relief under any applicable Federal or State law, or the consent by either
     the Company or a Subsidiary to the filing of such petition or to the
     appointment of or taking possession by a custodian, receiver, liquidator,
     assignee, trustee, sequestrator or other similar official of the Company or
     a Subsidiary or of any substantial part of their respective properties, or
     the making by either the Company or a Subsidiary of an assignment for the
     benefit of creditors, or the admission by either the Company or a
     Subsidiary in writing of an inability to pay the debts of either the
     Company or a Subsidiary generally as they become due, or the taking of
     corporate action by the Company or a Subsidiary in furtherance of any such
     action.

               SECTION 5.02. Acceleration of Maturity; Rescission and Annulment.
If an Event of Default (other than an Event of Default specified in Section
5.01(l), 5.01(2), 5.01(6) or 5.01(7)) occurs and is continuing, then in every
such case the Trustee or the Holders of not less than 25% in principal amount of
the Outstanding Securities may declare the principal of all the Securities to be
due and payable immediately, by a notice in writing to the Company (and to the
Trustee if given by Holders), and upon any such declaration such principal and
any accrued interest (including Additional Interest) thereon shall become
immediately due and payable. If an Event of Default specified in Section 5.01(6)
or 5.01(7) occurs, the principal of, and accrued interest (including Additional
Interest) on, all the Securities shall automatically, and without any
declaration or other action on the part of the Trustee or any Holder, become
immediately due and payable.

               At any time after such a declaration of acceleration has been
made and before a judgment or decree for payment of the money due has been
obtained by the Trustee as hereinafter in this Article V provided, the Holders
of a majority in principal amount of the Outstanding Securities, by written
notice to the Company and the Trustee, may rescind and annul such declaration
and its consequences if

               (1) the Company has paid or deposited with the Trustee a sum
     sufficient to pay

                       (A) all overdue interest (including Additional Interest)
               on all Securities,

                       (B) the principal of and premium, if any (including the
               Make-Whole Payment, if any), on any Securities which have become
               due otherwise than by such declaration of acceleration and
               interest thereon at

<PAGE>   58
                                                                              49

              the rate borne by the Securities,

                            (C) to the extent that payment of such interest is
              lawful, interest upon overdue interest at the rate borne by the
              Securities, and

                            (D) all sums paid or advanced by the Trustee
              hereunder and the reasonable compensation, expenses, disbursements
              and advances of the Trustee, its agents and counsel;

     and

              (2) all Events of Default, other than the nonpayment of the
     principal of Securities which have become due solely by such declaration of
     acceleration, have been cured or waived as provided in Section 5.13.

No such rescission shall affect any subsequent default or impair any right
consequent thereon.

              SECTION 5.03. Collection of Indebtedness and Suits for Enforcement
by Trustee. If

              (1) default is made in the payment of any interest on any Security
     when such interest becomes due and payable and such default continues for a
     period of 30 days, or

              (2) default is made in the payment of the principal of or premium,
     if any (including the Make-Whole Payment, if any), on any Security at the
     Maturity thereof,

the Trustee is authorized to recover judgment in its own name and as trustee of
an express trust against the Company for the whole amount then due and payable
on such Securities for principal and premium, if any (including the Make-Whole
Payment, if any), and interest, and, to the extent that payment of such interest
shall be legally enforceable, interest on any overdue principal and premium, if
any (including the Make-Whole Payment, if any), and on any overdue interest, at
the rate borne by the Securities, and, in addition thereto, such further amount
as shall be sufficient to cover the costs and expenses of collection, including
the reasonable compensation, expenses, disbursements

<PAGE>   59
                                                                              50

and advances of the Trustee, its agents and counsel.

              If an Event of Default occurs and is continuing, the Trustee may
in its discretion proceed to protect and enforce its rights and the rights of
the Holders by such appropriate judicial proceedings as the Trustee shall deem
most effectual to protect and enforce any such rights, whether for the specific
enforcement of any covenant or agreement in this Indenture or in aid of the
exercise of any power granted herein, or to enforce any other proper remedy.

              SECTION 5.04. Trustee May File Proofs of Claim. In case of any
judicial proceeding relative to the Company (or any other obligor upon the
Securities), its property or its creditors, the Trustee shall be entitled and
empowered, by intervention in such proceeding or otherwise,

              (1) to file and prove a claim for the whole amount of principal
     and interest owing and unpaid in respect of the Securities and to file such
     other papers or documents as may be necessary or advisable in order to have
     the claims of the Trustee (including any claim for the reasonable
     compensation, expenses, disbursements and advances of the Trustee, its
     agents and counsel) and of the Holders allowed in such judicial proceeding,
     and

               (2) to collect and receive any moneys or other property payable
     or deliverable on any such claim and to distribute the same;

and any custodian, receiver, assignee, trustee, liquidator, sequestrator or
other similar official in any such judicial proceeding is hereby authorized by
each Holder to make such 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 counsel, and any other
amounts due the Trustee under Section 6.07.

              No provision of this Indenture shall be deemed to authorize the
Trustee to authorize or consent to or accept or adopt on behalf of any Holder
any plan of reorganization, arrangement, adjustment or composition affecting the
Securities or the rights of any Holder thereof or to authorize the Trustee to
vote in respect of the claim of any Holder in any such proceeding; provided,
however, that the Trustee may, on behalf of the Holders, vote for the election
of a trustee in bankruptcy or similar official and be a member of a creditors'
or other similar committee.

              SECTION 5.05. Trustee May Enforce Claims Without Possession of

<PAGE>   60
                                                                              51

Securities. All rights of action and claims under this Indenture or the
Securities may be prosecuted and enforced by the Trustee without the possession
of any of the Securities or the production thereof in any proceeding relating
thereto, and any such proceeding instituted by the Trustee shall be brought in
its own name as trustee of an express trust, and any recovery of judgment shall,
after provision for the payment of the reasonable compensation, expenses,
disbursements and advances of the Trustee, its agents and counsel, be for the
ratable benefit of the Holders of the Securities in respect of which such
judgment has been recovered.

              SECTION 5.06. Application of Money Collected. Any money collected
by the Trustee pursuant to this Article V shall be applied in the following
order, at the date or dates fixed by the Trustee and, in case of the
distribution of such money on account of principal or premium, if any (including
the Make-Whole Payment, if any), or interest, upon presentation of the
Securities and the notation thereon of the payment if only partially paid and
upon surrender thereof if fully paid:

              FIRST: to the payment of all amounts due the Trustee under Section
          6.07;

              SECOND: subject to Article XII, to the payment of the amounts then
          due and unpaid for first, interest (including Additional Interest) on,
          and, second, for principal of and premium, if any (including the
          Make-Whole Payment, if any), on the Securities in respect of which or
          for the benefit of which such money has been collected, ratably,
          without preference or priority of any kind, according to the amounts
          due and payable on such Securities for interest and principal and
          premium, if any (including the Make-Whole Payment, if any),
          respectively;

              THIRD:  the balance, if any, to the Person or Persons entitled
          thereto, as their interest may appear or as a court of competent
          jurisdiction shall direct; and

              FOURTH:  to the Company.

              SECTION 5.07.  Limitation on Suits.  No Holder of any Security
shall have any right to institute any proceeding, judicial or otherwise, with
respect to this Indenture, or for the appointment of a receiver or trustee, or
for any other remedy hereunder, unless

                        (1) such Holder has previously given written notice to a
        Responsible

<PAGE>   61
                                                                              52

Officer the Trustee of a continuing Event of Default;

              (2) the Holders of not less than 25% in principal amount of the
     Outstanding Securities shall have made written request to the Trustee to
     institute proceedings in respect of such Event of Default in its own name
     as Trustee hereunder;

              (3) such Holder or Holders have offered to the Trustee indemnity
     satisfactory to it (which indemnity shall not be unreasonable) against the
     costs, expenses and liabilities to be incurred in compliance with such
     request;

              (4) the Trustee for 60 days after its receipt of such notice,
     request and offer of indemnity has failed to institute any such proceeding;
     and

              (5) no direction inconsistent with such written request has been
     given to the Trustee during such 60-day period by the Holders of a majority
     in principal amount of the Outstanding Securities;

it being understood and intended that no one or more of such Holders shall have
any right in any manner whatever by virtue of, or by availing of, any provision
of this Indenture to affect, disturb or prejudice the fights of any other of
such Holders, or to obtain or to seek to obtain priority or preference over any
other of such Holders or to enforce any right under this Indenture, except in
the manner herein provided and for the equal and ratable benefit of all of such
Holders.

              SECTION 5.08. Unconditional Right of Holders To Receive Principal,
Premium and Interest and To Convert. Notwithstanding any other provision in this
Indenture, the Holder of any Security shall have the right, which is absolute
and unconditional, to receive payment of the principal of and premium, if any
(including the Make-Whole Payment, if any), and (subject to Section 3.07)
interest on such Security on the respective Stated Maturities expressed in such
Security (or, in the case of redemption or repurchase, on the Redemption Date or
Repurchase Date, as the case may be) and to convert such Security in accordance
with Article XIII and to institute suit for the enforcement of any such payment
and right to convert, and such rights shall not be impaired without the consent
of such Holder.

              SECTION 5.09. Restoration of Rights and Remedies. If the Trustee
or any Holder has instituted any proceeding to enforce any right or remedy under
this Indenture and such proceeding has been discontinued or abandoned for any
reason, or has been determined adversely to the Trustee or to such Holder, then
and in every such case,

<PAGE>   62
                                                                              53

subject to any determination in such proceeding, the Company, the Trustee and
the Holders shall be restored severally and respectively to their former
positions hereunder and thereafter all rights and remedies of the Trustee and
the Holders shall continue as though no such proceeding had been instituted.

              SECTION 5.10. Rights and Remedies Cumulative. Except as otherwise
provided with respect to the replacement or payment of mutilated, destroyed,
lost or stolen Securities in the last paragraph of Section 3.06, no right or
remedy herein conferred upon or reserved to the Trustee or to the Holders is
intended to be exclusive of any other right or remedy, and every right and
remedy shall, to the extent permitted by law, be cumulative and in addition to
every other right and remedy given hereunder or now or hereafter existing at law
or in equity or otherwise. The assertion or employment of any right or remedy
hereunder, or otherwise, shall not prevent the concurrent assertion or
employment of any other appropriate right or remedy.

              SECTION 5.11. Delay or Omission Not Waiver. No delay or omission
of the Trustee or of any Holder of any Securities to exercise any right or
remedy accruing upon any Event of Default shall impair any such right or remedy
or constitute a waiver of any such Event of Default or an acquiescence therein.
Every right and remedy given by this Article V or by law to the Trustee or to
the Holders may be exercised from time to time, and as often as may be deemed
expedient, by the Trustee or by the Holders, as the case may be.

              SECTION 5.12. Control by Holders. The Holders of a majority in
principal amount of the Outstanding Securities shall have the right to direct
the time, method and place of conducting any proceeding for any remedy available
to the Trustee or exercising any trust or power conferred on the Trustee;
provided that

              (1) such direction shall not be in conflict with any rule of law
     or with this Indenture, and

              (2) the Trustee may take any other action deemed proper by the
     Trustee which is not inconsistent with such direction.

              SECTION 5.13.  Waiver of Past Defaults.  The Holders of not less
than a majority in principal amount of the Outstanding Securities may on behalf
of the Holders of all the Securities waive any past default hereunder and its
consequences, except a

<PAGE>   63
                                                                              54

default

              (1) in the payment of the principal of or premium, if any
     (including the Make-Whole Payment, if any), or interest on any Security, or

              (2) in respect of a covenant or provision hereof which under
     Article IX cannot be modified or amended without the consent of the Holder
     of each Outstanding Security affected.

              Upon any such waiver, such default shall cease to exist, and any
Event of Default arising therefrom shall be deemed to have been cured, for every
purpose of this Indenture; but no such waiver shall extend to any subsequent or
other default or impair any right consequent thereon.

              SECTION 5.14. 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, suffered or omitted by it as Trustee, a court
may require any party litigant in such suit to file an undertaking to pay the
costs of such suit, and may assess costs against any such party litigant, having
due regard to the merits and good faith of the claims or defenses made by such
party litigant; provided, that this Section 5.14 shall not be deemed to
authorize any court to require such an undertaking or to make such an assessment
in any suit instituted by the Trustee or the Company or in any suit for the
enforcement of the right to convert any Security in accordance with Article
XIII.

              SECTION 5.15. Waiver of Usury, Stay or Extension Laws. The Company
covenants (to the extent that it may lawfully do so) that it will not at any
time insist upon, or plead, or in any manner whatsoever claim or take the
benefit or advantage of, any usury, 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 Company (to the extent that it may
lawfully do so) hereby expressly waives all benefit or advantage of any such law
and covenants that it will not hinder, delay or impede the execution of any
power herein granted to the Trustee, but will suffer and permit the execution of
every such power as though no such law had been enacted.

                                   ARTICLE VI

                                   The Trustee

              SECTION 6.01. Certain Duties and Responsibilities. (a) Except
during

<PAGE>   64
                                                                              55

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; but in
     the case of any such certificates or opinions which by any provision hereof
     are specifically required to be furnished to the Trustee, the Trustee shall
     be under a duty to examine the same to determine whether or not they
     conform to the requirements of this Indenture.

              (b)  In case an Event of Default has occurred and is continuing,
the Trustee shall exercise such of the rights and powers vested in it by this
Indenture, and use the same degree of care and skill in their exercise, as a
prudent person would exercise or use under the circumstances in the conduct of
his or her own affairs.

              (c) No provision of this Indenture shall be construed to relieve
the Trustee from liability for its own negligent action, its own negligent
failure to act, or its own willful misconduct, except that

              (1) this paragraph (c) shall not be construed to limit the effect
     of paragraph (a) of this Section;

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

              (3) the Trustee shall not be liable with respect to any action
     taken or omitted to be taken by it in good faith in accordance with the
     direction of the Holders of a majority in principal amount of the
     Outstanding Securities relating to the time, method and place of conducting
     any proceeding for any remedy available to the Trustee, or exercising any
     trust or power conferred upon the Trustee, under this Indenture; and

<PAGE>   65
                                                                              56

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

              (d) Whether or not therein expressly so provided, every provision
of this Indenture relating to the conduct or affecting the liability of or
affording protection to the Trustee (as Trustee, Paying Agent, Authenticating
Agent or Security Registrar) shall be subject to the provisions of this Section.

              SECTION 6.02. Notice of Defaults. Within 90 days after the
occurrence of any default hereunder, the Trustee shall give the Holders, in the
manner provided in Section 1.06, notice of any default hereunder actually known
to a Responsible Officer of the Trustee; provided, however, that in the case of
any default of the character specified in Section 5.01(3), no such notice to
Holders shall be given until at least 30 days after the occurrence thereof. The
Trustee shall not be deemed to have notice of a default unless (i) the Trustee
has received written notice thereof from the Company or any Holder or (ii) a
Responsible Officer of the Trustee shall have actual knowledge thereof. For the
purpose of this Section, the term "default" means any event which is, or after
notice or lapse of time or both would become, an Event of Default.

              SECTION 6.03. Certain Rights of Trustee. Subject to the provisions
of Section 6.01:

              (a) the Trustee may conclusively rely and shall be protected in
     acting or refraining from acting upon any resolution, certificate,
     statement, instrument, opinion, report, notice, request, direction,
     consent, order, bond, debenture, note, other evidence of indebtedness or
     other paper or document believed by it to be genuine and to have been
     signed or presented by the proper party or parties;

              (b) any request or direction of the Company mentioned herein
     shall be sufficiently evidenced by a Company Request or Company Order and
     any resolution of the Board of Directors shall be sufficiently evidenced by
     a Board Resolution;

              (c) whenever in the administration of this Indenture the Trustee
     shall deem it desirable that a matter be proved or established prior to
     taking, suffering or omitting any action hereunder, the Trustee (unless
     other evidence be herein specifically prescribed) may require and, in the
     absence of bad faith on its part, conclusively rely upon an Officers'
     Certificate;

              (d) the Trustee may consult with counsel of its selection and the
     advice of

<PAGE>   66
                                                                              57

     such counsel or any Opinion of Counsel shall be full and complete
     authorization and protection in respect of any action taken, suffered or
     omitted by it hereunder in good faith and in reliance thereon;

              (e) the Trustee shall be under no obligation to exercise any of
     the rights or powers vested in it by this Indenture at the request or
     direction of any of the Holders pursuant to this Indenture, unless such
     Holders shall have offered to the Trustee security or indemnity
     satisfactory to the Trustee (which security or indemnity shall not be
     unreasonable) against the costs, expenses and liabilities which might be
     incurred by it in compliance with such request or direction;

              (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, direction, consent, order,
     bond, debenture, note, other evidence of indebtedness or other paper or
     document, but the Trustee, in its discretion, may make such further inquiry
     or investigation into such facts or matters as it may see fit, and, if the
     Trustee shall determine to make such further inquiry or investigation, it
     shall be entitled to examine the books, records and premises of the
     Company, personally or by agent or attorney; and

              (g) the Trustee may execute any of the trusts or powers hereunder
     or perform any duties hereunder either directly or by or through agents or
     attorneys and the Trustee shall not be responsible for any misconduct or
     negligence on the part of any agent or attorney appointed with due care by
     it hereunder.

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

              SECTION 6.04. Not Responsible for Recitals or Issuance of
Securities. The recitals contained herein and in the Securities, except the
Trustee's certificates of authentication, shall be taken as the statements of
the Company, and neither the Trustee nor any Authenticating Agent assumes any
responsibility for their correctness. The Trustee makes no representations as to
the validity or sufficiency of this Indenture or of the Securities. Neither the
Trustee nor any Authenticating Agent shall be accountable for the use or
application by the Company of Securities or the proceeds thereof.

<PAGE>   67
                                                                              58

              SECTION 6.05. May Hold Securities. The Trustee, any Authenticating
Agent, any Paying Agent, any Security Registrar or any other agent of the
Company, in its individual or any other capacity, may become the owner or
pledgee of Securities and, subject to Section 6.08 and Section 6.13, may
otherwise deal with the Company with the same rights it would have if it were
not Trustee, Authenticating Agent, Paying Agent, Security Registrar or such
other agent.

              SECTION 6.06. Money Held in Trust. Money held by the Trustee in
trust hereunder need not be segregated from other funds except to the extent
required by law. The Trustee shall be under no liability for interest on any
money received by it hereunder except as otherwise agreed with the Company in
writing.

              SECTION 6.07. Compensation and Reimbursement. The Company agrees:

              (1) to pay to the Trustee from time to time such compensation as
     shall be agreed in writing between the Company and the Trustee for all
     services rendered by it hereunder (which compensation shall not be limited
     by any provision of law in regard to the compensation of a trustee of an
     express trust);

              (2) except as otherwise expressly provided herein, to reimburse
     the Trustee upon its request for all reasonable expenses, disbursements and
     advances incurred or made by the Trustee in accordance with any provision
     of this Indenture (including the reasonable compensation and the expenses
     and disbursements of its agents and counsel), except any such expense,
     disbursement or advance as may be attributable to its negligence or willful
     misconduct;

              (3) to indemnify the Trustee for, and to hold it harmless against,
     any loss, liability or expense incurred without negligence or willful
     misconduct on its part, arising out of or in connection with the acceptance
     or administration of this trust, including the costs and expenses of
     defending itself against any claim (whether asserted by the Company, a
     Holder of Securities or any other Person) or liability in connection with
     the exercise or performance of any of its powers or duties hereunder. The
     Trustee shall notify the Company of any claim asserted against it for which
     it may seek indemnity;

              (4) all indemnifications and releases from liability granted
     hereunder to the Trustee shall extend to its officers, directors,
     employees, agents, successors and assigns;

<PAGE>   68
                                                                              59

              (5) when the Trustee incurs expenses or renders services after the
     occurrence of any Event of Default specified in Section 5.01, the expenses
     and the compensation for the services are intended to constitute expenses
     of administration under any bankruptcy, insolvency or similar laws; and

              (6) the obligations of the Company under this Section shall
     survive the satisfaction and discharge of this Indenture.

              SECTION 6.08. Disqualification; Conflicting Interests. If the
Trustee has or shall acquire a conflicting interest within the meaning of the
Trust Indenture Act, the Trustee shall either eliminate such interest or resign,
to the extent and in the manner provided by, and subject to the provisions of,
the Trust Indenture Act and this Indenture.

