<PAGE>   1

                                                                    EXHIBIT 4.1




                             COR THERAPEUTICS, INC.

                                     ISSUER

                                       TO


                               FIRSTAR BANK, N.A.

                                     TRUSTEE



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


                                    INDENTURE

                          DATED AS OF FEBRUARY 24, 2000


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

                             UP TO U.S.$300,000,000



             5.00% CONVERTIBLE SUBORDINATED NOTES DUE MARCH 1, 2007


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                                TABLE OF CONTENTS
                                   -----------

<TABLE>
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                                                                                                                   Page
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<S>                                                                                                                <C>
RECITALS OF THE COMPANY...........................................................................................   1

       ARTICLE ONE DEFINITIONS AND OTHER PROVISIONS OF GENERAL APPLICATION

SECTION 1.1.   Definitions........................................................................................   2
               Act................................................................................................   2
               Affiliate..........................................................................................   2
               Agent Member.......................................................................................   2
               Applicable Procedures..............................................................................   3
               Authenticating Agent...............................................................................   3
               Authorized Newspaper...............................................................................   3
               Board of Directors.................................................................................   3
               Board Resolution...................................................................................   3
               Business Day.......................................................................................   3
               Change in Control..................................................................................   3
               Closing Price Per Share............................................................................   3
               Code...............................................................................................   4
               Commission.........................................................................................   4
               Common Stock.......................................................................................   4
               Company............................................................................................   4
               Company Notice.....................................................................................   5
               Company Request....................................................................................   5
               Constituent Person.................................................................................   5
               Conversion Agent...................................................................................   5
               Conversion Price...................................................................................   5
               Conversion Rate....................................................................................   5
               Corporate Trust Office.............................................................................   5
               corporation........................................................................................   5
               Defaulted Interest.................................................................................   5
               Depositary.........................................................................................   5
               Designated Senior Debt.............................................................................   5
               Dollar.............................................................................................   6
               U.S.$..............................................................................................   6
               DTC................................................................................................   6
</TABLE>

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<TABLE>
<S>                                                                                                                 <C>
               Event of Default...................................................................................   6
               Exchange Act.......................................................................................   6
               Global Security....................................................................................   6
               Holder.............................................................................................   6
               Indenture..........................................................................................   6
               Initial Purchasers.................................................................................   6
               Interest Payment Date..............................................................................   6
               Liquidated Damages.................................................................................   7
               Maturity...........................................................................................   7
               Non-electing Share.................................................................................   7
               Notice of Default..................................................................................   7
               Officers' Certificate..............................................................................   7
               Opinion of Counsel.................................................................................   7
               Outstanding........................................................................................   7
               Paying Agent.......................................................................................   8
               Person.............................................................................................   8
               Place of Conversion................................................................................   9
               Place of Payment...................................................................................   9
               Predecessor Security...............................................................................   9
               Purchase Agreement.................................................................................   9
               Record Date........................................................................................   9
               Record Date Period.................................................................................   9
               Redemption Date....................................................................................   9
               Redemption Price...................................................................................   9
               Registrable Securities.............................................................................   9
               Registration Default...............................................................................   9
               Registration Rights Agreement......................................................................   9
               Regular Record Date................................................................................  10
               Repurchase Date....................................................................................  10
               Repurchase Price...................................................................................  10
               Responsible Officer................................................................................  10
               Restricted Global Security.........................................................................  10
               Restricted Securities Legend.......................................................................  10
               Rule 144A..........................................................................................  10
               Rule 144A Information..............................................................................  10
               Securities.........................................................................................  10
               Securities Act.....................................................................................  10
               Securities Act Legend..............................................................................  10
               Security Register..................................................................................  11
               Senior Debt........................................................................................  11
</TABLE>

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<TABLE>
<S>                                                                                                                <C>
               Shelf Registration Statement.......................................................................  12
               Special Record Date................................................................................  12
               Stated Maturity....................................................................................  12
               Subsidiary.........................................................................................  12
               Successor Security.................................................................................  12
               Trading Days.......................................................................................  13
               Trust Indenture Act................................................................................  13
               Trustee............................................................................................  13
               United States......................................................................................  13
               Vice President.....................................................................................  13
SECTION 1.2.   Compliance Certificates and Opinions...............................................................  13
SECTION 1.3.   Form of Documents Delivered to the Trustee.........................................................  14
SECTION 1.4.   Acts of Holders of Securities......................................................................  15
SECTION 1.5.   Notices, Etc., to Trustee and Company..............................................................  18
SECTION 1.6.   Notice to Holders of Securities; Waiver............................................................  19
SECTION 1.7.   Effect of Headings and Table of Contents...........................................................  20
SECTION 1.8.   Successors and Assigns.............................................................................  20
SECTION 1.9.   Separability Clause................................................................................  20
SECTION 1.10.  Benefits of Indenture..............................................................................  20
SECTION 1.11.  Governing Law......................................................................................  20
SECTION 1.12.  Legal Holidays.....................................................................................  20
SECTION 1.13.  Conflict with Trust Indenture Act..................................................................  21

                           ARTICLE TWO SECURITY FORMS

SECTION 2.1.   Form Generally.....................................................................................  21
SECTION 2.2.   Form of Security...................................................................................  22
SECTION 2.3.   Form of Certificate of Authentication..............................................................  42
SECTION 2.4.   Form of Conversion Notice..........................................................................  42

                          ARTICLE THREE THE SECURITIES

SECTION 3.1.   Title and Terms....................................................................................  44
SECTION 3.2.   Denominations......................................................................................  45
SECTION 3.3.   Execution,Authentication, Delivery and Dating......................................................  45
SECTION 3.4.   Global Securities; Non-Global Securities...........................................................  46
SECTION 3.5.   Registration, Registration of Transfer and Exchange; Restrictions on Transfer......................  48
SECTION 3.6.   Mutilated,Destroyed,Lost or Stolen Securities......................................................  52
SECTION 3.7.   Payment of Interest;Interest Rights Preserved......................................................  53
SECTION 3.8.   Persons Deemed Owners..............................................................................  55
</TABLE>

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<TABLE>
<S>                                                                                                                <C>
SECTION 3.9.   Cancellation.......................................................................................  55
SECTION 3.10.  Computation of Interest............................................................................  55
SECTION 3.11.  CUSIP Numbers......................................................................................  55

                     ARTICLE FOUR SATISFACTION AND DISCHARGE

SECTION 4.1.   Satisfaction and Discharge of Indenture............................................................  56
SECTION 4.2.   Application of Trust Money.........................................................................  57

                              ARTICLE FIVE REMEDIES

SECTION 5.1.   Events of Default..................................................................................  58
SECTION 5.2.   Acceleration of Maturity; Rescission and Annulment.................................................  60
SECTION 5.3.   Collection of Indebtedness and Suits for Enforcement by Trustee....................................  61
SECTION 5.4.   Trustee May File Proofs of Claim...................................................................  62
SECTION 5.5.   Trustee May Enforce Claims Without Possession of Securities........................................  64
SECTION 5.6.   Application of Money Collected.....................................................................  64
SECTION 5.7.   Limitation on Suits................................................................................  65
SECTION 5.8.   Unconditional Right of Holders to Receive Principal, Premium and Interest and to Convert...........  65
SECTION 5.9.   Restoration of Rights and Remedies.................................................................  66
SECTION 5.10.  Rights and Remedies Cumulative.....................................................................  66
SECTION 5.11.  Delay or Omission Not Waiver.......................................................................  66
SECTION 5.12.  Control by Holders of Securities...................................................................  67
SECTION 5.13.  Waiver of Past Defaults............................................................................  67
SECTION 5.14.  Undertaking for Costs..............................................................................  68
SECTION 5.15.  Waiver of Stay, Usury or Extension Laws............................................................  68

                             ARTICLE SIX THE TRUSTEE

SECTION 6.1.   Certain Duties and Responsibilities................................................................  69
SECTION 6.2.   Notice of Defaults.................................................................................  70
SECTION 6.3.   Certain Rights of Trustee..........................................................................  71
SECTION 6.4.   Not Responsible for Recitals or Issuance of Securities.............................................  72
SECTION 6.5.   May Hold Securities, Act as Trustee Under Other Indentures.........................................  72
SECTION 6.6.   Money Held in Trust................................................................................  73
SECTION 6.7.   Compensation and Reimbursement.....................................................................  73
SECTION 6.8.   Corporate Trustee Required; Eligibility............................................................  74
SECTION 6.9.   Resignation and Removal; Appointment of Successor..................................................  74
</TABLE>

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<TABLE>
<S>                                                                                                                <C>
SECTION 6.10.  Acceptance of Appointment by Successor.............................................................  76
SECTION 6.11.  Merger, Conversion, Consolidation or Succession to Business........................................  77
SECTION 6.12.  Authenticating Agents..............................................................................  77
SECTION 6.13.  Disqualification; Conflicting Interests............................................................  79
SECTION 6.14.  Preferential Collection of Claims Against Company..................................................  79

       ARTICLE SEVEN CONSOLIDATION, MERGER, CONVEYANCE, TRANSFER OR LEASE

SECTION 7.1.   Company May Consolidate, Etc., Only on Certain Terms...............................................  80
SECTION 7.2.   Successor Substituted..............................................................................  81

                      ARTICLE EIGHT SUPPLEMENTAL INDENTURES

SECTION 8.1.   Supplemental Indentures Without Consent of Holders of Securities...................................  81
SECTION 8.2.   Supplemental Indentures with Consent of Holders of Securities......................................  83
SECTION 8.3.   Execution of Supplemental Indentures...............................................................  84
SECTION 8.4.   Effect of Supplemental Indentures..................................................................  84
SECTION 8.5.   Reference in Securities to Supplemental Indentures.................................................  85
SECTION 8.6.   Notice of Supplemental Indentures..................................................................  85

                             ARTICLE NINE COVENANTS

SECTION 9.1    Payment of Principal, Premium and Interest.........................................................  85
SECTION 9.2.   Maintenance of Offices or Agencies.................................................................  86
SECTION 9.3.   Money for Security Payments To Be  Held in Trust...................................................  86
SECTION 9.4.   Existence..........................................................................................  88
SECTION 9.5.   Maintenance of Properties..........................................................................  88
SECTION 9.6.   Payment of Taxes and Other Claims..................................................................  89
SECTION 9.7.   Registration and Listing...........................................................................  89
SECTION 9.8.   Statement by Officers as to Default................................................................  90
SECTION 9.9.   Delivery of Certain Information....................................................................  90
SECTION 9.10.  Resale of Certain Securities; Reporting Issuer.....................................................  91
SECTION 9.11.  Registration Rights................................................................................  91
SECTION 9.12.  Waiver of Certain Covenants........................................................................  94
</TABLE>

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                      ARTICLE TEN REDEMPTION OF SECURITIES
<TABLE>
<S>                                                                                                                <C>
SECTION 10.1.  Right of Redemption................................................................................  95
SECTION 10.2.  Applicability of Article...........................................................................  95
SECTION 10.3.  Election to Redeem; Notice to Trustee..............................................................  95
SECTION 10.4.  Selection by Trustee of Securities To Be
               Redeemed...........................................................................................  96
SECTION 10.5.  Notice of Redemption...............................................................................  96
SECTION 10.6.  Deposit of Redemption Price........................................................................  97
SECTION 10.7.  Securities Payable on Redemption Date..............................................................  98
SECTION 10.8.  Securities Redeemed in Part........................................................................  98
SECTION 10.9.  Conversion Arrangement on Call for Redemption......................................................  99

                     ARTICLE ELEVEN CONVERSION OF SECURITIES

SECTION 11.1.  Conversion Privilege and Conversion Rate........................................................... 100
SECTION 11.2.  Exercise of Conversion Privilege................................................................... 100
SECTION 11.3.  Fractions of Shares................................................................................ 103
SECTION 11.4.  Adjustment of Conversion Rate...................................................................... 103
SECTION 11.5.  Notice of Adjustments of Conversion Rate........................................................... 110
SECTION 11.6.  Notice of Certain Corporate Action................................................................. 111
SECTION 11.7.  Company to Reserve Common Stock.................................................................... 112
SECTION 11.8.  Taxes on Conversions............................................................................... 112
SECTION 11.9.  Covenant as to Common Stock........................................................................ 112
SECTION 11.10. Cancellation of Converted Securities............................................................... 113
SECTION 11.11. Provision in Case of Consolidation, Merger or Sale of Assets....................................... 113
SECTION 11.12. Responsibility of Trustee for Conversion Provisions................................................ 114

                   ARTICLE TWELVE SUBORDINATION OF SECURITIES

SECTION 12.1.  Securities Subordinate to Senior Debt.............................................................. 115
SECTION 12.2.  No Payments in Certain Circumstances; Payment Over of Proceeds Upon Dissolution, Etc............... 115
SECTION 12.3.  Trustee to Effectuate Subordination................................................................ 118
SECTION 12.4.  No Waiver of Subordination Provisions.............................................................. 119
SECTION 12.5.  Notice to Trustee.................................................................................. 119
SECTION 12.6.  Reliance on Judicial Order or Certificate of Liquidating Agent..................................... 120
SECTION 12.7.  Trustee Not Fiduciary for Holders of Senior Debt................................................... 121
SECTION 12.8.  Reliance by Holders of Senior Debt on Subordination Provisions..................................... 121
</TABLE>

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<TABLE>
<S>                                                                                                                <C>
SECTION 12.9.  Rights of Trustee as Holder of Senior Debt; Preservation of Trustee's Rights....................... 121
SECTION 12.10. Article Applicable to Paying Agents................................................................ 122
SECTION 12.11. Certain Conversions and Repurchases Deemed Payment................................................. 122

 ARTICLE THIRTEEN REPURCHASE OF SECURITIES AT THE OPTION OF THE HOLDER UPON A CHANGE IN CONTROL

SECTION 13.1.  Right to Require Repurchase........................................................................ 123
SECTION 13.2.  Conditions to the Company's Election to Pay the Repurchase Price in Common Stock................... 124
SECTION 13.3.  Notices; Method of Exercising Repurchase Right, Etc................................................ 125
SECTION 13.4.  Certain Definitions................................................................................ 129

 ARTICLE FOURTEEN HOLDERS LISTS AND REPORTS BY TRUSTEE AND COMPANY; NON-RECOURSE

SECTION 14.1.  Company to Furnish Trustee Names and Addresses of Holders.......................................... 131
SECTION 14.2.  Preservation of Information........................................................................ 131
SECTION 14.3.  No Recourse Against Others......................................................................... 132
SECTION 14.4.  Reports by Trustee................................................................................. 132
SECTION 14.5.  Reports by Company................................................................................. 132

SIGNATURES
</TABLE>

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        INDENTURE, dated as of February 24, 2000, between COR Therapeutics,
Inc., a corporation duly organized and existing under the laws of the State of
Delaware, having its principal office at 256 East Grand Avenue, South San
Francisco, California 94080 (herein called the "Company"), and Firstar Bank,
N.A., a national banking association, as Trustee hereunder (herein called the
"Trustee").

                             RECITALS OF THE COMPANY

        The Company has duly authorized the creation of an issue of its 5.00%
Convertible Subordinated Notes due March 1, 2007 (herein called the
"Securities") of substantially the tenor and amount hereinafter set forth, and
to provide therefor the Company has duly authorized the execution and delivery
of this Indenture.

        All things necessary to make the Securities, when the Securities are
executed by the Company and authenticated and delivered hereunder, 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. Further, all
things necessary to duly authorize the issuance of the Common Stock of the
Company issuable upon the conversion of the Securities, and to duly reserve for
issuance the number of shares of Common Stock issuable upon such conversion,
have been done.

                   NOW, THEREFORE, THIS INDENTURE WITNESSETH:

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


<PAGE>   10

                                   ARTICLE ONE

                        DEFINITIONS AND OTHER PROVISIONS
                             OF GENERAL APPLICATION


SECTION 1.1.   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 accounting terms not otherwise defined herein have the
        meanings assigned to them in accordance with generally accepted
        accounting principles in the United States, and, 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; and

              (3) 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.

              "Act", when used with respect to any Holder of a Security, has the
meaning specified in Section 1.4.

              "Affiliate" of any specified Person means any other Person
directly or indirectly controlling or controlled by or under direct or indirect
common control with such specified Person. For the purposes of this definition,
"control", when used with respect to any 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.



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              "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, to the extent
applicable to such transaction and as in effect from time to time.

              "Authenticating Agent" means any Person authorized pursuant to
Section 6.12 to act on behalf of the Trustee to authenticate Securities.

              "Authorized Newspaper" means a newspaper in the English language,
customarily published on each Monday, Tuesday, Wednesday, Thursday and Friday,
whether or not published on Saturdays, Sundays or holidays, and of general
circulation in a Place of Payment.

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

              "Board Resolution" means a resolution duly adopted by the Board of
Directors, a copy of which, 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, shall have been
delivered to the Trustee.

              "Business Day", when used with respect to any Place of Payment,
Place of Conversion or any other place, as the case may be, means each Monday,
Tuesday, Wednesday, Thursday and Friday which is not a day on which banking
institutions in such Place of Payment, Place of Conversion or other place, as
the case may be, are authorized or obligated by law or executive order to close;
provided, however, that a day on which banking institutions in New York, New
York are authorized or obligated by law or executive order to close shall not be
a Business Day for purposes of Section 10.6 or Section 11.5.

              "Change in Control" has the meaning specified in Section 13.4(b).

              "Closing Price Per Share" means, with respect to the Common Stock
of the Company, for any day, (i) the closing price regular way on the New York
Stock Exchange or, (ii) if the Common Stock is not listed on the New York Stock




                                      -3-
<PAGE>   12

Exchange, the closing bid price regular way on the Nasdaq National Market, or
the reported last sales price regular way per share or, in case no such reported
sale takes place on such day, the average of the reported closing bid and asked
prices regular way, in either case, on the principal national securities
exchange on which the Common Stock is listed or admitted to trading, or (iii) if
the Common Stock is not quoted on the Nasdaq National Market or listed or
admitted to trading on any national securities exchange, the average of the
closing bid prices in the over-the-counter market as furnished by any New York
Stock Exchange member firm selected from time to time by the Company for that
purpose.

              "Code" has the meaning specified in Section 2.1.

              "Commission" means the United States 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" means the common stock, par value $0.0001 per
share, of the Company authorized at the date of this instrument as originally
executed. Subject to the provisions of Section 11.11, shares issuable on
conversion or repurchase of Securities shall include only shares of Common Stock
or shares of any class or classes of common stock resulting from any
reclassification or reclassifications thereof; provided, however, that if at any
time there shall be more than one such resulting class, the shares so issuable
on conversion of Securities shall include shares of all such classes, and 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.



                                      -4-
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              "Company Notice" has the meaning specified in Section 13.3.

              "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 Chief Executive Officer, its President or a Vice
President, and by its principal financial officer, Treasurer, an Assistant
Treasurer, its Secretary or an Assistant Secretary, and delivered to the
Trustee.

              "Constituent Person" has the meaning specified in Section 11.11.

              "Conversion Agent" means any Person authorized by the Company to
convert Securities in accordance with Article Eleven. The Company has initially
appointed the Trustee as its Conversion Agent in the State of Minnesota, County
of Ramsey, The City of St. Paul.

              "Conversion Price" has the meaning specified in Section 13.4(c).

              "Conversion Rate" has the meaning specified in Section 11.1.

              "Corporate Trust Office" means the office of the Trustee at which
at any particular time its corporate trust business shall be principally
administered (which at the date of this Indenture is located at 101 E. 5th
Street, 12th Floor, Corporate Trust, St. Paul, Minnesota 55101).

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

              "Defaulted Interest" has the meaning specified in Section 3.7.

              "Depositary" means, with respect to any Registered Securities, a
clearing agency that is registered as such under the Exchange Act and is
designated by the Company to act as Depositary for such Registered Securities
(or any successor securities clearing agency so registered).

              "Designated Senior Debt" means any particular Senior Debt in which
the instrument creating or evidencing the same or the assumption or guarantee
thereof (or related



                                      -5-
<PAGE>   14

agreements or documents to which the Company is a party) expressly provides that
such indebtedness shall be "Designated Senior Debt" for purposes of this
Indenture (provided that such instrument, agreement or other document may place
limitations and conditions on the right of such Senior Debt to exercise the
rights of Designated Senior Debt).

              "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 5.1.

              "Exchange Act" means the United States Securities Exchange Act of
1934 (or any successor statute), as amended from time to time.

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

              "Holder" means the Person in whose name the 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 Purchasers" means Goldman, Sachs & Co., Chase H&Q, A
Division of Chase Securities Inc., CIBC World Markets Corp., FleetBoston
Robertson Stephens Inc. and Warburg Dillon Read LLC, collectively.

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



                                      -6-
<PAGE>   15

              "Liquidated Damages" has the meaning specified in Section 9.11.

              "Maturity", when used with respect to any Security, means the date
on which the principal of such Security 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 set forth in
Article Thirteen or otherwise.

              "Non-electing Share" has the meaning specified in Section 11.11.

              "Notice of Default" has the meaning specified in Section 5.1.

              "Officers' Certificate" means a certificate signed by the Chairman
of the Board, a Vice Chairman of the Board, the Chief Executive Officer, the
President or a Vice President and by the principal financial officer, the
Treasurer, an Assistant Treasurer, the Secretary or an Assistant Secretary of
the Company, and delivered to the Trustee.

              "Opinion of Counsel" means a written opinion of counsel, who may
be counsel for the Company and who shall be acceptable to the Trustee.

              "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 the payment or redemption of which 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 segregated 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 has been duly given pursuant to



                                      -7-
<PAGE>   16

              this Indenture or provision therefor satisfactory to the Trustee
              has been made; and

                    (iii) Securities which have been paid pursuant to Section
              3.6 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;

provided, however, that in determining whether the Holders of the requisite
principal amount of Outstanding Securities are present at a meeting of Holders
of Securities for quorum purposes or have given any request, demand,
authorization, direction, notice, consent or waiver hereunder, Securities owned
by the Company or any other obligor upon the Securities or any Affiliate of the
Company or 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 determination as to the presence of a quorum or upon
any such request, demand, authorization, direction, notice, consent or waiver,
only Securities which a Responsible Officer of the Trustee actually 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 such other obligor.

              "Paying Agent" means any Person authorized by the Company to pay
the principal of or interest on any Securities on behalf of the Company and,
except as otherwise specifically set forth herein, such term shall include the
Company if it shall act as its own Paying Agent. The Company has initially
appointed the Trustee as its Paying Agent in the State of Minnesota, County of
Ramsey, The City of St. Paul.

