<PAGE>   1
                                                                    EXHIBIT 4.25

         FORM OF INDENTURE TO BE ENTERED INTO BETWEEN THE COMPANY AND A
                              TRUSTEE TO BE NAMED

================================================================================

                                     AVIRON

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

                                    INDENTURE

                           Dated as of _________, 200_

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

                                [Name of Trustee]

                                     Trustee

================================================================================

<PAGE>   2
                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                        Page
                                                                                                        ----
<S>                                                                                                    <C>
ARTICLE I. DEFINITIONS AND INCORPORATION BY REFERENCE..................................................    1
         Section 1.1.      Definitions.................................................................    1
         Section 1.2.      Other Definitions...........................................................    5
         Section 1.3.      Incorporation by Reference of Trust Indenture Act...........................    5
         Section 1.4.      Rules of Construction.......................................................    6
ARTICLE II. THE SECURITIES ............................................................................    6
         Section 2.1.      Issuable in Series..........................................................    6
         Section 2.2.      Establishment of Terms of Series of Securities..............................    6
         Section 2.3.      Execution and Authentication................................................    9
         Section 2.4.      Registrar and Paying Agent..................................................   10
         Section 2.5.      Paying Agent to Hold Money in Trust.........................................   10
         Section 2.6.      Securityholder Lists........................................................   11
         Section 2.7.      Transfer and Exchange.......................................................   11
         Section 2.8.      Mutilated, Destroyed, Lost and Stolen Securities............................   11
         Section 2.9.      Outstanding Securities......................................................   12
         Section 2.10.     Treasury Securities.........................................................   13
         Section 2.11.     Temporary Securities........................................................   13
         Section 2.12.     Cancellation................................................................   13
         Section 2.13.     Defaulted Interest..........................................................   13
         Section 2.14.     Global Securities...........................................................   13
         Section 2.15.     CUSIP Numbers...............................................................   15
ARTICLE III. REDEMPTION ...............................................................................   15
         Section 3.1.      Notice to Trustee...........................................................   15
         Section 3.2.      Selection of Securities to be Redeemed......................................   15
         Section 3.3.      Notice of Redemption........................................................   15
         Section 3.4.      Effect of Notice of Redemption..............................................   16
         Section 3.5.      Deposit of Redemption Price.................................................   16
         Section 3.6.      Securities Redeemed in Part.................................................   16
ARTICLE IV. COVENANTS .................................................................................   17
         Section 4.1.      Payment of Principal and Interest...........................................   17
         Section 4.2.      SEC Reports.................................................................   17
         Section 4.3.      Compliance Certificate......................................................   17
         Section 4.4.      Stay, Extension and Usury Laws..............................................   17
         Section 4.5.      Corporate Existence.........................................................   18
         Section 4.6.      Taxes.......................................................................   18
ARTICLE V. SUCCESSORS .................................................................................   18
         Section 5.1.      When Company May Merge, Etc.................................................   18
         Section 5.2.      Successor Corporation Substituted...........................................   18
</TABLE>