              SECTION 6.09. Corporate Trustee Required; Eligibility. There shall
at all times be a Trustee hereunder which shall be a corporation organized and
doing business under the laws of the United States, authorized under such laws
to exercise corporate trust powers, which shall have (or, in the case of a
corporation included in a bank holding company system, the related bank holding
company shall have) a combined capital and surplus of at least U.S.$50,000,000,
subject to supervision or examination by Federal or State authority, in good
standing and having an established place of business or agency in the Borough of
Manhattan, The City of New York. If such corporation or related bank holding
company publishes reports of condition at least annually, pursuant to law or to
the requirements of said supervising or examining authority, then for the
purposes of this Section, the combined capital and surplus of such corporation
or related bank holding company shall be deemed to be its combined capital and
surplus as set forth in its most recent report of condition so published. If at
any time the Trustee shall cease to be eligible in accordance with the
provisions of this Section, it shall resign immediately in the manner and with
the effect hereinafter specified in this Article VI.

              SECTION 6.10. Resignation and Removal; Appointment of Successor.
(a) No resignation or removal of the Trustee and no appointment of a successor
Trustee pursuant to this Article shall become effective until the acceptance of
appointment by the successor Trustee in accordance with the applicable
requirements of Section 6.11.

              (b) The Trustee may resign at any time by giving written notice
thereof to the Company. If the instrument of acceptance by a successor Trustee
required by Section 6.11 shall not have been delivered to the Trustee within 30
days after the giving of such notice of resignation, the resigning Trustee may
petition any court of competent jurisdiction for the appointment of a successor
Trustee.

<PAGE>   69

                                                                              60

          (c) The Trustee may be removed at any time by Act of the Holders of a
majority in principal amount of the Outstanding Securities, delivered to the
Trustee and to the Company. If the instrument of acceptance by a successor
Trustee required by Section 6.11 shall not have been delivered to the Trustee
within 30 days after the giving of such notice of resignation, the resigning
Trustee may petition any court of competent jurisdiction for the appointment of
a successor Trustee.

          (d) If at any time:

          (1) the Trustee shall fail to comply with Section 6.08 after written
     request therefor by the Company or by any Holder who has been a bona fide
     Holder of a Security for at least six months, or

          (2) the Trustee shall cease to be eligible under Section 6.09 and
     shall fail to resign after written request therefor by the Company or by
     any such Holder, or

          (3) the Trustee shall become incapable of acting or shall be adjudged
     a bankrupt or insolvent or a receiver of the Trustee or of its property
     shall be appointed or any public officer shall take charge or control of
     the Trustee or of its property or affairs for the purpose of
     rehabilitation, conservation or liquidation,

then, in any such case, (i) the Company by a Board Resolution may remove the
Trustee, or (ii) subject to Section 5.14, any Holder who has been a bona fide
Holder of a Security for at least six months may, on behalf of himself and all
others similarly situated, petition any court of competent jurisdiction for the
removal of the Trustee and the appointment of a successor Trustee.

          (e) If the Trustee shall resign, be removed or become incapable of
acting, or if a vacancy shall occur in the office of Trustee for any cause, the
Company, by a Board Resolution, shall promptly appoint a successor Trustee. If,
within one year after such resignation, removal or incapability, or the
occurrence of such vacancy, a successor Trustee shall be appointed by Act of the
Holders of a majority in principal amount of the Outstanding Securities
delivered to the Company and the retiring Trustee, the successor Trustee so
appointed shall, forthwith upon its acceptance of such appointment in accordance
with the applicable requirements of Section 6.11, become the successor Trustee
and to that extent supersede the successor Trustee appointed by the Company. If
no successor Trustee shall have been so appointed by the Company or the Holders
and

<PAGE>   70
                                                                              61

accepted appointment in the manner required by Section 6.11, any Holder who has
been a bona fide Holder of a Security for at least six months may, on behalf of
himself and all others similarly situated, petition any court of competent
jurisdiction for the appointment of a successor Trustee.

          (f) The Company shall give notice of each resignation and each removal
of the Trustee and each appointment of a successor Trustee to all Holders in the
manner provided in Section 1.06. Each notice shall include the name of the
successor Trustee and the address of its Corporate Trust Office.

          SECTION 6.11. Acceptance of Appointment by Successor. Every successor
Trustee appointed hereunder shall execute, acknowledge and deliver to the
Company and to the retiring Trustee an instrument accepting such appointment,
and thereupon the resignation or removal of the retiring Trustee shall become
effective and such successor Trustee, without any further act, deed or
conveyance, shall become vested with all the rights, powers, trusts and duties
of the retiring Trustee; but, on the request of the Company or the successor
Trustee, such retiring Trustee shall, upon payment of its charges, execute and
deliver an instrument transferring to such successor Trustee all the rights,
powers and trusts of the retiring Trustee and shall duly assign, transfer and
deliver to such successor Trustee all property and money held by such retiring
Trustee hereunder. Upon request of any such successor Trustee, the Company shall
execute any and all instruments for more fully and certainly vesting in and
confirming to such successor Trustee all such rights, powers and trusts.

          No successor Trustee shall accept its appointment unless at the time
of such acceptance such successor Trustee shall be qualified and eligible under
this Article VI.

          SECTION 6.12. Merger, Conversion, Consolidation or Succession to
Business. Any corporation into which the Trustee may be merged or converted or
with which it may be consolidated, or any corporation resulting from any merger,
conversion or consolidation to which the Trustee shall be a party, or any
corporation succeeding to all or substantially all the corporate trust business
of the Trustee, shall be the successor of the Trustee hereunder; provided such
corporation shall be otherwise qualified and eligible under this Article VI
without the execution or filing of any paper or any further act on the part of
any of the parties hereto. In case any Securities shall have been authenticated,
but not delivered, by the Trustee then in office, any successor by merger,
conversion or consolidation to such authenticating Trustee may adopt such
authentication and deliver the Securities so authenticated with the same effect
as if such successor Trustee had itself authenticated such Securities.

<PAGE>   71
                                                                              62

          SECTION 6.13. Preferential Collection of Claims Against Company. If
and when the Trustee shall be or become a creditor of the Company (or any other
obligor upon the Securities), the Trustee shall be subject to the provisions of
the Trust Indenture Act regarding the collection of claims against the Company
(or any such other obligor).

          SECTION 6.14. Appointment of Authenticating Agent. The Trustee may
appoint an Authenticating Agent or Agents which shall be authorized to act on
behalf of the Trustee to authenticate Securities issued upon original issue and
upon exchange, registration of transfer, partial conversion, partial redemption,
or partial repurchase or pursuant to Section 3.06, and Securities so
authenticated shall be entitled to the benefits of this Indenture and shall be
valid and obligatory for all purposes as if authenticated by the Trustee
hereunder. Wherever reference is made in this Indenture to the authentication
and delivery of Securities by the Trustee or the Trustee's certificate of
authentication, such reference shall be deemed to include authentication and
delivery on behalf of the Trustee by an Authenticating Agent and a certificate
of authentication executed on behalf of the Trustee by an Authenticating Agent.
Each Authenticating Agent shall be acceptable to the Company and shall at all
times be a corporation organized and doing business under the laws of the United
States, authorized under such laws to act as Authenticating Agent, which shall
have (or, in the case of a corporation included in a bank holding company
system, the related bank holding company shall have) a combined capital and
surplus of not less than U.S.$50,000,000 and be subject to supervision or
examination by Federal or State authority. If such Authenticating Agent
publishes reports of condition at least annually, pursuant to law or to the
requirements of said supervising or examining authority, then, for the purposes
of this Section, the combined capital and surplus of such Authenticating Agent
or related bank holding company shall be deemed to be its combined capital and
surplus as set forth in its most recent report of condition so published. If at
any time an Authenticating Agent shall cease to be eligible in accordance with
the provisions of this Section, such Authenticating Agent shall resign
immediately in the manner and with the effect specified in this Section.

          Any corporation into which an Authenticating Agent may be merged or
converted or with which it may be consolidated, or any corporation resulting
from any merger, conversion or consolidation to which such Authenticating Agent
shall be a party, or any corporation succeeding to all or substantially all the
corporate agency or corporate trust business of an Authenticating Agent, shall
continue to be an Authenticating Agent; provided such corporation shall be
otherwise eligible under this Section, without the

<PAGE>   72
                                                                              63

execution or filing of any paper or any further act on the part of the Trustee
or the Authenticating Agent.

          An Authenticating Agent may resign at any time by giving written
notice thereof to the Trustee and to the Company. The Trustee may at any time
terminate the agency of an Authenticating Agent by giving written notice thereof
to such Authenticating Agent and to the Company. Upon receiving such a notice of
resignation or upon such a termination, or in case at any time such
Authenticating Agent shall cease to be eligible in accordance with the
provisions of this Section 6.14, the Trustee may appoint a successor
Authenticating Agent which shall be acceptable to the Company and shall mail
written notice of such appointment by first-class mail, postage prepaid, to all
Holders as their names and addresses appear in the Security Register. Any
successor Authenticating Agent upon acceptance of its appointment hereunder
shall become vested with all the rights, powers and duties of its predecessor
hereunder, with like effect as if originally named as an Authenticating Agent.
No successor Authenticating Agent shall be appointed unless eligible under the
provisions of this Section 6.14.

          The Company agrees to pay to each Authenticating Agent from time to
time compensation for its services under this Section 6.14.

          If an appointment is made pursuant to this Section, the Securities may
have endorsed thereon, in addition to the Trustee's certificate of
authentication, an alternative certificate of authentication in the following
form:

          This is one of the Securities described in the within-mentioned
Indenture.

                                                The Bank of New York
                                            ------------------------------
                                                     As Trustee

                                         By
                                            ------------------------------
                                                 As Authenticating Agent

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

          SECTION 6.15. Appointment of Co-Trustee. Subject to the qualifications
set forth in Section 6.09, the Trustee may appoint an additional institution

<PAGE>   73
                                                                              64

as a separate trustee or co-trustee. If the Trustee appoints an additional
institution as a separate trustee or co-trustee, each and every remedy, power,
fight, claim, demand, cause of action, immunity, estate, duty, obligation,
title, interest and lien expressed or intended by this Indenture to be exercised
by, vested in and conveyed by the Trustee with respect thereto shall be
exercisable by, vested in and conveyed to such separate trustee or co-trustee,
but only to the extent necessary to enable such separate trustee or co-trustee
to exercise such powers, rights and remedies, and every covenant and obligation
necessary for the exercise thereby by such separate trustee or co-trustee shall
run to and be enforceable by either of them. Should any instrument in writing
from the Company be required by the separate trustee or co-trustee so appointed
by the Trustee for more fully vesting in and confirming to them such properties,
rights, powers, trusts, duties and obligations, any and all such instruments in
writing shall, on request, be executed, acknowledged and delivered by the
Company. If any separate trustee or co-trustee, or a successor to either, shall
become incapable of acting or not qualified to act, resign or be removed, all
the estate, properties, rights, powers, trusts, duties and obligations of such
separate trustee or co-trustee, so far as permitted by law, shall vest in and be
exercised by the Trustee until the appointment of a successor to such separate
trustee or co-trustee. The appointment of any separate trustee or co-trustee
shall be subject to written approval of the Company so long as no Event of
Default has occurred and is continuing under this Indenture.

                                   ARTICLE VII

                Holders' Lists and Reports by Trustee and Company

          SECTION 7.01. Company To Furnish Trustee Names and Addresses of
Holders. The Company will furnish or cause to be furnished to the Trustee

          (a) semi-annually, not more than 15 days after each Regular Record
     Date, a list, in such form as the Trustee may reasonably require, of the
     names and addresses of the Holders as of such Regular Record Date, and

          (b) at such other times as the Trustee may request in writing, within
     30 days after the receipt by the Company of any such request, a list of
     similar form and content as of a date not more than 15 days prior to the
     time such list is furnished;

<PAGE>   74
                                                                              65

excluding from any such list names and addresses received by the Trustee in its
capacity as Security Registrar.

          SECTION 7.02. Preservation of Information; Communications to Holders.
(a) The Trustee shall preserve, in as current a form as is reasonably
practicable, the names and addresses of Holders contained in the most recent
list furnished to the Trustee as provided in Section 7.01 and the names and
addresses of Holders received by the Trustee in its capacity as Security
Registrar. The Trustee may destroy any list furnished to it as provided in
Section 7.01 upon receipt of a new list so furnished.

          (b) The rights of Holders to communicate with other Holders with
respect to their rights under this Indenture or under the Securities, and the
corresponding rights and duties of the Trustee, shall be as provided by the
Trust Indenture Act.

          (c) Every Holder of Securities, by receiving and holding the same,
agrees with the Company and the Trustee that neither the Company nor the Trustee
nor any agent of either of them shall be held accountable by reason of any
disclosure of information as to names and addresses of Holders made pursuant to
the Trust Indenture Act.

          SECTION 7.03. Reports by Trustee. (a) The Trustee shall transmit to
Holders within 60 days after May 15th of each year such reports concerning the
Trustee and its actions under this Indenture as may be required pursuant to the
Trust Indenture Act at the times and in the manner provided pursuant thereto.

          (b) A copy of each such report shall, at the time of such transmission
to Holders, be filed by the Trustee with each stock exchange upon which the
Securities are listed, with the Commission, if applicable, and with the Company.
The Company will promptly notify the Trustee when the Securities are listed on
any stock exchange and of any delisting thereof.

          SECTION 7.04. Reports by Company. (a) The Company shall file with the
Trustee and the Commission, if applicable, and transmit to Holders, such
information, documents and other reports, and such summaries thereof, as may be
required pursuant to the Trust Indenture Act at the times and in the manner
provided pursuant to such Act; provided that any such information, documents or
reports required to be filed with the Commission pursuant to Section 13 or 15(d)
of the Exchange Act shall be filed with the Trustee within 15 days after the
same is so required to be filed with the Commission. 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

<PAGE>   75
                                                                              66

any information contained therein or determinable from information contained
therein, including the Company's compliance with any of its covenants hereunder
(as to which the Trustee is entitled to rely exclusively on Officers'
Certificates). Notwithstanding anything to the contrary contained herein, the
Trustee shall have no duty to review such documents for the purpose of
determining compliance with this Indenture.

          (b) The Company shall provide the Trustee with at least 30 days' prior
notice of any change in location of its principal executive offices or other
principal place of business.

                                  ARTICLE VIII

              Consolidation, Merger, Conveyance, Transfer or Lease

          SECTION 8.01. Company May Consolidate, etc., Only on Certain Terms.
The Company shall not consolidate with or merge into any other Person or,
directly or indirectly, convey, transfer, sell, lease or otherwise dispose of
all or substantially all of its properties and assets to any Person, and the
Company shall not permit any Person to consolidate with or merge into the
Company or convey, transfer, sell, lease or otherwise dispose of all or
substantially all of its properties and assets to the Company, unless:

          (1) in case the Company shall consolidate with or merge into another
     Person or convey, transfer or lease its properties and assets substantially
     as an entirety to any Person, the Person formed by such consolidation or
     into which the Company is merged or the Person which acquires by conveyance
     or transfer, or which leases, the properties and assets of the Company
     substantially as an entirety (i) shall be a corporation, partnership or
     trust, (ii) shall be an entity (A) organized and validly existing under the
     laws of the United States of America, any State thereof or the District of
     Columbia or (B) organized and validly existing under the laws of a
     jurisdiction outside of the United States of America, with its common
     stock, or American Depositary Shares representing such shares of common
     stock, traded on a national securities exchange in the United States of
     America or through Nasdaq and an average worldwide total market
     capitalization of its equity securities of at least U.S. $5 billion during
     the ten Trading Days immediately preceding the date of the Change in
     Control, and (iii) shall expressly assume, by an indenture supplemental
     hereto, executed and delivered to the Trustee, in form satisfactory to the
     Trustee, the

<PAGE>   76
                                                                              67

     due and punctual payment of the principal of and premium, if any (including
     the Make-Whole Payment, if any), and interest (including Additional
     Interest) on all the Securities and the performance or observance of every
     covenant of this Indenture on the part of the Company to be performed or
     observed and shall have provided for conversion rights in accordance with
     Article XIII;

          (2) immediately after giving effect to such transaction, no Event of
     Default, and no event which, after notice or lapse of time or both, would
     become an Event of Default, shall have happened and be continuing; and

          (3) the Company has delivered to the Trustee an Officers' Certificate
     and an Opinion of Counsel, each stating that such consolidation, merger,
     conveyance, transfer or lease and, if a supplemental indenture is required
     in connection with such transaction, such supplemental indenture comply
     with this Article VIII and that all conditions precedent herein provided
     for relating to such transaction have been complied with.

          SECTION 8.02. Successor Substituted. Upon any consolidation of the
Company with, or merger of the Company into, any other Person or any conveyance,
transfer or lease of the properties and assets of the Company substantially as
an entirety in accordance with Section 8.01, the successor Person formed by such
consolidation or into which the Company is merged or to which such conveyance,
transfer or lease is made shall succeed to, and be substituted for, and may
exercise every right and power of, the Company under this Indenture with the
same effect as if such successor Person had been named as the Company herein,
and thereafter, except in the case of a lease, the predecessor Person shall be
released from its obligations and covenants under this Indenture and the
Securities.

                                   ARTICLE IX

                             Supplemental Indentures

          SECTION 9.01. Supplemental Indentures Without Consent of Holders.
Without the consent of any Holders, the Company, when authorized by a Board
Resolution, and the Trustee, at any time and from time to time, may enter into
one or more indentures supplemental hereto, in form satisfactory to the Trustee,
for any of the following purposes:

          (1) to evidence the succession of another Person to the Company and
     the

<PAGE>   77
                                                                              68

     assumption by any such successor of the covenants of the Company herein
     and in the Securities; or

          (2) to add to the covenants of the Company for the equal and ratable
     benefit of the Holders, or to surrender any right or power herein conferred
     upon the Company; or

          (3) to make any change to this Indenture that would provide any
     additional benefit or right to the Holders; provided that any such action
     pursuant to this clause (3) shall not adversely affect the interests of the
     Holders of Securities; or

          (4) to secure the Company's obligations in respect of the Securities;
     or

          (5) to make provision with respect to the conversion rights of Holders
     pursuant to the requirements of Article XIII; or

          (6) to make any changes or modifications to this Indenture necessary
     in connection with the registration of any Transfer Restricted Securities
     under the Securities Act as contemplated by Section 10.11; provided that
     any such action pursuant to this clause (6) shall not adversely affect the
     interests of the Holders of Securities; or

          (7) to cure any ambiguity, to correct or supplement any provision
     herein which may be inconsistent with any other provision herein, to
     correct or supplement any provision herein which limits, qualifies or
     conflicts with a provision of the Trust Indenture Act which is required
     under such Act to be a part of and govern this Indenture, in any case to
     the extent necessary to qualify this Indenture under the Trust Indenture
     Act, or to make any other provisions with respect to matters or questions
     arising under this Indenture which shall not be inconsistent with the
     provisions of this Indenture; provided that such action pursuant to this
     clause (7) shall not adversely affect the interests or legal rights of the
     Holders in any material respect.

          SECTION 9.02. Supplemental Indentures with Consent of Holders. With
the consent of the Holders of not less than a majority in principal amount of
the Outstanding Securities, by the Act of said Holders delivered to the Company
and the Trustee, the Company, when authorized by a Board Resolution, and the
Trustee may

<PAGE>   78
                                                                              69

enter into an indenture or indentures supplemental hereto for the purpose of
adding any provisions to or changing in any manner or eliminating any of the
provisions of this Indenture or of modifying in any manner the rights of the
Holders under this Indenture; provided, however, that no such supplemental
indenture shall, without the consent of the Holder of each Outstanding Security
affected thereby,

          (1) change the Stated Maturity of the principal of, or any installment
     of interest on, any Security, or reduce the principal amount thereof or the
     rate of interest thereon or any premium (including the Make-Whole Payment)
     payable upon the redemption thereof, or change the place of payment where,
     or the coin or currency in which, any Security or any premium (including
     the Make-Whole Payment) or interest thereon is payable, or impair the right
     to institute suit for the enforcement of any such payment on or after the
     Stated Maturity thereof (or, in the case of redemption or repurchase, on or
     after the Redemption Date or Repurchase Date, as the case may be), or
     adversely affect the right to convert any Security as provided in Article
     XIII (except as permitted by Section 9.01(5)), or modify the provisions of
     this Indenture with respect to the subordination of the Securities in a
     manner adverse to the Holders, or modify the redemption provisions in a
     manner adverse to the Holders, or modify the provisions relating to the
     Company's requirement to offer to repurchase Notes upon a Change in Control
     in a manner adverse to the Holders, or

          (2) modify any of the provisions of this Section 9.02, Section 5.13 or
     Section 10.08, except to increase any such percentage or to provide that
     certain other provisions of this Indenture cannot be modified or waived
     without the consent of the Holder of each Outstanding Security affected
     thereby, or

          (3) modify the obligation of the Company to maintain an office or
     agency in the Borough of Manhattan, The City of New York pursuant to
     Section 10.02, or

          (4) modify any of the provisions of Section 10.09 or Section 10.10, or

          (5) reduce the percentage in principal amount of the Outstanding
     Securities, the consent of whose Holders is required for any such
     supplemental indenture, 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.