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



                                      -8-
<PAGE>   17

              "Place of Conversion" has the meaning specified in Section 3.1.

              "Place of Payment" has the meaning specified in Section 3.1.

              "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 3.6 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.

              "Purchase Agreement" means the Purchase Agreement, dated as of
February 17, 2000, between the Company and the Initial Purchasers, as such
agreement may be amended from time to time.

              "Record Date" means any Regular Record Date or Special Record
Date.

              "Record Date Period" means the period from the close of business
of any Regular Record Date next preceding any Interest Payment Date to the
opening of business on such Interest Payment Date.

              "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 Price", when used with respect to any Security to be
redeemed, means the price at which it is to be redeemed pursuant to this
Indenture.

              "Registrable Securities" has the meaning specified in Section
9.11.

              "Registration Default" has the meaning specified in Section 9.11.

              "Registration Rights Agreement" has the meaning specified in
Section 2.2.



                                      -9-
<PAGE>   18

              "Regular Record Date" for interest payable in respect of any
Registered Security on any Interest Payment Date means the 15th day of February
or the 15th day of August (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 13.1.

              "Repurchase Price" has the meaning specified in Section 13.1.

              "Responsible Officer", when used with respect to the Trustee,
means any officer within the Corporate Trust Office of the Trustee, including,
without limitation, any vice president, assistant vice president, assistant
treasurer, corporate trust officer or other employee of the Trustee customarily
performing functions similar to those performed by any of the above designated
officers, and also means, with respect to a particular corporate trust matter,
any other officer to whom such matter is referred because of his knowledge and
familiarity with the particular subject.

              "Restricted Global Security" has the meaning specified in Section
2.1.

              "Restricted Securities Legend" means, collectively, the legends
substantially in the forms of the legends required in the form of Security set
forth in Section 2.2 to be placed upon each Security.

              "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 9.9.

              "Securities" has the meaning ascribed to it in the first paragraph
under the caption "Recitals of the Company".

              "Securities Act" means the United States Securities Act of 1933
(or any successor statute), as amended from time to time.

              "Securities Act Legend" means a Restricted Securities Legend.



                                      -10-
<PAGE>   19

              "Security Register" and "Security Registrar" have the respective
meanings specified in Section 3.5.

              "Senior Debt" means the principal of (and premium, if any) and
interest (including all interest accruing subsequent to the commencement of any
bankruptcy or similar proceeding, whether or not a claim for post-petition
interest is allowable as a claim in any such proceeding) on, and all fees and
other amounts payable in connection with, the following, whether absolute or
contingent, secured or unsecured, due or to become due, outstanding on the date
of this Indenture or thereafter created, incurred or assumed: (a) all
indebtedness of the Company evidenced by credit or loan agreements, notes,
bonds, debentures, or other similar instruments, (b) all obligations of the
Company for money borrowed, (c) all obligations of the Company (1) as lessee
under leases required to be capitalized on the balance sheet of the lessee under
generally accepted accounting principles and (2) as lessee under other leases
for facilities, equipment, or other assets, whether or not capitalized, entered
into for financing purposes (including any so-called "synthetic leases"), (d)
all obligations of the Company under interest rate and currency swaps, caps,
floors, collars, hedge agreements, forward contracts, or similar agreements or
arrangements including, without limitation, agreements and arrangements intended
to protect the Company against fluctuations in interest or currency exchange
rates or commodity prices, (e) all obligations of the Company with respect to
letters of credit, bank guarantees, bankers' acceptances and similar facilities
issued for the account of the Company and all reimbursement obligations of the
Company with respect to the foregoing, (f) all obligations of the Company issued
or assumed as the deferred purchase price of any business, property, assets
(including intangibles) or services (but excluding trade accounts payable and
accrued liabilities that constitute liabilities arising in the ordinary course
of business), (g) all obligations of the Company of the type referred to in
clauses (a) through (f) above of another Person and all dividends of another
Person, the payment of which, in either case, the Company has assumed or
guaranteed, or for which the Company is responsible or liable, directly or
indirectly, jointly or severally, as obligor, guarantor or otherwise, or which
is secured by a lien on property of the Company, and (h) renewals, extensions,
modifications, replacements, restatements and refundings of, or any indebtedness
or



                                      -11-
<PAGE>   20

obligation issued in exchange for, any such indebtedness or obligation described
in clauses (a) through (g) of this paragraph; provided, however, that Senior
Debt shall not include the Securities or any such indebtedness or obligation if
the terms of such indebtedness or obligation (or the terms of the instrument
under which, or pursuant to which it is issued) expressly provides that such
indebtedness or obligation is not superior in right of payment to the
Securities; provided, further, that Senior Debt shall not include any
indebtedness or obligation owed by the Company to any direct or indirect
Subsidiary.

              "Shelf Registration Statement" has the meaning specified in
Section 9.11.

              "Special Record Date" for the payment of any Defaulted Interest
means a date fixed by the Company pursuant to Section 3.7.

              "Stated Maturity", when used with respect to any Security or any
installment of interest thereon, means the date specified in such Security as
the fixed date on which the principal of such Security or such installment of
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 or
other similar interests in the corporation which ordinarily has or have voting
power for the election of directors, or persons performing similar functions,
whether at all times or only so long as no senior class of stock or other
interests has or have such voting power by reason of any contingency.

              "Successor Security" of any particular Security means every
Security issued after, and 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 3.6 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.



                                      -12-
<PAGE>   21

              "Trading Days" means (i) if the Common Stock is listed or admitted
for trading on any national securities exchange, days on which such national
securities exchange is open for business; (ii) if the Common Stock is quoted on
the Nasdaq National Market or any other system of automated dissemination of
quotations of securities prices, days on which trades may be effected through
such system; or (iii) if the Common Stock is not listed or admitted for trading
on any national securities exchange or quoted on the Nasdaq National Market or
any other system of automated dissemination of quotation of securities prices,
days on which the Common Stock is traded regular way in the over-the-counter
market and for which a closing bid and a closing asked price for the Common
Stock are available.

              "Trust Indenture Act" means the Trust Indenture Act of 1939 as in
force at the date as of which this instrument was executed; provided, however,
that in the event the Trust Indenture Act of 1939 is amended after such date,
"Trust Indenture Act" means, to the extent required by any such amendment, the
Trust Indenture Act of 1939 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 and the District of Columbia), its territories, its possessions and other
areas subject to its jurisdiction (its "possessions" including Puerto Rico, the
U.S. Virgin Islands, Guam, American Samoa, Wake Island and the Northern Mariana
Islands).

              "Vice President", when used with respect to the Company, 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 1.2. 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 stating that all conditions precedent,
if any, provided for in this Indenture relating to the proposed



                                      -13-
<PAGE>   22

action have been complied with and, if required by the Trust Indenture Act, an
Opinion of Counsel stating that in the opinion of such counsel all such
conditions precedent, if any, have been complied with, except that in the case
of any such application or request as to which the furnishing of such documents
is specifically required by any provision of this Indenture relating to such
particular application or request, no additional certificate or opinion need be
furnished.

              Every certificate or opinion with respect to compliance with a
condition or covenant provided for in this Indenture (including certificates
provided for in Section 9.8) shall include:

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

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

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

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

SECTION 1.3. Form of Documents Delivered to the 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.



                                      -14-
<PAGE>   23

              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 such certificate or opinion is based are
erroneous. Any such certificate or opinion of 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 or any other Person
stating that the information with respect to such factual matters is in the
possession of the Company or such other Person, 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 1.4. Acts of Holders of Securities.

              (a) 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 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 or proxy duly appointed in writing by such Holders. Such
action shall become effective when such instrument or instruments record is
delivered to the Trustee and, where it is hereby expressly required, to the
Company. The Trustee shall promptly deliver to the Company copies of all such
instruments delivered to the Trustee. Such instrument or instruments (and the
action embodied therein and evidenced thereby) are herein sometimes referred to
as the "Act" of the Holders of Securities signing such instrument or
instruments. Proof of execution of any such instrument or of a writing
appointing any such agent or proxy, or of the holding by any Person of a
Security, shall be sufficient for any purpose of this Indenture and (subject to
Section 6.1) conclusive in favor of the Trustee and the Company if made in the
manner provided in this Section.



                                      -15-
<PAGE>   24

              (b) 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.

              (c) The principal amount and serial number of any Registered
Security held by any Person, and the date of his holding the same, shall be
proved by the Security Register.

              (d) The fact and date of execution of any such instrument or
writing and the authority of the Person executing the same may also be proved in
any other manner which the Trustee deems sufficient; and the Trustee may in any
instance require further proof with respect to any of the matters referred to in
this Section 1.4.

              (e) The Company may set any day as the record date for the purpose
of determining the Holders entitled to give or take any request, demand,
authorization, direction, notice, consent, waiver or other action, or to vote on
any action, authorized or permitted by this Indenture to be given or taken by
Holders. Promptly and in any case not later than ten days after setting a record
date, the Company shall notify the Trustee and the Holders of such record date.
If not set by the Company prior to the first solicitation of a Holder made by
any Person in respect of any such action, or, in the case of any such vote,
prior to such vote, the record date for any such action or vote shall be the
30th day (or, if later, the date of the most recent list of Holders required to
be provided pursuant to Section 14.1) prior to such first solicitation or vote,
as the case may be. With regard to any record date, the Holders on such date (or
their duly appointed agents or proxies), and only such Persons, shall be
entitled to give or take, or vote on, the relevant action, whether or not such
Holders remain Holders after such record date. Notwithstanding the foregoing,
the Company shall not set a record date for, and the provisions of this
paragraph shall not apply with respect to, any notice, declaration or direction
referred to in the next paragraph.



                                      -16-
<PAGE>   25

              Upon receipt by the Trustee from any Holder of (i) any notice of
default or breach referred to in Section 5.1(4), if such default or breach has
occurred and is continuing and the Trustee shall not have given such a notice to
the Company, (ii) any declaration of acceleration referred to in Section 5.2, if
an Event of Default has occurred and is continuing and the Trustee shall not
have given such a declaration to the Company, or (iii) any direction referred to
in Section 5.12, if the Trustee shall not have taken the action specified in
such direction, then, with respect to clauses (ii) and (iii), a record date
shall automatically and without any action by the Company or the Trustee be set
for determining the Holders entitled to join in such declaration or direction,
which record date shall be the close of business on the tenth day (or, if such
day is not a Business Day, the first Business Day thereafter) following the day
on which the Trustee receives such declaration or direction, and, with respect
to clause (i), the Trustee may set any day as a record date for the purpose of
determining the Holders entitled to join in such notice of default. Promptly
after such receipt by the Trustee of any such declaration or direction referred
to in clause (ii) or (iii), and promptly after setting any record date with
respect to clause (i), and as soon as practicable thereafter, the Trustee shall
notify the Company and the Holders of any such record date so fixed. The Holders
on such record date (or their duly appointed agents or proxies), and only such
Persons, shall be entitled to join in such notice, declaration or direction,
whether or not such Holders remain Holders after such record date; provided
that, unless such notice, declaration or direction shall have become effective
by virtue of Holders of the requisite principal amount of Securities on such
record date (or their duly appointed agents or proxies) having joined therein on
or prior to the 90th day after such record date, such notice, declaration or
direction shall automatically and without any action by any Person be cancelled
and of no further effect. Nothing in this paragraph shall be construed to
prevent a Holder (or a duly appointed agent or proxy thereof) from giving,
before or after the expiration of such 90-day period, a notice, declaration or
direction contrary to or different from, or, after the expiration of such
period, identical to, the notice, declaration or direction to which such record
date relates, in which event a new record date in respect thereof shall be set
pursuant to this paragraph. In addition, nothing in this paragraph shall be
construed to render ineffective any notice,



                                      -17-
<PAGE>   26

declaration or direction of the type referred to in this paragraph given at any
time to the Trustee and the Company by Holders (or their duly appointed agents
or proxies) of the requisite principal amount of Securities on the date such
notice, declaration or direction is so given.

              (f) Except as provided in Sections 5.12 and 5.13, any request,
demand, authorization, direction, notice, consent, election, waiver or other Act
of the Holder of any Security shall bind every future Holder of the same
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.

SECTION 1.5. Notices, Etc., to Trustee and Company.

              Any request, demand, authorization, direction, notice, consent,
election, waiver or other Act of Holders of Securities 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 of Securities or by the Company
        shall be sufficient for every purpose hereunder if made, given,
        furnished or filed in writing to or with the Trustee and received at its
        Corporate Trust Office, Attention: Corporate Trust Department, and shall
        be deemed given when received.

              (2) the Company by the Trustee or by any Holder of Securities
        shall be sufficient for every purpose hereunder (unless otherwise herein
        expressly provided) if in writing, mailed, first-class postage prepaid,
        or telecopied and confirmed by mail, first-class postage prepaid, or
        delivered by hand or overnight courier, addressed to the Company at 256
        E. Grand Avenue, South, San Francisco, CA 94080, Attention: Vice
        President, Finance, or at any other address previously furnished in
        writing to the Trustee by the Company, and shall be deemed given when
        received.

              Any request, demand, authorization, direction, notice, consent,
election or waiver required or permitted under this Indenture shall be in the
English language,



                                      -18-
<PAGE>   27

except that any published notice may be in an official language of the country
of publication.

SECTION 1.6. Notice to Holders of Securities; Waiver.

              Except as otherwise expressly provided herein, where this
Indenture provides for notice to Holders of Securities of any event, such notice
shall be sufficiently given to Holders if in writing and mailed, first-class
postage prepaid, to each Holder of a Security affected by such event, at the
address of such Holder as it appears in the Security Register, not earlier than
the earliest date and not later than the latest date prescribed for the giving
of such notice.

              Neither the failure to mail such notice, nor any defect in any
notice so mailed, to any particular Holder of a Registered Security shall affect
the sufficiency of such notice with respect to other Holders of Registered
Securities. 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 to Holders of Registered Securities as shall be made with
the approval of the Trustee, which approval shall not be unreasonably withheld
or delayed, shall constitute a sufficient notification to such Holders for every
purpose hereunder.

              Such notice shall be deemed to have been given when such notice is
mailed.

              In addition to notices by mail, the Company undertakes that any
notice of redemption of the Securities, or notice of any Change in Control and
of the related repurchase right arising as a result thereof, shall further
include a public announcement thereof by release made to Reuters Economic
Services and Bloomberg Business News.

              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 of Securities 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.



                                      -19-
<PAGE>   28

SECTION 1.7. Effect of Headings and Table of Contents.

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

SECTION 1.8. 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 1.9. Separability Clause.

              In case any provision in this Indenture or 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 1.10. Benefits of Indenture.

              Except as provided in the next sentence, nothing in this Indenture
or in the Securities, express or implied, shall give to any Person, other than
the parties hereto and their successors and assigns hereunder and the Holders of
Securities, any benefit or legal or equitable right, remedy or claim under this
Indenture. The provisions of Article Twelve are intended to be for the benefit
of, and shall be enforceable directly by, the holders of Senior Debt.

SECTION 1.11. Governing Law.

              THIS INDENTURE AND THE SECURITIES SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, THE UNITED
STATES OF AMERICA, WITHOUT REGARD TO THE CONFLICTS OF LAWS PRINCIPLES THEREOF.

SECTION 1.12. Legal Holidays.

              In any case where any Interest Payment Date, Redemption Date,
Repurchase Date or Stated Maturity of any Security or the last day on which a
Holder of a Security has a right to convert his Security shall not be a Business
Day at a Place of Payment or Place of Conversion, as the case may be, then
(notwithstanding any other provision of this



                                      -20-
<PAGE>   29

Indenture or of the Securities) payment of principal of, premium, if any, or
interest on, or the payment of the Repurchase Price (whether the same is payable
in cash or in shares of Common Stock) with respect to, or delivery for
conversion of, such Security need not be made at such Place of Payment or Place
of Conversion, as the case may be, on or by such day, but may be made on or by
the next succeeding Business Day at such Place of Payment or Place of
Conversion, as the case may be, with the same force and effect as if made on the
Interest Payment Date, Redemption Date or Repurchase Date, or at the Stated
Maturity or by such last day for conversion; provided, however, that in the case
that payment is made on such succeeding Business Day, no interest shall accrue
on the amount so payable for the period from and after such Interest Payment
Date, Redemption Date, Repurchase Date, Stated Maturity or last day for
conversion, as the case may be.

SECTION 1.13. Conflict with Trust Indenture Act.

              If any provision hereof limits, qualifies or conflicts with a
provision of the Trust Indenture Act that 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 that 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. Until such time as this Indenture shall be qualified under the Trust
Indenture Act, this Indenture, the Company and the Trustee shall be deemed for
all purposes hereof to be subject to and governed by the Trust Indenture Act to
the same extent as would be the case if this Indenture were so qualified on the
date hereof.


                                   ARTICLE TWO

                                 SECURITY FORMS


SECTION 2.1. Form Generally.

              The Securities shall be in substantially the form 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



                                      -21-
<PAGE>   30

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 the Internal Revenue Code of 1986, as amended, and
regulations thereunder (the "Code"), or as may, consistently herewith, be
determined by the officers executing such Securities, as evidenced by their
execution thereof. All Securities shall be issued in registered form, as opposed
to bearer form, and shall sometimes be referred to as "Registered Securities".

              The Trustee's certificates of authentication shall be in
substantially the form set forth in Section 2.3.

              Conversion notices shall be in substantially the form set forth in
Section 2.4.

              Repurchase notices shall be substantially in the form set forth in
Section 2.2.

              The Securities shall be printed, lithographed, typewritten or
engraved or produced by any combination of these methods on steel engraved
borders if so required by any securities exchange upon which the Securities may
be listed, or may be produced in any other manner permitted by the rules of any
such securities exchange, or, if the Securities are not listed on a securities
exchange, in any other manner approved by the Company, all as determined by the
officers executing such Securities, as evidenced by their execution thereof.

              Upon their original issuance, Securities shall be issued in the
form of one or more Global Securities without interest coupons and shall be
registered in the name of DTC, as Depositary, or its nominee 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".

SECTION 2.2. Form of Security

                                 [FORM OF FACE]

[THE FOLLOWING LEGEND SHALL APPEAR ON THE FACE OF EACH RESTRICTED SECURITY OTHER
THAN ANY RESTRICTED GLOBAL SECURITY:



                                      -22-
<PAGE>   31

              THIS NOTE AND ANY COMMON STOCK ISSUABLE UPON THE CONVERSION OF
THIS NOTE HAVE NOT BEEN REGISTERED UNDER THE U.S. SECURITIES ACT OF 1933, AS
AMENDED (THE "SECURITIES ACT"), AND MAY NOT BE SOLD OR OTHERWISE TRANSFERRED IN
THE ABSENCE OF SUCH REGISTRATION OR AN APPLICABLE EXEMPTION THEREFROM. EACH
PURCHASER OF THIS NOTE IS HEREBY NOTIFIED THAT THE SELLER OF THIS NOTE MAY BE
RELYING ON THE EXEMPTION FROM THE PROVISIONS OF SECTION 5 OF THE SECURITIES ACT
PROVIDED BY RULE 144A THEREUNDER.

              THIS NOTE AND ANY COMMON STOCK ISSUABLE UPON CONVERSION OF THIS
NOTE MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT (A)(1)
TO A PERSON WHO THE TRANSFEROR REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL
BUYER WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT ACQUIRING FOR ITS
OWN ACCOUNT OR THE ACCOUNT OF A QUALIFIED INSTITUTIONAL BUYER IN A TRANSACTION
MEETING THE REQUIREMENTS OF RULE 144A, (2) PURSUANT TO AN EXEMPTION FROM
REGISTRATION UNDER THE SECURITIES ACT PROVIDED BY RULE 144 THEREUNDER (IF
AVAILABLE), (3) TO AN INSTITUTIONAL INVESTOR THAT IS AN ACCREDITED INVESTOR
WITHIN THE MEANING OF RULE 501(A)(1), (2), (3) OR (7) OF REGULATION D UNDER THE
SECURITIES ACT PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE SECURITIES
ACT (IF AVAILABLE) OR (4) PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER
THE SECURITIES ACT, AND (B) IN ACCORDANCE WITH ALL APPLICABLE SECURITIES LAWS OF
THE STATES OF THE UNITED STATES AND OTHER JURISDICTIONS.

              THIS NOTE, ANY SHARES OF COMMON STOCK ISSUABLE UPON ITS CONVERSION
AND ANY RELATED DOCUMENTATION MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME
TO MODIFY THE RESTRICTIONS ON RESALES AND OTHER TRANSFERS OF THIS NOTE AND ANY
SUCH SHARES TO REFLECT ANY CHANGE IN APPLICABLE LAW OR REGULATION (OR THE
INTERPRETATION THEREOF) OR IN PRACTICES RELATING TO THE RESALE OR TRANSFER OF
RESTRICTED SECURITIES GENERALLY. THE HOLDER OF THIS NOTE AND SUCH SHARES SHALL
BE DEEMED BY THE ACCEPTANCE OF THIS NOTE AND ANY SUCH SHARES TO HAVE AGREED TO
ANY SUCH AMENDMENT OR SUPPLEMENT.]

[THE FOLLOWING LEGEND SHALL APPEAR ON THE FACE OF EACH RESTRICTED GLOBAL
SECURITY:

              THE SECURITIES EVIDENCED BY THIS GLOBAL SECURITY AND ANY COMMON
STOCK ISSUABLE UPON THE CONVERSION OF THE SECURITIES HAVE NOT BEEN REGISTERED
UNDER THE U.S. SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND
MAY NOT BE SOLD OR OTHERWISE TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR
AN APPLICABLE EXEMPTION THEREFROM. EACH PURCHASER OF ANY BENEFICIAL INTEREST IN
THE SECURITIES IS HEREBY NOTIFIED THAT THE SELLER OF SUCH BENEFICIAL INTEREST IN
THE SECURITIES MAY BE RELYING ON THE EXEMPTION FROM THE PROVISIONS OF SECTION 5
OF THE SECURITIES ACT PROVIDED BY RULE 144A THEREUNDER.