          It shall not be necessary for any Act of Holders under this Section
9.02 to approve the particular form of any proposed supplemental indenture, but
it shall be sufficient if such Act shall approve the substance thereof.

<PAGE>   79
                                                                              70

          SECTION 9.03. Execution of Supplemental Indentures. In executing, or
accepting the additional trusts created by, any supplemental indenture permitted
by this Article IX or the modifications thereby of the trusts created by this
Indenture, the Trustee shall receive, and (subject to Section 6.01 and Section
6.03) shall be fully protected in relying upon, an Opinion of Counsel stating
that the execution of such supplemental indenture is authorized or permitted by
this Indenture, complies with its terms and will, upon the execution and
delivery thereof, be valid and binding upon the Company in accordance with its
terms. The Trustee may, but shall not be obligated to, enter into any such
supplemental indenture which affects the Trustee's own rights, duties or
immunities under this Indenture or otherwise.

          SECTION 9.04. Effect of Supplemental Indentures. Upon the execution of
any supplemental indenture under this Article, this Indenture shall be modified
in accordance therewith, and such supplemental indenture shall form a part of
this Indenture for all purposes; and every Holder of Securities theretofore or
thereafter authenticated and delivered hereunder shall be bound thereby.

          SECTION 9.05. Conformity with Trust Indenture Act. Every supplemental
indenture executed pursuant to this Article shall conform to the requirements of
the Trust Indenture Act.

          SECTION 9.06. Reference in Securities to Supplemental Indentures.
Securities authenticated and delivered after the execution of any supplemental
indenture pursuant to this Article may, and shall if required by the Trustee,
bear a notation in form approved by the Trustee as to any matter provided for in
such supplemental indenture. If the Company shall so determine, new Securities
so modified as to conform, in the judgment of the Trustee and the Company, to
any such supplemental indenture may be prepared and executed by the Company and
authenticated and delivered by the Trustee in exchange for Outstanding
Securities.

                                    ARTICLE X

                                    Covenants

          SECTION 10.01. Payment of Principal, Premium and Interest. The Company
will duly and punctually pay the principal of and premium, if any (including

<PAGE>   80
                                                                              71

the Make-Whole Payment, if any, upon redemption pursuant to Article XI), and
interest on the Securities in accordance with the terms of the Securities and
this Indenture.

          SECTION 10.02. Maintenance of Office or Agency. The Company will
maintain in the Borough of Manhattan, The City of New York an office or agency
where Securities may be presented or surrendered for payment, where Securities
may be surrendered for registration of transfer or exchange, where Securities
may be surrendered for conversion and where notices and demands to or upon the
Company in respect of the Securities and this Indenture may be served. The
Company will give prompt written notice to the Trustee of the location, and any
change in the location, of such office or agency. If at any time the Company
shall fail to maintain any such required office or agency or shall fail to
furnish the Trustee with the address thereof, such presentations, surrenders,
notices and demands may be made or served at the Corporate Trust Office of the
Trustee or the office or agency of the Trustee in the Borough of Manhattan, The
City of New York. The Company hereby appoints the Trustee as its agent to
receive all such presentations, surrenders, notices and demands.

          The Company may also from time to time designate one or more other
offices or agencies (in or outside the Borough of Manhattan, The City of New
York) where the Securities may be presented or surrendered for any or all such
purposes and may from time to time rescind such designations; provided, however,
that no such designation or rescission shall in any manner relieve the Company
of its obligation to maintain an office or agency in the Borough of Manhattan,
The City of New York for such purposes. The Company will give prompt written
notice to the Trustee of any such designation or rescission and of any change in
the location of any such other office or agency.

          SECTION 10.03. Money for Security Payments To Be Held in Trust. If the
Company shall at any time act as its own Paying Agent, it will, on or before
each due date of the principal of and premium, if any (including the Make-Whole
Payment, if any), or interest (together with any Additional Interest in respect
thereof) on any of the Securities, segregate and hold in trust for the benefit
of the Persons entitled thereto a sum sufficient to pay the principal and
premium, if any (including the Make-Whole Payment, if any), or interest
(together with any Additional Interest in respect thereof) so becoming due until
such sums shall be paid to such Persons or otherwise disposed of as herein
provided and will promptly notify the Trustee of its action or failure so to
act.

          Whenever the Company shall have one or more Paying Agents, it will,
prior to each due date of the principal of and premium, if any (including the
Make-Whole Payment, if any), or interest (together with any Additional Interest
in respect thereof) on

<PAGE>   81
                                                                              72

any Securities, deposit with a Paying Agent a sum sufficient to pay such amount,
such sum to be held in trust for the benefit of the Persons entitled to such
principal, premium, if any (including the Make-Whole Payment, if any), or
interest, and (unless such Paying Agent is the Trustee) the Company will
promptly notify the Trustee of its action or failure so to act.

          The Company will cause each Paying Agent other than the Trustee to
execute and deliver to the Trustee an instrument in which such Paying Agent
shall agree with the Trustee, subject to the provisions of this Section 10.03,
that such Paying Agent will:

          (1) hold all sums held by it for the payment of the principal of,
     premium, if any (including the Make-Whole Payment, if any), or interest on
     Securities in trust for the benefit of the Persons entitled thereto until
     such sums shall be paid to such Persons or otherwise disposed of as herein
     provided;

          (2) give the Trustee notice of any default by the Company (or any
     other obligor upon the Securities) in the making of any payment of
     principal, premium, if any (including the Make-Whole Payment, if any), or
     interest; and

          (3) at any time during the continuance of any such default, upon the
     written request of the Trustee, forthwith pay to the Trustee all sums so
     held in trust by such Paying Agent.

          The Company may at any time, for the purpose of obtaining the
satisfaction and discharge of this Indenture or for any other purpose, pay, or
by Company Order direct any Paying Agent to pay, to the Trustee all sums held in
trust by the Company or such Paying Agent, such sums to be held by the Trustee
upon the same trusts as those upon which such sums were held by the Company or
such Paying Agent; and, upon such payment by any Paying Agent to the Trustee,
such Paying Agent shall be released from all further liability with respect to
such money.

          Any money deposited with the Trustee or any Paying Agent, or then held
by the Company, in trust for the payment of the principal of and premium, if any
(including the Make-Whole Payment, if any), or interest (together with any
Additional Interest in respect thereof) on any Security and remaining unclaimed
for two years after such principal and premium, if any (including the Make-Whole
Payment, if any), or interest has become due and payable shall be paid to the
Company on Company Request,

<PAGE>   82
                                                                              73

or (if then held by the Company) shall be discharged from such trust; and the
Holder of such Security shall thereafter, as an unsecured general creditor, look
only to the Company for payment thereof, and all liability of the Trustee or
such Paying Agent with respect to such trust money, and all liability of the
Company as trustee thereof, shall thereupon cease; provided, however, that the
Trustee or such Paying Agent, before being required to make any such repayment,
may at the expense of the Company cause to be published once, in a newspaper
published in the English language, customarily published on each Business Day
and of general circulation in the Borough of Manhattan, The City of New York,
notice that such money remains unclaimed and that, after a date specified
therein, which shall not be less than 30 days from the date of such publication,
any unclaimed balance of such money then remaining will be repaid to the
Company.

          SECTION 10.04. Statement by Officers as to Default. The Company shall
deliver to the Trustee, within 120 days after the end of each fiscal year of the
Company ending after the date hereof, an Officers' Certificate, stating whether
or not to the best knowledge of the signers thereof the Company is in default in
the performance and observance of any of the terms, provisions and conditions of
this Indenture (without regard to any period of grace or requirement of notice
provided hereunder) and, if the Company shall be in default, specifying all such
defaults and the nature and status thereof of which they may have knowledge.

          SECTION 10.05. Existence. Subject to Article VIII, the Company shall
do or cause to be done all things necessary to preserve and keep in full force
and effect its existence, rights (charter and statutory) and franchises;
provided, however, that the Company shall not be required to preserve any such
right or franchise if the Board of Directors shall determine that the
preservation thereof is no longer desirable in the conduct of the business of
the Company and that the loss thereof is not disadvantageous in any material
respect to the Holders.

          SECTION 10.06. Maintenance of Properties. The Company shall cause all
properties used or useful in the conduct of its business or the business of any
Subsidiary to be maintained and kept in good condition, repair and working order
and supplied with all necessary equipment and shall cause to be made all
necessary repairs, renewals, replacements, betterments and improvements thereof,
all as in the judgment of the Company may be necessary so that the business
carried on in connection therewith may be properly and advantageously conducted
at all times; provided, however, that nothing in this Section 10.06 shall
prevent the Company from discontinuing the operation or maintenance of any of
such properties, or disposing of any of them, if such discontinuance or
disposition is, in the judgment of the Company, desirable in the conduct of its
business or the business of any Subsidiary and not disadvantageous in any

<PAGE>   83
                                                                              74

material respect to the Holders.

          SECTION 10.07. Payment of Taxes and Other Claims. The Company shall
pay or discharge or cause to be paid or discharged, before the same shall become
delinquent, (1) all taxes, assessments and governmental charges levied or
imposed upon the Company or any Subsidiary or upon the income, profits or
property of the Company or any Subsidiary, and (2) all lawful claims for labor,
materials and supplies which, if unpaid, might by law become a lien upon the
property of the Company or any Subsidiary; provided, however, that the Company
shall not be required to pay or discharge or cause to be paid or discharged any
such tax, assessment, charge or claim whose amount, applicability or validity is
being contested in good faith by appropriate proceedings.

          SECTION 10.08. Waiver of Certain Covenants. The Company may omit in
any particular instance to comply with any covenant or condition set forth in
Sections 10.05 to 10.07, inclusive, if before the time for such compliance the
Holders of at least a majority in principal amount of the Outstanding Securities
shall, by Act of such Holders, either waive such compliance in such instance or
generally waive compliance with such covenant or condition, but no such waiver
shall extend to or affect such covenant or condition except to the extent so
expressly waived, and, until such waiver shall become effective, the obligations
of the Company and the duties of the Trustee in respect of any such covenant or
condition shall remain in full force and effect.

          SECTION 10.09. Delivery of Certain Information. At any time when the
Company is not subject to Section 13 or 15(d) of the Exchange Act, upon the
request of a Holder or the holder of shares of Common Stock issued upon
conversion thereof, the Company shall promptly furnish or cause to be furnished
Rule 144A Information (as defined below) to such Holder or such holder of shares
of Common Stock issued upon conversion of Securities, or to a prospective
purchaser of any such security designated by any such Holder or holder, as the
case may be, to the extent required to permit compliance by such Holder or
holder with Rule 144A under the Securities Act in connection with the resale of
any such security. "Rule 144A Information" shall be such information as is
specified pursuant to Rule 144A(d)(4) under the Securities Act.

          SECTION 10.10. Resale of Certain Securities; Reporting Issuer. During
the period beginning on the last date of original issuance of the Securities and
ending on the date that is two years from such date, the Company will not, and
will use its best efforts not to permit any of its "affiliates" (as defined
under Rule 144 under the Securities Act or any successor provision thereto) to,
resell (x) any Securities which constitute "restricted securities" under
Rule 144 or (y) any securities into which the Securities have been converted
under this Indenture which constitute "restricted securities" under

<PAGE>   84

Rule 144, that in either case have been reacquired by any of them. The Trustee
shall have no responsibility in respect of the Company's performance of its
agreement in the preceding sentence.

          SECTION 10.11. Registration Rights. (a) The Company agrees that the
Holders (and any Person that has a beneficial interest in a Security) from time
to time of Transfer Restricted Securities are entitled to the benefits of a
Registration Rights Agreement, dated as of March 10, 2000 (the "Registration
Rights Agreement"), executed by the Company. Pursuant to the Registration Rights
Agreement, the Company has agreed for the benefit of the Holders from time to
time of Transfer Restricted Securities, at the Company's expense, (i) to file
within 60 days after the first date of original issuance of the Securities, a
shelf registration statement (the "Shelf Registration Statement") with the
Commission with respect to resales of the Transfer Restricted Securities, (ii)
to use its best efforts to cause such Shelf Registration Statement to be
declared effective by the Commission not later than 120 days after the first
date of original issuance of the Securities, and (iii) to use its best efforts
to maintain such Shelf Registration Statement continuously effective under the
Securities Act subject to and in accordance with the terms of the Registration
Rights Agreement.

          Additional interest (the "Additional Interest") with respect to the
Securities shall be assessed as follows if any of the following events occur
(each such event in clauses (i) through (iii) below being herein called a
"Registration Default"):

          (i)  if on or prior to the 60th day after the first date of original
     issuance of the Securities the Shelf Registration Statement has not been
     filed with the Commission;

          (ii) if on or prior to the 120th day after the first date of original
     issuance of the Securities the Shelf Registration Statement has not been
     declared effective by the Commission; or

          (iii) if after the Shelf Registration Statement is declared effective
     (A) the Shelf Registration Statement thereafter ceases to be effective; or
     (B) the Shelf Registration Statement or the related prospectus ceases to be
     usable (in each case except as permitted in the Registration Rights
     Agreement) in connection with resales of Transfer Restricted Securities in
     accordance with and during the periods specified herein because either (1)
     any event occurs as a result of which the related prospectus

<PAGE>   85
                                                                              76

     forming part of such Shelf Registration Statement would include any untrue
     statement of a material fact or omit to state any material fact necessary
     to make the statements therein in the light of the circumstances under
     which they were made not misleading, or (2) it shall be necessary to amend
     such Shelf Registration Statement or supplement the related prospectus, to
     comply with the Securities Act or the Exchange Act or the respective rules
     thereunder.

          Additional Interest shall accrue on the Securities over and above the
interest set forth in the title of the Securities from and including the date on
which any such Registration Default shall occur, to but excluding the date on
which all such Registration Defaults have been cured, at a rate of 0.50% per
annum.

          (b) Any amounts of Additional Interest due pursuant to clause (a)(i),
(a)(ii) or (a)(iii) of this Section 10.11 shall be payable in cash on the
regular Interest Payment Dates. The amount of Additional Interest shall be
determined by multiplying the applicable Additional Interest rate by the
principal amount of the Securities, multiplied by a fraction, the numerator of
which is the number of days such Additional Interest rate was applicable during
such period (determined on the basis of a 360-day year comprised of twelve
30-day months), and the denominator of which is 360.

          Whenever in this Indenture there is mentioned, in any context, the
payment of the principal of, premium, if any, or interest on, or in respect of,
any Security, such mention shall be deemed to include mention of the payment of
Additional Interest provided for in this Section to the extent that, in such
context, Additional Interest are, were or would be payable in respect thereof
pursuant to the provisions of this Section 10.11 and express mention of the
payment of Additional Interest (if applicable) in any provisions hereof shall
not be construed as excluding Additional Interest in those provisions hereof
where such express mention is not made.

                                   ARTICLE XI

                            Redemption of Securities

          SECTION 11.01. Right of Provisional Redemption. (a) The Securities may
be redeemed by the Company (a "Provisional Redemption"), in whole or in part, at
any time prior to March 21, 2003, upon notice as set forth in Section 11.06, at
a redemption price equal to $1,000 per Security to be redeemed plus accrued and
unpaid interest, if any (including Additional Interest, if any), to the date of
redemption (the "Provisional Redemption Date") if (i) the closing price of the
Common Stock shall have

<PAGE>   86
                                                                              77

exceeded 150% of the conversion price then in effect for at least 20 Trading
Days in any consecutive 30-Trading Day period ending on the Trading Day prior to
the date of mailing of the notice of redemption pursuant to Section 11.06 (the
"Redemption Notice Date") and (ii) the Shelf Registration Statement is effective
and available for use and is expected to remain effective and available for use
for the 30 days immediately following the Provisional Redemption Date. Upon any
such Provisional Redemption, the Company shall make an additional payment, at
the Company's option, in (A) cash or (B) if the conditions set forth in
paragraph (b) are met, shares of Common Stock (the "Make- Whole Payment") with
respect to the Securities called for redemption to Holders on the Redemption
Notice Date in an amount equal to $112.50 per $1,000 Security, less the amount
of any interest actually paid or accrued and unpaid on such Security prior to
the Redemption Notice Date, except that the Make-Whole Payment for any
Securities converted into Common Stock pursuant to the terms hereof after the
Redemption Notice Date and prior to the Provisional Redemption Date shall not be
reduced by any accrued and unpaid interest. The Company shall make the
Make-Whole Payment on all Securities called for Provisional Redemption,
including any Securities converted into Common Stock pursuant to the terms
hereof after the Redemption Notice Date and prior to the Provisional Redemption
Date.

          (b) The Company has the option to make the Make-Whole Payment in
shares of Common Stock if a shelf registration statement with respect to such
shares of Common Stock is effective and available for use and is expected to
remain effective and available for use for the 30 days immediately following the
Provisional Redemption Date; provided that such a shelf registration statement
shall not be required for shares of Common Stock used to make the Make-Whole
Payment to the extent such shares of Common Stock are freely tradeable and the
Company delivers to the Holders an opinion of its counsel that as of the
Provisional Redemption Date such shares of Common Stock are freely tradeable. If
the Company elects to make the Make-Whole Payment in shares of Common Stock, the
number of shares of Common Stock due to make such payments is determined by
dividing the amount of such Make-Whole Payment by the market price of the Common
Stock (valued at 97% of the average of the closing bid prices of the Common
Stock for the five Trading Days ending on the Trading Day prior to the
Redemption Date) with fractional shares to be paid in cash.

          SECTION 11.02. Right of Optional Redemption. The Securities may be
redeemed at the election of the Company (an "Optional Redemption"), as a whole
or from time to time in part, at any time on or after March 21, 2003 through
March 15, 2004 at 101.88% of the principal amount, and thereafter, at the
following Redemption Prices (expressed as percentages of the principal amount),
if redeemed during the 12-month period beginning on March 16 of the years
indicated,

<PAGE>   87
                                                                              78

<TABLE>
<CAPTION>
                                                                     Redemption
Year                                                                   Price
----                                                                 ----------
<S>                                                                   <C>
2004                                                                   101.25%
------------------------------------------------------------
2005                                                                   100.63%
------------------------------------------------------------
2006                                                                   100.00%
------------------------------------------------------------
</TABLE>

and thereafter at a Redemption Price equal to 100% of the principal amount,
together in the case of any such redemption with accrued interest to (but not
including) the Redemption Date, but interest installments whose Stated Maturity
is on or prior to such Redemption Date will be payable to the Holders of such
Securities, or one or more Predecessor Securities, of record at the close of
business on the relevant Record Dates referred to on the face hereof, all as
provided in this Indenture.

          SECTION 11.03. Applicability of Article. Redemption of Securities at
the election of the Company or otherwise, as permitted or required by any
provision of this Indenture, shall be made in accordance with such provision and
this Article XI.

          SECTION 11.04. Election to Redeem; Notice to Trustee. The election of
the Company to redeem any Securities pursuant to Section 11.01 or 11.02 shall be
evidenced by a Board Resolution. In case of any redemption at the election of
the Company, the Company shall, at least 45 days prior to the Redemption Date
fixed by the Company (unless a shorter notice shall be satisfactory to the
Trustee), notify the Trustee of such Redemption Date and of the principal amount
of Securities to be redeemed.

          SECTION 11.05. Selection by Trustee of Securities to Be Redeemed. If
less than all the Securities are to be redeemed, the particular Securities to be
redeemed shall be selected not less than 20 days or more than 60 days prior to
the Redemption Date by the Trustee, from the Outstanding Securities not
previously called for redemption, by lot or by such method as the Trustee shall
deem fair and appropriate in the circumstances and which may provide for the
selection for redemption of portions (equal to U.S.$1,000 or any integral
multiple thereof) of the principal amount of Securities of a denomination larger
than U.S.$1,000.

          If any Security selected for partial redemption is converted in part
before

<PAGE>   88
                                                                              79

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.

          The Trustee shall promptly notify the Company and each Security
Registrar in writing of the Securities selected for redemption and, in the case
of any Securities selected for partial redemption, the principal amount thereof
to be redeemed.

          For all purposes of this Indenture, unless the context otherwise
requires, all provisions relating to the redemption of Securities shall relate,
in the case of any Securities redeemed or to be redeemed only in part, to the
portion of the principal amount of such Securities which has been or is to be
redeemed.

          SECTION 11.06. Notice of Redemption. Notice of redemption shall be
given by first-class mail, postage prepaid, mailed not less than 20 nor more
than 60 days prior to the Redemption Date, to each Holder of Securities to be
redeemed, at his address appearing in the Security Register.

          All notices of redemption shall describe the Securities, including
CUSIP number, and state:

          (1) the Redemption Date;

          (2) the Redemption Price;

          (3) if less than all the Outstanding Securities are to be redeemed,
     the identification (and, in the case of partial redemption of any
     Securities, the principal amounts) of the particular Securities to be
     redeemed;

          (4) whether such redemption is a Provisional Redemption or an Optional
     Redemption;

          (5) that on the Redemption Date the Redemption Price shall become due
     and payable upon each such Security to be redeemed and that interest
     thereon shall cease to accrue on and after said date;

          (6) the conversion price, the date on which the right to convert the
     Securities to be redeemed will terminate and the place or places where such

<PAGE>   89
                                                                              80

     Securities may be surrendered for conversion;

          (7) the place or places where such Securities are to be surrendered
     for payment of the Redemption Price; and

          (8) if such a redemption is a Provisional Redemption, (i) the amount
     of the Make-Whole Payment, (ii) whether such Make-Whole Payment will be
     made in cash or shares of Common Stock (fractional shares to be paid in
     cash) and (iii) if such Make-Whole Payment is made in shares of Common
     Stock, the method according to which the number of shares of Common Stock
     is determined.

          Notice of redemption of Securities to be redeemed at the election of
the Company shall be given by the Company or, at the Company's request, by the
Trustee in the name and at the expense of the Company, and shall be irrevocable.

          SECTION 11.07. Deposit of Redemption Price. On or prior to any
Redemption Date, the Company shall deposit with the Trustee or with a Paying
Agent (or, if the Company is acting as its own Paying Agent, segregate and hold
in trust as provided in Section 10.03) (i) an amount of money sufficient to pay
the Redemption Price of, and (except if the Redemption Date shall be an Interest
Payment Date) accrued interest on, all the Securities which are to be redeemed
on that date other than any Securities called for redemption on that date which
have been converted prior to the date of such deposit and (ii) with respect to
Securities called for Provisional Redemption pursuant to Section 11.01, (A) an
amount of money or (B) a number of shares of Common Stock sufficient to make the
Make-Whole Payment for all the Securities (or portions thereof) called for
redemption (including those surrendered for conversion into Common Stock after
the Redemption Notice Date and prior to the Provisional Redemption Date);
provided that if such payment is made on the Redemption Date, it must be
received by the Trustee or Paying Agent, as the case may be, by 10:00 a.m. New
York City time on such date.

          If any Security called for redemption is converted, any money or
Common Stock, as the case may be, deposited with the Trustee or with any Paying
Agent or so segregated and held in trust for the redemption of such Security
shall (subject to any right of the Holder of such Security or any Predecessor
Security to receive interest as provided in the last paragraph of Section 3.07)
be paid to the Company as soon as practicable upon Company Request or, if then
held by the Company, shall be released from such trust;

<PAGE>   90
                                                                              81

provided that, with respect to a Provisional Redemption, any money or Common
Stock, as the case may be, so deposited for payment of the Make-Whole Payment
shall remain segregated and held in trust for payment of the Make-Whole Payment
which shall be made on all Securities called for Provisional Redemption,
including Securities converted into Common Stock after the Redemption Notice
Date and prior to the Provisional Redemption Date.

          SECTION 11.08. Securities Payable on Redemption Date. Notice of
redemption having been given as aforesaid, the Securities so to be redeemed
shall, on the Redemption Date, become due and payable at the Redemption Price
therein specified, and, with respect to Securities called for Provisional
Redemption, the Make-Whole Payment, and from and after such date (unless the
Company shall default in the payment of the Redemption Price and accrued
interest or the Make-Whole Payment, if any) such Securities shall cease to bear
or accrue any interest. Upon surrender of any such Security for redemption in
accordance with said notice, such Security shall be paid by the Company at the
Redemption Price, together with accrued interest to (but not including) the
Redemption Date and, with respect to Securities called for Provisional
Redemption (including Securities converted into Common Stock pursuant to the
terms hereof after the Redemption Notice Date and prior to the Provisional
Redemption Date), the Make- Whole Payment; provided, however, that installments
of interest whose Stated Maturity is on or prior to the Redemption Date shall be
payable to the Holders of such Securities, or one or more Predecessor
Securities, registered as such at the close of business on the relevant Record
Dates according to their terms and the provisions of Section 3.07; and provided
further that, with respect to a Provisional Redemption, the holder of any
Securities converted into Common Stock pursuant to the terms of this Indenture
after the Redemption Notice Date and prior to the Provisional Redemption Date
shall have the right to the Make-Whole Payment, if any, with respect to such
Securities regardless of the conversion of such Securities.

          If the Company shall fail to deposit the Redemption Price (and Make-
Whole Payment, if any) with the Trustee and any Security called for redemption
shall not be so paid upon surrender thereof for redemption, the principal and
premium, if any (including the amount of the Make-Whole Payment on the
Redemption Date, if any), shall, until paid, bear and accrue interest from the
Redemption Date at the rate borne by the Security.

          SECTION 11.09. Securities Redeemed in Part. Any Security which is to
be redeemed only in part shall be surrendered at an office or agency of the
Company designated for that purpose pursuant to Section 10.02 (with, if the
Company or the Trustee so requires, due endorsement by, or a written instrument
of transfer in form

<PAGE>   91
                                                                              82

satisfactory to the Company and the Trustee duly executed by, the Holder thereof
or his attorney-in-fact duly authorized in writing), and the Company 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 equal to
and in exchange for the unredeemed portion of the principal amount of the
Security so surrendered.

          SECTION 11.10. Conversion Arrangement on Call for Redemption. In
connection with any redemption of Securities, the Company may arrange for the
purchase and conversion of any Securities by an agreement with one or more
investment bankers or other purchasers to purchase such Securities by paying to
the Trustee in trust for the Holders, on or before the Redemption Date, an
amount not less than the applicable Redemption Price of such Securities,
together with interest accrued to the Redemption Date, and, in connection with a
Provisional Redemption, the Make-Whole Payment. Notwithstanding anything to the
contrary contained in this Article XI, the obligation of the Company to pay the
Redemption Price of such Securities, together with interest accrued to, but
excluding, the Redemption Date and, in connection with a Provisional Redemption,
the Make-Whole Payment, 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, a copy of which shall be filed with the Trustee prior to the
Redemption Date, any Securities not duly surrendered for conversion by the
holders thereof may, at the option of the Company, 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 XIII) surrendered
by such purchasers for conversion, all as of immediately prior to the close of
business on the Redemption Date (and the right to convert any such Securities
shall be deemed to have been extended through such time), subject to payment of
the above amount as aforesaid (including the Make-Whole Payment, if any, with
respect to all Securities called for Provisional Redemption). At the direction
of the Company, the Trustee shall hold and dispose of any such amount paid to it
in the same manner as it would monies deposited with it by the Company for the
redemption of Securities. Without the Trustee's prior written consent, no
arrangement between the Company 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 Company 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 Company and such purchasers to which the Trustee has not
consented in writing, 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

<PAGE>   92
                                                                              83

Indenture. Nothing in the preceding sentence shall be deemed to limit the rights
and protections afforded to the Trustee in Article VI hereof, including, but not
limited to, the right to indemnification pursuant to Section 6.07.

                                   ARTICLE XII

                           Subordination of Securities

          SECTION 12.01. Securities Subordinate to Senior Indebtedness. The
Company covenants and agrees, and each Holder of a Security, by his acceptance
thereof, likewise covenants and agrees, that, to the extent and in the manner
hereinafter set forth in this Article XII, the indebtedness represented by the
Securities and the payment of the principal of and premium, if any (including
the Make-Whole Payment, if any), and interest on each and all of the Securities
and all obligations of the Company under this Indenture are hereby expressly
made subordinate and subject in right of payment to the prior payment in full of
all Senior Indebtedness.

          SECTION 12.02. Payment over of Proceeds Upon Dissolution, Etc. In the
event of (a) any insolvency or bankruptcy case or proceeding, or any
receivership, liquidation, reorganization or other similar case or proceeding in
connection therewith, relative to the Company or to its creditors, as such, or
to its assets, or (b) any liquidation, dissolution or other winding-up of the
Company, whether voluntary or involuntary and whether or not involving
insolvency or bankruptcy, or (c) any assignment for the benefit of creditors or
any other marshalling of assets and liabilities of the Company, then and in any
such event the holders of Senior Indebtedness shall be entitled to receive
payment in full of all amounts due or to become due on or in respect of all
Senior Indebtedness, or provision shall be made for such payment in cash or cash
equivalents or otherwise in a manner satisfactory to the holders of Senior
Indebtedness, before the Holders of the Securities are entitled to receive any
payment on account of principal of or premium, if any (including the Make-Whole
Payment, if any), or interest on the Securities, and to that end the holders of
Senior Indebtedness shall be entitled to receive, for application to the payment
thereof, any payment or distribution of any kind or character, whether in cash,
property or securities, which may be payable or deliverable in respect of the
Securities in any such case, proceeding, dissolution, liquidation or other
winding-up or event.

          In the event that, notwithstanding the foregoing provisions of this

<PAGE>   93
                                                                              84

Section 12.02, the Trustee or the Holder of any Security shall have received any
payment or distribution of assets of the Company prohibited by the foregoing
paragraph of any kind or character, whether in cash, property or securities,
before all Senior Indebtedness is paid in full or payment thereof provided for,
and if such fact shall, at or prior to the time of such payment or distribution,
have been made actually known to a Responsible Officer of the Trustee or, as the
case may be, such Holder, then and in such event such payment or distribution
shall be paid over or delivered forthwith to the trustee in bankruptcy,
receiver, liquidating trustee, custodian, assignee, agent or other Person making
payment or distribution of assets of the Company for application to the payment
of all Senior Indebtedness remaining unpaid, to the extent necessary to pay all
Senior Indebtedness in full, after giving effect to any concurrent payment or
distribution to or for the holders of Senior Indebtedness.

          For purposes of this Article XII only, the words "cash, property or
securities" shall not be deemed to include shares of capital stock of the
Company as reorganized or readjusted, or securities of the Company or any other
corporation provided for by a plan of reorganization or readjustment which in
either case are subordinated in right of payment to all Senior Indebtedness
which may at the time be outstanding to substantially the same extent as, or to
a greater extent than, the Securities are so subordinated as provided in this
Article XII. The consolidation of the Company with, or the merger of the Company
into, another Person or the liquidation or dissolution of the Company following
the conveyance or transfer of its properties and assets substantially as an
entirety to another Person upon the terms and conditions set forth in Article
VIII shall not be deemed a dissolution, winding-up, liquidation, reorganization,
assignment for the benefit of creditors or marshalling of assets and liabilities
of the Company for the purposes of this Section 12.02 if the Person formed by
such consolidation or into which the Company is merged or which acquires by
conveyance or transfer such properties and assets substantially as an entirety,
as the case may be, shall, as a part of such consolidation, merger, conveyance
or transfer, comply with the conditions set forth in Article VIII.

          SECTION 12.03. No Payment When Senior Indebtedness in Default. (a) In
the event and during the continuation of any default in the payment of principal
of or premium, if any (including the Make-Whole Payment, if any), or interest on
any Senior Indebtedness beyond any applicable grace period with respect thereto
(unless and until such payment default shall have been cured or waived in
writing by the holders of such Senior Indebtedness), or (b) in the event any
judicial proceeding shall be pending with respect to any such default, then no
payment shall be made by the Company on account of principal of or premium, if
any (including the Make-Whole Payment, if any), or interest on the Securities or
on account of the purchase or other acquisition of

<PAGE>   94
                                                                              85

Securities (including pursuant to Articles XI and XIII).

          In the event that, notwithstanding the foregoing, the Company shall
make any payment to the Trustee or the Holder of any Security prohibited by the
foregoing provisions of this Section 12.03, and if such fact shall, at or prior
to the time of such payment, have been made actually known to a Responsible
Officer of the Trustee or, as the case may be, such Holder, then and in such
event such payment shall be paid over and delivered forthwith to the Company.

          The provisions of this Section 12.03 shall not apply to any payment
with respect to which Section 12.02 would be applicable.

          SECTION 12.04. Payment Permitted If No Default. Nothing contained in
this Article XII or elsewhere in this Indenture or in any of the Securities
shall prevent (a) the Company, at any time except during the pendency of any
case, proceeding, dissolution, liquidation or other winding-up, assignment for
the benefit of creditors or other marshalling of assets and liabilities of the
Company referred to in Section 12.02 or under the conditions described in
Section 12.03, from making payments at any time of principal of and premium, if
any (including the Make-Whole Payment, if any), or interest on the Securities,
or (b) the application by the Trustee of any money deposited with it hereunder
to the payment of or on account of the principal of and premium, if any
(including the Make-Whole Payment, if any), or interest on the Securities or the
retention of such payment by the Holders, if, at the time of such application by
the Trustee, a Responsible Officer of the Trustee did not have actual knowledge
that such payment would have been prohibited by the provisions of this Article
XII.

          SECTION 12.05. Subrogation to Rights of Holders of Senior
Indebtedness. Subject to the payment in full of all Senior Indebtedness, and
until the Securities are paid in full, the Holders of the Securities shall be
subrogated (equally and ratably with the holders of all indebtedness of the
Company which by its express terms is subordinated to indebtedness of the
Company to substantially the same extent as the Securities are subordinated and
is entitled to like rights of subrogation) to the rights of the holders of such
Senior Indebtedness to receive payments and distributions of cash, property and
securities applicable to the Senior Indebtedness to the extent that payments and
distributions otherwise payable to Holders of Securities have been applied to
the payment of Senior Indebtedness as provided by this Article XII. For purposes
of such subrogation, no payments or distributions to the holders of the Senior
Indebtedness of any

<PAGE>   95
                                                                              86

cash, property or securities to which the Holders of the Securities or the
Trustee would be entitled, except for the provisions of this Article XII, and no
payments over pursuant to the provisions of this Article XII to the holders of
Senior Indebtedness by Holders of the Securities or the Trustee, shall, as among
the Company, its creditors other than holders of Senior Indebtedness and the
Holders of the Securities, be deemed to be a payment or distribution by the
Company to or on account of the Senior Indebtedness.

          SECTION 12.06. Provisions Solely To Define Relative Rights. The
provisions of this Article XII are and are intended solely for the purpose of
defining the relative rights of the Holders of the Securities on the one hand
and the holders of Senior Indebtedness on the other hand. Nothing contained in
this Article XII or elsewhere in this Indenture or in the Securities is intended
to or shall

          (a) impair, as among the Company, its creditors other than holders of
     Senior Indebtedness and the Holders of the Securities, the obligation of
     the Company, which is absolute and unconditional (and which, subject to the
     rights under this Article XII of the holders of Senior Indebtedness, is
     intended to rank equally with all other general obligations of the
     Company), to pay to the Holders of the Securities the principal of and
     premium, if any (including the Make-Whole Payment, if any), and interest on
     the Securities as and when the same shall become due and payable in
     accordance with their terms; or

          (b) affect the relative rights against the Company of the Holders of
     the Securities and creditors of the Company other than the holders of
     Senior Indebtedness; or

          (c) prevent the Trustee or the Holder of any Security from exercising
     all remedies otherwise permitted by applicable law upon default under this
     Indenture, subject to the rights, if any, under this Article XII of the
     holders of Senior Indebtedness to receive cash, property and securities
     otherwise payable or deliverable to the Trustee or such Holder.

          SECTION 12.07. Trustee to Effectuate Subordination. Each Holder of a
Security by his acceptance thereof authorizes and directs the Trustee on his
behalf to take such action as may be necessary or appropriate to effectuate the
subordination provided in this Article XII and appoints the Trustee his
attorney-in-fact for any and all such purposes.

          SECTION 12.08. No Waiver of Subordination Provisions. No right of any
present or future holder of any Senior Indebtedness to enforce subordination as
herein

<PAGE>   96
                                                                              87

provided shall at any time in any way be prejudiced or impaired by any act or
failure to act on the part of the Company or by any act or failure to act, in
good faith, by any such holder, or by any non-compliance by the Company with the
terms, provisions and covenants of this Indenture, regardless of any knowledge
thereof any such holder may have or be otherwise charged with.

          Without in any way limiting the generality of the foregoing paragraph,
the holders of Senior Indebtedness may, at any time and from time to time,
without the consent of or notice to the Trustee or the Holders of the
Securities, without incurring responsibility to the Holders of the Securities
and without impairing or releasing the subordination provided in this Article
XII or the obligations hereunder of the Holders of the Securities to the holders
of Senior Indebtedness, do any one or more of the following:

          (i) change the manner, place or terms of payment or extend the time of
     payment of, or renew or alter, Senior Indebtedness, or otherwise amend or
     supplement in any manner Senior Indebtedness or any instrument evidencing
     the same or any agreement under which Senior Indebtedness is outstanding;

          (ii) sell, exchange, release or otherwise deal with any property
     pledged, mortgaged or otherwise securing Senior Indebtedness;

          (iii) release any Person liable in any manner for the collection of
     Senior Indebtedness;

          (iv) exercise or refrain from exercising any rights against the
     Company and any other Person;

          (v) apply any and all sums received from time to time to the Senior
     Indebtedness.

          SECTION 12.09. Notice to Trustee. The Company shall give prompt
written notice to the Trustee of any fact known to the Company which would
prohibit the making of any payment to or by the Trustee in respect of the
Securities. Notwithstanding the provisions of this Article XII or any other
provision of this Indenture, the Trustee shall not be charged with knowledge of
the existence of any facts which would prohibit the making of any payment to or
by the Trustee in respect of the Securities, unless and until the Trustee shall
have received written notice thereof from the Company or a holder of Senior
Indebtedness or from any trustee therefor; and, prior to the receipt of any such
written notice, the Trustee, subject to the provisions of Section 6.01, shall be
entitled in all respects to assume that no such facts exist; provided, however,
that if the Trustee shall

<PAGE>   97
                                                                              88

not have received the notice provided for in this Section 12.09 at least two
Business Days prior to the date upon which by the terms hereof any money may
become payable for any purpose (including, without limitation, the payment of
the principal of and premium, if any (including the Make-Whole Payment, if any),
or interest on any Security), then, anything herein contained to the contrary
notwithstanding, the Trustee shall have full power and authority to receive such
money and to apply the same to the purpose for which such money was received and
shall not be affected by any notice to the contrary which may be received by it
within two Business Days prior to such date.

          Subject to the provisions of Section 6.01, the Trustee shall be
entitled to rely on the delivery to it of a written notice by a Person
representing himself to be a holder of Senior Indebtedness (or a trustee
therefor) to establish that such notice has been given by a holder of Senior
Indebtedness (or a trustee therefor). In the event that the Trustee determines
in good faith that further evidence is required with respect to the right of any
Person as a holder of Senior Indebtedness to participate in any payment or
distribution pursuant to this Article XII, the Trustee may request such Person
to furnish evidence to the reasonable satisfaction of the Trustee as to the
amount of Senior Indebtedness held by such Person, the extent to which such
Person is entitled to participate in such payment or distribution and any other
facts pertinent to the rights of such Person under this Article XII, and if such
evidence is not furnished, the Trustee may defer any payment to such Person
pending judicial determination as to the right of such Person to receive such
payment.

          SECTION 12.10. Reliance on Judicial Order or Certificate of
Liquidating Agent. Upon any payment or distribution of assets of the Company
referred to in this Article XII, the Trustee, subject to the provisions of
Section 6.01, and the Holders of the Securities shall be entitled to rely upon
any order or decree entered by any court of competent jurisdiction in which such
insolvency, bankruptcy, receivership, liquidation, reorganization, dissolution,
winding up or similar case or proceeding is pending, or a certificate of the
trustee in bankruptcy, receiver, liquidating trustee, custodian, assignee for
the benefit of creditors, agent or other Person making such payment or
distribution, delivered to the Trustee or to the Holders of Securities, for the
purpose of ascertaining the Persons entitled to participate in such payment or
distribution, the holders of the Senior Indebtedness and other indebtedness of
the Company, the amount thereof or payable thereon, the amount or amounts paid
or distributed thereon and all other facts pertinent thereto or to this Article
XII.

<PAGE>   98
                                                                              89

          SECTION 12.11. Trustee Not Fiduciary for Holders of Senior
Indebtedness. The Trustee shall not be deemed to owe any fiduciary duty to the
holders of Senior Indebtedness and shall not be liable to any such holders if it
shall in good faith mistakenly pay over or distribute to Holders of Securities
or to the Company or to any other Person cash, property or securities to which
any holders of Senior Indebtedness shall be entitled by virtue of this Article
XII or otherwise.