                                      -23-
<PAGE>   32

              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 ANY SUCH
PARTICIPANT) AGREES FOR THE BENEFIT OF COR THERAPEUTICS, INC. (THE "COMPANY")
THAT (A) ANY BENEFICIAL INTEREST IN THE SECURITIES AND ANY SHARES OF COMMON
STOCK ISSUABLE UPON THEIR CONVERSION MAY BE RESOLD, PLEDGED OR OTHERWISE
TRANSFERRED ONLY (I) TO A PERSON WHO THE SELLER REASONABLY BELIEVES IS A
QUALIFIED INSTITUTIONAL BUYER WITHIN THE MEANING OF RULE 144A UNDER THE
SECURITIES ACT ACQUIRING FOR ITS OWN ACCOUNT OR THE ACCOUNT OF A QUALIFIED
INSTITUTIONAL BUYER IN A TRANSACTION MEETING THE REQUIREMENTS OF RULE 144A, (II)
PURSUANT TO THE EXEMPTION FROM REGISTRATION UNDER THE SECURITIES ACT PROVIDED BY
RULE 144 THEREUNDER (IF AVAILABLE), (III) TO AN INSTITUTIONAL INVESTOR THAT IS
AN ACCREDITED INVESTOR WITHIN THE MEANING OF RULE 501(a)(1), (2), (3) OR (7) OF
REGULATION D UNDER THE SECURITIES ACT PURSUANT TO AN EXEMPTION FROM REGISTRATION
UNDER THE SECURITIES ACT (IF AVAILABLE) OR (IV) PURSUANT TO AN EFFECTIVE
REGISTRATION STATEMENT UNDER THE SECURITIES ACT AND IN EACH OF CASES (I) THROUGH
(V) IN ACCORDANCE WITH ANY APPLICABLE SECURITIES LAWS OF THE STATES AND OTHER
JURISDICTIONS OF THE UNITED STATES AND THAT (B) THE BENEFICIAL OWNER WILL, AND
EACH SUBSEQUENT BENEFICIAL OWNER OF AN INTEREST IN ANY OF THE SECURITIES
EVIDENCED BY THIS GLOBAL SECURITY OR ANY COMMON STOCK ISSUABLE UPON CONVERSION
THEREOF IS REQUIRED TO, NOTIFY ANY PURCHASER OF ANY BENEFICIAL INTEREST IN THE
SECURITIES OR SUCH COMMON STOCK ISSUABLE UPON ITS CONVERSION FROM IT OF THE
RESALE RESTRICTIONS REFERRED TO IN (A) ABOVE.

              THIS SECURITY, ANY SHARES OF COMMON STOCK ISSUABLE UPON ITS
CONVERSION AND ANY RELATED DOCUMENTATION MAY BE AMENDED OR SUPPLEMENTED FROM
TIME TO TIME TO MODIFY THE RESTRICTIONS ON RESALES AND OTHER TRANSFERS OF THIS
SECURITY AND ANY SUCH SHARES TO REFLECT ANY CHANGE IN APPLICABLE LAW OR
REGULATION (OR THE INTERPRETATION THEREOF) OR IN PRACTICES RELATING TO THE
RESALE OR TRANSFER OF RESTRICTED SECURITIES GENERALLY. THE HOLDER AND BENEFICIAL
OWNERS OF AN INTEREST IN THIS SECURITY AND ANY SHARES OF COMMON STOCK ISSUABLE
ON CONVERSION SHALL BE DEEMED BY THE ACCEPTANCE OF THIS SECURITY AND THE
BENEFICIAL INTERESTS THEREIN AND ANY SUCH SHARES TO HAVE AGREED TO ANY SUCH
AMENDMENT OR SUPPLEMENT.]

[THE FOLLOWING LEGEND SHALL APPEAR ON THE FACE OF EACH GLOBAL SECURITY:

              THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE
INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE
DEPOSITARY OR A NOMINEE OF THE DEPOSITARY, WHICH MAY



                                      -24-
<PAGE>   33

BE TREATED BY THE COMPANY, THE TRUSTEE AND ANY AGENT THEREOF AS OWNER AND HOLDER
OF THIS SECURITY FOR ALL PURPOSES.]

[THE FOLLOWING LEGEND SHALL APPEAR ON THE FACE OF EACH GLOBAL SECURITY FOR WHICH
THE DEPOSITORY TRUST COMPANY IS TO BE THE DEPOSITARY:

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



                                      -25-
<PAGE>   34

                             COR THERAPEUTICS, INC.

                       5.00% CONVERTIBLE SUBORDINATED NOTE
                                DUE MARCH 1, 2007

No. _____________                                                     U.S.$_____

CUSIP No._______

              COR THERAPEUTICS, 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 referred to on the reverse
hereof), for value received, hereby promises to pay to _______________, or
registered assigns, the principal sum of _____________ United States Dollars
(U.S.$ _____) [if this Security is a Global Security, then insert -- (which
principal amount may from time to time be increased or decreased to such other
principal amounts (which, taken together with the principal amounts of all other
Outstanding Securities, shall not exceed $300,000,000 in the aggregate at any
time) by adjustments made on the records of the Trustee hereinafter referred to
in accordance with the Indenture)] on March 1, 2007 and to pay interest thereon,
from February 24, 2000, or from the most recent Interest Payment Date (as
defined below) to which interest has been paid or duly provided for,
semi-annually in arrears on March 1 and September 1 in each year (each, an
"Interest Payment Date"), commencing September 1, 2000, at the rate of 5.00% per
annum, until the principal hereof is due, and at the rate of 5.00% per annum on
any overdue principal and premium, if any, and, to the extent permitted by law,
on any overdue interest. The interest so payable, and punctually paid or duly
provided for, on any Interest Payment Date will, as provided in the 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 the 15th day of February or the 15th day of
August (whether or not a Business Day), as the case may be, next preceding such
Interest Payment Date. Except as otherwise provided in the Indenture, 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



                                      -26-
<PAGE>   35

Defaulted Interest to be fixed by the Company, notice whereof shall be given to
Holders of Registered 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 the Indenture. Payments of principal shall be made upon the
surrender of this Security at the option of the Holder at the Corporate Trust
Office of the Trustee, or at such other office or agency of the Company as may
be designated by it for such purpose in such coin or currency of the United
States of America as at the time of payment shall be legal tender for the
payment of public and private debts, or at such other offices or agencies as the
Company may designate, by United States Dollar check drawn on, or wire transfer
to, a United States Dollar account (such a wire transfer to be made only to a
Holder of an aggregate principal amount of Registered Securities in excess of
U.S.$2,000,000, and only if such Holder shall have furnished wire instructions
in writing to the Trustee no later than 15 days prior to the relevant payment
date) maintained by the payee with a bank. Payment of interest on this Security
may be made by United States Dollar check mailed to the address of the Person
entitled thereto as such address shall appear in the Security Register, or, upon
written application by the Holder to the Security Registrar setting forth wire
instructions not later than the relevant Record Date, by wire transfer to a
United States Dollar account (such a wire transfer to be made only to a Holder
of an aggregate principal amount of Registered Securities in excess of
U.S.$2,000,000 and only if such Holder shall have furnished wire instructions in
writing to the Trustee no later than 15 days prior to the relevant payment date)
maintained by the payee with a bank.

              Except as specifically provided herein and in the Indenture, the
Company shall not be required to make any payment with respect to any tax,
assessment or other governmental charge imposed by any government or any
political subdivision or taxing authority thereof or therein.

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



                                      -27-
<PAGE>   36

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



                                      -28-
<PAGE>   37

              IN WITNESS WHEREOF, the Company has caused this Security to be
duly executed under its corporate seal.

                                       COR THERAPEUTICS, INC.

[Corporate Seal]

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

Attest:


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



                                      -29-
<PAGE>   38

                                [FORM OF REVERSE]

              This Security is one of a duly authorized issue of securities of
the Company designated as its "5.00% Convertible Subordinated Notes due March 1,
2007" (herein called the "Securities"), limited in aggregate principal amount to
U.S.$300,000,000, issued and to be issued under an Indenture, dated as of
February 24, 2000 (herein called the "Indenture"), between the Company and
Firstar Bank, N.A., as Trustee (herein called the "Trustee", which term includes
any successor trustee under the Indenture), to which Indenture and all
indentures supplemental thereto reference is hereby made for a statement of the
respective rights, limitations of rights, duties and immunities thereunder of
the Company, the Trustee, the holders of Senior Debt and the Holders of the
Securities and of the terms upon which the Securities are, and are to be,
authenticated and delivered. As provided in the Indenture and subject to certain
limitations therein set forth, Registered Securities are exchangeable for a like
aggregate principal amount of Registered Securities of any authorized
denominations as requested by the Holder surrendering the same upon surrender of
the Registered Security or Registered Securities to be exchanged, at the
Corporate Trust Office of the Trustee. The Trustee upon such surrender by the
Holder will issue the new Registered Securities in the requested denominations.

              No sinking fund is provided for the Securities.

              The Securities are subject to redemption at the option of the
Company at any time on or after March 1, 2003, in whole or in part, upon not
less than 30 nor more than 60 days' notice to the Holders prior to the
Redemption Date at the following Redemption Prices (expressed as percentages of
the principal amount) for the twelve-month period beginning on March 1 of the
following years:


<TABLE>
<CAPTION>
           Year                                     Redemption Price
           ----                                     ----------------
<S>                                                 <C>
2003............................                         102.857%

2004............................                         102.143%

2005............................                         101.429%

2006............................                         100.714%
</TABLE>



                                      -30-
<PAGE>   39

and at a Redemption Price equal to 100% of the principal amount on and after
March 1, 2007, together, in each case, with accrued interest to the Redemption
Date; provided, however, that interest installments on Securities 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 the event of a redemption of the Securities, the Company will
not be required (a) to register the transfer or exchange of Registered
Securities for a period of 15 days immediately preceding the date notice is
given identifying the serial numbers of the Securities called for such
redemption or (b) to register the transfer or exchange of any Registered
Security, or portion thereof, called for redemption.

              Notice to the Holders will be given not less than 30 nor more than
60 days prior to the Redemption Date as provided in the Indenture.

              In any case where the due date for the payment of the principal
of, premium, if any, interest, or Liquidated Damages on any Security or the last
day on which a Holder of a Security has a right to convert his Security shall
be, at any Place of Payment or Place of Conversion, as the case may be, a day on
which banking institutions at such Place of Payment or Place of Conversion are
authorized or obligated by law or executive order to close, then payment of
principal, premium, if any, interest, or Liquidated Damages, or delivery for
conversion of such Security need not be made on or by such date at such place
but may be made on or by the next succeeding day at such place which is not a
day on which banking institutions are authorized or obligated by law or
executive order to close, with the same force and effect as if made on the date
for such payment or the date fixed for redemption or repurchase, or by such last
day for conversion, and no interest shall accrue on the amount so payable for
the period from and after such due date.

              Subject to and upon compliance with the provisions of the
Indenture, the Holder of this Security is entitled, at his option, at any time
following the original issue date



                                      -31-
<PAGE>   40

of the Securities and on or before the close of business on March 1, 2007, or in
case this Security or a portion hereof is called for redemption or the Holder
hereof has exercised his right to require the Company to repurchase this
Security or such portion hereof, then in respect of this Security until and
including, but (unless the Company defaults in making the payment due upon
redemption or repurchase, as the case may be) not after, the close of business
on the Business Day immediately preceding the Redemption Date or the Repurchase
Date, as the case may be, to convert this Security (or any portion of the
principal amount hereof that is an integral multiple of U.S.$1,000, provided
that the unconverted portion of such principal amount is U.S.$1,000 or any
integral multiple of U.S.$1,000 in excess thereof) into fully paid and
nonassessable shares of Common Stock of the Company at an initial Conversion
Rate of 14.8028(or at the current adjusted Conversion Rate if an adjustment has
been made as provided in the Indenture) by surrender of this Security, duly
endorsed or assigned to the Company or in blank and, in case such surrender
shall be made during the period from the close of business on any Regular Record
Date next preceding any Interest Payment Date to the opening of business on such
Interest Payment Date (except if this Security has been called for redemption on
a Redemption Date or is repurchasable on a Repurchase Date, with the consequence
that the conversion right of such Security would terminate between such Regular
Record Date and the close of business on such Interest Payment Date), also
accompanied by payment in New York Clearing House or other 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, and also the
conversion notice hereon duly executed, to the Company at the Corporate Trust
Office of the Trustee, or at such other office or agency of the Company, subject
to any laws or regulations applicable thereto and subject to the right of the
Company to terminate the appointment of any Conversion Agent (as defined below)
as may be designated by it for such purpose in the State of Minnesota, County of
Ramsey, City of St. Paul, or at such other offices or agencies as the Company
may designate (each a "Conversion Agent"), provided, further, that in case
surrender of this Security for conversion shall be made during the period from
the close of business on any Regular Record Date next preceding any Interest
Payment Date to the opening of business on such Interest Payment Date and if
this Security or portion hereof has been called for redemption on a Redemption
Date or is



                                      -32-
<PAGE>   41

repurchasable on a Repurchase Date, with the consequence that the conversion
right of such Security would terminate between such Regular Record Date and the
close of business on such Interest Payment Date, then the Holder of this
Security will be entitled to receive the interest accruing hereon from the
Interest Payment Date next preceding the date of such conversion to such
succeeding Interest Payment Date and shall not be required to pay such interest
upon surrender of this Security for conversion. Subject to the provisions of the
preceding sentence and, in the case of a conversion after the close of business
on the Regular Record Date next preceding any Interest Payment Date and on or
before the close of business on such Interest Payment Date, to the right of the
Holder of this Security (or any Predecessor Security of record as of such
Regular Record Date) to receive the related installment of interest to the
extent and under the circumstances provided in the Indenture, no cash payment or
adjustment is to be made on conversion for interest accrued hereon from the
Interest Payment Date next preceding the day of conversion, or for dividends on
the Common Stock issued on conversion hereof. The Company shall thereafter
deliver to the Holder the fixed number of shares of Common Stock (together with
any cash adjustment, as provided in the Indenture) into which this Security is
convertible and such delivery will be deemed to satisfy the Company's obligation
to pay the principal amount of this Security. No fractions of shares or scrip
representing fractions of shares will be issued on conversion, but instead of
any fractional interest (calculated to the nearest 1/100th of a share) the
Company shall pay a cash adjustment as provided in the Indenture. The Conversion
Rate is subject to adjustment as provided in the Indenture. In addition, the
Indenture provides that in case of certain consolidations or mergers to which
the Company is a party or the conveyance, transfer, sale or lease of all or
substantially all of the property and assets of the Company, 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 such
consolidation, merger, conveyance, transfer, sale or lease by a holder of the
number of shares of Common Stock of the Company into which this Security could
have been converted immediately prior to such consolidation, merger, conveyance,
transfer, sale or lease (assuming such holder of Common Stock is not a



                                      -33-
<PAGE>   42

Constituent Person, 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). No adjustment in the Conversion Rate will be made until such adjustment
would require an increase or decrease of at least one percent of such rate,
provided that any adjustment that would otherwise be made will be carried
forward and taken into account in the computation of any subsequent adjustment.

              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, as amended, upon the request of a Holder of a
Security 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 of Securities 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 of 1933, as amended (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).

              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 hereof is entitled
to the benefits of a Registration Rights Agreement, dated as of February 24,
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 Registered Securities and the Common Stock issuable
upon conversion thereof, in each case, that are Registrable Securities, at the
Company's expense, (a) to file within 90 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
Registrable Securities, (b) thereafter to use its best efforts to cause such
Shelf Registration Statement to be declared effective by the Commission within
180 days after the first date of original issuance of the Securities, and (c) to
use its



                                      -34-
<PAGE>   43

reasonable efforts to maintain such Shelf Registration Statement continuously
effective under the Securities Act until a period of the two years from the date
of the effectiveness of the Shelf Registration Statement or, if earlier, until
(A) there are no outstanding Registrable Securities registered under the Shelf
Registration Statement or (B) the expiration of the period referred to in Rule
144(k) (or any successor provision thereto) under the Securities Act with
respect to all Registrable Securities held by Persons that are not Affiliates of
the Company.

              Section 2(a) of the Registration Rights Agreement provides that,
upon written notice to each Holder of a Registrable Security, the Company may
postpone having the Shelf Registration Statement declared effective as required
by Section 2(a) of the Registration Rights Agreement for a reasonable time
specified in the notice but not exceeding 90 days if the Company is in
possession of material non-public information the disclosure of which would have
a material adverse effect on the business, operations, prospects, condition
(financial or otherwise) of the Company and its subsidiaries, taken as a whole.
Notwithstanding any postponement pursuant to Section 2(a) of the Registration
Rights Agreement, if (i) on or prior to 90 days following the date of original
issuance of the Registrable Securities, a Shelf Registration Statement has not
been filed with the Commission, or (ii) on or prior to the 180th day following
the date of original issuance of the Registrable Securities, such Shelf
Registration Statement is not declared effective (each, a "Registration
Default"), additional interest ("Liquidated Damages") 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 or, if
earlier, the last day upon which the Shelf Registration Statement is required to
be kept effective. See Section 7(a) of Registration Rights. Liquidated Damages
will be paid semi-annually in arrears, with the first semi-annual payment due on
the first interest payment date in respect of the Registrable Securities
following the date on which such Liquidated Damages begin to accrue, and will
accrue at a rate per annum equal to an additional one-quarter of one percent
(.25%) of the principal amount of the Registrable Securities to and including
the 90th day following such Registration Default and at a rate per annum equal
to one-half of one percent (.50%) thereof from and after the 91st day following
such Registration Default. In the event that the Shelf Registration Statement
ceases to be effective



                                      -35-
<PAGE>   44

prior to the second annual anniversary of the initial effective date of the
Shelf Registration Statement or such earlier date as is provided in the
Registration Rights Agreement for a period in excess of 45 days, whether or not
consecutive, during any 90-day period or more than 90 days, whether or not
consecutive, during any 12-month period, then the interest rate borne by the
Registrable Securities shall increase by an additional one-half of one percent
(.50%) per annum from the 46th day of the 90-day period or the 91st day of the
applicable 12-month period such Shelf Registration Statement ceases to be
effective to but excluding the day on which the Shelf Registration Statement
again becomes effective or, if earlier, the last day upon which the Shelf
Registration Statement is required to be kept effective.

              Whenever in this Security there is a reference, in any context, to
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 Liquidated Damages payable as described in the preceding paragraph to the
extent that, in such context, Liquidated Damages are, were or would be payable
in respect of this Security pursuant to such paragraph, and an express mention
of the payment of Liquidated Damages (if applicable) in any provisions of this
Security shall not be construed as excluding Liquidated Damages in those
provisions of this Security where such express mention is not made.

              If 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)] elects to sell this Security pursuant to the Shelf Registration
Statement then, by its acceptance hereof, such Holder of this Security agrees to
be bound by the terms of the Registration Rights Agreement relating to the
Registrable Securities which are the subject of such election.

              If a Change in Control occurs, the Holder of this Security, at the
Holder's option, shall have the right, in accordance with the provisions of the
Indenture, to require the Company to repurchase this Security (or any portion of
the principal amount hereof that is equal to U.S.$5,000 or any greater integral
multiple of U.S.$1,000) for cash at a Repurchase Price equal to 100% of the
principal amount thereof plus interest accrued to the Repurchase Date. At the
option of the Company, the Repurchase Price may be paid in cash or, subject to
the conditions provided in the Indenture, by delivery of shares of Common Stock
having a



                                      -36-
<PAGE>   45

fair market value equal to the Repurchase Price. For purposes of this paragraph,
the fair market value of shares of Common Stock shall be determined by the
Company and shall be equal to 95% of the average of the Closing Price Per Share
for the five consecutive Trading Days immediately preceding and including the
third Trading Day prior to the Repurchase Date. Whenever in this Security there
is a reference, in any context, to the principal of any Security as of any time,
such reference shall be deemed to include reference to the Repurchase Price
payable in respect of such Security to the extent that such Repurchase Price is,
was or would be so payable at such time, and express mention of the Repurchase
Price in any provision of this Security shall not be construed as excluding the
Repurchase Price so payable in those provisions of this Security when such
express mention is not made; provided, however, that, for the purposes of the
paragraph below concerning the consequences of an Event of Default, such
reference shall be deemed to include reference to the Repurchase Price only to
the extent the Repurchase Price is payable in cash.

              [The following paragraph shall appear in each Registered Security
that is not a Global Security:

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

              [The following paragraph shall appear in each Global Security:

              In the event of a deposit or withdrawal of an interest in this
Security, including an exchange, transfer, redemption, repurchase or conversion
of this Security in part only, the Trustee, as custodian of the Depositary,
shall make an adjustment on its records to reflect such deposit or withdrawal in
accordance with the Applicable Procedures.]

              The indebtedness evidenced by this Security is, to the extent and
in the manner provided in the Indenture, subordinate and subject in right of
payment to the prior payment in full of all Senior Debt of the Company, and this
Security is issued subject to such provisions of the Indenture with respect
thereto. Each Holder of this Security, by



                                      -37-
<PAGE>   46

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, together with accrued interest to the date of
declaration, may be declared due and payable in the manner and with the effect
provided in the Indenture. Upon payment (i) of the amount of principal so
declared due and payable, together with accrued interest to the date of
declaration, and (ii) of interest on any overdue principal and, to the extent
permitted by applicable law, overdue interest, all of the Company's obligations
in respect of the payment of the principal of and interest on the Securities
shall terminate.

              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 written
consent of the Holders of a majority in principal amount of the Securities at
the time Outstanding. The Indenture also contains provisions permitting the
Holders of specified percentages in 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
in exchange herefor or in lieu hereof, whether or not notation of such consent
or waiver is made upon this Security or such other Security.

              As provided in and subject to the provisions of the Indenture, the
Holder of this Security shall not have the right to institute any proceeding
with respect to the Indenture or for the appointment of a receiver or trustee or
for any other remedy thereunder, unless such Holder shall have previously given
the Trustee written notice of a continuing Event of Default, the Holders of not
less than 25% in principal amount of the Outstanding Securities shall have made
written request to the Trustee to institute



                                      -38-
<PAGE>   47

proceedings in respect of such Event of Default as Trustee and offered the
Trustee reasonable indemnity, and shall have failed to institute any such
proceeding, for 60 days after receipt of such notice, request and offer of
indemnity. The foregoing shall not apply to any suit instituted by the Holder of
this Security for the enforcement of any payment of principal hereof, premium,
if any, or interest hereon (including Liquidated Damages) on or after the
respective due dates expressed herein or for the enforcement of the right to
convert this Security as provided in the Indenture.