          SECTION 12.12. Rights of Trustee as Holder of Senior Indebtedness;
Preservation of Trustee's Rights. The Trustee in its individual capacity shall
be entitled to all the rights set forth in this Article XII with respect to any
Senior Indebtedness which may at any time be held by it, to the same extent as
any other holder of Senior Indebtedness, and nothing in this Indenture shall
deprive the Trustee of any of its rights as such holder.

          Nothing in this Article XII shall apply to claims of, or payments to,
the Trustee under or pursuant to Section 6.07.

          SECTION 12.13. Article Applicable to Paying Agents. In case at any
time any Paying Agent other than the Trustee shall have been appointed by the
Company and be then acting hereunder, the term "Trustee" as used in this Article
XII shall in such case (unless the context otherwise requires) be construed as
extending to and including such Paying Agent within its meaning as fully for all
intents and purposes as if such Paying Agent were named in this Article XII in
addition to or in place of the Trustee; provided, however, that Section 12.12
shall not apply to the Company or any Affiliate of the Company if it or such
Affiliate acts as Paying Agent.

          SECTION 12.14. Certain Conversions Deemed Payment. For the purposes of
this Article XII only, (1) the issuance and delivery of junior securities upon
conversion of Securities in accordance with Article XIII shall not be deemed to
constitute a payment or distribution on account of the principal of or premium
or interest on Securities or on account of the purchase or other acquisition of
Securities, and (2) the payment, issuance or delivery of cash, property or
securities (other than junior securities) upon conversion of a Security shall be
deemed to constitute payment on account of the principal of such Security. For
the purposes of this Section 12.14, the term "junior securities" means (a)
shares of any stock of any class of the Company and (b) securities of the
Company which are subordinated in right of payment to the prior payment in full
of all Senior Indebtedness which may be outstanding at the time of issuance or
delivery of such securities to substantially the same extent as, or to a greater
extent than, the Securities are so subordinated as provided in this Article XII.
Nothing contained in this Article XII or elsewhere in this Indenture or in the
Securities is intended to or shall

<PAGE>   99
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impair, as among the Company, its creditors other than holders of Senior
Indebtedness and the Holders of the Securities, the right, which is absolute and
unconditional, of the Holder of any Security to convert such Security in
accordance with Article XIII.

                                  ARTICLE XIII

                            Conversion of Securities

          SECTION 13.01. Conversion Privilege and Conversion Price. Subject to
and upon compliance with the provisions of this Article XIII, at the option of
the Holder thereof, any Security or any portion of the principal amount thereof
which is U.S.$1,000 or an integral multiple of U.S.$1,000 may be converted at
the principal amount thereof, or of such portion thereof, into fully paid and
nonassessable shares of Common Stock of the Company at any time following the
latest date of original issuance of Securities at the conversion price,
determined as hereinafter provided, in effect at the time of conversion. Such
conversion right shall expire at the close of business on the Business Day
immediately preceding March 15, 2007, subject, in the case of conversion of any
Global Security, to any Applicable Procedures. In case a Security or portion
thereof is called for redemption at the election of the Company or the Holder
thereof exercised his right to require the Company to repurchase the Security,
such conversion right in respect of the Security or portion so called shall
expire at the close of business, New York or time, on the Business Day
immediately preceding the corresponding Redemption Date or Repurchase Date, as
the case may be, unless the Company defaults in making the payment due upon
redemption or repurchase, as the case may be (in each case subject as aforesaid
to any Applicable Procedures with respect to any Global Security).

          The price at which shares of Common Stock shall be delivered upon
conversion (herein called the "conversion price") shall be initially U.S.$219.00
per share of Common Stock. The conversion price shall be adjusted in certain
instances as provided in Section 13.04.

          In case the Company shall, by dividend or otherwise, declare or make a
distribution on its Common Stock referred to in paragraph (4) or (5) of Section
13.04 (including, without limitation, dividends or distributions referred to in
the last sentence of paragraph (4) of Section 13.04), the Holder of each
Security, upon the conversion thereof pursuant to this Article XIII subsequent
to the close of business on the date fixed for the

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                                                                              91

determination of shareholders entitled to receive such distribution and prior to
the effectiveness of the conversion price adjustment in respect of such
distribution pursuant to paragraph (4) or (5) of Section 13.04, shall also be
entitled to receive for each share of Common Stock into which such Security is
converted, the portion of the evidences of indebtedness, shares of capital
stock, securities, cash and other property so distributed applicable to one
share of Common Stock; provided, however, that, at the election of the Company
(whose election shall be evidenced by a Board Resolution) with respect to all
Holders so converting, the Company may, in lieu of distributing to such Holder
any portion of such distribution not consisting of cash or securities of the
Company, pay such Holder an amount in cash equal to the fair market value
thereof (as determined in good faith by the Board of Directors, whose
determination shall be conclusive and described in a Board Resolution). If any
conversion of a Security described in the immediately preceding sentence occurs
prior to the payment date for a distribution to holders of Common Stock which
the Holder of the Security so converted is entitled to receive in accordance
with the immediately preceding sentence, the Company may elect (such election to
be evidenced by a Board Resolution) to distribute to such Holder a due bill for
the evidences of indebtedness, shares of capital stock, securities, cash or
assets to which such Holder is so entitled; provided that such due bill (i)
meets any applicable requirements of the principal national securities exchange
or other market on which the Common Stock is then traded and (ii) requires
payment or delivery of such evidences of indebtedness, shares of capital stock,
securities, cash or assets no later than the date of payment or delivery thereof
to holders of Common Stock receiving such distribution.

          SECTION 13.02. Exercise of Conversion Privilege. In order to exercise
the conversion privilege, the Holder of any Security to be converted shall
surrender such Security, duly endorsed or assigned to the Company or in blank,
at any office or agency maintained by the Company pursuant to Section 10.02,
accompanied by (a) written notice (as set forth in Section 2.05 herein) to the
Company at such office or agency that the Holder elects to convert such Security
or, if less than the entire principal amount thereof is to be converted, the
portion thereof to be converted and (b) if shares or any portion of such
Security not to be converted are to be issued in the name of a Person other than
the Holder thereof, and the restrictions on transfer of such Security, set forth
in the first paragraph of Section 2.02 remain in effect, a certification of the
Holder as to compliance with such restrictions (as set forth in Section 2.06).

          If the restrictions on transfer of a Security set forth in the first
paragraph of Section 2.02 remain in effect, all shares of Common Stock delivered
upon conversion thereof shall bear a restrictive legend substantially in the
form of such paragraph.

          Except as described in the last paragraph of Section 3.07, no Holder
of

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                                                                              92

Securities will be entitled upon conversion thereof to any payment or adjustment
on account of accrued and unpaid interest thereon or on account of dividends on
the shares of Common Stock issued in connection therewith. Securities
surrendered for conversion during the period from the close of business on any
Regular Record Date to the opening of business on the corresponding Interest
Payment Date (except Securities called for redemption on a Redemption Date
within such period between and including such Regular Record Date and such
Interest Payment Date) must be accompanied by payment to the Company in New York
Clearing House Funds or other funds acceptable to the Company of an amount equal
to the interest payable on such Interest Payment Date on the principal amount
converted.

          Securities shall be deemed to have been converted immediately prior to
the close of business on the day of surrender of such Securities for conversion
in accordance with the foregoing provisions, and at such time the rights of the
Holders of such Securities as Holders shall cease, and the Person or Persons
entitled to receive the Common Stock issuable upon conversion shall be treated
for all purposes as the record holder or holders of such Common Stock at such
time. As promptly as practicable on or after the conversion date, the Company
shall issue and shall deliver at such office or agency a certificate or
certificates for the number of full shares of Common Stock issuable upon
conversion, together with payment in lieu of any fraction of a share as provided
in Section 13.03.

          In the case of any Security which is converted in part only, upon such
conversion the Company shall execute and the Trustee shall authenticate and
deliver to the Holder thereof, at the expense of the Company, a new Security or
Securities of authorized denominations in aggregate principal amount equal to
the unconverted portion of the principal amount of such Security. Any
requirements for notice, surrender or delivery of Securities pursuant to this
Article XIII shall, with respect to any Global Security, be subject to any
Applicable Procedures.

          SECTION 13.03. Fractions of Shares. No fractional shares of Common
Stock shall be issued upon conversion of Securities. If more than one Security
shall be surrendered for conversion at one time by the same Holder, the number
of full shares which shall be issuable upon conversion thereof shall be computed
on the basis of the aggregate principal amount of the Securities (or specified
portions thereof) so surrendered. Instead of any fractional share of Common
Stock which would otherwise be issuable upon conversion of any Security or
Securities (or specified portions thereof), the Company shall pay a cash
adjustment in respect of such fraction in an amount equal to the same fraction
of the Closing Price per share of the Common Stock at the close of business on
the day of conversion (or, if such day is not a Trading Day, on the Trading

<PAGE>   102
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Day immediately preceding such day) or, alternatively, the Company shall round
up to the next higher whole share.

          SECTION 13.04. Adjustment of Conversion Price. (1) In case the Company
shall pay or make a dividend or other distribution on its Common Stock
exclusively in Common Stock, the conversion price in effect at the opening of
business on the day next following the date fixed for the determination of
shareholders entitled to receive such dividend or other distribution shall be
reduced by multiplying such conversion price by a fraction of which the
numerator shall be the number of shares of Common Stock outstanding at the close
of business on the date fixed for such determination and the denominator shall
be the sum of such number of shares and the total number of shares constituting
such dividend or other distribution, such reduction to become effective
immediately after the opening of business on the day next following the date
fixed for such determination. For the purposes of this paragraph (1), the number
of shares of Common Stock at any time outstanding shall not include shares held
in the treasury of the Company but shall include shares issuable in respect of
scrip certificates issued in lieu of fractions of shares of Common Stock. The
Company shall not pay any dividend or make any distribution on shares of Common
Stock held in the treasury of the Company.

          (2) In case the Company shall pay or make a dividend or other
distribution on its Common Stock consisting exclusively of, or shall otherwise
issue to all holders of its Common Stock, rights, warrants or options entitling
the holders thereof to subscribe for or purchase shares of Common Stock at a
price per share less than the current market price per share (determined as
provided in paragraph (7) of this Section 13.04) of the Common Stock on the date
fixed for the determination of shareholders entitled to receive such rights,
warrants or options, the conversion price in effect at the opening of business
on the day following the date fixed for such determination shall be reduced by
multiplying such conversion price by a fraction of which the numerator shall be
the number of shares of Common Stock outstanding at the close of business on the
date fixed for such determination plus the number of shares of Common Stock
which the aggregate of the offering price of the total number of shares of
Common Stock so offered for subscription or purchase would purchase at such
current market price and the denominator shall be the number of shares of Common
Stock outstanding at the close of business on the date fixed for such
determination plus the number of shares of Common Stock so offered for
subscription or purchase, such reduction to become effective immediately after
the opening of business on the day

<PAGE>   103
                                                                              94

following the date fixed for such determination. For the purposes of this
paragraph (2), the number of shares of Common Stock at any time outstanding
shall not include shares held in the treasury of the Company but shall include
shares issuable in respect of scrip certificates issued in lieu of fractions of
shares of Common Stock. The Company shall not issue any rights, warrants or
options in respect of shares of Common Stock held in the treasury of the
Company.

          (3) In case outstanding shares of Common Stock shall be subdivided
into a greater number of shares of Common Stock, the conversion price in effect
at the opening of business on the day following the day upon which such
subdivision becomes effective shall be proportionately reduced, and, conversely,
in case outstanding shares of Common Stock shall each be combined into a smaller
number of shares of Common Stock, the conversion price in effect at the opening
of business on the day following the day upon which such combination becomes
effective shall be proportionately increased, such reduction or increase, as the
case may be, to become effective immediately after the opening of business on
the day following the day upon which such subdivision or combination becomes
effective.

          (4) Subject to the last sentence of this paragraph (4), in case the
Company shall, by dividend or otherwise, distribute to all holders of its Common
Stock evidences of its indebtedness, shares of any class of capital stock,
securities, cash or property (excluding any rights, warrants or options referred
to in paragraph (2) of this Section 13.04, any dividend or distribution paid
exclusively in cash and any dividend or distribution referred to in paragraph
(1) of this Section 13.04), the conversion price shall be reduced so that the
same shall equal the price determined by multiplying the conversion price in
effect immediately prior to the effectiveness of the conversion price reduction
contemplated by this paragraph (4) by a fraction of which the numerator shall be
the current market price per share (determined as provided in paragraph (7) of
this Section 13.04) of the Common Stock on the date of such effectiveness less
the fair market value (as determined in good faith by the Board of Directors,
whose determination shall be conclusive and described in a Board Resolution and
shall, in the case of securities being distributed for which prior thereto there
is an actual or when issued trading market, be no less than the value determined
by reference to the average of the closing prices in such market over the period
specified in the succeeding sentence), on the date of such effectiveness, of the
portion of the evidences of indebtedness, shares of capital stock, securities,
cash and property so distributed applicable to one share of Common Stock and the
denominator shall be such current market price per share of the Common Stock,
such reduction to become effective immediately prior to the opening of business
on the day next following the later of (a) the date fixed for the payment of
such distribution and (b) the date 20 days after the notice relating to such
distribution is given pursuant to

<PAGE>   104
                                                                              95

Section 13.06(a) (such later date of (a) and (b) being referred to as the
"Reference Date"). If the Board of Directors determines the fair market value of
any distribution for purposes of this paragraph (4) by reference to the actual
or when issued trading market for any securities comprising such distribution,
it must in doing so consider the prices in such market over the same period used
in computing the current market price per share pursuant to paragraph (7) of
this Section. For purposes of this paragraph (4), any dividend or distribution
that includes shares of Common Stock or rights, warrants or options to subscribe
for or purchase shares of Common Stock shall be deemed instead to be (a) a
dividend or distribution of the evidences of indebtedness, cash, property,
shares of capital stock or securities other than such shares of Common Stock or
such rights, warrants or options (making any conversion price reduction required
by this paragraph (4)) immediately followed by (b) a dividend or distribution of
such shares of Common Stock or such rights (making any further conversion price
reduction required by paragraph (1) or (2) of this Section 13.04, except (i) the
Reference Date of such dividend or distribution as defined in this paragraph (4)
shall be substituted as "the date fixed for the determination of shareholders
entitled to receive such dividend or other distributions", "the date fixed for
the determination of shareholders entitled to receive such rights, warrants or
options" and "the date fixed for such determination" within the meaning of
paragraphs (1) and (2) of this Section 13.04 and (ii) any shares of Common Stock
included in such dividend or distribution shall not be deemed "outstanding at
the close of business on the date fixed for such determination" within the
meaning of paragraph (1) of this Section 13.04).

          (5) In case the Company shall, by dividend or otherwise, make a
distribution to all holders of its Common Stock exclusively in cash in an
aggregate amount that, together with (i) the aggregate amount of any other
distributions to all holders of its Common Stock made exclusively in cash within
the 12 months preceding the date of payment of such distribution and in respect
of which no conversion price adjustment pursuant to this paragraph (5) has been
made and (ii) the aggregate of any cash plus the fair market value (as
determined in good faith by the Board of Directors, whose determination shall be
conclusive and described in a Board Resolution), as of the expiration of the
tender or exchange offer referred to below, of consideration payable in respect
of any tender or exchange offer by the Company or a Subsidiary for all or any
portion of the Common Stock concluded within the 12 months preceding the date of
payment of such distribution and in respect of which no conversion price
adjustment pursuant to paragraph (6) of this Section 13.04 has been made,
exceeds 12.5% of the product of the current market price per share (determined
as provided in paragraph (7) of

<PAGE>   105
                                                                              96

this Section 13.04) of the Common Stock on the date fixed for shareholders
entitled to receive such distribution times the number of shares of Common Stock
outstanding on such date, the conversion price shall be reduced so that the same
shall equal the price determined by multiplying the conversion price in effect
immediately prior to the effectiveness of the conversion price reduction
contemplated by this paragraph (5) by a fraction of which the numerator shall be
the current market price per share (determined as provided in paragraph (7) of
this Section 13.04) of the Common Stock on the date of such effectiveness less
the amount of cash so distributed applicable to one share of Common Stock and
the denominator shall be such current market price per share of the Common
Stock, such reduction to become effective immediately prior to the opening of
business on the later of (a) the day following the date fixed for the payment of
such distribution and (b) the date 20 days after the notice relating to such
distribution is given pursuant to Section 13.06(a).

          (6) In case a successful tender or exchange offer made by the Company
or any Subsidiary for all or any portion of the Common Stock shall involve an
aggregate consideration having a fair market value (as determined in good faith
by the Board of Directors, whose determination shall be conclusive and described
in a Board Resolution) at the last time (the "Expiration Time") tenders or
exchanges may be made pursuant to such tender or exchange offer (as it may be
amended) that, together with (i) the aggregate of the cash plus the fair market
value (as determined in good faith by the Board of Directors, whose
determination shall be conclusive and described in a Board Resolution), as of
the expiration of the other tender or exchange offer referred to below, of
consideration payable in respect of any other tender or exchange offer by the
Company or a Subsidiary for all or any portion of the Common Stock concluded
within the preceding 12 months and in respect of which no conversion price
adjustment pursuant to this paragraph (6) has been made and (ii) the aggregate
amount of any distributions to all holders of the Common Stock made exclusively
in cash within the preceding 12 months and in respect of which no conversion
price adjustment pursuant to paragraph (5) of this Section 13.04 has been made,
exceeds 12.5% of the product of the current market price per share (determined
as provided in paragraph (7) of this Section 13.04) of the Common Stock on the
Expiration Time times the number of shares of Common Stock outstanding
(including any tendered shares) on the Expiration Time, the conversion price
shall be reduced (but not increased) so that the same shall equal the price
determined by multiplying the conversion price in effect immediately prior to
the Expiration Time by a fraction of which the numerator shall be (i) the
product of the current market price per share (determined as provided in
paragraph (7) of this Section 13.04) of the Common Stock at the Expiration Time
times the number of shares of Common Stock outstanding (including any tendered
or exchanged shares) at the Expiration Time minus (ii) the fair
market value (determined as aforesaid) of the aggregate consideration payable to

<PAGE>   106
                                                                              97

shareholders based on the acceptance (up to any maximum specified in the terms
of the tender or exchange offer) of all shares validly tendered or exchanged and
not withdrawn as of the Expiration Time (the shares deemed so accepted, up to
any such maximum, being referred to as the "Purchased Shares") and the
denominator shall be the product of (i) such current market price per share at
the Expiration Time times (ii) such number of outstanding shares at the
Expiration Time less the number of Purchased Shares, such reduction to become
effective immediately prior to the opening of business on the day following the
Expiration Time.

          (7) For the purpose of any computation under this paragraph and
paragraphs (2), (4) and (5) of this Section 13.04, the current market price per
share of Common Stock on any date in question shall be deemed to be the average
of the daily Closing Prices for the 5 consecutive Trading Days selected by the
Company commencing not more than 20 Trading Days before, and ending not later
than, the date in question; provided, however, that (i) if the "ex" date (as
hereinafter defined) for any event (other than the issuance or distribution
requiring such computation) that requires an adjustment to the conversion price
pursuant to paragraph (1), (2), (3), (4), (5) or (6) above ("Other Event")
occurs on or after the 20th Trading Day prior to the date in question and prior
to the "ex" date for the issuance or distribution requiring such computation
(the "Current Event"), the Closing Price for each Trading Day prior to the "ex"
date for such Other Event shall be adjusted by multiplying such Closing Price by
the same fraction by which the conversion price is so required to be adjusted as
a result of such Other Event, (ii) if the "ex" date for any Other Event occurs
after the "ex" date for the Current Event and on or prior to the date in
question, the Closing Price for each Trading Day on and after the "ex" date for
such Other Event shall be adjusted by multiplying such Closing Price by the
reciprocal of the fraction by which the conversion price is so required to be
adjusted as a result of such Other Event, (iii) if the "ex" date for any Other
Event occurs on the "ex" date for the Current Event, one of those events shall
be deemed for purposes of clauses (i) and (ii) of this proviso to have an "ex"
date occurring prior to the "ex" date for the other event, and (iv) if the "ex"
date for the Current Event is on or prior to the date in question, after taking
into account any adjustment required pursuant to clause (ii) of this proviso,
the Closing Price for each Trading Day on or after such "ex" date shall be
adjusted by adding thereto the amount of any cash and the fair market value on
the date in question (as determined in good faith by the Board of Directors in a
manner consistent with any determination of such value for purposes of paragraph
(4) or (5) of this Section 13.04, whose determination shall be conclusive and
described in a Board Resolution) of the portion of the rights, warrants,
options, evidences of indebtedness, shares of capital stock,

<PAGE>   107
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securities, cash or property being distributed applicable to one share of Common
Stock. For the purpose of any computation under paragraph (6) of this Section
13.04, the current market price per share of Common Stock on any date in
question shall be deemed to be the average of the daily Closing Prices for the 5
consecutive Trading Days selected by the Company commencing on or after the
latest (the "Commencement Date") of (i) the date 20 Trading Days before the date
in question, (ii) the date of commencement of the tender or exchange offer
requiring such computation and (iii) the date of the last amendment, if any, of
such tender or exchange offer involving a change in the maximum number of shares
for which tenders are sought or a change in the consideration offered, and
ending not later than the date of the Expiration Time of such tender or exchange
offer (or, if such Expiration Time occurs before the close of trading on a
Trading Day, not later than the Trading Day immediately preceding the date of
such Expiration Time); provided, however, that if the "ex" date for any Other
Event (other than the tender or exchange offer requiring such computation)
occurs on or after the Commencement Date and on or prior to the date of the
Expiration Time for the tender or exchange offer requiring such computation, the
Closing Price for each Trading Day prior to the "ex" date for such Other Event
shall be adjusted by multiplying such Closing Price by the same fraction by
which the conversion price is so required to be adjusted as a result of such
other event. For purposes of this paragraph, the term "ex" date, (i) when used
with respect to any issuance or distribution, means the first date on which the
Common Stock trades regular way on the relevant exchange or in the relevant
market from which the Closing Price was obtained without the right to receive
such issuance or distribution, (ii) when used with respect to any subdivision or
combination of shares of Common Stock, means the first date on which the Common
Stock trades regular way on such exchange or in such market after the time at
which such subdivision or combination becomes effective, and (iii) when used
with respect to any tender or exchange offer means the first date on which the
Common Stock trades regular way on such exchange or in such market after the
Expiration Time of such tender or exchange offer.