              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,
if any, and interest on (including Liquidated Damages) this Security at the
times, places 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 Registered Securities is registrable on the
Security Register upon surrender of a Registered Security for registration of
transfer at the Corporate Trust Office of the Trustee or at such other office or
agency of the Company as may be designated by it for such purpose in the State
of Minnesota, County of Ramsey, City of St. Paul, or at such other offices or
agencies as the Company may designate, 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 thereof or his attorney duly
authorized in writing, and thereupon one or more new Registered Securities, of
authorized denominations and for the same aggregate principal amount, will be
issued to the designated transferee or transferees by the Registrar. 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 recover any tax or other
governmental charge payable in connection therewith.

              Prior to due presentation of a Registered 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 Registered Security is
registered as the owner thereof for all purposes, whether or not such Security



                                      -39-
<PAGE>   48

be overdue, and neither the Company, the Trustee nor any such agent shall be
affected by notice to the contrary.

              Interest on the Securities (including any Liquidated Damages)
shall be computed on the basis of a 360-day year of twelve 30-day months.

              The Indenture and this Security shall be governed by and construed
in accordance with the laws of the State of New York, United States of America,
without regard to the conflicts of laws principles thereof.

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



                                      -40-
<PAGE>   49

                    ELECTION OF HOLDER TO REQUIRE REPURCHASE

              1. Pursuant to Section 13.1 of the Indenture, the undersigned
hereby elects to have this Security repurchased by the Company.

              2. The undersigned hereby directs the Trustee or the Company to
pay it or __________________ an amount in cash or, at the Company's election,
Common Stock valued as set forth in the Indenture, equal to 100% of the
principal amount to be repurchased (as set forth below), plus interest accrued
to the Repurchase Date, as provided in the Indenture.


                                       Dated:
                                             -----------------------------------


                                       ------------------------------------
                                                   Signature


                                       ------------------------------------
                                              Signature Guaranteed

Principal amount to be repurchased
(must be equal to U.S. $5,000 or any greater integral multiple of U.S.$1,000):

Remaining principal amount following such repurchase:


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


NOTICE: The signature to the foregoing Election must correspond to the Name as
written upon the face of this Security in every particular, without alteration
or any change whatsoever.



                                      -41-
<PAGE>   50

SECTION 2.3. Form of Certificate of Authentication.

              The Trustee's certificates of authentication shall be in
substantially the following form:

Dated: [Date of Authentication]

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


                                       ------------------------------------
                                            as Trustee


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

SECTION 2.4. Form of Conversion Notice.

                                CONVERSION NOTICE

              The undersigned Holder of this Security hereby irrevocably
exercises the option to convert this Security, or any portion of the principal
amount hereof (which is an integral multiple of U.S.$1,000) below designated,
into shares of Common Stock in accordance with the terms of the Indenture
referred to in this Security, and directs that such shares, together with a
check in payment for any fractional share and any Securities representing any
unconverted principal amount hereof, be delivered to and be registered in the
name of the undersigned unless a different name has been indicated below. If
shares of Common Stock or Securities are to be registered in the name of a
Person other than the undersigned, the undersigned will pay all transfer taxes
payable with respect thereto. Any amount required to be paid by the undersigned
on account of interest accompanies this Security.


Dated:
      -----------------------------

                                             ------------------------------
                                                      Signature


                                             If only a portion of the Securities
                                             is to be
If shares or Registered Securities
are to be


                                      -42-
<PAGE>   51
registered in the name of a Person
other than the Holder, please print
such Person's name and address:



-----------------------------------
               Name



-----------------------------------
             Address


-----------------------------------
Social Security or other Taxpayer
Identification Number, if any


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

converted, please indicate:


1.      Principal amount to be converted:

U.S.$___________

(any integral multiple of U.S.$1,000)

2.      Principal amount and denomination of Registered Securities representing
        unconverted principal amount to be issued:

Amount: U.S.$________

Denominations:
U.S.$______
(any integral multiple of U.S.$1,000)


-----------------------------------
      [Signature Guaranteed]



                                      -43-
<PAGE>   52

                                  ARTICLE THREE

                                 THE SECURITIES

SECTION 3.1. Title and Terms.

              The aggregate principal amount of Securities which may be
authenticated and delivered under this Indenture is limited to U.S.$300,000,000,
except for Securities authenticated and delivered in exchange for, or in lieu
of, other Securities pursuant to Section 3.4, 3.5, 3.6, 8.5, 10.8, 11.2 or
13.3(e).

              The Securities shall be known and designated as the "5.00%
Convertible Subordinated Notes due March 1, 2007" of the Company. Their Stated
Maturity shall be March 1, 2007 and they shall bear interest on their principal
amount from February 24, 2000, payable semi-annually in arrears on March 1 and
September 1 in each year, commencing September 1, 2000, at the rate of 5.00% per
annum until the principal thereof is due and at the rate of 5.00% per annum on
any overdue principal and, to the extent permitted by law, on any overdue
interest; provided, however, that payments shall only be made on Business Days
as provided in Section 1.12.

              The principal of, premium, if any, and interest on the Securities
shall be payable as provided in the form of Securities set forth in Section 2.2,
and the Repurchase Price, whether payable in cash or in shares of Common Stock,
shall be payable at such places as are identified in the Company Notice given
pursuant to Section 13.3 (any city in which any Paying Agent is located being
herein called a "Place of Payment").

              The Registrable Securities are entitled to the benefits of a
Registration Rights Agreement as provided by Sections 2.2 and 9.11. The
Securities are entitled to the payment of Liquidated Damages and additional
interest as provided by Section 9.11.

              The Securities shall be redeemable at the option of the Company,
as provided in Article Ten and in the form of Securities set forth in Section
2.2.



                                      -44-
<PAGE>   53

              The Securities shall be convertible as provided in Article Eleven
(any city in which any Conversion Agent is located being herein called a "Place
of Conversion").

              The Securities shall be subordinated in right of payment to Senior
Debt of the Company as provided in Article Twelve.

              The Securities shall be subject to repurchase by the Company at
the option of the Holders as provided in Article Thirteen.

SECTION 3.2. Denominations.

              The Securities shall be issuable only in registered form, without
coupons, in denominations of U.S.$1,000 and integral multiples thereof.

SECTION 3.3. Execution, Authentication, Delivery and Dating.

              The Securities shall be executed on behalf of the Company by its
Chairman of the Board, its Vice Chairman of the Board, its Chief Executive
Officer, its President or one of its Vice Presidents, under a facsimile of its
corporate seal reproduced thereon attested by its Secretary or one of its
Assistant Secretaries. Any such signature may be manual or facsimile.

              Securities bearing the manual or facsimile signature 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 executed by the Company to
the Trustee or to its order 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 make available for
delivery such Securities as in this Indenture provided and not otherwise.



                                      -45-
<PAGE>   54

              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 of an authorized signatory, 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 3.4. Global Securities; Non-Global Securities.

        (A)   Global Securities

              (a) 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.

              (b) 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 (i) such Depositary (A) has notified the Company that it
is unwilling or unable to continue as Depositary for such Global Security or (B)
has ceased to be a clearing agency registered as such under the Exchange Act or
announces an intention permanently to cease business or does in fact do so or
(ii) there shall have occurred and be continuing an Event of Default with
respect to such Global Security.

              (c) If any Global Security is to be exchanged for other Securities
or canceled 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 Three. 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



                                      -46-
<PAGE>   55

Security, in each case, as provided in Section 3.5, then either (i) such Global
Security shall be so surrendered for exchange or cancellation, as provided in
this Article Three, 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 3.5(c) and as
otherwise provided in this Article Three, authenticate and make available for
delivery 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 Three if such order, direction or request is given
or made in accordance with the Applicable Procedures.

              (d) 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, whether pursuant to this Article Three or otherwise, shall be
authenticated and delivered in the form of, and shall be, a registered 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
Registered Security shall be authenticated and delivered in definitive, fully
registered form, without interest coupons.

              (e) 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 Registered Securities, and owners of beneficial interests in



                                      -47-
<PAGE>   56

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.

        (B)   Non-Global Securities

              Pending the preparation of definitive Securities, the Company may
execute, and upon Company Order the Trustee shall authenticate and make
available for delivery, temporary Securities which are printed, lithographed,
typewritten, mimeographed or otherwise produced, in any authorized denomination,
substantially of the tenor of the definitive Registered Securities in lieu of
which they are issued and with such appropriate insertions, omissions,
substitutions and other variations as the officers executing such Registered
Securities may determine, as evidenced by their execution of such Securities.

              If temporary Securities are issued, the Company will cause
definitive Securities to be prepared without unreasonable delay. After the
preparation of definitive Securities, the temporary Securities shall be
exchangeable for definitive Securities upon surrender of the temporary
Securities at any office or agency of the Company designated pursuant to Section
9.2, without charge to the Holder. Upon surrender for cancellation of any one or
more temporary Securities the Company shall execute and the Trustee shall
authenticate and make available for delivery in exchange therefor a like
principal amount of definitive Securities of authorized denominations. Until so
exchanged the temporary Securities shall in all respects be entitled to the same
benefits under this Indenture as definitive Securities.

SECTION 3.5. Registration, Registration of Transfer and Exchange; Restrictions
on Transfer.

              (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 of the Company designated pursuant to Section 9.2
being herein sometimes collectively referred to as the "Security Register") in
which, subject to such reasonable



                                      -48-
<PAGE>   57

regulations as it may prescribe, the Company shall provide for the registration
of Registered Securities and of transfers of Registered Securities. The Trustee
is hereby appointed "Security Registrar" for the purpose of registering
Registered Securities and transfers and exchanges of Registered Securities as
herein provided.

              Upon surrender for registration of transfer of any Security at an
office or agency of the Company designated pursuant to Section 9.2 for such
purpose, 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 and bearing such restrictive legends as may be required by this
Indenture.

              At the option of the Holder, and subject to the other provisions
of this Section 3.5, Securities may be exchanged for other Securities of any
authorized denomination and of a like aggregate principal amount, upon surrender
of the Securities to be exchanged at any such office or agency. Whenever any
Securities are so surrendered for exchange, and subject to the other provisions
of this Section 3.5, the Company shall execute, and the Trustee shall
authenticate and make available for delivery, the Securities which the Holder
making the exchange is entitled to receive. Every Security presented or
surrendered for registration of transfer or for exchange shall (if so required
by the Company or the Security Registrar) be duly endorsed, or be accompanied by
a written instrument of transfer in form satisfactory to the Company and the
Security Registrar duly executed, by the Holder thereof or his attorney duly
authorized in writing.

              All Securities issued upon any registration of transfer or
exchange of Securities shall be the valid obligations of the Company, evidencing
the same debt, and subject to the other provisions of this Section 3.5, entitled
to the same benefits under this Indenture, as the Securities surrendered upon
such registration of transfer or exchange.

              No service charge shall be made for any registration of transfer
or exchange of Securities except as provided in Section 3.6, 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



                                      -49-
<PAGE>   58

registration of transfer or exchange of Securities, other than exchanges
pursuant to Section 3.4, 8.5, 10.8, 11.2 or 13.3 (other than where the shares of
Common Stock are to be issued or delivered in a name other than that of the
Holder of the Security) not involving any transfer and other than any stamp and
other duties, if any, which may be imposed in connection with any such transfer
or exchange by the United States or any political subdivision thereof or
therein, which shall be paid by the Company.

              In the event of a redemption of the Securities, the Company will
not be required (a) to register the transfer of or exchange Securities for a
period of 15 days immediately preceding the date notice is given identifying the
serial numbers of the Securities called for such redemption or (b) to register
the transfer of or exchange any Security, or portion thereof, called for
redemption.

              (b) Securities Act Legends. All Securities shall bear the
applicable Restricted Securities Legend subject to the following:

                       (i) subject to the following Clauses of this Section
        3.5(b), a Security or any portion thereof which is exchanged, upon
        transfer or otherwise, for a Global Security or any portion thereof
        shall bear the Securities Act Legend borne by such Global Security while
        represented thereby;

                       (ii) subject to the following Clauses of this Section
        3.5(b), a new Security which is not a Global Security and is issued in
        exchange for another Security (including a Global Security) or any
        portion thereof, upon transfer or otherwise, shall bear the Securities
        Act Legend borne by such other Security;

                       (iii) any Securities which are sold or otherwise disposed
        of pursuant to an effective registration statement under the Securities
        Act (including the Shelf Registration Statement), together with their
        Successor Securities shall not bear a Securities Act Legend; the Company
        shall inform the Trustee in writing of the effective date of any such
        registration statement registering the Securities under the Securities
        Act and shall notify the Trustee at any time when



                                      -50-
<PAGE>   59

        prospectuses may not be delivered with respect to Securities to be sold
        pursuant to such registration statement. 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 registration statement;

                       (iv) at any time after the Securities may be freely
        transferred without registration under the Securities Act or without
        being subject to transfer restrictions pursuant to the Securities Act, a
        new Security which does not bear a Securities Act Legend may be issued
        in exchange for or in lieu of a Security (other than a Global Security)
        or any portion thereof which bears such a legend if the Trustee has
        received an Unrestricted Securities Certificate, satisfactory to the
        Trustee and duly executed by the Holder of such legended Security or his
        attorney duly authorized in writing, and after such date and receipt of
        such certificate, the Trustee shall authenticate and make available for
        delivery such a new Security in exchange for or in lieu of such other
        Security as provided in this Article Three;

                       (v) a new Security which does not bear a Securities Act
        Legend may be issued in exchange for or in lieu of a Security (other
        than a Global Security) or any portion thereof which bears such a legend
        if, in the Company's judgment, placing such a legend upon such new
        Security is not necessary to ensure compliance with the registration
        requirements of the Securities Act, and the Trustee, at the direction of
        the Company, shall authenticate and make available for delivery such a
        new Security as provided in this Article Three; and

                       (vi) notwithstanding the foregoing provisions of this
        Section 3.5(b), a Successor Security of a Security that does not bear a
        particular form of Securities Act Legend shall not bear such form of
        legend unless the Company has reasonable cause to believe that such
        Successor Security is a "restricted security" within the meaning of Rule
        144, in which case the Trustee, at the direction of the Company, shall
        authenticate



                                      -51-
<PAGE>   60

        and make available for delivery a new Security bearing a Restricted
        Securities Legend in exchange for such Successor Security as provided in
        this Article Three.

              (c) Neither the Trustee, the Paying Agent nor any of their agents
shall (1) have any duty to monitor compliance with or with respect to any
federal or state or other securities or tax laws or (2) have any duty to obtain
documentation on any transfers or exchanges other than as specifically required
hereunder.

SECTION 3.6. Mutilated, Destroyed, Lost or Stolen Securities.

              If any mutilated Security is surrendered to the Trustee, the
Company shall execute and the Trustee shall authenticate and make available for
delivery in exchange therefor a new Security of like tenor and principal amount
and bearing a number not contemporaneously outstanding.

              If there be delivered to the Company and to the Trustee:

              (1) evidence to their satisfaction of the destruction, loss or
        theft of any Security, and

              (2) such security or indemnity as may be satisfactory to the
        Company and the Trustee to save each of them and any agent of either of
        them harmless,

then, in the absence of actual 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 make available for delivery, 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 satisfaction of the conditions set forth in the preceding
paragraph.



                                      -52-
<PAGE>   61

              Upon the issuance of any new Security under this Section 3.6, 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 (other than any
stamp and other duties, if any, which may be imposed in connection therewith by
the United States or any political subdivision thereof or therein, which shall
be paid by the Company) and any other expenses (including the fees and expenses
of the Trustee) connected therewith.

              Every new Security issued pursuant to this Section 3.6 in lieu of
any mutilated, destroyed, lost or stolen Security shall constitute an original
additional contractual obligation of the Company, whether or not the mutilated,
destroyed, lost or stolen Security shall be at any time enforceable by anyone,
and such new Security 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 3.6 are exclusive and shall
preclude (to the extent lawful) all other rights and remedies of any Holder with
respect to the replacement or payment of mutilated, destroyed, lost or stolen
Securities.

SECTION 3.7. 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 such
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)



                                      -53-
<PAGE>   62

        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, the
        date of the proposed payment and the Special Record Date, 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 provided. The
        Special Record Date for the payment of such Defaulted Interest 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, 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 such
        Holder's 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).

              (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, such manner of payment shall be deemed practicable by the
        Trustee.

              Subject to the foregoing provisions of this Section and Section
3.5, each Security delivered under this Indenture upon registration of transfer
of or in exchange



                                      -54-
<PAGE>   63

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.

              Interest on any Security which is converted in accordance with
Section 11.2 during a Record Date Period shall be payable in accordance with the
provisions of Section 11.2.

SECTION 3.8. 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, and (subject to Section 3.7) 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 3.9. 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. All Securities so
delivered to the Trustee shall be canceled promptly by the Trustee. No
Securities shall be authenticated in lieu of or in exchange for any Securities
canceled as provided in this Section 3.9. The Trustee shall dispose of all
canceled Securities in accordance with applicable law and its customary
practices in effect from time to time.

SECTION 3.10. Computation of Interest.

              Interest on the Securities (including any Liquidated Damages)
shall be computed on the basis of a 360-day year of twelve 30-day months.

SECTION 3.11. CUSIP Numbers.

              The Company in issuing Securities may use "CUSIP" numbers (if then
generally in use) in addition to serial numbers; the Trustee shall use such
CUSIP numbers in addition to serial numbers in notices of redemption and
repurchase as a convenience to Holders; provided that any



                                      -55-
<PAGE>   64

such notice may state that no representation is made as to the correctness of
such CUSIP numbers either as printed on the Securities or as contained in any
notice of a redemption or repurchase and that reliance may be placed only on the
serial or other identification numbers printed on the Securities, and any such
redemption or repurchase shall not be affected by any defect in or omission of
such CUSIP numbers. The Company shall promptly notify the Trustee in writing of
any change in any such CUSIP number.


                                  ARTICLE FOUR

                           SATISFACTION AND DISCHARGE


SECTION 4.1. 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, or registration of
transfer or exchange, or replacement of Securities herein expressly provided for
and any right to receive Liquidated Damages as provided in the form of
Securities set forth in Section 2.2 and the Company's obligations to the Trustee
pursuant to Section 6.7), and the Trustee, at the expense of the Company, shall
execute proper instruments in form and substance satisfactory to the Trustee
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 3.6 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 9.3) have been delivered to the Trustee for cancellation; or

              (B) all such Securities not theretofore delivered to the Trustee
        or its agent for cancellation (other than Securities referred to in
        clauses (i) and (ii) of clause (1)(A) above)



                                      -56-
<PAGE>   65

                    (i) have become due and payable, or

                    (ii) will have 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,

              and the Company, in the case of clause (i), (ii) or (iii) above,
has deposited or caused to be deposited with the Trustee as trust funds
(immediately available to the Holders in the case of clause (i)) in trust for
the purpose an amount sufficient to pay and discharge the entire indebtedness on
such Securities not theretofore delivered to the Trustee for cancellation, for
principal, premium, if any, and interest (including any Liquidated Damages) 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; and

              (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.

              Notwithstanding the satisfaction and discharge of this Indenture,
the obligations of the Company to the Trustee under Section 6.7, the obligations
of the Company to any Authenticating Agent under Section 6.12, the obligation of
the Company to pay Liquidated Damages, if money shall have been deposited with
the Trustee pursuant to clause (1)(B) of this Section 4.1, the obligations of
the Trustee under Section 4.2 and the last paragraph of Section 9.3 and the
obligations of the Company and the Trustee under Section 3.5 and Article Eleven
shall survive. Funds held in trust pursuant to this Section are not subject to
the provisions of Article Twelve.

SECTION 4.2. Application of Trust Money.



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<PAGE>   66

              Subject to the provisions of the last paragraph of Section 9.3,
all money deposited with the Trustee pursuant to Section 4.1 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), to the Persons entitled
thereto, of the principal, premium, if any, and interest for whose payment such
money has been deposited with the Trustee.

              All moneys deposited with the Trustee pursuant to Section 4.1 (and
held by it or any Paying Agent) for the payment of Securities subsequently
converted shall be returned to the Company upon Company Request.


                                  ARTICLE FIVE

                                    REMEDIES

SECTION 5.1. 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 Twelve 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 the principal of or premium, if any,
        on any Security at its Maturity, whether or not the such payment is
        prohibited by the subordination provisions of this Indenture; or

              (2) default in the payment of any interest (including any
        Liquidated Damages) upon any Security when it becomes due and payable,
        and continuance of such default for a period of 30 days, whether or not
        the such payment is prohibited by the subordination provisions of this
        Indenture; or

              (3) failure by the Company to give the Company notice in
        accordance with Section 13.3; or



                                      -58-
<PAGE>   67

              (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 the performance or breach of which is specifically
        dealt with elsewhere in this Section), 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;

              (5) a default in the payment when due of the principal of, or
        acceleration of, any indebtedness under any bond, debenture, note or
        other evidence of indebtedness for money borrowed by the Company or any
        Subsidiary of the Company or under any mortgage, indenture or instrument
        under which there may be issued or by which there may be secured or
        evidenced any indebtedness for money borrowed by the Company or any
        Subsidiary of the Company with a principal amount then outstanding in
        excess of U.S.$10,000,000, whether such indebtedness now exists or shall
        hereafter be created, if such indebtedness is not discharged, or such
        acceleration is not rescinded or annulled, within a period of 30 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 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 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 a bankrupt or insolvent, or
        approving as properly filed a petition seeking reorganization,
        arrangement, adjustment or composition of or in respect of the Company
        under any applicable Federal or State law, or



                                      -59-
<PAGE>   68

        appointing a custodian, receiver, liquidator, assignee, trustee,
        sequestrator or other similar official of the Company or of any
        substantial part of its property, or ordering the winding up or
        liquidation of its affairs, 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 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 it to the
        entry of a decree or order for relief in respect of the Company 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
        it, or the filing by it of a petition or answer or consent seeking
        reorganization or similar relief under any applicable Federal or State
        law, or the consent by it 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 of any substantial part of its property, or the making by
        it of an assignment for the benefit of creditors, or the admission by it
        in writing of its inability to pay its debts generally as they become
        due, or the taking of corporate action by the Company in furtherance of
        any such action.

SECTION 5.2. Acceleration of Maturity; Rescission and Annulment.

              If an Event of Default (other than an Event of Default specified
in Section 5.1(6) or 5.1(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 the Holders), and upon any such declaration such principal
and all accrued interest thereon shall become immediately due and payable. If an
Event of Default specified in Section 5.1(6) or 5.1(7) occurs, the principal of,
and accrued interest on, all the Securities shall ipso facto



                                      -60-
<PAGE>   69

become immediately due and payable without any declaration or other Act of the
Holder or any act on the part of the Trustee.

              At any time after such 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 Five 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 any Liquidated Damages)
              on all Securities,

                    (B) the principal of and premium, if any, on any Securities
              which have become due otherwise than by such declaration of
              acceleration and any interest (including any Liquidated Damages)
              thereon at the rate borne by the Securities,

                    (C) to the extent permitted by applicable law, interest upon
              overdue interest at a rate of 5.00% per annum, 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 its counsel;

        and

              (2) all Events of Default, other than the non-payment of the
        principal of, and any premium and interest on, Securities which have
        become due solely by such declaration of acceleration, have been cured
        or waived as provided in Section 5.13.

              No rescission or annulment referred to above shall affect any
subsequent default or impair any right consequent thereon.

SECTION 5.3. Collection of Indebtedness and Suits for Enforcement by Trustee.



                                      -61-
<PAGE>   70

             The Company covenants that if

              (1) default is made in the payment of any interest (including any
        Liquidated Damages) on any Security when it 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, on any Security at the Maturity thereof,

the Company will upon demand of the Trustee pay to it, for the benefit of the
Holders of such Securities the whole amount then due and payable on such
Securities for principal and interest (including any Liquidated Damages) and
interest on any overdue principal and premium, if any, and, to the extent
permitted by applicable law, on any overdue interest (including any Liquidated
Damages), at a rate of 5.00% per annum, and in addition thereto, such further
amount as shall be sufficient to cover the reasonable costs and expenses of
collection, including the reasonable compensation, expenses, disbursements and
advances of the Trustee, its agents and its counsel.

              If the Company fails to pay such amounts forthwith upon such
demand, the Trustee, in its own name and as trustee of an express trust, may
institute a judicial proceeding for the collection of the sums so due and
unpaid, may prosecute such proceeding to judgment or final decree and may
enforce the same against the Company or any other obligor upon the Securities
and collect the moneys adjudged or decreed to be payable in the manner provided
by law out of the property of the Company or any other obligor upon the
Securities, wherever situated.

              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 of Securities 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 5.4. Trustee May File Proofs of Claim.



                                      -62-
<PAGE>   71

              In case of the pendency of any receivership, insolvency,
liquidation, bankruptcy, reorganization, arrangement, adjustment, composition or
other judicial proceeding relative to the Company or any other obligor upon the
Securities or the property of the Company or of such other obligor or the
creditors of either, the Trustee (irrespective of whether the principal of, and
any interest on, the Securities shall then be due and payable as therein
expressed or by declaration or otherwise and irrespective of whether the Trustee
shall have made any demand on the Company for the payment of overdue principal
or interest) 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,
        premium, if any, and interest (including any Liquidated Damages) owing
        and unpaid in respect of the Securities and take such other actions,
        including participating as a member, voting or otherwise, of any
        official committee of creditors appointed in such matter, and to file
        such other papers or documents, in each of the foregoing cases, 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 its counsel)
        and of the Holders of Securities 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 of Securities 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 of Securities to pay to the Trustee any amount due to it for the
reasonable compensation, expenses, disbursements and advances of the Trustee,
its agents and its counsel and any other amounts due the Trustee under Section
6.7.

              Nothing herein contained shall be deemed to authorize the Trustee
to authorize or consent to or accept or



                                      -63-
<PAGE>   72

adopt on behalf of any Holder of a Security 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 of a Security in any such proceeding; provided, however, that the
Trustee may, on behalf of such Holders, vote for the election of a trustee in
bankruptcy or similar official.

SECTION 5.5. Trustee May Enforce Claims Without Possession of 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 its counsel, be for
the ratable benefit of the Holders of the Securities in respect of which
judgment has been recovered.

SECTION 5.6. Application of Money Collected.

              Subject to Article Twelve, any money collected by the Trustee
pursuant to this Article Five 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, premium, 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
        6.7;

              SECOND: To the payment of the amounts then due and unpaid for
        principal of, premium, if any, or interest (including any Liquidated
        Damages) 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



                                      -64-
<PAGE>   73

        principal, premium, if any, and interest (including any Liquidated
        Damages), respectively; and

              THIRD: Any remaining amounts shall be repaid to the Company.

SECTION 5.7. 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 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 reasonable
        indemnity against the costs, expenses and liabilities to be incurred in
        compliance with such request; and

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

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 rights of any other of
such Holders, or to obtain or 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 such
Holders.

SECTION 5.8. Unconditional Right of Holders to Receive Principal, Premium and
             Interest and to Convert.



                                      -65-
<PAGE>   74

              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, premium, if any, and (subject to Section
3.7) interest (including any Liquidated Damages) 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 Eleven, 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 5.9. Restoration of Rights and Remedies.

              If the Trustee or any Holder of a Security 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, subject to any determination in such proceeding, the Company, the Trustee
and the Holders of Securities shall be restored severally and respectively to
their former positions hereunder and thereafter all rights and remedies of the
Trustee and such 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 3.6, no right or remedy herein conferred upon or reserved to the
Trustee or to the Holders of Securities 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
Security to exercise any right or remedy



                                      -66-
<PAGE>   75

accruing upon any Event of Default shall impair any such right or remedy or
constitute a waiver of any such Event of Default or any acquiescence therein.
Every right and remedy given by this Article Five or by law to the Trustee or to
the Holders of Securities may be exercised from time to time, and as often as
may be deemed expedient, by the Trustee or (subject to the limitations contained
in this Indenture) by the Holders of Securities as the case may be.

SECTION 5.12. Control by Holders of Securities.

              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, either (a) through the written consent of not less
than a majority in principal amount of the Outstanding Securities, or (b) by the
adoption of a resolution, at a meeting of Holders of the Outstanding Securities
at which a quorum is present, by the Holders of at least a majority in principal
amount of the Outstanding Securities represented at such meeting, may on behalf
of the Holders of all the Securities waive any past default hereunder and its
consequences, except a default (1) in the payment of the principal of, premium,
if any, or interest (including any Liquidated Damages) on any Security, or (2)
in respect of a covenant or provision hereof which under Article Eight 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.



                                      -67-
<PAGE>   76

SECTION 5.14. Undertaking for Costs.

              All parties to this Indenture agree, and each Holder of any
Security by his acceptance thereof shall be deemed to have agreed, that any
court may in its discretion require, 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, the filing by any party
litigant in such suit of an undertaking to pay the costs of such suit, and that
such court may in its discretion assess reasonable costs, including reasonable
attorneys' fees and expenses, against any party litigant in such suit, having
due regard to the merits and good faith of the claims or defenses made by such
party litigant; but the provisions of this Section 5.14 shall not apply to any
suit instituted by the Company, to any suit instituted by the Trustee, to any
suit instituted by any Holder, or group of Holders, holding in the aggregate
more than 10% in principal amount of the Outstanding Securities, or to any suit
instituted by any Holder of any Security for the enforcement of the payment of
the principal of, premium, if any, or interest (including any Liquidated
Damages) on any Security on or after the respective Stated Maturity or
Maturities expressed in such Security (or, in the case of redemption or
repurchase, on or after the Redemption Date or Repurchase Date, as the case may
be) or for the enforcement of the right to convert any Security in accordance
with Article Eleven.

SECTION 5.15. Waiver of Stay, Usury 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 stay, usury 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 by reason of
such law 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 SIX



                                      -68-
<PAGE>   77

                                   THE TRUSTEE


SECTION 6.1. Certain Duties and Responsibilities.

              (a) Except during the continuance of an Event of Default,

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

              (2) in the absence of bad faith on its part, the Trustee may
        conclusively rely, as to the truth of the statements and the correctness
        of the opinions expressed therein, upon certificates or opinions
        furnished to the Trustee and conforming to the requirements of this
        Indenture; 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, but not to verify the contents thereof.

              (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 man would exercise or use under the circumstances in the conduct of his
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;



                                      -69-
<PAGE>   78

              (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

              (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, if it shall have reasonable grounds for
        believing that repayment of such funds or adequate indemnity against
        such risk or liability is not reasonably assured to it.

              (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 shall be subject to the provisions of this
Section.

SECTION 6.2. Notice of Defaults.

              Within 90 days after the occurrence of any default hereunder as to
which the Trustee has actually received written notice, the Trustee shall give
to all Holders of Securities, in the manner provided in Section 1.6, notice of
such default, unless such default shall have been cured or waived; provided,
however, that, except in the case of a default in the payment of the principal
of, premium, if any, or interest on any Security the Trustee shall be protected
in withholding such notice if and so long as the board of directors, the
executive committee or a trust committee of directors or Responsible Officers of
the Trustee in good faith determine that the withholding of such notice is in
the interest of the Holders; and provided, further, that in the case of any
default of the character specified in Section 5.1(4), no such notice to Holders
of Securities shall be given until at least 60 days after the occurrence
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.



                                      -70-
<PAGE>   79

SECTION 6.3. Certain Rights of Trustee.

              Subject to the provisions of Section 6.1:

              (1) the Trustee may rely and shall be protected in acting or
        refraining from acting upon any resolution, Officers' Certificate, other
        certificate, statement, instrument, opinion, report, notice, request,
        direction, consent, order, bond, debenture, note, coupon, 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;

              (2) 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;

              (3) 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, in the absence of
        bad faith on its part, rely upon an Officers' Certificate;

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

              (5) 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 of Securities pursuant to this
        Indenture, unless such Holders shall have offered to the Trustee
        reasonable security or indemnity against the costs, expenses and
        liabilities which might be incurred by it in compliance with such
        request or direction;

              (6) 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,



                                      -71-
<PAGE>   80

        order, bond, debenture, note, coupon, other evidence of indebtedness or
        other paper or document, but the Trustee 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

              (7) 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.

SECTION 6.4. 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 the Trustee assumes no responsibility for their correctness.
The Trustee makes no representations as to the validity or sufficiency of this
Indenture, of the Securities or of the Common Stock issuable upon the conversion
of the Securities. The Trustee shall not be accountable for the use or
application by the Company of Securities or the proceeds thereof.

SECTION 6.5. May Hold Securities, Act as Trustee Under Other Indentures.

              The Trustee, any Authenticating Agent, any Paying Agent, any
Conversion Agent or any other agent of the Company or the Trustee, in its
individual or any other capacity, may become the owner or pledgee of Securities
and may otherwise deal with the Company with the same rights it would have if it
were not Trustee, Authenticating Agent, Paying Agent, Conversion Agent or such
other agent.

              The Trustee may become and act as trustee under other indentures
under which other securities, or certificates of interest or participation in
other securities, of the Company are outstanding in the same manner as if it
were not Trustee hereunder.



                                      -72-
<PAGE>   81

SECTION 6.6. 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 in writing with the Company.

SECTION 6.7. Compensation and Reimbursement.

              The Company agrees

              (1) to pay to the Trustee from time to time such compensation as
        the Company and the Trustee shall from time to time agree in writing 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 bad faith; and

              (3) to indemnify the Trustee (and its directors, officers,
        employees and agents) for, and to hold it harmless against, any and all
        loss, damage, claim, liability or expense, including taxes (other than
        taxes based on the income of the Trustee), incurred without negligence
        or bad faith on its part, arising out of or in connection with the
        acceptance or administration of this trust, including the reasonable
        costs, expenses and reasonable attorneys' fees of defending itself
        against any claim or liability in connection with the exercise or
        performance of any of its powers or duties hereunder.

              When the Trustee incurs expenses or renders services in connection
with an Event of Default specified in



                                      -73-
<PAGE>   82

Section 5.1(6) or Section 5.1(7), the expenses (including the reasonable charges
of its counsel) and the compensation for the services are intended to constitute
expenses of the administration under any applicable Federal or State bankruptcy,
insolvency or other similar law.

              The Trustee shall have a lien prior to the Securities as to all
property and funds held by it hereunder for any amount owing it or any
predecessor Trustee pursuant to this Section 6.7, except with respect to funds
held in trust for the benefit of the Holders of particular Securities.

              The provisions of this Section shall survive the termination of
this Indenture or the earlier resignation or removal of the Trustee.

SECTION 6.8. Corporate Trustee Required; Eligibility.

              There shall at all times be a Trustee hereunder which shall be a
Person that is eligible pursuant to the Trust Indenture Act to act as such,
having a combined capital and surplus (or for such purposes, the combined
capital and surplus of any parent holding company) of at least U.S.$25,000,000,
subject to supervision or examination by Federal or State authority, in good
standing and having an office or agent in the Borough of Manhattan, The City of
New York. If such corporation 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 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 and a successor shall be
appointed pursuant to Section 6.9.

SECTION 6.9. 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



                                      -74-
<PAGE>   83

appointment by the successor Trustee in accordance with the applicable
requirements of Section 6.10.

              (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 6.10 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.

              (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 the Company. If the instrument of acceptance by a successor
Trustee required by Section 6.10 shall not have been delivered to the Trustee
within 30 days after the giving of such notice of removal, the removed Trustee
may petition any court of competent jurisdiction for the appointment of a
successor Trustee.

              (d) If at any time:

              (1) the Trustee shall cease to be eligible under Section 6.8 and
        shall fail to resign after written request therefor by the Company or by
        any Holder of a Security who has been a bona fide Holder of a Security
        for at least six months, or

              (2) 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 of a Security 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



                                      -75-
<PAGE>   84

the office of Trustee for any cause, the Company, by a Board Resolution, shall
promptly appoint a successor Trustee and shall comply with the applicable
requirements of this Section and Section 6.10. If, within one year after such
resignation, removal or incapability, or 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
6.10, become the successor Trustee and supersede the successor Trustee appointed
by the Company. If no successor Trustee shall have been so appointed by the
Company or the Holders of Securities and accepted appointment in the manner
required by this Section and Section 6.10, any Holder of a Security 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 of Securities in the manner provided in Section 1.6. Each notice shall
include the name of the successor Trustee and the address of its Corporate Trust
Office.

SECTION 6.10. 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



                                      -76-
<PAGE>   85

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 eligible under this
Article.

SECTION 6.11. 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 of the corporate trust
business of the Trustee, shall be the successor of the Trustee hereunder,
provided such corporation shall be otherwise eligible under this Article,
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.

SECTION 6.12. Authenticating Agents.

              The Trustee may, with the consent of the Company, appoint an
Authenticating Agent or Agents acceptable to the Company with respect to the
Securities which shall be authorized to act on behalf of the Trustee to
authenticate Securities issued upon exchange or substitution pursuant to this
Indenture.

              Securities authenticated by an Authenticating Agent 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, and every reference
in this Indenture to the authentication and delivery of Securities by the
Trustee or the Trustee's certificate of authentication 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
subject to acceptance by the Company and



                                      -77-
<PAGE>   86

shall at all times be a corporation organized and doing business under the laws
of the United States of America, any State thereof or the District of Columbia,
authorized under such laws to act as Authenticating Agent and subject to
supervision or examination by government or other fiscal authority. If at any
time an Authenticating Agent shall cease to be eligible in accordance with the
provisions of this Section 6.12, such Authenticating Agent shall resign
immediately in the manner and with the effect specified in this Section 6.12.

              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 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 6.12, without the 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 6.12, the Trustee may appoint a successor
Authenticating Agent which shall be subject to acceptance by the Company. 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 6.12.

              The Company agrees to pay to each Authenticating Agent from time
to time reasonable compensation for its services under this Section 6.12.

              If an Authenticating Agent is appointed with respect to the
Securities pursuant to this Section 6.12, the



                                      -78-
<PAGE>   87

Securities may have endorsed thereon, in addition to or in lieu of the Trustee's
certification of authentication, an alternative certificate of authentication in
the following form:

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


                                       ------------------------------,
                                         as Trustee
                                         By [Authenticating Agent],
                                           as Authenticating Agent


                                       By
                                          ----------------------------
                                              Authorized Signature


SECTION 6.13. 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 6.14. 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).



                                      -79-
<PAGE>   88

                                  ARTICLE SEVEN

              CONSOLIDATION, MERGER, CONVEYANCE, TRANSFER OR LEASE


SECTION 7.1. Company May Consolidate, Etc., Only on Certain Terms.

              The Company shall not consolidate with or merge into any other
Person or convey, transfer or lease all its properties and assets substantially
as an entirety to any Person, and the Company shall not permit any Person to
consolidate with or merge into the Company or convey, transfer or lease 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, shall be a
        corporation, limited liability company, partnership or trust, shall be
        organized and validly existing under the laws of the United States of
        America, any State thereof or the District of Columbia and shall
        expressly assume, by an indenture supplemental hereto, executed and
        delivered to the Trustee, in form satisfactory to the Trustee, the due
        and punctual payment of the principal of, premium, if any, and interest
        (including Liquidated Damages, if any, payable pursuant to Section 9.11)
        on all of the Securities as applicable, 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 Eleven;

              (2) immediately after giving effect to such transaction, no Event
        of Default, and no event that 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



                                      -80-
<PAGE>   89

        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 and
        that all conditions precedent herein provided for relating to such
        transaction have been complied with, together with any documents
        required under Section 8.3.

SECTION 7.2. 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 all or
substantially all the properties and assets of the Company in accordance with
Section 7.1, the successor Person formed by such consolidation or into or with
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 relieved of all obligations
and covenants under this Indenture and the Securities.


                                  ARTICLE EIGHT

                             SUPPLEMENTAL INDENTURES


SECTION 8.1. Supplemental Indentures Without Consent of Holders of Securities.

              Without the consent of any Holders of Securities, 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 for any
of the following purposes:

              (1) to evidence the succession of another Person to the Company
        and the assumption by any such successor of the covenants and
        obligations of the Company herein and in the Securities as permitted by
        this Indenture; or



                                      -81-
<PAGE>   90

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

              (3) to secure the Securities; or

              (4) to make provision with respect to the conversion rights of
        Holders of Securities pursuant to Section 11.11; or

              (5) to make any changes or modifications to this Indenture
        necessary in connection with the registration of any Registrable
        Securities under the Securities Act as contemplated by Section 9.11,
        provided, such action pursuant to this clause (5) shall not, in the
        judgment of the Company, adversely affect the interests of the Holders
        of Securities in any material respect; or

              (6) to comply with the requirements of the Trust Indenture Act or
        the rules and regulations of the Commission thereunder in order to
        effect or maintain the qualification of this Indenture under the Trust
        Indenture Act, as contemplated by this Indenture or otherwise; or

              (7) to evidence and provide for the acceptance of appointment
        hereunder by a successor Trustee; or

              (8) to cure any ambiguity, to correct or supplement any provision
        herein which may be inconsistent with any other provision herein or
        which is otherwise defective, or to make any other provisions with
        respect to matters or questions arising under this Indenture as the
        Company and the Trustee may deem necessary or desirable, provided such
        action pursuant to this clause (8) shall not, in the judgment of the
        Company, adversely affect the interests of the Holders of Securities in
        any material respect.

              Upon Company Request, accompanied by a Board Resolution
authorizing the execution of any such supplemental indenture, and subject to and
upon receipt by the Trustee of the documents described in Section 8.3 hereof,
the Trustee shall join with the Company in the execution of any supplemental
indenture authorized or permitted by the terms of this Indenture and to make any



                                      -82-
<PAGE>   91

further appropriate agreements and stipulations which may be therein contained.

SECTION 8.2. Supplemental Indentures with Consent of Holders of Securities.

              With either (a) the written 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, or (b) by the adoption of
a resolution, at a meeting of Holders of the Outstanding Securities at which a
quorum is present, by the Holders of a majority in principal amount of the
Outstanding Securities represented at such meeting, the Company, when authorized
by a Board Resolution, and the Trustee may 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 of Securities under this
Indenture; provided, however, that no such supplemental indenture shall, without
the consent or affirmative vote 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
        or the rate of interest payable thereon or any amount payable upon
        redemption or repurchase pursuant to Article Thirteen hereof, or change
        the obligation of the Company to pay Liquidated Damages pursuant to
        Section 9.11 in a manner adverse to the Holders, or change the coin or
        currency in which any Security or the interest or any premium thereon or
        any other amount in respect thereof is payable, or impair the right to
        institute suit for the enforcement of any payment in respect of any
        Security on or after the Stated Maturity thereof (or, in the case of
        redemption or any repurchase, on or after the Redemption Date or
        Repurchase Date, as the case may be) or, except as permitted by Section
        11.11, adversely affect the right to convert any Security as provided in
        Article Eleven, or modify the provisions of this Indenture with respect
        to the subordination of the Securities in a manner adverse to the
        Holders of Securities; or



                                      -83-
<PAGE>   92

              (2) 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; or

              (3) modify any of the provisions of this Section and Section 5.13
        or 9.12, except to increase any percentage contained herein or therein
        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

              (4) modify the provisions of Article Thirteen in a manner adverse
        to the Holders; or

              (5) modify any of the provisions of Section 9.9 or 9.10.

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

SECTION 8.3. Execution of Supplemental Indentures.

              In executing, or accepting the additional trusts created by, any
supplemental indenture permitted by this Article or the modifications thereby of
the trusts created by this Indenture, the Trustee shall be entitled to receive,
and (subject to Sections 6.1 and 6.3) 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, and that such supplemental
indenture has been duly authorized, executed and delivered by the Company and
constitutes a valid and legally binding obligation of the Company enforceable
against 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 8.4. Effect of Supplemental Indentures.



                                      -84-
<PAGE>   93

              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 appertaining thereto shall be bound thereby.

SECTION 8.5. 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 opinion of the Company and the
Trustee, 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.

SECTION 8.6. Notice of Supplemental Indentures.

              Promptly after the execution by the Company and the Trustee of any
supplemental indenture pursuant to the provisions of Section 8.2, the Company
shall give notice to all Holders of Securities of such fact, setting forth in
general terms the substance of such supplemental indenture, in the manner
provided in Section 1.6. Any failure of the Company to give such notice, or any
defect therein, shall not in any way impair or affect the validity of any such
supplemental indenture.


                                  ARTICLE NINE

                                    COVENANTS

SECTION 9.1 Payment of Principal, Premium and Interest.

              The Company covenants and agrees that it will duly and punctually
pay the principal of and premium, if any, and interest on the Securities in
accordance with the terms of the Securities and this Indenture. The Company will
deposit or cause to be deposited with the Trustee, no later than the opening of
business on the date of the Stated Maturity of



                                      -85-
<PAGE>   94

any Security or no later than the opening of business on the due date for any
installment of interest, all payments so due, which payments shall be in
immediately available funds on the date of such Stated Maturity or due date, as
the case may be.

SECTION 9.2. Maintenance of Offices or Agencies.