          (8) The Company may make such reductions in the conversion price, in
addition to those required by paragraphs (1), (2), (3), (4), (5) and (6) of this
Section, as it considers to be advisable in order that any event treated for
Federal income tax purposes as a dividend of stock or stock rights shall not be
taxable to the recipients, or to diminish the amount of such tax payable.

          (9) No adjustment in the conversion price shall be required unless
such adjustment would require an increase or decrease of at least 1% in the
conversion price; provided, however, that any adjustments which by reason of
this paragraph (9) are not required to be made shall be carried forward and
taken into account in any subsequent adjustment.

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          (10) In the event that the Company distributes rights or warrants
(other than those referred to in paragraph (2) above) pro rata to holders of
Common Stock, so long as any such rights or warrants have not expired or been
redeemed by the Company, the Company shall make proper provision so that the
Holder of any Security surrendered for conversion will be entitled to receive
upon such conversion, in addition to the Conversion Shares, a number of rights
and warrants to be determined as follows: (i) if such conversion occurs on or
prior to the date for the distribution to the holders of rights or warrants of
separate certificates evidencing such rights or warrants (the "Distribution
Date"), the same number of rights or warrants to which a holder of a number of
shares of Common Stock equal to the number of Conversion Shares is entitled at
the time of such conversion in accordance with the terms and provisions of and
applicable to the rights or warrants, and (ii) if such conversion occurs after
such Distribution Date, the same number of rights or warrants to which a holder
of the number of shares of Common Stock into which the principal amount of such
Security so converted was convertible immediately prior to such Distribution
Date would have been entitled on such Distribution Date in accordance with the
terms and provisions of and applicable to the rights or warrants.

          SECTION 13.05. Notice of Adjustments of Conversion Price. Whenever the
conversion price is adjusted as herein provided:

          (a) the Company shall compute the adjusted conversion price in
     accordance with Section 13.04 and shall prepare a certificate signed by the
     Treasurer of the Company setting forth the adjusted conversion price and
     showing in reasonable detail the facts upon which such adjustment is based,
     and such certificate shall forthwith be filed (with a copy to the Trustee)
     at each office or agency maintained for the purpose of conversion of
     Securities pursuant to Section 10.02; and

          (b) a notice stating that the conversion price has been adjusted and
     setting forth the adjusted conversion price shall forthwith be required,
     and as soon as practicable after it is required, such notice shall be
     mailed by the Company to all Holders at their last addresses as they shall
     appear in the Security Register.

          SECTION 13.06. Notice of Certain Corporate Action. In case:

          (a) the Company shall declare a dividend (or any other distribution)
     on its Common Stock that would require a conversion price adjustment
     pursuant to paragraph (5) of Section 13.04; or

<PAGE>   109
                                                                             100

          (b) the Company shall authorize the granting to all holders of its
     Common Stock of rights, warrants or options to subscribe for or purchase
     any shares of capital stock of any class or of any other rights (excluding
     rights distributed pursuant to any shareholder rights plan); or

          (c) of any reclassification of the Common Stock of the Company (other
     than a subdivision or combination of its outstanding shares of Common
     Stock), or of any consolidation or merger to which the Company is a party
     and for which approval of any shareholders of the Company is required, or
     of the sale or transfer of all or substantially all of the assets of the
     Company; or

          (d) of the voluntary or involuntary dissolution, liquidation or
     winding, up of the Company; or

          (e) the Company or any Subsidiary of the Company shall commence a
     tender or exchange offer for all or a portion of the Company's outstanding
     shares of Common Stock (or shall amend any such tender or exchange offer);

then the Company shall cause to be filed at each office or agency maintained for
the purpose of conversion of Securities pursuant to Section 10.02, and shall
cause to be mailed to all Holders at their last addresses as they shall appear
in the Security Register, at least 20 days (or 10 days in any case specified in
clause (a) or (b) above) prior to the applicable record, effective or expiration
date hereinafter specified, a notice stating (x) the date on which a record is
to be taken for the purpose of such dividend, distribution or granting of
rights, warrants or options, or, if a record is not to be taken, the date as of
which the holders of Common Stock of record to be entitled to such dividend,
distribution, rights, warrants or options are to be determined, or (y) the date
on which such reclassification, consolidation, merger, sale, transfer,
dissolution, liquidation or winding up is expected to become effective, and the
date as of which it is expected that holders of Common Stock of record shall be
entitled to exchange their shares of Common Stock for securities, cash or other
property deliverable upon such reclassification, consolidation, merger, sale,
transfer, dissolution, liquidation or winding up, or (z) the date on which such
tender offer commenced, the date on which such tender offer is scheduled to
expire unless extended, the consideration offered and the other material terms
thereof (or the material terms of any amendment thereto).

          SECTION 13.07. Company to Reserve Common Stock. The Company

<PAGE>   110
                                                                             101

shall at all times reserve and keep available, free from preemptive rights, out
of its authorized but unissued Common Stock, solely for the purpose of effecting
the conversion of Securities, the whole number of shares of Common Stock then
issuable upon the conversion in full of all outstanding Securities.

          SECTION 13.08. Taxes on Conversions. The Company will pay any and all
taxes that may be payable in respect of the issue or delivery of shares of
Common Stock on conversion of Securities pursuant hereto. The Company shall not,
however, be required to pay any tax which may be payable in respect of any
transfer involved in the issue and delivery of shares of Common Stock in a name
other than that of the Holder of the Security or Securities to be converted, and
no such issue or delivery shall be made unless and until the Person requesting
such issue has paid to the Company the amount of any such tax, or has
established to the satisfaction of the Company that such tax has been paid.

          SECTION 13.09. Covenant as to Common Stock. The Company covenants that
all shares of Common Stock which may be issued upon conversion of Securities
will upon issue be newly issued (and not treasury shares) and be duly
authorized, validly issued, fully paid and nonassessable and, except as provided
in Section 13.08, the Company will pay all taxes, liens and charges with respect
to the issue thereof.

          SECTION 13.10. Cancellation of Converted Securities. All Securities
delivered for conversion shall be delivered to the Trustee to be cancelled by or
at the direction of the Trustee, which shall dispose of the same as provided in
Section 3.09.

          SECTION 13.11. Provisions in Case of Reclassification, Consolidation,
Merger or Sale of Assets. In the event that the Company shall be a party to any
transaction (including without limitation any (i) recapitalization or
reclassification of the Common Stock (other than a change in par value, or from
par value to no par value, or from no par value to par value, or as a result of
a subdivision or combination of the Common Stock), (ii) any consolidation of the
Company with, or merger of the Company into, any other person. any merger of
another person into the Company (other than a merger which does not result in a
reclassification, conversion, exchange or cancellation of outstanding shares of
Common Stock of the Company), (iii) any sale or transfer of all or substantially
all of the assets of the Company, or (iv) any other transaction) pursuant to
which the Common Stock is converted into the right to receive other securities,
cash or other property, then lawful provision shall be made as part of the terms
of such transaction whereby the Holder of each Security then outstanding shall
have the right thereafter to convert such Security only into (subject to funds
being legally available for

<PAGE>   111
                                                                             102

such purpose under applicable law at the time of such conversion) the kind and
amount of securities, cash and other property receivable upon such transaction
by a holder of the number of shares of Common Stock into which such Security
might have been converted immediately prior to such transaction. The Company or
the person formed by such consolidation or resulting from such merger or which
acquired such assets or which acquired the Company's shares, as the case may be,
shall execute and deliver to the Trustee a supplemental indenture establishing
such rights. Such supplemental indenture shall provide for adjustments which,
for events subsequent to the effective date of such supplemental indenture,
shall be as nearly equivalent as may be practicable to the adjustments provided
for in this Article. The above provisions of this Section 13.11 shall similarly
apply to successive transactions of the foregoing type.

                                   ARTICLE XIV

                           Right to Require Repurchase

          SECTION 14.01. Right to Require Repurchase. In the event that there
shall occur a Change in Control (as defined in Section 14.06), then each Holder
shall have the right, at such Holder's option, to require the Company, subject
to the provisions of Section 12.03, to purchase all or any designated part of
such Holder's Securities on the date (the "Repurchase Date") fixed by the
Company that is not less than 30 days nor more than 45 days after the date the
Company gives notice of the Change in Control as contemplated in Section
14.02(a) at a price (the "Repurchase Price") equal to 100% of the principal
amount thereof, together with accrued and unpaid interest through the Repurchase
Date. Such right to require the repurchase of Securities shall not continue
after a discharge of the Company from its obligations with respect to the
Securities in accordance with Article IV. Any requirements for notice, surrender
or delivery of Securities pursuant to this Article XIV shall, with respect to
any Global Security, be subject to any Applicable Procedures.

          SECTION 14.02. Notice, Method of Exercising Repurchase Right. (a) On
or before the 15th day after the Company knows or reasonably should know a
Change in Control has occurred, the Company, or at the written request of the
Company, the Trustee (in the name and at the expense of the Company), shall give
notice of the occurrence of the Change in Control and of the repurchase right
set forth herein arising as a result thereof by first-class mail, postage
prepaid, or by telefacsimile with written

<PAGE>   112
                                                                             103

acknowledgment of transmittal to each Holder of the Securities at such Holder's
address appearing in the Security Register. The Company shall also deliver a
copy of such notice of a repurchase right to the Trustee.

          Each notice of a repurchase right shall state:

          (1) the Repurchase Date,

          (2) the date by which the repurchase right must be exercised,

          (3) the Repurchase Price, and

          (4) the instructions a Holder must follow to exercise its repurchase
     right.

          No failure of the Company to give the foregoing notice shall limit any
Holder's right to exercise a repurchase right. The Trustee shall have no
affirmative obligation to determine if there shall have occurred a Change in
Control.

          (b) To exercise a repurchase right, a Holder shall deliver to the
Company (or an agent designated by the Company for such purpose in the notice
referred to in (a) above) and to the Trustee on or before the 30th day after the
date of transmittal of the notice referred to in (a) above (i) written notice of
the Holder's exercise of such right, which notice shall set forth the name of
the Holder, the principal amount of the Security or Securities (or portion of a
Security) to be repurchased, and a statement that an election to exercise the
repurchase right is being made thereby, and (ii) the Security or Securities with
respect to which the repurchase right is being exercised, duly endorsed for
transfer to the Company. Such written notice shall be irrevocable. If the
Repurchase Date falls between any Regular Record Date and the corresponding
succeeding Interest Payment Date, Securities to be repurchased must be
accompanied by payment from the Holder of an amount equal to the interest
thereon which the registered Holder thereof is to receive on such Interest
Payment Date.

          (c) In the event a repurchase right shall be exercised in accordance
with the terms hereof, the Company shall on the Repurchase Date pay or cause to
be paid in cash to the Holder thereof the Repurchase Price of the Security or
Securities as to which the repurchase right had been exercised.

          SECTION 14.03. Deposit of Repurchase Price. On or prior to the
Repurchase Date, the Company shall deposit with the Trustee or with a Paying
Agent (or, if the Company is acting as its own Paying Agent, segregate and hold
in trust as provided in Section 10.03) an amount of money sufficient to pay the
Repurchase Price of the

<PAGE>   113
                                                                             104

Securities which are to be repaid on the Repurchase Date.

          SECTION 14.04. Securities Not Repurchased on Repurchase Date. If any
Security surrendered for repurchase shall not be so paid on the Repurchase Date,
the principal of such Security shall, until paid, bear interest from the
Repurchase Date at a rate borne by such Security.

          SECTION 14.05. Securities Repurchased in Part. Any Security which is
to be repurchased only in part shall be surrendered at any office or agency of
the Company designated for that purpose pursuant to Section 10.02 (with, if the
Company or the Trustee so requires, due endorsement by, or written instrument of
transfer in form satisfactory to the Company and the Trustee duly executed by,
the Holder thereof or his attorney duly authorized in writing), and the Company
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 equal to and in exchange for the unrepurchased portion of the principal
of the Security so surrendered.

          SECTION 14.06. Certain Definitions. For purposes of this Article: The
term "Beneficial Owner" shall be determined in accordance with Rules 13d-3 and
13d-5 promulgated by the Commission under the Exchange Act, or any successor
provision thereto, except that a Person shall be deemed to have "beneficial
ownership" of all shares that such Person has the right to acquire, whether such
right is exercisable immediately or only after the passage of time.

          A "Change in Control" shall be deemed to have occurred at such time as
(a) any Person, or any Persons acting together in a manner which would
constitute a "group" (a "Group") for purposes of Section 13(d) of the Exchange
Act, or any successor provision thereto, together with any Affiliates thereof,
(i) become the Beneficial Owners, directly or indirectly, of capital stock of
the Company, entitling such Person or Persons and its or their Affiliates to
exercise more than 50% of the total voting power of all classes of the Company's
capital stock entitled to vote generally in the election of directors or (ii)
shall succeed in having sufficient of its or their nominees (who are not
supported by a majority of the then current Board of Directors of the Company)
elected to the Board of Directors of the Company such that such nominees, when
added to any existing directors remaining on the Board of Directors of the
Company after such election who are Affiliates of or acting in concert with any
such Persons, shall constitute a

<PAGE>   114
                                                                             105

majority of the Board of Directors of the Company, (b) the Company shall be a
party to any transaction pursuant to which the Common Stock is converted into
the right to receive other securities (other than common stock), cash and/or
property (or the Company, by dividend, tender or exchange offer or otherwise,
distributes other securities, cash and/or property to holders of Common Stock)
and the value of all such securities, cash and/or property distributed in such
transaction and any other transaction effected within the 12 months preceding
consummation of such transaction (as determined in good faith by the Board of
Directors, whose determination shall be conclusive and described in a Board
Resolution) is more than 50% of the average of the daily Closing Prices for the
five consecutive Trading Days ending on the Trading Day immediately preceding
the date of such transaction (or, if earlier, the Trading Day immediately
preceding the "ex" date (as defined in paragraph (7) of Section 13.04) for such
transaction) or (c) the Company shall consolidate with or merge into any other
Person or sell, convey, transfer or lease its properties and assets
substantially as an entirety to any Person other than a Subsidiary, or any other
Person shall consolidate with or merge into the Company (other than, in the case
of this clause (c), pursuant to any consolidation or merger where Persons who
are shareholders of the Company immediately prior thereto become the Beneficial
Owners of shares of capital stock of the surviving company entitling such
Persons to exercise more than 50% of the total voting power of all classes of
such surviving company's capital stock entitled to vote generally in the
election of directors).

          Notwithstanding the foregoing, a "Change in Control" will be deemed
not to have occurred (i) if the Closing Price of the Common Stock for any five
Trading Days during the ten Trading Days immediately preceding the Change in
Control is at least equal to 105% of the conversion price in effect immediately
preceding the Change in Control or (ii) if at least 90% of the consideration
(excluding cash payments for fractional shares or cash payments for appraisal
rights) received or to be received by the shareholders of the Company in the
transaction or transactions constituting the Change in Control consists of (x)
shares of common stock or securities convertible into such shares of common
stock, of an entity organized and validly existing under the laws of the United
States of America, any State thereof or the District of Columbia the common
stock of which is, or upon issuance will be, traded on a national securities
exchange in the United States of America or through Nasdaq or (y) shares of
common stock of an entity organized and validly existing under the laws of a
jurisdiction outside of the United States of America, or American Depositary
Shares representing such shares of common stock, that are, or upon issuance will
be, traded on a national securities exchange in the United States of America or
through Nasdaq, if such entity has an average worldwide total market
capitalization of its equity securities of at least U.S. $5 billion during the
ten Trading Days immediately preceding the date of the Change in Control.

<PAGE>   115
                                                                             106

                                   ARTICLE XV

                       Defeasance and Covenant Defeasance

          SECTION 15.01. Company's Option to Effect Defeasance or Covenant
Defeasance. The Company may at its option by Board Resolution, at any time,
elect to have either Section 15.02 or Section 15.03 applied to the Outstanding
Securities upon compliance with the conditions set forth below in this Article
XV.

          SECTION 15.02. Defeasance and Discharge. Upon the Company's exercise
of the option provided in Section 15.01 applicable to this Section, the Company
shall be deemed to have been discharged from its obligations with respect to the
Outstanding Securities (other than those specified below), the Holders and any
holders of Senior Indebtedness, and the provisions of Article XII hereof shall
cease to be effective, on the date the conditions set forth below are satisfied
(hereinafter, "defeasance"). For this purpose, such defeasance means that the
Company shall be deemed to have paid and discharged the entire indebtedness
represented by the Outstanding Securities, the Company shall be deemed to have
satisfied all their other obligations under such Securities and this Indenture
insofar as such Securities are concerned (and the Trustee, at the expense of the
Company, shall execute proper instruments acknowledging the same), except for
the following which shall survive until otherwise terminated or discharged
hereunder: (A) the rights of Holders of such Securities to receive, solely from
the trust fund described in Section 15.04 and as more fully set forth in such
Section, payments in respect of the principal of, premium, if any (including the
Make-Whole Payment, if any), and interest on such Securities when such payments
are due, (B) the Company's obligations with respect to such Securities under
Sections 3.04, 3.05, 3.06, 10.02, 10.03, 10.11, Article XIII and Article XIV,
(C) the rights, powers, trusts, duties and immunities of the Trustee hereunder
and (D) this Article XV. Subject to compliance with this Article XV, the Company
may exercise its option under this Section 15.02 notwithstanding the prior
exercise of its option under Section 15.03.

          SECTION 15.03. Covenant Defeasance. Upon the Company's exercise of the
option provided in Section 15.01 applicable to this Section, (i) the Company
shall be released from its obligations under Section 10.06 and Section 10.07,
(ii) the occurrence of an event specified in Section 5.01(4) (with respect to
either of Section 10.06 or Section 10.07) or 5.01(5) shall not be deemed to be
an Event of Default and (iii) the provisions of Article XII hereof shall cease
to be effective on and after the date the conditions set forth below are
satisfied (hereinafter, "covenant defeasance"). For this purpose, such covenant
defeasance means that the Company may omit to comply with

<PAGE>   116
                                                                             107

and shall have no liability in respect of any term, condition or limitation set
forth in any such Section or Article, whether directly or indirectly by reason
of any reference elsewhere herein to any such Section or Article or by reason of
any reference in any such Section or Article to any other provision herein or in
any other document, but the remainder of this Indenture and such Securities
shall be unaffected thereby.