              The Company hereby appoints the Corporate Trust Office of the
Trustee or such other office or agency of the Trustee as its agent in the
Borough of Manhattan, The City of New York, 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 may at any time and from time to time vary or
terminate the appointment of any such agent or appoint any additional agents for
any or all of such purposes; provided, however, that until all of the Securities
have been delivered to the Trustee for cancellation, or moneys sufficient to pay
the principal of, premium, if any, and interest on the Securities have been made
available for payment and either paid or returned to the Company pursuant to the
provisions of Section 9.3, the Company will maintain in the State of Minnesota,
County of Ramsey, The City of St. Paul, an office or agency where Securities may
be presented or surrendered for payment and conversion, where Securities may be
surrendered for registration of transfer or exchange 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, and
notice to the Holders in accordance with Section 1.6, of the appointment or
termination of any such agents and of the location and any change in the
location of any 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, presentations and surrenders may be made and notices and demands may be
served on the Corporate Trust Office of the Trustee.

SECTION 9.3. Money for Security Payments To Be Held in Trust.



                                      -86-
<PAGE>   95

              If the Company shall act as its own Paying Agent, it will, on or
before each due date of the principal of, premium, if any, or interest 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, premium, if any, or
interest so becoming due until such sums shall be paid to such Persons or
otherwise disposed of as herein provided and the Company 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, no later than the opening of business on each due date of the principal
of, premium, if any, or interest on any Securities, deposit with the Trustee a
sum sufficient to pay the principal, premium, if any, or interest so becoming
due, such sum to be held for the benefit of the Persons entitled to such
principal, premium, if any, or interest, and (unless such Paying Agent is the
Trustee) the Company will promptly notify the Trustee of any 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, that
such Paying Agent will:

              (1) hold all sums held by it for the payment of the principal of,
        premium, if any, or interest on Securities 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, 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 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



                                      -87-
<PAGE>   96

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.

              Anything contained herein to the contrary notwithstanding, any
money held by the Trustee or any Paying Agent in trust for the payment and
discharge of the principal of, premium, if any, or interest on any Security
which remains unclaimed for two (2) years after the date when each payment of
such principal, premium or interest has become payable shall be repaid within
sixty (60) days of such date by the Trustee to the Company as its absolute
property free from trust, and the Trustee shall thereupon be released and
discharged with respect thereto and the Holders shall look only to the Company
for the payment of the principal, premium or interest on such Security. The
Trustee shall not be liable to the Company or any Holder for interest on funds
held by it for the payment and discharge of the principal, premium or interest
on any of the Securities to any Holder. The Company shall not be liable for any
interest on the sums paid to it pursuant to this paragraph and shall not be
regarded as a trustee of such money.

SECTION 9.4. Existence.

              Subject to Article Seven, the Company will 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 9.5. Maintenance of Properties.

              The Company will 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 will cause to be made all necessary repairs,



                                      -88-
<PAGE>   97

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 shall prevent the Company from
discontinuing the operation or maintenance of any of such properties if such
discontinuance 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
material respect to the Holders.

SECTION 9.6. Payment of Taxes and Other Claims.

              The Company will pay or discharge, or cause to be paid or
discharged, before the same may 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, (2) all
claims for labor, materials and supplies which, if unpaid, might by law become a
lien or charge upon the property of the Company or any Subsidiary, and (3) all
stamps and other duties, if any, which may be imposed by the United States or
any political subdivision thereof or therein in connection with the issuance,
transfer, exchange or conversion of any Securities or with respect to this
Indenture; provided, however, that, in the case of clauses (1) and (2), the
Company shall not be required to pay or discharge or cause to be paid or
discharged any such tax, assessment, charge or claim (a) if the failure to do so
will not, in the aggregate, have a material adverse impact on the Company, or
(b) if the amount, applicability or validity is being contested in good faith by
appropriate proceedings.

SECTION 9.7. Registration and Listing.

              Within a reasonable time after the issuance of the Global
Security, the Company (i) will effect all registrations with, and obtain all
approvals by, all governmental authorities that may be necessary under any
United States Federal or state law (including the Securities Act, the Exchange
Act and state securities and Blue Sky laws) before the shares of Common Stock
issuable upon conversion of Securities may be lawfully issued and delivered, and
qualified or listed as contemplated by clause (ii) (it being understood that the
Company shall not be required to register the Securities under the Securities



                                      -89-
<PAGE>   98

Act, except pursuant to the Registration Rights Agreement referred to in Section
9.11); and (ii) will cause the shares of Common Stock required to be issued and
delivered upon conversion of Securities, prior to such issuance or delivery, to
be listed on the New York Stock Exchange or, if the Common Stock is not then
listed on the New York Stock Exchange, list the Common Stock or qualify the
Common Stock for quotation on each national securities exchange or quotation
system on which outstanding Common Stock is listed or quoted at the time of such
delivery. Nothing in this Section 9.7 will limit the application of Section
9.11.

SECTION 9.8. 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 (one of the signers of which shall be the Company's
principal executive, principal financial or principal accounting officer),
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.

              The Company will deliver to the Trustee, forthwith upon becoming
aware of any default in the performance or observance of any covenant, agreement
or condition contained in this Indenture, or any Event of Default, an Officers'
Certificate specifying with particularity such default or Event of Default and
further stating what action the Company has taken, is taking or proposes to take
with respect thereto.

              Any notice required to be given under this Section 9.8 shall be
delivered to the Trustee at its Corporate Trust Office.

SECTION 9.9. Delivery of Certain Information.



                                      -90-
<PAGE>   99

              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 of a Security 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 of Securities 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 (or any successor provision thereto) in connection with the
resale of any such security; provided, however, that the Company shall not be
required to furnish such information in connection with any request made on or
after the date which is two years from the later of (i) the date such a security
(or any such predecessor security) was last acquired from the Company or (ii)
the date such a security (or any such predecessor security) was last acquired
from an "affiliate" of the Company within the meaning of Rule 144 under the
Securities Act (or any successor provision thereto). "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).

SECTION 9.10. 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 not permit any of its subsidiaries or other
"affiliates" (as defined under Rule 144 under the Securities Act or any
successor provision thereto) controlled by it 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 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 9.11. Registration Rights.



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<PAGE>   100

              The Company agrees that the Holders from time to time of
Registrable Securities (as defined below) are entitled to the benefits of a
Registration Rights Agreement, dated as of February 24, 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 Registrable Securities, at the Company's expense, (i) to file within 90
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 Registrable Securities, (ii) thereafter use
reasonable efforts to cause such Shelf Registration Statement to be declared
effective by the Commission within 180 days after the first date of original
issuance of the Securities, and (iii) to use reasonable efforts to maintain such
Shelf Registration Statement continuously effective under the Securities Act of
1933, as amended, until a period of two years from the date of the effectiveness
of the Shelf Registration Statement or, if earlier, until (A) there are no
outstanding Registrable Securities registered under the Shelf Registration
Statement or (B) the expiration of the period referred to in Rule 144(k) (or any
successor provision thereto) under the Securities Act with respect to all
Registrable Securities held by Persons that are not Affiliates of the Company.

              Section 2(a) of the Registration Rights Agreement provides that,
upon written notice to each Holder of a Registrable Security, the Company may
postpone having the Shelf Registration Statement declared effective as required
by Section 2(a) of the Registration Rights Agreement for a reasonable time
specified in the notice but not exceeding 90 days if the Company is in
possession of material non-public information the disclosure of which would have
a material adverse effect on the business, operations, prospects, condition
(financial or otherwise) of the Company and its subsidiaries, taken as a whole.
Notwithstanding any postponement pursuant to Section 2(a) of the Registration
Rights Agreement, if (i) on or prior to 90 days following the date of original
issuance of the Registrable Securities, a Shelf Registration Statement has not
been filed with the Commission, or (ii) on or prior to the 180th day following
the date of original issuance of the Registrable Securities, such Shelf
Registration Statement is not declared effective (each, a "Registration
Default"), additional interest ("Liquidated Damages") will accrue on the
Registrable



                                      -92-
<PAGE>   101

Securities from and including the day following such Registration Default to but
excluding the day on which such Registration Default has been cured or, if
earlier, the last day upon which the Shelf Registration Statement is required to
be kept effective. Liquidated Damages will be paid semi-annually in arrears,
with the first semi-annual payment due on the first Interest Payment Date in
respect of the Registrable Securities following the date on which such
Liquidated Damages begin to accrue, and will accrue at a rate per annum equal to
an additional one-quarter of one percent (.25%) of the principal amount of the
Registrable Securities to and including the 90th day following such Registration
Default and at a rate per annum equal to one-half of one percent (.50%) thereof
from and after the 91st day following such Registration Default. In the event
that the Shelf Registration Statement ceases to be effective prior to the second
annual anniversary of the initial effective date of the Shelf Registration
Statement or such earlier date as is provided in the Registration Rights
Agreement for a period in excess of 45 days, whether or not consecutive, during
any 90-day period or more than 90 days, whether or not consecutive, during any
12-month period, then the interest rate borne by the Registrable Securities
shall increase by an additional one-half of one percent (.50%) per annum on the
46th day of the 90-day period or the 91st day of the applicable 12-month period
such Shelf Registration Statement ceases to be effective to but excluding the
day on which the Shelf Registration Statement again becomes effective, or if
earlier, the last day upon which the Shelf Registration Statement is required to
be kept effective.

              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 Registrable Security, such mention shall be deemed to include mention of the
payment of Liquidated Damages provided for in this Section to the extent that,
in such context, Liquidated Damages are, were or would be payable in respect
thereof pursuant to the provisions of this Section, and express mention of the
payment of Liquidated Damages (if applicable) in any provisions hereof shall not
be construed as excluding Liquidated Damages in those provisions hereof where
such express mention is not made.

              For the purposes of the Registration Rights Agreement,
"Registrable Securities" means all or any portion of the Registered Securities
issued from time to time under



                                      -93-
<PAGE>   102

this Indenture and the shares of Common Stock issuable upon conversion of such
Securities; provided, however, that a Security or the shares of Common Stock
issuable upon conversion of a Security ceases to be a Registrable Security when
it (i) has been effectively registered under the Securities Act and sold in a
manner contemplated by the Shelf Registration Statement, (ii) has been
transferred in compliance with Rule 144 under the Securities Act (or any
successor provisions thereto)or is transferable pursuant to paragraph (k) of
Rule 144 (or any successor provision thereto) or (iii) otherwise has been
transferred and a new Security or share of Common Stock not subject to transfer
restrictions under the Securities Act has been delivered by or on behalf of the
Company in accordance with Section 3.5(b).

              If a Security, or the shares of Common Stock issuable upon
conversion of a Security, is a Registrable Security, and the Holder thereof
elects to sell such Registrable Security pursuant to the Shelf Registration
Statement then, by its acceptance thereof, the Holder of such Registrable
Security will have agreed to be bound by the terms of the Registration Rights
Agreement relating to the Registrable Securities which are the subject of such
election.

              For the purposes of the Registration Rights Agreement, the term
"Holder" includes any Person that has a beneficial interest in any Global
Security or any beneficial interest in a global security representing shares of
Common Stock issuable upon conversion of a Security. The Company will give the
Trustee prompt written notice of any Registration Default, and of any cure
thereof.

SECTION 9.12. Waiver of Certain Covenants.

              The Company may omit in any particular instance to comply with any
covenant or conditions set forth in Sections 9.5 and 9.6, inclusive (other than
a covenant or condition which under Article Eight cannot be modified or amended
without the consent of the Holder of each Outstanding Security affected), if
before the time for such compliance the Holders shall, through the written
consent of, not less than a majority in principal amount of the Outstanding
Securities, 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



                                      -94-
<PAGE>   103

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 or any Paying or Conversion Agent in respect of any such covenant or
condition shall remain in full force and effect.


                                   ARTICLE TEN

                            REDEMPTION OF SECURITIES


SECTION 10.1. Right of Redemption.

              The Securities may be redeemed in accordance with the provisions
of the form of Securities set forth in Section 2.2.

SECTION 10.2. Applicability of Article.

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

SECTION 10.3. Election to Redeem; Notice to Trustee.

              The election of the Company to redeem any Securities shall be
evidenced by a Board Resolution. In case of any redemption at the election of
the Company of any of the Securities, 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 in writing of such Redemption
Date. If the Securities are to be redeemed pursuant to an election of the
Company which is subject to a condition specified in the form of Securities set
forth in Section 2.2, the Company shall furnish the Trustee with an Officers'
Certificate stating that the Company is entitled to effect such redemption and
setting forth a statement of facts showing that the conditions precedent to the
right of the Company so to redeem have occurred.



                                      -95-
<PAGE>   104

SECTION 10.4. 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 by the Trustee within three Business
Days after it receives the notice described in Section 10.3, from the
Outstanding Securities not previously called for redemption, by such method as
the Trustee may deem fair and appropriate.

              If any Registered Security selected for partial redemption is
converted in part before termination of the conversion right with respect to the
portion of the Security so selected, the converted portion of such Security
shall be deemed (so far as may be) to be the portion selected for redemption.
Securities which have been converted during a selection of Securities to be
redeemed may 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 and
certificate numbers 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 10.5. Notice of Redemption.

              Notice of redemption shall be given in the manner provided in
Section 1.6 to the Holders of Securities to be redeemed not less than 30 nor
more than 60 days prior to the Redemption Date, and such notice shall be
irrevocable.

              All notices of redemption shall identify the Securities to be
redeemed (including CUSIP numbers) and shall state:

              (1) the Redemption Date,

              (2) the Redemption Price, and accrued interest, if any,



                                      -96-
<PAGE>   105

              (3) if less than all Outstanding Securities are to be redeemed,
        the aggregate principal amount of Securities to be redeemed,

              (4) that on the Redemption Date the Redemption Price, and accrued
        interest, if any, will become due and payable upon each such Security to
        be redeemed, and that interest thereon shall cease to accrue on and
        after said date,

              (5) the Conversion Rate, the date on which the right to convert
        the Securities to be redeemed will terminate and the places where such
        Securities may be surrendered for conversion, and

              (6) the place or places where such Securities are to be
        surrendered for payment of the Redemption Price and accrued interest, if
        any.

              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 written
request, by the Trustee in the name of and at the expense of the Company. Notice
of redemption of Securities to be redeemed at the election of the Company
received by the Trustee shall be given by the Trustee to each Paying Agent in
the name of and at the expense of the Company.

SECTION 10.6. Deposit of Redemption Price.

              Not less than one Business Day prior to any Redemption Date, the
Company shall deposit with the Trustee (or, if the Company is acting as its own
Paying Agent, segregate and hold in trust as provided in Section 9.3) an amount
of money (which shall be in immediately available funds on such Redemption Date)
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.

              If any Security called for redemption is converted, any money
deposited with the Trustee or so segregated and held in trust for the redemption
of such Security shall (subject to any right of the Holder of such



                                      -97-
<PAGE>   106

Security or any Predecessor Security to receive interest as provided in the last
paragraph of Section 3.7) be paid to the Company on Company Request or, if then
held by the Company, shall be discharged from such trust.

SECTION 10.7. 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 from and after such date
(unless the Company shall default in the payment of the Redemption Price,
including accrued interest) such Securities shall cease to bear interest. Upon
surrender of any Security for redemption in accordance with said notice such
Security shall be paid by the Company at the Redemption Price together with
accrued and unpaid interest to the Redemption Date; provided, however, that
installments of interest on Securities 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 on the relevant Record Date
according to their terms and the provisions of Section 3.7.

              If any Security called for redemption shall not be so paid upon
surrender thereof for redemption, the principal amount of, premium, if any, and,
to the extent permitted by applicable law, accrued interest on such Security
shall, until paid, bear interest from the Redemption Date at a rate of __% per
annum and such Security shall remain convertible until the principal of such
Security (or portion thereof, as the case may be) shall have been paid or duly
provided for.

SECTION 10.8. 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 9.2 (with, if the Company or the Trustee so requires, due
endorsement by, or a 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 make available for delivery to the Holder of such
Security without service charge, a new Registered Security or Securities, of any
authorized denomination as requested by such Holder, in aggregate principal
amount equal to and



                                      -98-
<PAGE>   107

in exchange for the unredeemed portion of the principal of the Security so
surrendered.

SECTION 10.9. Conversion Arrangement on Call for Redemption.

              In connection with any redemption of the 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 (the "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, together with interest accrued and unpaid to the Redemption Date, of such
Securities. Notwithstanding anything to the contrary contained in this Article
Ten, the obligation of the Company to pay the Redemption Price, together with
interest accrued and unpaid to the Redemption Date, 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 close of business on the second Business Day
immediately prior to the Redemption Date), any Securities called for redemption
that are 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, and
consistent with any agreement or agreements with such Purchasers, to be acquired
by such Purchasers from such Holders and (notwithstanding anything to the
contrary contained in this Article Ten) 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 extended
through such time), subject to payment of the above amount as aforesaid. At the
direction of the Company, the Trustee shall hold and dispose of any such amount
paid to it by the Purchasers to the Holders 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, including the costs and expenses, including reasonable legal fees,
incurred by the Trustee in the defense of any claim or



                                      -99-
<PAGE>   108

liability arising out of or in connection with the exercise or performance of
any of its powers, duties, responsibilities or obligations under this Indenture.

                                 ARTICLE ELEVEN

                            CONVERSION OF SECURITIES


SECTION 11.1. Conversion Privilege and Conversion Rate.

              Subject to and upon compliance with the provisions of this
Article, at the option of the Holder thereof, any Security or any portion of the
principal amount thereof that is U.S.$1,000 or an integral multiple of
U.S.$1,000 may be converted into fully paid and nonassessable shares (calculated
as to each conversion to the nearest 1/100th of a share) of Common Stock of the
Company at the Conversion Rate, determined as hereinafter provided, in effect at
the time of conversion. Such conversion right shall commence upon the original
issuance of the Securities and expire at the close of business on March 1, 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 exercises his right to require
the Company to repurchase the Security, such conversion right in respect of the
Security, or portion thereof so called, shall expire at the close of business on
the Business Day immediately preceding the Redemption Date or the 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 rate at which shares of Common Stock shall be delivered upon
conversion (herein called the "Conversion Rate") shall be initially 14.8028
shares of Common Stock for each U.S.$1,000 principal amount of Securities. The
Conversion Rate shall be adjusted in certain instances as provided in this
Article Eleven.

SECTION 11.2. Exercise of Conversion Privilege.

              In order to exercise the conversion privilege, the Holder of any
Security to be converted shall surrender such



                                     -100-
<PAGE>   109

Security, duly endorsed or assigned to the Company or in blank, at any office or
agency of the Company maintained for that purpose pursuant to Section 9.2,
accompanied by a duly signed conversion notice substantially in the form set
forth in Section 2.4 stating 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. Each Security surrendered for conversion (in whole or
in part) during the period from the close of business on any Regular Record Date
next preceding any Interest Payment Date to the opening of business on such
Interest Payment Date shall (except in the case of any Security or portion
thereof which has been called for redemption on a Redemption Date, or is to be
repurchased on a Repurchase Date, with the consequence that the conversion right
of such Security would terminate between such Regular Record Date and the close
of business on such Interest Payment Date) be accompanied by payment 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 of
such Security (or part thereof, as the case may be) being surrendered for
conversion. The interest so payable on such Interest Payment Date with respect
to any Security (or portion thereof, if applicable) which is surrendered for
conversion during the period from the close of business on any Record Date next
preceding any Interest Payment Date to the opening of business on such Interest
Payment Date and which Security has been called for redemption on a Redemption
Date, or is repurchasable on a Repurchase Date, with the consequence that the
conversion right of such Security would terminate between such Regular Record
Date and the close of business on such Interest Payment Date, shall be paid to
the Holder of such Security being converted in an amount equal to the interest
that would have been payable on such Security if such Security had been
converted as of the close of business on such Interest Payment Date. The
interest so payable on such Interest Payment Date in respect of any Security (or
portion thereof, as the case may be) which has not been called for redemption on
a Redemption Date, or is not eligible for repurchase on a Repurchase Date, with
the consequence of termination of the conversion right as aforesaid, which
Security (or portion thereof, as the case may be) is surrendered for conversion
during the period from the close of business on any Record Date next preceding
any Interest Payment Date to the opening of business on such Interest Payment
Date, shall be paid to the Holder of such



                                     -101-
<PAGE>   110

Security as of such Regular Record Date. Interest payable in respect of any
Security surrendered for conversion on or after an Interest Payment Date shall
be paid to the Holder of such Security as of the next preceding Regular Record
Date, notwithstanding the exercise of the right of conversion. Except as
provided in this paragraph and subject to the last paragraph of Section 3.7, no
cash payment or adjustment shall be made upon any conversion on account of any
interest accrued from the Interest Payment Date next preceding the conversion
date, in respect of any Security (or part thereof, as the case may be)
surrendered for conversion, or on account of any dividends on the Common Stock
issued upon conversion. The Company's delivery to the Holder of the number of
shares of Common Stock (and cash in lieu of fractions thereof, as provided in
this Indenture) into which a Security is convertible will be deemed to satisfy
the Company's obligation to pay the principal amount of the Security.

              Securities shall be deemed to have been converted 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 deliver to the
Trustee, for delivery to the Holder, 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 11.3.

              All shares of Common Stock delivered upon such conversion of
Securities shall bear restrictive legends substantially in the form of the
legends required to be set forth on the Securities pursuant to Section 3.5 and
shall be subject to the restrictions on transfer provided in such legends.
Neither the Trustee nor any agent maintained for the purpose of such conversion
shall have any responsibility for the inclusion or content of any such
restrictive legends on such Common Stock; provided, however, that the Trustee or
any agent maintained for the purpose of such conversion shall have provided to
the Company or to the Company's transfer agent for such Common Stock, prior to
or concurrently with a request to the Company to deliver such



                                     -102-
<PAGE>   111

Common Stock, written notice that the Securities delivered for conversion are
Securities.

              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
make available for delivery to the Holder thereof, at the expense of the
Company, a new Registered Security or Securities of authorized denominations in
an aggregate principal amount equal to the unconverted portion of the principal
amount of such Security. A Security may be converted in part, but only if the
principal amount of such Security to be converted is any integral multiple of
U.S.$1,000 and the principal amount of such security to remain Outstanding after
such conversion is equal to U.S.$1,000 or any integral multiple of U.S.$1,000 in
excess thereof.

SECTION 11.3. Fractions of Shares.

              No fractional shares of Common Stock shall be issued upon
conversion of any Security or 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 calculate and pay a cash
adjustment in respect of such fraction (calculated to the nearest 1/100th of a
share) in an amount equal to the same fraction of the Closing Price Per Share at
the close of business on the day of conversion.