          SECTION 15.04. Conditions to Defeasance or Covenant Defeasance. The
following shall be the conditions to application of either Section 15.02 or
Section 15.03 to the then Outstanding Securities:

          (1) The Company shall irrevocably have deposited or caused to be
     deposited with the Trustee (or another trustee satisfying the requirements
     of Section 6.09 who shall agree to comply with the provisions of this
     Article XV applicable to it) as trust funds in trust for the purpose of
     making the following payments, specifically pledged as security for, and
     dedicated solely to, the benefit of the Holders of such Securities, (A)
     money in an amount, or (B) U.S. Government Obligations which through the
     scheduled payment of principal and interest in respect thereof in
     accordance with their terms will provide, not later than one day before the
     due date of any payment, money in an amount, or (C) a combination thereof,
     sufficient, in the written opinion of a nationally recognized firm of
     independent public accountants expressed in a written certification thereof
     delivered to the Trustee, to pay and discharge, and which shall be applied
     by the Trustee (or other qualifying trustee) to pay and discharge, the
     principal of, premium, if any (including the Make-Whole Payment, if any),
     and each installment of interest on the Securities on the Stated Maturity
     of such principal or installment of interest in accordance with the terms
     of this Indenture and of such Securities. For this purpose, "U.S.
     Government Obligations" means securities that are (x) direct obligations of
     the United States of America for the payment of which its full faith and
     credit is pledged or (y) obligations of a Person controlled or supervised
     by and acting as an agency or instrumentality of the United States of
     America the payment of which is unconditionally guaranteed as a full faith
     and credit obligation by the United States of America, which, in either
     case, are not callable or redeemable at the option of the issuer thereof,
     and shall also include a depository receipt issued by a bank (as defined in
     Section 3(a)(2) of the Securities Act) as custodian with respect to any
     such U.S. Government Obligation or a specific payment of principal of or
     interest on any such U.S. Government Obligation held by such custodian for
     the account of the holder of such depository receipt; provided that (except
     as required by law) such custodian is not authorized to make any deduction
     from the amount payable to the holder of such depository receipt from any
     amount received by the custodian in respect of the U.S. Government
     Obligation or the specific payment of principal of or

<PAGE>   117
                                                                             108

     interest on the U.S. Government Obligation evidenced by such depository
     receipt.

          (2) In the case of an election under Section 15.02, the Company shall
     have delivered to the Trustee an Opinion of Counsel stating that (x) the
     Company has received from, or there has been published by, the Internal
     Revenue Service a ruling, or (y) since the date of this Indenture there has
     been a change in the applicable Federal income tax law, in either case to
     the effect that, and based thereon such opinion shall confirm that, the
     Holders of the Outstanding Securities will not recognize gain or loss for
     Federal income tax purposes as a result of such deposit, defeasance and
     discharge and will be subject to Federal income tax on the same amount, in
     the same manner and at the same times as would have been the case if such
     deposit, defeasance and discharge had not occurred.

          (3) In the case of an election under Section 15.03, the Company shall
     have delivered to the Trustee an Opinion of Counsel to the effect that the
     Holders of the Outstanding Securities will not recognize gain or loss for
     Federal income tax purposes as a result of such deposit and covenant
     defeasance and will be subject to Federal income tax on the same amount, in
     the same manner and at the same times as would have been the case if such
     deposit and covenant defeasance had not occurred.

          (4) The Company shall have delivered to the Trustee an Officers'
     Certificate to the effect that the Securities, if then listed on any
     securities exchange, will not be delisted as a result of such deposit.

          (5) Such defeasance or covenant defeasance shall not cause the Trustee
     to have a conflicting interest as defined in Section 6.08 and for purposes
     of the Trust Indenture Act with respect to any securities of the Company.

          (6) At the time of such deposit: (A) no default in the payment of all
     or a portion of principal of or premium, if any (including the Make-Whole
     Payment, if any), or interest on or other obligations in respect of any
     Senior Indebtedness shall have occurred and be continuing, and no event of
     default with respect to any Senior Indebtedness shall have occurred and be
     continuing and shall have resulted in such Senior Indebtedness becoming or
     being declared due and payable prior to the date on which it would
     otherwise have become due and payable and (B) no other event with respect
     to any Senior Indebtedness shall have occurred and be continuing permitting

<PAGE>   118
                                                                             109

     (after notice or the lapse of time, or both) the holders of such Senior
     Indebtedness (or a trustee on behalf of the holders thereof) to declare
     such Senior Indebtedness due and payable prior to the date on which it
     would otherwise have become due and payable, or, in the case of either
     clause (A) or clause (B) above, each such default or event of default shall
     have been cured or waived or shall have ceased to exist.

          (7) No Event of Default or event which with notice or lapse of time or
     both would become an Event of Default shall have occurred and be continuing
     on the date of such deposit or, insofar as subsections 5.01(6) and (7) are
     concerned, at any time during the period ending on the 121st day after the
     date of such deposit (it being understood that this condition shall not be
     deemed satisfied until the expiration of such period).

          (8) Such defeasance or covenant defeasance shall not result in a
     breach or violation of, or constitute a default under, any other agreement
     or instrument to which the Company is a party or by which it is bound.

          (9) The Company shall have delivered to the Trustee an Officers'
     Certificate and an Opinion of Counsel, each stating that all conditions
     precedent provided for relating to either the defeasance under Section
     15.02 or the covenant defeasance under Section 15.03 (as the case may be)
     have been complied with.

          (10) Such defeasance or covenant defeasance shall not result in the
     trust arising from such deposit constituting an investment company as
     defined in the Investment Company Act of 1940, as amended, or such trust
     shall be qualified under such act or exempt from regulation thereunder.

          SECTION 15.05. Deposited Money and U.S. Government Obligations to Be
Held in Trust; Other Miscellaneous Provisions. Subject to the provisions of the
last paragraph of Section 10.03, all money and U.S. Government Obligations
(including the proceeds thereof) deposited with the Trustee (or other qualifying
trustee collectively, for purposes of this Section 15.05, the "Trustee")
pursuant to Section 15.04 in respect of the Securities shall be held in trust
and applied by the Trustee, in accordance with the provisions of such Securities
and this Indenture, to the payment, either directly or through any Paying Agent
(including the Company acting as its own Paying Agent) as the Trustee may
determine, to the Holders of such Securities, of all sums due and to become due
thereon in respect of principal, premium, if any (including the Make-Whole
Payment, if any), and interest. Money so held in trust shall not be subject to
the provisions of Article XII.

<PAGE>   119
                                                                             110

          The Company shall pay and indemnify the Trustee against any tax, fee
or other charge imposed on or assessed against the U.S. Government Obligations
deposited pursuant to Section 15.04 or the principal and interest received in
respect thereof other than any such tax, fee or other charge which by law is for
the account of the Holders of the Outstanding Securities.

          Anything in this Article XV to the contrary notwithstanding, the
Trustee shall deliver or pay to the Company from time to time upon Company
Request any money or U.S. Government Obligations held by it as provided in
Section 15.04 which, in the opinion of a nationally recognized firm of
independent public accountants expressed in a written certification thereof
delivered to the Trustee, are in excess of the amount thereof which would then
be required to be deposited to effect an equivalent defeasance or covenant
defeasance.

          SECTION 15.06. Reinstatement. If the Trustee or the Paying Agent is
unable to apply any money in accordance with Section 15.02 or 15.03 by reason of
any order or judgment of any court or governmental authority enjoining,
restraining or otherwise prohibiting such application, then the Company's
obligations under this Indenture and the Securities shall be revived and
reinstated as though no deposit had occurred pursuant to this Article XV until
such time as the Trustee or Paying Agent is permitted to apply all such money in
accordance with Section 15.02 or 15.03; provided, however, that if the Company
makes any payment of principal of, premium, if any (including the Make-Whole
Payment, if any), or interest on any Security following the reinstatement of its
obligations, the Company shall be subrogated to the rights of the Holders of
such Securities to receive such payment from the money held by the Trustee or
the Paying Agent.

                                   ARTICLE XVI

                                    Immunity

          SECTION 16.01. Personal Immunity of Incorporators, Shareholders,
Directors and Officers. No recourse for the payment of the principal of or
interest on the Securities, and no recourse under or upon any obligation,
covenant or agreement contained in this Indenture or in any indenture
supplemental hereto, or in the Securities, or because of any indebtedness
evidenced thereby, shall be had against any incorporator, or against any past,
present or future shareholder, officer or director, as such, of the Company or
any successor corporation, either directly or through the Company or any
successor corporation, under any rule of law, statute or constitutional
provision or by the

<PAGE>   120
                                                                             111

enforcement of any assessment or by any legal or equitable proceeding or
otherwise, all such liability being expressly waived and released by the
acceptance of the Securities by the Holders thereof and as part of the
consideration for the issue of the Securities. Each and every Holder of the
Securities, by receiving and holding the same, agrees to the provisions of this
Section 16.01 and waives and releases any and all such recourse, claim and
liability.

<PAGE>   121
                                                                             112

          This instrument may be executed in any number of counterparts, each of
which so executed shall be deemed to be an original, but all such counterparts
shall together constitute but one and the same instrument.

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

                                             HUMAN GENOME SCIENCES, INC.

               by  /s/ Craig A. Rosen,
                   --------------------------------
             Name: Craig A. Rosen, Ph.D.

                                             Title:   Executive Vice President,
                                                      Research and Development

<PAGE>   122

                                    THE BANK OF NEW YORK

                                    by /s/ Thomas C. Knight
                                           ----------------------------------
                                  Name:       Thomas C. Knight
                                          Title:      Assistant Vice President<PAGE>   1

                                                                  EXECUTION COPY

                                                                     EXHIBIT 4.2

                               Up to $350,000,000

                           Human Genome Sciences, Inc.

            3 3/4% Convertible Subordinated Notes Due March 15, 2007

                          REGISTRATION RIGHTS AGREEMENT

                                                                  March 10, 2000

Credit Suisse First Boston Corporation
Eleven Madison Avenue
New York, New York  10010-3629

Dear Sirs:

          Human Genome Sciences, Inc., a Delaware corporation (the "Company"),
proposes to issue and sell to Credit Suisse First Boston Corporation ("CSFBC"),
(the "Initial Purchaser"), upon the terms set forth in a purchase agreement of
even date herewith (the "Purchase Agreement"), $300,000,000 aggregate principal
amount (plus up to an additional $50,000,000 principal amount at the option of
the Initial Purchaser) of 3 3/4% Convertible Subordinated Notes Due March 15,
2007 (the "Notes") of the Company. The Notes will be convertible into shares of
Common Stock, par value $0.01 per share, of the Company (the "Common Stock") at
the conversion price set forth in the Offering Circular dated March 6, 2000. The
Notes will be issued pursuant to an Indenture, dated as of March 10, 2000 (the
"Indenture"), between the Company and The Bank of New York (the "Trustee"). As
an inducement to the Initial Purchaser to enter into the Purchase Agreement and
in satisfaction of a condition to the Initial Purchaser's obligations
thereunder, the Company agrees with the Initial Purchaser, (i) for the benefit
of the Initial Purchaser and (ii) for the benefit of the holders of the Notes
and the Common Stock issuable upon conversion of the Notes (collectively, the
"Securities") from time to time until such time as such Securities have been
sold pursuant to a Shelf Registration Statement (as defined below) (each of the
foregoing a "Holder" and together the "Holders"), as follows:

          1. Shelf Registration. The Company shall take the following actions:

          (a) The Company shall, at its cost, prepare and, as promptly as
practicable (but in no event more than 60 days after the first date of original

<PAGE>   2
                                                                               2

issuance of the Notes) file with the Securities and Exchange Commission (the
"Commission") and thereafter shall use its best efforts to cause to be declared
effective as soon as practicable, but no later than 120 days after the first
date of original issuance of the Notes, a registration statement on Form S-3
(the "Shelf Registration Statement") covering the offer and sale of the Transfer
Restricted Securities (as defined in Section 5(d) hereof) by the Holders thereof
from time to time in accordance with the methods of distribution set forth in
the Shelf Registration Statement and Rule 415 under the Securities Act of 1933
(the "Securities Act") (hereinafter, the "Shelf Registration"); provided,
however, that no Holder (other than the Initial Purchaser) shall be entitled to
have the Securities held by it covered by such Shelf Registration Statement
unless such Holder agrees in writing to be bound by all the provisions of this
Agreement applicable to such Holder.

          (b) The Company shall use its best efforts to keep the Shelf
Registration Statement continuously effective, in order to permit the prospectus
included therein to be lawfully delivered by the Holders of the relevant
Securities, for a period of two years (or for such longer period if extended
pursuant to Section 2(h) below) from the date of its effectiveness or such
shorter period that will terminate when all the Securities covered by the Shelf
Registration Statement (i) have been sold pursuant thereto or (ii) may be sold
pursuant to Rule 144(k) under the Securities Act (or any successor rule
therefore), assuming for this purpose that the Holders thereof are not
affiliates of the Company (in any such case, such period being called the "Shelf
Registration Period"). The Company shall be deemed not to have used its best
efforts to keep the Shelf Registration Statement effective during the requisite
period if it voluntarily takes any action that would result in Holders of
Securities covered thereby not being able to offer and sell such Securities
during that period, unless (i) such action is required by applicable law or (ii)
upon the occurrence of any event contemplated by paragraph 2(b)(v) below, such
action is taken by the Company in good faith and for valid business reasons and
the Company thereafter complies with the requirements of paragraph 2(h).

          (c) Notwithstanding any other provisions of this Agreement to the
contrary, the Company shall cause the Shelf Registration Statement and the
related prospectus and any amendment or supplement thereto, as of the effective
date of the Shelf Registration Statement, amendment or supplement, (i) to comply
in all material respects with the applicable requirements of the Securities Act
and the rules and regulations of the Commission and (ii) not to contain any
untrue statement of a material fact or omit to state a material fact

<PAGE>   3
                                                                               3

required to be stated therein or necessary to make the statements therein, in
light of the circumstances under which they were made, not misleading.

          2. Registration Procedures. In connection with the Shelf Registration
the following provisions shall apply:

          (a) The Company shall (i) furnish to the Initial Purchaser, prior to
the filing thereof with the Commission, a copy of the Shelf Registration
Statement and each amendment thereof and each amendment or supplement, if any,
to the prospectus included therein and, in the event that an Initial Purchaser
(with respect to any portion of an unsold allotment from the original offering)
is participating in the Shelf Registration Statement, shall use its best efforts
to reflect in each such document, when so filed with the Commission, such
comments as the Initial Purchaser reasonably may propose; and (ii) include the
names of the Holders who propose to sell Securities pursuant to the Shelf
Registration Statement, as selling security holders.

          (b) The Company shall give written notice to the Initial Purchaser and
the Holders (which notice pursuant to clauses (ii)-(v) hereof shall be
accompanied by an instruction to suspend the use of the prospectus until the
requisite changes have been made):

          (i) when the Shelf Registration Statement or any amendment thereto has
     been filed with the Commission and when the Shelf Registration Statement or
     any post-effective amendment thereto has become effective;

          (ii) of any request by the Commission for amendments or supplements to
     the Shelf Registration Statement or the prospectus included therein or for
     additional information;

          (iii) of the issuance by the Commission of any stop order suspending
     the effectiveness of the Shelf Registration Statement or the initiation of
     any proceedings for that purpose;

          (iv) of the receipt by the Company or its legal counsel of any
     notification with respect to the suspension of the qualification of the
     Securities for sale in any jurisdiction or the initiation or threatening of
     any proceeding for such purpose; and

<PAGE>   4
                                                                               4

          (v) of the happening of any event or circumstance that would require
     the Company to make changes in the Shelf Registration Statement or the
     prospectus in order that the Shelf Registration Statement or the prospectus
     do not contain an untrue statement of a material fact nor omit to state a
     material fact required to be stated therein or necessary to make the
     statements therein (in the case of the prospectus, in light of the
     circumstances under which they were made) not misleading, which written
     notice need not provide any detail as to the nature of such event.

          (c) The Company shall make every reasonable effort to obtain the
withdrawal, at the earliest possible time, of any order suspending the
effectiveness of the Shelf Registration Statement.

          (d) The Company shall furnish to each Holder of Securities included
within the coverage of the Shelf Registration, without charge, at least one copy
of the Shelf Registration Statement and any post-effective amendment thereto,
including financial statements and schedules, and, if the Holder so requests in
writing, all exhibits thereto (including those, if any, incorporated by
reference).

          (e) The Company shall, during the Shelf Registration Period, deliver
to each Holder of Securities included within the coverage of the Shelf
Registration Statement, without charge, as many copies of the prospectus
(including each preliminary prospectus) included in the Shelf Registration
Statement and any amendment or supplement thereto as such person may reasonably
request. The Company consents, subject to the provisions of this Agreement, to
the use of the prospectus or any amendment or supplement thereto by each of the
selling Holders in connection with the offering and sale of the Securities
covered by the prospectus, or any amendment or supplement thereto, included in
the Shelf Registration Statement.

          (f) Prior to any public offering of the Securities, pursuant to the
Shelf Registration Statement, the Company shall register or qualify or cooperate
with the Holders of the Securities included therein and their respective counsel
in connection with the registration or qualification of such Securities for
offer and sale under the securities or "blue sky" laws of such states of the
United States as any such Holder reasonably requests in writing and do any and
all other acts or

<PAGE>   5
                                                                               5

things necessary or advisable to enable the offer and sale in such jurisdictions
of the Securities covered by the Shelf Registration Statement; provided,
however, that the Company shall not be required to (i) qualify generally to do
business in any jurisdiction where it is not then so qualified or (ii) take any
action which would subject it to general service of process or to taxation in
any jurisdiction where it is not then so subject.

          (g) The Company shall cooperate with the Holders of the Securities to
facilitate the timely preparation and delivery of certificates representing the
Securities to be sold pursuant to the Shelf Registration Statement free of any
restrictive legends and in such denominations and registered in such names as
the Holders may request a reasonable period of time prior to sales of the
Securities pursuant to the Shelf Registration Statement.

          (h)  Upon the occurrence of any event contemplated by paragraphs (ii)
through (v) of Section 2(b) above during the period for which the Company is
required to maintain an effective Shelf Registration Statement, the Company
shall, as required hereby, prepare and file a post-effective amendment to the
Shelf Registration Statement or an amendment or supplement to the related
prospectus and any other required document so that, as thereafter delivered to
Holders or purchasers of Securities, the prospectus will not contain an 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 light of the
circumstances under which they were made, not misleading. If the Company
notifies the Initial Purchaser and the Holders in accordance with paragraphs
(ii) through (v) of Section 2(b) above to suspend the use of the prospectus
until the requisite changes to the prospectus have been made, then the Initial
Purchaser and the Holders shall suspend use of such prospectus and the period of
effectiveness of the Shelf Registration Statement provided for in Section 1(b)
above shall be extended by the number of days from and including the date of
giving such notice to and including the date when the Initial Purchaser and the
Holders shall have received such amended or supplemented prospectus pursuant to
this Section 2(h). Any such amendment, supplement or document will be prepared
and filed as promptly as practicable under the circumstances, as determined in
good faith by the Company, it being understood that the Company may have bona
fide reasons to delay such preparation and filing for a period which may not in
any event exceed 60 days.

          (i) Not later than the effective date of the Shelf Registration
Statement, the Company will provide CUSIP numbers for the Notes and the

<PAGE>   6
                                                                               6

Common Stock registered under the Shelf Registration Statement, and provide the
Trustee with printed certificates for such Notes, in form eligible for deposit
with The Depository Trust Company.

          (j) The Company will comply with all rules and regulations of the
Commission to the extent and so long as they are applicable to the Shelf
Registration and will make generally available to its security holders (or
otherwise provide in accordance with Section 11(a) of the Securities Act) an
earnings statement satisfying the provisions of Section 11(a) of the Securities
Act, no later than 45 days after the end of a 12-month period (or 90 days, if
such period is a fiscal year) beginning with the first month of the Company's
first fiscal quarter commencing after the effective date of the Shelf
Registration Statement, which statement shall cover such 12-month period.

          (k) The Company shall cause the Indenture to be qualified under the
Trust Indenture Act of 1939 (the "Trust Indenture Act"), in a timely manner and
containing such changes, if any, as shall be necessary for such qualification.
In the event that such qualification would require the appointment of a new
trustee under the Indenture, the Company shall appoint a new trustee thereunder
pursuant to the applicable provisions of the Indenture.

          (l) The Company may require each Holder of Securities to be sold
pursuant to the Shelf Registration Statement to furnish to the Company such
information regarding the Holder and the distribution of the Securities as the
Company may from time to time reasonably require for inclusion in the Shelf
Registration Statement, and the Company may exclude from such registration the
Securities of any Holder that fails to furnish such information within a
reasonable time after receiving such request.

          (m) The Company shall enter into such customary agreements (including,
if requested, an underwriting agreement in customary form) and take any other
actions any Holder shall reasonably request in order to facilitate the
disposition of the Securities pursuant to the Shelf Registration Statement,
provided, however, that the Company shall not be required to facilitate an
underwritten offering pursuant to the Shelf Registration Statement by any
Holders unless the offering relates to at least $50,000,000 principal amount of
the Notes or the equivalent number of shares of Common Stock into which such
Notes are convertible.

<PAGE>   7
                                                                               7

          (n) The Company shall (i) make reasonably available for inspection by
the Holders of the Securities, any underwriter participating in any distribution
pursuant to the Shelf Registration Statement and any attorney, accountant or
other agent retained by the Holders of the Securities or any such underwriter
all relevant financial and other records, pertinent corporate documents and
properties of the Company and (ii) cause the Company's officers, directors,
employees, accountants and auditors to supply all relevant information
reasonably requested by the Holders of the Securities or any such underwriter,
attorney, accountant or agent in connection with the Shelf Registration
Statement, in each case, as shall be reasonably necessary to enable such
persons, to conduct a reasonable investigation within the meaning of Section 11
of the Securities Act; provided, however, that the foregoing inspection and
information gathering (i) shall be coordinated on behalf of the Initial
Purchaser by you and on behalf of the other parties, by one counsel designated
by and on behalf of the other parties as described in Section 3 hereof.

          (o) The Company, if requested by any Holder of Securities covered by
the Shelf Registration Statement, shall cause (i) its counsel (which may include
the Company's general counsel for one or more of the opinions) to deliver an
opinion and updates thereof relating to the Securities in customary form
addressed to such Holders, and the managing underwriters, if any, thereof, and
dated, in the case of the initial opinion, the effective date of such Shelf
Registration Statement (it being agreed that the matters to be covered by such
opinion shall include, without limitation, the due incorporation and good
standing of the Company; the qualification of the Company to transact business
as a foreign corporation; the due authorization, execution and delivery of the
relevant agreement of the type referred to in Section 2(m) hereof; the due
authorization, execution, authentication and issuance, and the validity and
enforceability, of the applicable Securities; the absence of material legal or
governmental proceedings involving the Company; the absence of governmental
approvals required to be obtained in connection with the Shelf Registration
Statement, the offering and sale of the applicable Securities, or any agreement
of the type referred to in Section 2(m) hereof; the compliance as to form of
such Shelf Registration Statement and any documents incorporated by reference
therein and of the Indenture with the requirements of the Securities Act and the
Trust Indenture Act, respectively; and, as of the date of the opinion and as of
the effective date of the Shelf Registration Statement or most recent
post-effective amendment thereto, as the case may be, the absence from such
Shelf Registration Statement and the prospectus included therein, as then
amended or

<PAGE>   8
                                                                               8

supplemented, and from any documents incorporated by reference therein of an
untrue statement of a material fact or the omission to state therein a material
fact required to be stated therein or necessary to make the statements therein
not misleading (in the case of any such documents, in the light of the
circumstances existing at the time that such documents were filed with the
Commission under the Securities Exchange Act of 1934 (the "Exchange Act")), (ii)
its officers to execute and deliver all customary documents and certificates and
updates thereof requested by any underwriters of the applicable Securities or
counsel for the Holders and (iii) its independent public accountants and the
independent public accountants with respect to any other entity for which
financial information is provided in the Shelf Registration Statement to provide
to the selling Holders of the applicable Securities and any underwriter therefor
a comfort letter in customary form and covering matters of the type customarily
covered in comfort letters in connection with primary underwritten offerings,
subject to receipt of appropriate documentation as contemplated, and only if
permitted, by Statement of Auditing Standards No. 72.

          (p) The Company shall use its best efforts to take all other steps
necessary to effect the registration of the Securities covered by the Shelf
Registration Statement contemplated hereby.

          3. Registration Expenses. The Company shall bear all fees and expenses
incurred in connection with the performance of its obligations under Sections 1
through 2 hereof (including the reasonable fees and expenses, if any, of
Cravath, Swaine & Moore, counsel for the Initial Purchaser, incurred in
connection with the Shelf Registration), whether or not the Shelf Registration
Statement is filed or becomes effective, and shall bear or reimburse the Holders
of the Securities covered by the Shelf Registration for the reasonable fees and
disbursements of one firm of counsel designated by the Holders of a majority in
principal amount of the Securities covered by the Shelf Registration Statement
(provided that Holders of Common Stock issued upon the conversion of the Notes
shall be deemed to be Holders of the aggregate principal amount of Notes from
which such Common Stock was converted) to act as counsel for the Holders in
connection therewith.

          4. Indemnification. (a) The Company agrees to indemnify and hold
harmless each Holder and each person, if any, who controls such Holder

<PAGE>   9
                                                                               9

within the meaning of the Securities Act or the Exchange Act (each Holder and
such controlling persons are referred to collectively as the "Indemnified
Parties") from and against any losses, claims, damages or liabilities, joint or
several, or any actions in respect thereof (including, but not limited to, any
losses, claims, damages, liabilities or actions relating to purchases and sales
of the Securities) to which each Indemnified Party becomes subject under the
Securities Act, the Exchange Act or otherwise, insofar as such losses, claims,
damages, liabilities or actions arise out of or are based upon any untrue
statement or alleged untrue statement of a material fact contained in the Shelf
Registration Statement or prospectus, including any document incorporated by
reference therein, or in any amendment or supplement thereto or in any
preliminary prospectus relating to the Shelf Registration, 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 shall reimburse, as incurred, the Indemnified Parties for
any legal or other expenses reasonably incurred by them in connection with
investigating or defending any such loss, claim, damage, liability or action in
respect thereof; provided, however, that (i) the Company shall not be liable in
any such case to the extent that such loss, claim, damage or liability arises
out of or is based upon any untrue statement or alleged untrue statement or
omission or alleged omission made in the Shelf Registration Statement or
prospectus or in any amendment or supplement thereto or in any preliminary
prospectus relating to the Shelf Registration in reliance upon and in conformity
with written information pertaining to such Holder and furnished to the Company
by or on behalf of such Holder specifically for inclusion therein and (ii) with
respect to any untrue statement or omission or alleged untrue statement or
omission made in any preliminary prospectus relating to the Shelf Registration
Statement, the indemnity agreement contained in this subsection (a) shall not
inure to the benefit of any Holder from whom the person asserting any such
losses, claims, damages or liabilities purchased the Securities concerned, to
the extent that a prospectus relating to such Securities was required to be
delivered by such Holder under the Securities Act in connection with such
purchase and any such loss, claim, damage or liability of such Holder results
from the fact that there was not sent or given to such person, at or prior to
the written confirmation of the sale of such Securities to such person, a copy
of the final prospectus if the Company had previously furnished copies thereof
to such Holder; provided further, however, that this indemnity agreement will be
in addition to any liability which the Company may otherwise have to such
Indemnified Party.

          The Company shall also indemnify the underwriters, their officers

<PAGE>   10
                                                                              10

and directors and each person who controls such underwriters within the meaning
of the Securities Act or the Exchange Act to the same extent as provided above
with respect to the indemnification of the Holders if requested by such Holders.

          (b) Each Holder, severally and not jointly, will indemnify and hold
harmless the Company, its officers and directors and each person, if any, who
controls the Company within the meaning of the Securities Act or the Exchange
Act from and against any losses, claims, damages or liabilities or any actions
in respect thereof, to which the Company or any such controlling person may
become subject under the Securities Act, the Exchange Act or otherwise, insofar
as such losses, claims, damages, liabilities or actions arise out of or are
based upon any untrue statement or alleged untrue statement of a material fact
contained in a Shelf Registration Statement or prospectus or in any amendment or
supplement thereto or in any preliminary prospectus relating to a Shelf
Registration, or arise out of or are based upon the omission or alleged omission
to state therein a material fact necessary to make the statements therein not
misleading, but in each case only to the extent that the untrue statement or
omission or alleged untrue statement or omission was made in reliance upon and
in conformity with written information pertaining to such Holder and furnished
to the Company by or on behalf of such Holder specifically for inclusion
therein; and, subject to the limitation set forth immediately preceding this
clause, shall reimburse, as incurred, the Company for any legal or other
expenses reasonably incurred by the Company or any such controlling person in
connection with investigating or defending any loss, claim, damage, liability or
action in respect thereof. This indemnity agreement will be in addition to any
liability which such Holder may otherwise have to the Company or any of its
controlling persons.

          (c) Promptly after receipt by an indemnified party under this Section
4 of notice of the commencement of any action or proceeding (including a
governmental investigation), such indemnified party will, if a claim in respect
thereof is to be made against the indemnifying party under this Section 4,
notify the indemnifying party of the commencement thereof; but the omission so
to notify the indemnifying party will not, in any event, relieve the
indemnifying party from any obligations to any indemnified party other than the
indemnification obligation provided in subsections (a) or (b) above. 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 wish, jointly
with any other indemnifying party similarly notified, to assume the defense
thereof, with counsel reasonably

<PAGE>   11
                                                                              11

satisfactory to such indemnified party (who shall not, except with the consent
of the indemnified party, be counsel to the indemnifying party), and after
notice from the indemnifying party to such indemnified party of its election so
to assume the defense thereof the indemnifying party will not be liable to such
indemnified party under this Section 4 for any legal or other expenses, other
than reasonable costs of investigation, subsequently incurred by such
indemnified party in connection with the defense thereof. 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.

          (d) If the indemnification provided for in this Section 4 is
unavailable or insufficient to hold harmless an indemnified party under
subsections (a) or (b) above, then each indemnifying party shall contribute to
the amount paid or payable by such indemnified party as a result of the losses,
claims, damages or liabilities (or actions in respect thereof) referred to in
subsections (a) or (b) above (i) in such proportion as is appropriate to reflect
the relative benefits received by the indemnifying party or parties on the one
hand and the indemnified party on the other from the registration of the
Securities, pursuant to the Shelf Registration, or (ii) if the allocation
provided by the foregoing clause (i) is not permitted by applicable law, in such
proportion as is appropriate to reflect not only the relative benefits referred
to in clause (i) above but also the relative fault of the indemnifying party or
parties on the one hand and the indemnified party on the other in connection
with the statements or omissions that resulted in such losses, claims, damages
or liabilities (or actions in respect thereof) as well as any other relevant
equitable considerations. The relative fault of the parties shall be determined
by reference to, among other things, whether the untrue or alleged untrue
statement of a material fact or the omission or alleged omission to state a
material fact relates to information supplied by the Company on the one hand or
such Holder or such other indemnified party, as the case may be, on the other,
and the parties' relative intent, knowledge, access to information and
opportunity to correct or prevent such statement or omission. The amount paid by
an indemnified party as a result of the losses, claims, damages or liabilities
referred to in the first sentence

<PAGE>   12
                                                                              12

of this subsection (d) shall be deemed to include any legal or other expenses
reasonably incurred by such indemnified party in connection with investigating
or defending any action or claim which is the subject of this subsection (d).
Notwithstanding any other provision of this Section 4(d), the Holders shall not
be required to contribute any amount in excess of the amount by which the net
proceeds received by such Holders from the sale of the Securities pursuant to
the Shelf Registration Statement exceeds the amount of damages which such
Holders have 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. For purposes of this paragraph (d), each person,
if any, who controls such indemnified party within the meaning of the Securities
Act or the Exchange Act shall have the same rights to contribution as such
indemnified party and each person, if any, who controls the Company within the
meaning of the Securities Act or the Exchange Act shall have the same rights to
contribution as the Company.

          (e) The agreements contained in this Section 4 shall survive the sale
of the Securities pursuant to the Shelf Registration Statement and shall remain
in full force and effect, regardless of any termination or cancelation of this
Agreement or any investigation made by or on behalf of any indemnified party.

          5. Additional Interest Under Certain Circumstances. (a) Additional
interest (the "Additional Interest") with respect to the Notes shall be assessed
as follows if any of the following events occur (each such event in clauses (i)
through (iii) below being herein called a "Registration Default"):

          (i) if on or prior to the 60th day after the first date of original
     issuance of the Notes, the Shelf Registration Statement has not been filed
     with the Commission;

     (ii) if on or prior to the 120th day after the first date of original
     issuance of the Notes, the Shelf Registration Statement has not been
     declared effective by the Commission; or

     (iii) if after the Shelf Registration Statement is declared effective (A)
     the

<PAGE>   13
                                                                              13

     Shelf Registration Statement thereafter ceases to be effective; or (B) the
     Shelf Registration Statement or the related prospectus ceases to be usable
     in connection with resales of Transfer Restricted Securities (as defined
     below) during the periods specified herein because either (1) any event
     occurs as a result of which the related prospectus forming part of such
     Shelf Registration Statement would include any untrue statement of a
     material fact or omit to state any material fact necessary to make the
     statements therein in the light of the circumstances under which they were
     made not misleading, or (2) it shall be necessary to amend such Shelf
     Registration Statement or supplement the related prospectus, to comply with
     the Securities Act or the Exchange Act or the respective rules thereunder.

          Additional Interest shall accrue on the Notes over and above the
interest set forth in the title of the Notes from and including the date on
which any such Registration Default shall occur, to but excluding the date on
which all such Registration Defaults have been cured, at a rate of 0.50% per
annum.

          (b) A Registration Default referred to in Section 5(a)(iii)(B) shall
be deemed not to have occurred and be continuing in relation to the Shelf
Registration Statement or the related prospectus if (i) such Registration
Default has occurred solely as a result of (x) the filing of a post-effective
amendment to the Shelf Registration Statement to incorporate annual audited
financial information with respect to the Company where such post-effective
amendment is not yet effective and needs to be declared effective to permit
Holders to use the related prospectus or (y) other material events, with respect
to the Company that would need to be described in the Shelf Registration
Statement or the related prospectus and (ii) in the case of clause (y), the
Company is proceeding in good faith to amend or supplement the Shelf
Registration Statement and related prospectus to describe such events as
required by paragraph 2(h) hereof; provided, however, that in any case if such
Registration Default occurs for a continuous period in excess of 60 days,
Additional Interest shall be payable in accordance with the above paragraph from
the day such Registration Default occurs until such Registration Default is
cured.

          (c) Any amounts of Additional Interest due pursuant to clause (a)(i),
(a)(ii) or (a)(iii) of this Section 5 will be payable in cash on the regular
interest payment dates with respect to the Notes. The amount of Additional
Interest will be determined by multiplying the applicable Additional Interest
rate by the principal amount of the Notes, multiplied by a fraction, the
numerator of

<PAGE>   14
                                                                              14

which is the number of days such Additional Interest rate was applicable during
such period (determined on the basis of a 360-day year comprised of twelve
30-day months), and the denominator of which is 360. The indebtedness
represented by the Additional Interest shall be subordinated in right of payment
to all existing and future Senior Indebtedness (as defined in the Indenture) as
and to the same extent as the Notes.

          (d) "Transfer Restricted Securities" means each Security until (i) the
date on which such Security has been effectively registered under the Securities
Act and disposed of in accordance with the Shelf Registration Statement or (ii)
the date on which such Security is distributed to the public pursuant to Rule
144 under the Securities Act or is saleable pursuant to Rule 144(k) under the
Securities Act.

          6. Rules 144 and 144A. The Company shall use its best efforts to file
the reports required to be filed by it under the Securities Act and the Exchange
Act in a timely manner and, if at any time the Company is not required to file
such reports, it will, upon the request of any Holder, make publicly available
other information so long as necessary to permit sales of their securities
pursuant to Rules 144 and 144A. The Company covenants that it will take such
further action as any Holder of Securities may reasonably request, all to the
extent required from time to time to enable such Holder to sell Transfer
Restricted Securities without registration under the Securities Act within the
limitations of the exemptions provided by Rules 144 and 144A (including the
requirements of Rule 144A(d)(4)). The Company will provide a copy of this
Agreement to prospective purchasers of Securities identified to the Company by
the Initial Purchaser upon request. Upon the request of any Holder, the Company
shall deliver to such Holder a written statement as to whether it has complied
with such requirements. Notwithstanding the foregoing, nothing in this Section 6
shall be deemed to require the Company to register any of its securities
pursuant to the Exchange Act.

          7. Underwritten Registrations. If any of the Transfer Restricted
Securities covered by the Shelf Registration are to be sold in an underwritten
offering, the investment banker or investment bankers and manager or managers
that will administer the offering ("Managing Underwriters") will be selected by
the Holders of a majority in aggregate principal amount of such

<PAGE>   15
                                                                              15

Transfer Restricted Securities to be included in such offering (provided that
Holders of Common Stock issued upon conversion of Notes shall not be deemed
Holders of Common Stock, but shall be deemed to be Holders of the aggregate
principal amount of Notes from which such Common Stock was converted).

          No person may participate in any underwritten registration hereunder
unless such person (i) agrees to sell such person's Transfer Restricted
Securities on the basis reasonably provided in any underwriting arrangements
approved by the persons entitled hereunder to approve such arrangements and (ii)
completes and executes all questionnaires, powers of attorney, indemnities,
underwriting agreements and other documents reasonably required under the terms
of such underwriting arrangements.

          8. Miscellaneous. (a) Amendments and Waivers. The provisions of this
Agreement may not be amended, modified or supplemented, and waivers or consents
to departures from the provisions hereof may not be given, except by the Company
and the written consent of the Holders of a majority in principal amount of the
Securities (provided that Holders of Common Stock issued upon conversion of
Notes shall not be deemed Holders of Common Stock, but shall be deemed to be
Holders of the aggregate principal amount of Notes from which such Common Stock
was converted) affected by such amendment, modification, supplement, waiver or
consents.

          (b) Notices. All notices and other communications provided for or
permitted hereunder shall be made in writing by hand delivery, first-class mail,
facsimile transmission, or air courier which guarantees overnight delivery:

          (1) if to a Holder, at the most current address given by such Holder
     to the Company;

          (2) if to the Initial Purchaser, at its address as follows:

                   Credit Suisse First Boston Corporation
                   Eleven Madison Avenue
                   New York, NY 10010-3629
                   Fax No.:  (212) 325-8278
                   Attention:  Transactions Advisory Group

          with a copy to:

<PAGE>   16
                                                                              16

                   Cravath, Swaine & Moore
                   Worldwide Plaza
                   825 Eighth Avenue
                   New York, NY 10019
                   Fax No.:  (212) 474-3700
                   Attention:  Robert Rosenman, Esq.

          (3) if to the Company, at its address as follows:

                   Human Genome Sciences, Inc.
                   9410 Key West Avenue
                   Rockville, MD 20850
                   Fax No.:  (301) 309-8439
                   Attention:  James H. Davis, Esq.

          with a copy to:

                   Piper Marbury Rudnick & Wolfe LLP
                   6225 Smith Avenue
                   Baltimore, Maryland 21209-3600
                   Fax No.:  (410) 580-3001
                   Attention:  R. W. Smith, Jr., Esq.

          All such notices and communications shall be deemed to have been duly
given: at the time delivered by hand, if personally delivered; three business
days after being deposited in the mail, postage prepaid, if mailed; when receipt
is acknowledged by recipient's facsimile machine operator, if sent by facsimile
transmission; and on the day delivered, if sent by overnight air courier
guaranteeing next day delivery.

          (c) No Inconsistent Agreements. The Company has not, as of the date
hereof, entered into, nor shall it, on or after the date hereof, without the
prior consent of CSFBC, enter into, any agreement with respect to its securities
that is inconsistent with the rights granted to the Holders herein or otherwise
conflicts with the provisions hereof.

          (d) Successors and Assigns. This Agreement shall be binding

<PAGE>   17
                                                                              17

upon the Company and its successors and assigns.

          (e) Counterparts. This Agreement may be executed in any number of
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be an original and all of which taken
together shall constitute one and the same agreement.

          (f) Headings. The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

          (g) Governing Law. THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED
IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO
PRINCIPLES OF CONFLICTS OF LAWS.

          By the execution and delivery of this Agreement, the Company submits
to the nonexclusive jurisdiction of any federal or state court in the State of
New York.

          (h) Severability. If any one or more of the provisions contained
herein, or the application thereof in any circumstance, is held invalid, illegal
or unenforceable, the validity, legality and enforceability of any such
provision in every other respect and of the remaining provisions contained
herein shall not be affected or impaired thereby.

          (i) Securities Held by the Company. Whenever the consent or approval
of Holders of a specified percentage of principal amount of Securities is
required hereunder, Securities held by the Company or its affiliates (other than
subsequent Holders of Securities if such subsequent Holders are deemed to be
affiliates solely by reason of their holdings of such Securities)shall not be
counted in determining whether such consent or approval was given by the Holders
of such required percentage.

<PAGE>   18
                                                                              18

          If the foregoing is in accordance with your understanding of our
agreement, please sign and return to the Company a counterpart hereof, whereupon
this instrument, along with all counterparts, will become a binding agreement
among the Initial Purchaser and the Company in accordance with its terms.

                                   Very truly yours,

                                   HUMAN GENOME SCIENCES, INC.

                                   By:/s/ Craig A. Rosen
                                         ----------------------
                           Name:  Craig A. Rosen, Ph.D.

                                    Title: Executive Vice
                                             President, Research
                                             and Development

The foregoing Registration
Rights Agreement is hereby confirmed
and accepted as of the date first
above written.

CREDIT SUISSE FIRST BOSTON CORPORATION

By:/s/  Robert A. Hansen
   ----------------------------
   Name:    Robert A. Hansen
   Title:   Director

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