SECTION 11.4. Adjustment of Conversion Rate.

              The Conversion Rate shall be subject to adjustments from time to
time as follows:

              (1) In case the Company shall pay or make a dividend or other
distribution on any class of capital stock of the Company payable in shares of
Common Stock, the Conversion Rate in effect at the opening of business on the
day following the date fixed for the determination of stockholders entitled to
receive such dividend or other distribution shall be increased by dividing such
Conversion



                                     -103-
<PAGE>   112

Rate 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 increase to become effective immediately after the opening of business on
the day following the date fixed for such determination. If, after any such date
fixed for determination, any dividend or distribution is not in fact paid, the
Conversion Rate shall be immediately readjusted, effective as of the date the
Board of Directors determines not to pay such dividend or distribution, to the
Conversion Rate that would have been in effect if such determination date had
not been fixed. 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
will 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 issue rights, options or warrants to
all holders of its Common Stock entitling them 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 (8) of this Section 11.4) of the
Common Stock on the date fixed for the determination of stockholders entitled to
receive such rights, options or warrants (other than any rights, options or
warrants that by their terms will also be issued to any Holder upon conversion
of a Security into shares of Common Stock without any action required by the
Company or any other Person), the Conversion Rate in effect at the opening of
business on the day following the date fixed for such determination shall be
increased by dividing such Conversion Rate 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 increase to become effective immediately



                                     -104-
<PAGE>   113

after the opening of business on the day following the date fixed for such
determination. If, after any such date fixed for determination, any such rights,
options or warrants are not in fact issued, the Conversion Rate shall be
immediately readjusted, effective as of the date the Board of Directors
determines not to issue such rights, options or warrants, to the Conversion Rate
that would have been in effect if such determination date had not been fixed.
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 will not
issue any rights, options or warrants 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 Rate in effect
at the opening of business on the day following the day upon which such
subdivision becomes effective shall be proportionately increased, and,
conversely, in case outstanding shares of Common Stock shall each be combined
into a smaller number of shares of Common Stock, the Conversion Rate in effect
at the opening of business on the day following the day upon which such
combination becomes effective shall be proportionately reduced, such increase or
reduction, 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) 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, or other property (including cash or
assets or securities, but excluding (i) any rights, options or warrants referred
to in paragraph (2) of this Section, (ii) any dividend or distribution paid
exclusively in cash, (iii) any dividend or distribution referred to in paragraph
(1) of this Section and (iv) any merger or consolidation to which Section 11.11
applies), the Conversion Rate shall be adjusted so that the same shall equal the
rate determined by dividing the Conversion Rate in effect immediately prior to
the close of business on the date fixed for the determination of stockholders
entitled to receive such distribution by a fraction of which the numerator shall
be the current market price per share (determined as provided



                                     -105-
<PAGE>   114

in paragraph (8) of this Section 11.4) of the Common Stock on the date fixed for
such determination less the then fair market value (as determined by the Board
of Directors, whose determination shall be conclusive and described in a Board
Resolution filed with the Trustee) of the portion of the assets, shares or
evidences of indebtedness 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 adjustment to become effective immediately prior to the opening of
business on the day following the date fixed for the determination of
stockholders entitled to receive such distribution. If, after any such date
fixed for determination, any such distribution is not in fact made, the
Conversion Rate shall be immediately readjusted, effective as of the date the
Board of Directors determines not to make such distribution, to the Conversion
Rate that would have been in effect if such determination date had not been
fixed.

              (5) In case the Company shall, by dividend or otherwise,
distribute to all holders of its Common Stock cash (excluding any cash that is
distributed upon a merger or consolidation to which Section 11.11 applies or as
part of a distribution referred to in paragraph (4) of this Section) in an
aggregate amount that, combined together with (I) the aggregate amount of any
other cash 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 adjustment pursuant to this paragraph (5) has been made
and (II) the aggregate of any cash plus the fair market value (as determined by
the Board of Directors, whose determination shall be conclusive and described in
a Board Resolution) of consideration payable in respect of any tender offer by
the Company or any of its subsidiaries 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 adjustment pursuant to paragraph (6) of
this Section 11.4 has been made (the "combined cash and tender amount") exceeds
10% of the product of the current market price per share (determined as provided
in paragraph (8) of this Section 11.4) of the Common Stock on the date for the
determination of holders of shares of Common Stock entitled to receive such
distribution times the number of shares of Common Stock outstanding on such date
(the "aggregate current market price"), then, and in each such case, immediately
after the close of business on such date for



                                     -106-
<PAGE>   115

determination, the Conversion Rate shall be adjusted so that the same shall
equal the rate determined by dividing the Conversion Rate in effect immediately
prior to the close of business on the date fixed for determination of the
stockholders entitled to receive such distribution by a fraction (i) the
numerator of which shall be equal to the current market price per share
(determined as provided in paragraph (8) of this Section) of the Common Stock on
the date fixed for such determination less an amount equal to the quotient of
(x) the excess of such combined cash and tender amount over such aggregate
current market price divided by (y) the number of shares of Common Stock
outstanding on such date for determination and (ii) the denominator of which
shall be equal to the current market price per share (determined as provided in
paragraph (8) of this Section 11.4) of the Common Stock on such date for
determination.

              (6) In case a tender offer made by the Company or any Subsidiary
for all or any portion of the Common Stock shall expire and such tender offer
(as amended upon the expiration thereof) shall require the payment to
stockholders (based on the acceptance (up to any maximum specified in the terms
of the tender offer) of Purchased Shares (as defined below)) of an aggregate
consideration having a fair market value (as determined by the Board of
Directors, whose determination shall be conclusive and described in a Board
Resolution) that combined together with (I) the aggregate of the cash plus the
fair market value (as determined by the Board of Directors, whose determination
shall be conclusive and described in a Board Resolution), as of the expiration
of such tender offer, of consideration payable in respect of any other tender
offer by the Company or any Subsidiary for all or any portion of the Common
Stock expiring within the 12 months preceding the expiration of such tender
offer and in respect of which no adjustment pursuant to this paragraph (6) has
been made and (II) the aggregate amount of any cash distributions to all holders
of the Company's Common Stock within 12 months preceding the expiration of such
tender offer and in respect of which no adjustment pursuant to paragraph (5) of
this Section has been made (the "combined tender and cash amount") exceeds 10%
of the product of the current market price per share of the Common Stock
(determined as provided in paragraph (8) of this Section 11.4) as of the last
time (the "Expiration Time") tenders could have been made pursuant to such
tender offer (as it may be amended) times the number of shares of



                                     -107-
<PAGE>   116

Common Stock outstanding (including any tendered shares) as of the Expiration
Time, then, and in each such case, immediately prior to the opening of business
on the day after the date of the Expiration Time, the Conversion Rate shall be
adjusted so that the same shall equal the rate determined by dividing the
Conversion Rate immediately prior to close of business on the date of the
Expiration Time by a fraction (i) the numerator of which shall be equal to (A)
the product of (I) the current market price per share of the Common Stock
(determined as provided in paragraph (8) of this Section 11.4) on the date of
the Expiration Time multiplied by (II) the number of shares of Common Stock
outstanding (including any tendered shares) on the Expiration Time less (B) the
combined tender and cash amount, and (ii) the denominator of which shall be
equal to the product of (A) the current market price per share of the Common
Stock (determined as provided in paragraph (8) of this Section 11.4) as of the
Expiration Time multiplied by (B) the number of shares of Common Stock
outstanding (including any tendered shares) as of the Expiration Time less the
number of all shares validly tendered 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").

              (7) The reclassification of Common Stock into securities including
other than Common Stock (other than any reclassification upon a consolidation or
merger to which Section 11.11 applies) shall be deemed to involve (a) a
distribution of such securities other than Common Stock to all holders of Common
Stock (and the effective date of such reclassification shall be deemed to be
"the date fixed for the determination of stockholders entitled to receive such
distribution" and "the date fixed for such determination" within the meaning of
paragraph (4) of this Section), and (b) a subdivision or combination, as the
case may be, of the number of shares of Common Stock outstanding immediately
prior to such reclassification into the number of shares of Common Stock
outstanding immediately thereafter (and the effective date of such
reclassification shall be deemed to be "the day upon which such subdivision
becomes effective" or "the day upon which such combination becomes effective",
as the case may be, and "the day upon which such subdivision or combination
becomes effective" within the meaning of paragraph (3) of this Section 11.4).



                                     -108-
<PAGE>   117


              (8) For the purpose of any computation under paragraphs (2), (4),
(5) or (6) of this Section 11.4, the current market price per share of Common
Stock on any date shall be calculated by the Company and be deemed to be the
average of the daily Closing Prices Per Share for the five consecutive Trading
Days selected by the Company commencing not more than 10 Trading Days before,
and ending not later than, the earlier of the day in question and the day before
the "ex" date with respect to the issuance or distribution requiring such
computation. For purposes of this paragraph, the term "`ex' date", when used
with respect to any issuance or distribution, means the first date on which the
Common Stock trades regular way in the applicable securities market or on the
applicable securities exchange without the right to receive such issuance or
distribution.

              (9) No adjustment in the Conversion Rate shall be required unless
such adjustment (plus any adjustments not previously made by reason of this
paragraph (9)) would require an increase or decrease of at least one percent in
such rate; 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. All calculations under this Article
shall be made to the nearest cent or to the nearest one-hundredth of a share, as
the case may be.

              (10) The Company may make such increases in the Conversion Rate,
for the remaining term of the Securities or any shorter term, in addition to
those required by paragraphs (1), (2), (3), (4), (5) and (6) of this Section
11.4, as it considers to be advisable in order to avoid or diminish any income
tax liability to any holders of shares of Common Stock resulting from any
dividend or distribution of Common Stock or issuance of rights or warrants to
purchase or subscribe for Common Stock or from any event treated as such for
income tax purposes.

              To the extent permitted by applicable law, the Company from time
to time may increase the Conversion Rate by any amount for any period of time if
the period is at least twenty (20) days and the Board of Directors shall have
made a determination that such increase would be in the best interests of the
Company, which determination shall be conclusive; provided, however, that such
increase shall not be taken into account for purposes of determining whether the
Closing Price Per Share of the Common Stock exceeds the



                                     -109-

<PAGE>   118

Conversion Price by 105% in connection with an event which would otherwise be a
Change in Control. Whenever the Conversion Rate is increased pursuant to the
preceding sentence, the Company shall give notice of the increase to the Holders
of Securities in the manner provided in Section 1.6 at least fifteen (15) days
prior to the date the increased Conversion Rate takes effect, and such notice
shall state the increased Conversion Rate and the period during which it will be
in effect.

              (11) Notwithstanding the foregoing provisions of this Section, no
adjustment of the Conversion Rate shall be required to be made (a) upon the
issuance of shares of Common Stock pursuant to any present or future plan for
the reinvestment of dividends or (b) because of a tender or exchange offer of
the character described in Rule 13e-4(h)(5) under the Exchange Act or any
successor rule thereto.

SECTION 11.5. Notice of Adjustments of Conversion Rate.

              Whenever the Conversion Rate is adjusted as herein provided:

              (1) the Company shall compute the adjusted Conversion Rate in
        accordance with Section 11.4 and shall prepare a certificate signed by
        the Chief Financial Officer of the Company setting forth the adjusted
        Conversion Rate and showing in reasonable detail the facts upon which
        such adjustment is based, and such certificate shall promptly be filed
        with the Trustee and with each Conversion Agent; and

              (2) upon each such adjustment, a notice stating that the
        Conversion Rate has been adjusted and setting forth the adjusted
        Conversion Rate shall be required, and as soon as practicable after it
        is required, such notice shall be provided by the Company to all Holders
        in accordance with Section 1.6.

Neither the Trustee nor any Conversion Agent shall be under any duty or
responsibility with respect to any such certificate or the information and
calculations contained therein, except to exhibit the same to any Holder of
Securities desiring inspection thereof at its office during normal business
hours.



                                     -110-
<PAGE>   119

SECTION 11.6. Notice of Certain Corporate Action.

              In case:

              (a) the Company shall declare a dividend (or any other
        distribution) on its Common Stock payable (i) otherwise than exclusively
        in cash or (ii) exclusively in cash in an amount that would require any
        adjustment pursuant to Section 11.4; or

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

              (c) of any reclassification of the Common Stock of the Company, or
        of any consolidation, merger or share exchange to which the Company is a
        party and for which approval of any stockholders of the Company is
        required, or of the conveyance, sale, transfer or lease 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;

then the Company shall cause to be filed at each office or agency maintained for
the purpose of conversion of Securities pursuant to Section 9.2, and shall cause
to be provided to all Holders in accordance with Section 1.6, at least 20 days
(or 10 days in any case specified in clause (a) or (b) above) prior to the
applicable record or effective date hereinafter specified, a notice stating (x)
the date on which a record is to be taken for the purpose of such dividend,
distribution, rights, options or warrants, 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, options or warrants are to be determined or
(y) the date on which such reclassification, consolidation, merger, conveyance,
transfer, sale, lease, 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



                                     -111-
<PAGE>   120

reclassification, consolidation, merger, conveyance, transfer, sale, lease,
dissolution, liquidation or winding up. Neither the failure to give such notice
or the notice referred to in the following paragraph nor any defect therein
shall affect the legality or validity of the proceedings described in clauses
(a) through (d) of this Section 11.6. If at the time the Trustee shall not be
the Conversion Agent, a copy of such notice shall also forthwith be filed by the
Company with the Trustee.

              The Company shall cause to be filed at each office or agency
maintained for the purpose of conversion of Securities pursuant to Section 9.2,
and shall cause to be provided to all Holders in accordance with Section 1.6,
notice of any tender offer by the Company or any Subsidiary for all or any
portion of the Common Stock at or about the time that such notice of tender
offer is provided to the public generally.

SECTION 11.7. Company to Reserve Common Stock.

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

SECTION 11.8. Taxes on Conversions.

              Except as provided in the next sentence, the Company will pay any
and all taxes and duties 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 or duty 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 duty, or has established to the satisfaction of the Company that
such tax or duty has been paid.

SECTION 11.9. Covenant as to Common Stock.



                                     -112-
<PAGE>   121

              The Company agrees that all shares of Common Stock which may be
delivered upon conversion of Securities, upon such delivery, will be newly
issued shares and will have been duly authorized and validly issued and will be
fully paid and nonassessable and, except as provided in Section 11.8, the
Company will pay all taxes, liens and charges with respect to the issue thereof.

SECTION 11.10. Cancellation of Converted Securities.

              All Securities delivered for conversion shall be delivered to the
Trustee or its agent to be canceled by or at the direction of the Trustee, which
shall dispose of the same as provided in Section 3.9.

SECTION 11.11. Provision in Case of Consolidation, Merger or Sale of Assets.

              In case of any consolidation or merger of the Company with or into
any other Person, any merger of another Person with or into the Company (other
than a merger which does not result in any reclassification, conversion,
exchange or cancellation of outstanding shares of Common Stock of the Company)
or any conveyance, sale, transfer or lease of all or substantially all of the
assets of the Company, the Person formed by such consolidation or resulting from
such merger or which acquires such assets, as the case may be, shall execute and
deliver to the Trustee a supplemental indenture providing that the Holder of
each Security then Outstanding shall have the right thereafter, during the
period such Security shall be convertible as specified in Section 11.1, to
convert such Security only into the kind and amount of securities, cash and
other property receivable upon such consolidation, merger, conveyance, sale,
transfer or lease by a holder of the number of shares of Common Stock of the
Company into which such Security might have been converted immediately prior to
such consolidation, merger, conveyance, sale, transfer or lease, assuming such
holder of Common Stock of the Company (i) is not a Person with which the Company
consolidated or merged with or into or which merged into or with the Company or
to which such conveyance, sale, transfer or lease was made, as the case may be
("Constituent Person"), or an Affiliate of a Constituent Person and (ii) failed
to exercise his rights of election, if any, as to the kind or amount of
securities, cash and other property receivable



                                     -113-
<PAGE>   122

upon such consolidation, merger, conveyance, sale, transfer or lease (provided
that if the kind or amount of securities, cash and other property receivable
upon such consolidation, merger, conveyance, sale, transfer, or lease is not the
same for each share of Common Stock of the Company held immediately prior to
such consolidation, merger, conveyance, sale, transfer or lease by others than a
Constituent Person or an Affiliate thereof and in respect of which such rights
of election shall not have been exercised ("Non-electing Share"), then for the
purpose of this Section 11.11 the kind and amount of securities, cash and other
property receivable upon such consolidation, merger, conveyance, sale, transfer
or lease by the holders of each Non-electing Share shall be deemed to be the
kind and amount so receivable per share by a plurality of the Non-electing
Shares). 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 11.11 shall similarly apply
to successive consolidations, mergers, conveyances, sales, transfers or leases.
Notice of the execution of such a supplemental indenture shall be given by the
Company to the Holder of each Security as provided in Section 1.6 promptly upon
such execution.

              Neither the Trustee nor any Conversion Agent shall be under any
responsibility to determine the correctness of any provisions contained in any
such supplemental indenture relating either to the kind or amount of shares of
stock or other securities or property or cash receivable by Holders of
Securities upon the conversion of their Securities after any such consolidation,
merger, conveyance, transfer, sale or lease or to any such adjustment, but may
accept as conclusive evidence of the correctness of any such provisions, and
shall be protected in relying upon, an Officers Certificate or an Opinion of
Counsel with respect thereto, which the Company shall cause to be furnished to
the Trustee upon request.

SECTION 11.12. Responsibility of Trustee for Conversion Provisions.

              The Trustee, subject to the provisions of Section 6.1, and any
Conversion Agent shall not at any time be under any duty or responsibility to
any Holder of Securities to determine whether any facts exist which may require
any



                                     -114-
<PAGE>   123

adjustment of the Conversion Rate, or with respect to the nature or extent of
any such adjustment when made, or with respect to the method employed, or herein
or in any supplemental indenture provided to be employed, in making the same, or
whether a supplemental indenture need be entered into. Neither the Trustee,
subject to the provisions of Section 6.1, nor any Conversion Agent shall be
accountable with respect to the validity or value (or the kind or amount) of any
Common Stock, or of any other securities or property or cash, which may at any
time be issued or delivered upon the conversion of any Security; and it or they
do not make any representation with respect thereto. Neither the Trustee,
subject to the provisions of Section 6.1, nor any Conversion Agent shall be
responsible for any failure of the Company to make or calculate any cash payment
or to issue, transfer or deliver any shares of Common Stock or share
certificates or other securities or property or cash upon the surrender of any
Security for the purpose of conversion; and the Trustee, subject to the
provisions of Section 6.1, and any Conversion Agent shall not be responsible for
any failure of the Company to comply with any of the covenants of the Company
contained in this Article.


                                 ARTICLE TWELVE

                           SUBORDINATION OF SECURITIES

SECTION 12.1. Securities Subordinate to Senior Debt.

              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 (subject to the
provisions of Article Four), the indebtedness represented by the Securities and
the payment of the principal of (and premium, if any) and interest on, and any
payment of the Repurchase Price with respect to, each and all of the Securities
are hereby expressly made subordinate and subject in right of payment to the
prior payment in full of all Senior Debt.

SECTION 12.2. No Payments in Certain Circumstances; Payment Over of Proceeds
Upon Dissolution, Etc.



                                     -115-
<PAGE>   124

              No payment on account of principal of, premium, if any, or
interest on, or redemption or repurchase of, the Securities or any coupons
appertaining thereto shall be made if, at the time of such payment or
immediately after giving effect thereto: (i) a default in the payment of
principal, premium, if any, or interest or other amounts due on any Senior Debt,
including any default under any redemption or repurchase obligation, occurs and
is continuing (or, in the case of Senior Debt for which there is a period of
grace, in the event of such a default that continues beyond the period of grace,
if any, specified in the instrument or lease evidencing such Senior Debt),
unless and until such default shall have been cured or waived or shall have
ceased to exist; or (ii) a default, other than a payment default, on Designated
Senior Debt occurs and is continuing that then permits holders of such
Designated Senior Debt to accelerate its maturity and the Trustee receives a
notice of the default (a "Payment Blockage Notice") from a Person who may give
it pursuant to Sections 12.5 and 12.6 hereof. Notwithstanding the foregoing, the
Company may make, and the Trustee may receive and shall apply, any payment in
respect of the Securities (for principal, premium, if any, or interest or
repurchase) if such payment was made prior to the occurrence of any of the
contingencies specified in clauses (i) and (ii) above.

              If the Trustee receives any Payment Blockage Notice pursuant to
clause (ii) above, no subsequent Payment Blockage Notice shall be effective for
purposes of this Section unless and until (A) at least 365 days shall have
elapsed since the effectiveness of the immediately prior Payment Blockage
Notice, and (B) all scheduled payments of principal, premium, if any, and
interest on the Securities that have come due have been paid in full in cash. No
nonpayment default that existed or was continuing on the date of delivery of any
Payment Blockage Notice to the Trustee shall be, or be made, the basis for a
subsequent Payment Blockage Notice.

              The Company may and shall resume payments on and distributions in
respect of the Securities upon the earlier of: (i) the date upon which the
default is cured or waived, or (ii) in the case of a default referred to in
clause (ii) of the second preceding paragraph, 179 days pass after notice is
received if the maturity of such Designated Senior Debt has not been
accelerated, unless this Article otherwise



                                     -116-
<PAGE>   125

prohibits the payment or distribution at the time of such payment or
distribution.

              Upon (i) any acceleration of the principal amount due on the
Securities or (ii) any payment or distribution of assets of the Company of any
kind or character, whether in cash, property or securities, to creditors upon
any dissolution, winding up or total or partial liquidation or reorganization of
the Company, whether voluntary or involuntary, or in bankruptcy, insolvency,
receivership or other proceedings, all principal of, premium, if any, sinking
fund and interest or other amounts due or to become due upon all Senior Debt
shall first be paid in full, or payment thereof provided for in money or money's
worth in accordance with its terms, before any payment is made on account of the
principal of, premium, if any, or interest on, or repurchase of, the
indebtedness evidenced by the Securities or any coupon appertaining thereto, and
upon any such dissolution or winding up or liquidation or reorganization any
payment or distribution of assets of the Company of any kind or character,
whether in cash, property or securities, to which the Holders of the Securities
or any coupons appertaining thereto or the Trustee under this Indenture would be
entitled, except for the provisions hereof, shall be paid by the Company or by
any receiver, trustee in bankruptcy, liquidating trustee, agent or other Person
making such payment or distribution, or by the Holders of the Securities or any
coupons appertaining thereto or by the Trustee under this Indenture if received
by them or it, as the case may be, directly to the holders of Senior Debt (pro
rata to each such holder on the basis of the respective amounts of Senior Debt
held by such holder) or their representatives, to the extent necessary to pay
all Senior Debt in full, in money or money's worth, after giving effect to any
concurrent payment or distribution to or for the holders of Senior Debt, before
any payment or distribution is made to the Holders of the Securities or any
coupons appertaining thereto or to the Trustee under this Indenture.

              In the event that, contrary to the foregoing, any payment or
distribution of assets of the Company of any kind or character, whether in cash,
property or securities, shall be received by the Trustee or the Holders of the
Securities before all Senior Debt is paid in full or provision made for such
payment, in accordance with its terms, such payment or distribution shall be
paid over or delivered to, the holders



                                     -117-
<PAGE>   126

of such Senior Debt or their representative or representatives, or to the
trustee or trustees under any indenture pursuant to which any instruments
evidencing any of such Senior Debt have been issued, as their respective
interests may appear, for application to the payment of all Senior Debt
remaining unpaid to the extent necessary to pay all such Senior Debt in full in
accordance with its terms, after giving effect to any concurrent payment or
distribution to or for the holders of such Senior Debt.

              Subject to the payment in full of all Senior Debt, the Holders of
the Securities and any coupons (together with the holders of any other
indebtedness of the Company which is subordinated in right of payment to the
payment in full of all Senior Debt, which is not subordinated in right of
payment to the Securities and which by its terms grants such right of
subrogation to the holders thereof) shall be subrogated to the rights of the
holders of Senior Debt to receive payments or distribution of assets of the
Company made on the Senior Debt until the principal of, premium, if any, and
interest on, or amounts payable upon repurchase of, the Securities shall be paid
in full; and, for the purposes of such subrogation, no payments or distributions
to the holders of Senior Debt of any cash, property or securities to which the
Holders of the Securities and any coupons appertaining thereto or the Trustee
would be entitled except for the provisions of this Article, and no payment over
pursuant to the provisions of this Article to the holders of Senior Debt by the
Holders of the Securities or any coupon or the Trustee, shall, as between the
Company, its creditors other than the holders of Senior Debt, and the Holders of
Securities and coupons, be deemed to be a payment by the Company to the holders
of or on account of Senior Debt, it being understood that the provisions of this
Article are and are intended solely for the purpose of defining the relative
rights of the Holders of the Securities and coupons, on the one hand, and the
holders of Senior Debt, on the other hand.

SECTION 12.3. 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 and
appoints the Trustee his attorney-in-fact for any and all such purposes.



                                     -118-
<PAGE>   127

SECTION 12.4. No Waiver of Subordination Provisions.

              No right of any present or future holder of any Senior Debt to
enforce subordination as herein 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 of any Senior
Debt, 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 Debt 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 or
the obligations hereunder of the Holders of the Securities to the holders of
Senior Debt, 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
Debt, or otherwise amend or supplement in any manner Senior Debt or any
instrument evidencing the same or any agreement under which Senior Debt is
outstanding; (ii) sell, exchange, release or otherwise deal with any property
pledged, mortgaged or otherwise securing Senior Debt; (iii) release any Person
liable in any manner for the collection of Senior Debt; and (iv) exercise or
refrain from exercising any rights against the Company and any other Person.

SECTION 12.5. 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 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 Debt or from any trustee, agent or representative
therefor; and, prior to the receipt of any such written notice, the Trustee,
subject to the provisions of



                                     -119-
<PAGE>   128

Section 6.1, shall be entitled in all respects to assume that no such facts
exist; provided, however, that if the Trustee shall not have received the notice
provided for in this Section 12.5 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) 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 6.1, 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 Debt (or a trustee, agent or
representative therefor) to establish that such notice has been given by a
holder of Senior Debt (or a trustee, agent or representative 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 Debt to
participate in any payment or distribution pursuant to this Article, the Trustee
may request such Person to furnish evidence to the reasonable satisfaction of
the Trustee as to the amount of Senior Debt 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, 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 12.6. Reliance on Judicial Order or Certificate of Liquidating Agent.

              Upon any payment or distribution of assets of the Company referred
to in this Article, the Trustee, subject to the provisions of Section 6.1, 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



                                     -120-
<PAGE>   129

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 Debt 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.

SECTION 12.7. Trustee Not Fiduciary for Holders of Senior Debt.

              The Trustee shall not be deemed to owe any fiduciary duty to the
holders of Senior Debt 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 Debt shall be entitled by virtue of this Article or otherwise.
With respect to the holders of Senior Debt, the Trustee undertakes to perform or
to observe only such of its covenants or obligations as are specifically set
forth in this Article Twelve, and no implied covenants or obligations with
respect to holders of Senior Debt shall be read into this Indenture against the
Trustee.

SECTION 12.8. Reliance by Holders of Senior Debt on Subordination Provisions.

              Each Holder by accepting a Security acknowledges and agrees that
the foregoing subordination provisions are, and are intended to be, an
inducement and a consideration to each holder of any Senior Debt, whether such
Senior Debt was created or acquired before or after the issuance of the
Securities, to acquire and continue to hold, or to continue to hold, such Senior
Debt and such holder of Senior Debt shall be deemed conclusively to have relied
on such subordination provisions in acquiring and continuing to hold, or in
continuing to hold, such Senior Debt.

SECTION 12.9. Rights of Trustee as Holder of Senior Debt; Preservation of
Trustee's Rights.

              The Trustee in its individual capacity shall be entitled to all
the rights set forth in this Article with respect to any Senior Debt which may
at any time be held by it, to the same extent as any other holder of Senior
Debt,



                                     -121-
<PAGE>   130

and nothing in this Indenture shall deprive the Trustee of any of its rights as
such holder.

              Nothing in this Article shall apply to claims of, or payments to,
the Trustee under or pursuant to Section 6.7.

SECTION 12.10. 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 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 in addition to or in place of the Trustee; provided,
however, that Section 12.9 shall not apply to the Company or any Affiliate of
the Company if it or such Affiliate acts as Paying Agent.

SECTION 12.11. Certain Conversions and Repurchases Deemed Payment.

              For the purposes of this Article only, (1) the issuance and
delivery of junior securities upon conversion of Securities in accordance with
Article Eleven or upon the repurchase of Securities in accordance with Article
Thirteen 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, the term "junior
securities" means (a) shares of any stock of any class of the Company and any
cash, property or securities into which the Securities are convertible pursuant
to Article Eleven and (b) securities of the Company which are subordinated in
right of payment to all Senior Debt 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. Nothing contained in this Article or elsewhere in this Indenture or in
the Securities is intended to or shall impair, as among the Company, its



                                     -122-
<PAGE>   131

creditors other than holders of Senior Debt 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 Eleven or to exchange such
Security for Common Stock in accordance with Article Thirteen if the Company
elects to satisfy the obligations under Article Thirteen by the delivery of
Common Stock.

                                ARTICLE THIRTEEN

                  REPURCHASE OF SECURITIES AT THE OPTION OF THE
                         HOLDER UPON A CHANGE IN CONTROL

SECTION 13.1. Right to Require Repurchase.

              In the event that a Change in Control (as hereinafter defined)
shall occur, then each Holder shall have the right, at the Holder's option, but
subject to the provisions of Section 13.2, to require the Company to repurchase,
and upon the exercise of such right the Company shall repurchase, all of such
Holder's Securities not theretofore called for redemption, or any portion of the
principal amount thereof that is equal to U.S.$5,000 or any greater integral
multiple of U.S.$1,000, on the date (the "Repurchase Date") that is 45 days
after the date of the Company Notice (as defined in Section 13.3) at a purchase
price equal to 100% of the principal amount of the Securities to be repurchased
plus interest accrued to the Repurchase Date (the "Repurchase Price"); provided,
however, that installments of interest on Securities whose Stated Maturity is on
or prior to the Repurchase Date shall be payable to the Holders of such
Securities, or one or more Predecessor Securities, registered as such on the
relevant Record Date according to their terms and the provisions of Section 3.7.
Such right to require the repurchase of the Securities shall not continue after
a discharge of the Company from its obligations with respect to the Securities
in accordance with Article Four, unless a Change in Control shall have occurred
prior to such discharge. At the option of the Company, the Repurchase Price may
be paid in cash or, subject to the fulfillment by the Company of the conditions
set forth Section 13.2, by delivery of shares of Common Stock having a fair
market value equal to the Repurchase Price. Whenever in this Indenture
(including Sections 2.2, 3.1, 5.1(1) and 5.8) there is a reference, in any
context, to the principal of any Security as of any time, such reference shall
be deemed to include reference to the



                                     -123-
<PAGE>   132

Repurchase Price payable in respect of such Security to the extent that such
Repurchase Price is, was or would be so payable at such time, and express
mention of the Repurchase Price in any provision of this Indenture shall not be
construed as excluding the Repurchase Price in those provisions of this
Indenture when such express mention is not made; provided, however, that for the
purposes of Article Twelve such reference shall be deemed to include reference
to the Repurchase Price only to the extent the Repurchase Price is payable in
cash.

SECTION 13.2. Conditions to the Company's Election to Pay the Repurchase Price
in Common Stock.

        The Company may elect to pay the Repurchase Price by delivery of shares
of Common Stock pursuant to Section 13.1 if and only if the following conditions
shall have been satisfied:

              (a) The shares of Common Stock deliverable in payment of the
Repurchase Price shall have a fair market value as of the Repurchase Date of not
less than the Repurchase Price. For purposes of Section 13.1 and this Section
13.2, the fair market value of shares of Common Stock shall be determined by the
Company and shall be equal to 95% of the average of the Closing Price Per Share
for the five consecutive Trading Days immediately preceding and including the
third Trading Day prior to the Repurchase Date;

              (b) As to each Holder, the Repurchase Price shall be paid only in
cash in the event any shares of Common Stock to be issued upon repurchase of
Securities hereunder (i) require registration under any federal securities law
before such shares may be freely transferrable without being subject to any
transfer restrictions under the Securities Act upon repurchase and if such
registration is not completed or does not become effective prior to the
Repurchase Date, and/or (ii) require registration with or approval of any
governmental authority under any state law or any other federal law before such
shares may be validly issued or delivered upon repurchase and if such
registration is not completed or does not become effective or such approval is
not obtained prior to the Repurchase Date;

              (c) Payment of the Repurchase Price may not be made in Common
Stock unless such stock is, or shall have



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<PAGE>   133

been, approved for listing on the New York Stock Exchange or listed or quoted on
a national securities exchange or quotation system, in either case, prior to the
Repurchase Date; and

              (d) All shares of Common Stock which may be issued upon repurchase
of Securities will be issued out of the Company's authorized but unissued Common
Stock and, will upon issue, be duly and validly issued and fully paid and
non-assessable and free of any preemptive rights.

              If all of the conditions set forth in this Section 13.2 are not
satisfied in accordance with the terms thereof, the Repurchase Price shall be
paid by the Company only in cash.

SECTION 13.3. Notices; Method of Exercising Repurchase Right, Etc.

              (a) Unless the Company shall have theretofore called for
redemption all of the Outstanding Securities, on or before the 30th day after
the occurrence of a Change in Control, the Company or, at the request and
expense of the Company on or before the 30th day after such occurrence, the
Trustee, shall give to all Holders of Securities, in the manner provided in
Section 1.6, notice (the "Company Notice") of the occurrence of the Change of
Control and of the repurchase right set forth herein arising as a result
thereof. 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 whether the Repurchase Price shall
        be paid by the Company in cash or by delivery of shares of Common Stock,

              (4) a description of the procedure which a Holder must follow to
        exercise a repurchase right, and the place or places where such
        Securities, are to be surrendered for payment of the Repurchase Price
        and accrued interest, if any,



                                     -125-
<PAGE>   134

              (5) that on the Repurchase Date the Repurchase Price, and accrued
        interest, if any, will become due and payable upon each such Security
        designated by the Holder to be repurchased, and that interest thereon
        shall cease to accrue on and after said date,

              (6) the Conversion Rate then in effect, the date on which the
        right to convert the principal amount of the Securities to be
        repurchased will terminate and the place or places where such Securities
        may be surrendered for conversion,

              (7) the place or places that the Notice of Election of Holder To
        Require Repurchase as provided in Section 2.2 shall be delivered, and
        the form of such Notice, and

              (8) the Cusip number or numbers of such Securities.

              No failure of the Company to give the foregoing notices or defect
therein shall limit any Holder's right to exercise a repurchase right or affect
the validity of the proceedings for the repurchase of Securities.

              If any of the foregoing provisions or other provisions of this
Article Thirteen are inconsistent with applicable law, such law shall govern.

              (b) To exercise a repurchase right, a Holder shall deliver to the
Trustee on or before the 30th day after the date of the Company Notice (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 Securities to be
repurchased (and, if any Security is to repurchased in part, the serial number
thereof, the portion of the principal amount thereof to be repurchased and the
name of the Person in which the portion thereof to remain Outstanding after such
repurchase is to be registered) and a statement that an election to exercise the
repurchase right is being made thereby, and, in the event that the Repurchase
Price shall be paid in shares of Common Stock, the name or names (with
addresses) in which the certificate or certificates for shares of Common Stock
shall be issued, and (ii) the Securities with respect to which the repurchase
right is being exercised. Such written notice shall be



                                     -126-
<PAGE>   135

irrevocable, except that the right of the Holder to convert the Securities with
respect to which the repurchase right is being exercised shall continue until
the close of business on the Repurchase Date.

              (c) In the event a repurchase right shall be exercised in
accordance with the terms hereof, the Company shall pay or cause to be paid to
the Trustee the Repurchase Price in cash or shares of Common Stock, as provided
above, for payment to the Holder on the Repurchase Date or, if shares of Common
Stock are to be paid, as promptly after the Repurchase Date as practicable,
together with accrued and unpaid interest to the Repurchase Date payable with
respect to the Securities as to which the purchase right has been exercised;
provided, however, that installments of interest that mature on or prior to the
Repurchase Date shall be payable in cash to the Holders of such Securities, or
one or more Predecessor Securities, registered as such at the close of business
on the relevant Regular Record Date.

              (d) If any Security (or portion thereof) surrendered for
repurchase shall not be so paid on the Repurchase Date, the principal amount of
such Security (or portion thereof, as the case may be) shall, until paid, bear
interest to the extent permitted by applicable law from the Repurchase Date at
the rate of 5.00% per annum, and each Security shall remain convertible into
Common Stock until the principal of such Security (or portion thereof, as the
case may be) shall have been paid or duly provided for.

              (e) Any Security which is to be repurchased only in part shall be
surrendered to the Trustee (with, if the Company or the Trustee so requires, due
endorsement by, or a 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 make available for delivery to the Holder of such
Security without service charge, a new Security or Securities, containing
identical terms and conditions, each in an authorized denomination in aggregate
principal amount equal to and in exchange for the unrepurchased portion of the
principal of the Security so surrendered.

              (f) Any issuance of shares of Common Stock in respect of the
Repurchase Price shall be deemed to have been effected immediately prior to the
close of business on the



                                     -127-
<PAGE>   136

Repurchase Date and the Person or Persons in whose name or names any certificate
or certificates for shares of Common Stock shall be issuable upon such
repurchase shall be deemed to have become on the Repurchase Date the holder or
holders of record of the shares represented thereby; provided, however, that any
surrender for repurchase on a date when the stock transfer books of the Company
shall be closed shall constitute the Person or Persons in whose name or names
the certificate or certificates for such shares are to be issued as the record
holder or holders thereof for all purposes at the opening of business on the
next succeeding day on which such stock transfer books are open. No payment or
adjustment shall be made for dividends or distributions on any Common Stock
issued upon repurchase of any Security declared prior to the Repurchase Date.

              (g) No fractions of shares shall be issued upon repurchase of
Securities. If more than one Security shall be repurchased from the same Holder
and the Repurchase Price shall be payable in shares of Common Stock, the number
of full shares which shall be issuable upon such repurchase shall be computed on
the basis of the aggregate principal amount of the Securities so repurchased.
Instead of any fractional share of Common Stock which would otherwise be
issuable on the repurchase of any Security or Securities, the Company will
deliver to the applicable Holder its check for the current market value of such
fractional share. The current market value of a fraction of a share is
determined by multiplying the current market price of a full share by the
fraction, and rounding the result to the nearest cent. For purposes of this
Section, the current market price of a share of Common Stock is the Closing
Price Per Share of the Common Stock on the Trading Day immediately preceding the
Repurchase Date.

              (h) Any issuance and delivery of certificates for shares of Common
Stock on repurchase of Securities shall be made without charge to the Holder of
Securities being repurchased for such certificates or for any tax or duty in
respect of the issuance or delivery of such certificates or the securities
represented thereby; provided, however, that the Company shall not be required
to pay any tax or duty which may be payable in respect of (i) income of the
Holder or (ii) any transfer involved in the issuance or delivery of certificates
for shares of Common Stock in a name other than that of the Holder of the
Securities being repurchased, and no such issuance or delivery shall be made
unless and until



                                     -128-
<PAGE>   137

the Person requesting such issuance or delivery has paid to the Company the
amount of any such tax or duty or has established, to the satisfaction of the
Company, that such tax or duty has been paid.


              (i) All Securities delivered for repurchase shall be delivered to
the Trustee to be canceled at the direction of the Trustee, which shall dispose
of the same as provided in Section 3.9.

SECTION 13.4. Certain Definitions.

              For purposes of this Article Thirteen,

              (a) the term "beneficial owner" shall be determined in accordance
with Rule 13d-3, as in effect on the date of the original execution of this
Indenture, promulgated by the Commission pursuant to the Exchange Act;

              (b) a "Change in Control" shall be deemed to have occurred at the
time, after the original issuance of the Securities, of:

              (i)    the acquisition by any person of beneficial ownership,
                     directly or indirectly, through a purchase, merger or other
                     acquisition transaction or series of transactions, of
                     shares of capital stock of the Company entitling such
                     person to exercise 50% or more of the total voting power of
                     all shares of capital stock of the Company entitled to vote
                     generally in the elections of directors (any shares of
                     voting stock of which such person or group is the
                     beneficial owner that are not then outstanding being deemed
                     outstanding for purposes of calculating such percentage),
                     other than any such acquisition by the Company, any
                     Subsidiary of the Company or any employee benefit plan of
                     the Company existing on the date of this Indenture; or



                                     -129-
<PAGE>   138

              (ii)   any consolidation or merger of the Company with or into any
                     other person, or any merger of another person with or into
                     the Company(other than (a) any such transaction (x) which
                     does not result in any reclassification, conversion,
                     exchange or cancellation of outstanding shares of Common
                     Stock and (y) pursuant to which holders of Common Stock
                     immediately prior to such transaction have the entitlement
                     to exercise, directly or indirectly, 50% or more of the
                     total voting power of all shares of capital stock entitled
                     to vote generally in the election of directors of the
                     continuing or surviving person immediately after such
                     transaction and (b) any merger which is effected solely to
                     change the jurisdiction of incorporation of the Company and
                     results in a reclassification, conversion or exchange of
                     outstanding shares of Common Stock into solely shares of
                     common stock); or

              (iii)  any conveyance, transfer, sale, lease or similar
                     disposition of all or substantially all of the Company's
                     assets to another person;

provided, however, that a Change in Control shall not be deemed to have occurred
if the Closing Price Per Share on any five Trading Days within the period of 10
consecutive Trading Days ending immediately after the later of the date of the
Change in Control or the date of the public announcement of the Change in
Control (in the case of a Change in Control under Clause (i) above) or the
period of 10 consecutive Trading Days ending immediately prior to the date of
the Change in Control (in the case of a Change in Control under Clause (ii)
above) shall equal or exceed 105% of the Conversion Price of the Securities in
effect on each such Trading Day;

              (c) the term "Conversion Price" shall equal U.S.$1,000 divided by
the Conversion Rate; and



                                     -130-
<PAGE>   139

              (d) for purposes of Section 13.4(b)(i), the term "person" shall
include any syndicate or group which would be deemed to be a "person" under
Section 13(d)(3) of the Exchange Act, as in effect on the date of the original
execution of this Indenture.


                                ARTICLE FOURTEEN

                            HOLDERS LISTS AND REPORTS
                      BY TRUSTEE AND COMPANY; NON-RECOURSE


SECTION 14.1. 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 the Regular Record
        Date, a list, in such form as the Trustee may reasonably require, of the
        names and addresses of the Holders of Securities as of such Regular
        Record Date, and

              (b) at such other times as the Trustee may reasonably 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;

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

SECTION 14.2. Preservation of Information.

              (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 14.1 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 14.1 upon receipt of a new list so furnished.

              (b) After this Indenture has been qualified under the Trust
Indenture Act, the rights of Holders to



                                     -131-
<PAGE>   140

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 14.3. No Recourse Against Others.

              An incorporator or any past, present or future director, officer,
employee or stockholder, as such, of the Company shall not have any liability
for any obligations of the Company under the Securities or this Indenture or for
any claim based on, in respect of or by reason of such obligations or their
creation. By accepting a Security, each Holder shall waive and release all such
liability. Such waiver and release shall be part of the consideration for the
issue of the Securities.

SECTION 14.4. Reports by Trustee.

              (a) After this Indenture has been qualified under the Trust
Indenture Act, the Trustee shall transmit to Holders 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. If
required by Section 313(a) of the Trust Indenture Act, the Trustee shall, within
sixty days after each July 15 following the date of this Indenture, deliver to
Holders a brief report, dated as of such July 15, which complies with the
provisions of such Section 313(a).

              (b) After this Indenture has been qualified under the Trust
Indenture Act, 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 and with the Company. The
Company will promptly notify the Trustee when the Securities are listed on any
stock exchange.

SECTION 14.5. Reports by Company.



                                     -132-
<PAGE>   141

              After this Indenture has been qualified under the Trust Indenture
Act, the Company shall file with the Trustee and the Commission, 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 thereof shall not
constitute constructive notice of 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).

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

              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.



                                     -133-
<PAGE>   142

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

                                       COR THERAPEUTICS, INC.

                                       By /s/ PETER S. RODDY
                                         ------------------------------------
                                            Name:  Peter S. Roddy
                                            Title:  Vice President, Finance

                                       FIRSTAR BANK, N.A., Trustee

                                       By /s/ FRANK P. LESLIE
                                         ------------------------------------
                                            Name:   Frank P. Leslie
                                            Title:  Vice President