                                       i
<PAGE>   3

<TABLE>
<S>                                                                                                    <C>
ARTICLE VI. DEFAULTS AND REMEDIES......................................................................   19
         Section 6.1.      Events of Default...........................................................   19
         Section 6.2.      Acceleration of Maturity; Rescission and Annulment..........................   20
         Section 6.3.      Collection of Indebtedness and Suits for Enforcement by Trustee ............   21
         Section 6.4.      Trustee May File Proofs of Claim............................................   22
         Section 6.5.      Trustee May Enforce Claims Without Possession of Securities.................   23
         Section 6.6.      Application of Money Collected..............................................   23
         Section 6.7.      Limitation on Suits.........................................................   23
         Section 6.8.      Unconditional Right of Holders to Receive Principal and Interest ...........   24
         Section 6.9.      Restoration of Rights and Remedies..........................................   24
         Section 6.10.     Rights and Remedies Cumulative..............................................   24
         Section 6.11.     Delay or Omission Not Waiver................................................   25
         Section 6.12.     Control by Holders..........................................................   25
         Section 6.13.     Waiver of Past Defaults.....................................................   25
         Section 6.14.     Undertaking for Costs.......................................................   25
ARTICLE VII. TRUSTEE ..................................................................................   26
         Section 7.1.      Duties of Trustee...........................................................   26
         Section 7.2.      Rights of Trustee...........................................................   27
         Section 7.3.      Individual Rights of Trustee................................................   28
         Section 7.4.      Trustee's Disclaimer........................................................   28
         Section 7.5.      Notice of Defaults..........................................................   28
         Section 7.6.      Reports by Trustee to Holders...............................................   28
         Section 7.7.      Compensation and Indemnity..................................................   29
         Section 7.8.      Replacement of Trustee......................................................   29
         Section 7.9.      Successor Trustee by Merger, etc............................................   30
         Section 7.10.     Eligibility; Disqualification...............................................   30
         Section 7.11.     Preferential Collection of Claims Against Company...........................   31
ARTICLE VIII. SATISFACTION AND DISCHARGE; DEFEASANCE...................................................   31
         Section 8.1.      Satisfaction and Discharge of Indenture.....................................   31
         Section 8.2.      Application of Trust Funds; Indemnification.................................   32
         Section 8.3.      Legal Defeasance of Securities of any Series................................   32
         Section 8.4.      Covenant Defeasance.........................................................   34
         Section 8.5.      Repayment to Company........................................................   35
ARTICLE IX. AMENDMENTS AND WAIVERS.....................................................................   35
         Section 9.1.      Without Consent of Holders..................................................   35
         Section 9.2.      With Consent of Holders.....................................................   36
         Section 9.3.      Limitations.................................................................   36
         Section 9.4.      Compliance with Trust Indenture Act.........................................   37
         Section 9.5.      Revocation and Effect of Consents...........................................   37
         Section 9.6.      Notation on or Exchange of Securities.......................................   37
         Section 9.7.      Trustee Protected...........................................................   38
ARTICLE X. MISCELLANEOUS ..............................................................................   38
         Section 10.1.     Trust Indenture Act Controls................................................   38
</TABLE>


                                       ii
<PAGE>   4

<TABLE>
<S>                                                                                                    <C>
         Section 10.2.     Notices.....................................................................   38
         Section 10.3.     Communication by Holders with Other Holders.................................   39
         Section 10.4.     Certificate and Opinion as to Conditions Precedent..........................   39
         Section 10.5.     Statements Required in Certificate or Opinion...............................   39
         Section 10.6.     Rules by Trustee and Agents.................................................   39
         Section 10.7.     Legal Holidays..............................................................   40
         Section 10.8.     No Recourse Against Others..................................................   40
         Section 10.9.     Counterparts................................................................   40
         Section 10.10.    Governing Laws..............................................................   40
         Section 10.11.    No Adverse Interpretation of Other Agreements...............................   40
         Section 10.12.    Successors..................................................................   40
         Section 10.13.    Severability................................................................   41
         Section 10.14.    Table of Contents, Headings, Etc............................................   41
         Section 10.15.    Securities in a Foreign Currency or in ECU..................................   41
         Section 10.16.    Judgment Currency...........................................................   42
ARTICLE XI. SINKING FUNDS .............................................................................   42
         Section 11.1.     Applicability of Article....................................................   42
         Section 11.2.     Satisfaction of Sinking Fund Payments with Securities.......................   42
         Section 11.3.     Redemption of Securities for Sinking Fund...................................   43
</TABLE>


                                      iii
<PAGE>   5
                                     AVIRON

         Reconciliation and tie between Trust Indenture Act of 1939 and
                     Indenture, dated as of _________, 200_

<TABLE>
<S>                 <C>                                       <C>
Section 310(a)(1)   ......................................    7.10
           (a)(2)   ......................................    7.10
           (a)(3)   ......................................    Not Applicable
           (a)(4)   ......................................    Not Applicable
           (a)(5)   ......................................    7.10
              (b)   ......................................    7.10
   Section 311(a)   ......................................    7.11
              (b)   ......................................    7.11
              (c)   ......................................    Not Applicable
   Section 312(a)   ......................................    2.6
              (b)   ......................................    10.3
              (c)   ......................................    10.3
   Section 313(a)   ......................................    7.6
           (b)(1)   ......................................    7.6
           (b)(2)   ......................................    7.6
           (c)(1)   ......................................    7.6
              (d)   ......................................    7.6
   Section 314(a)   ......................................    4.2, 10.5
              (b)   ......................................    Not Applicable
           (c)(1)   ......................................    10.4
           (c)(2)   ......................................    10.4
           (c)(3)   ......................................    Not Applicable
              (d)   ......................................    Not Applicable
              (e)   ......................................    10.5
              (f)   ......................................    Not Applicable
   Section 315(a)   ......................................    7.1
              (b)   ......................................    7.5
              (c)   ......................................    7.1
              (d)   ......................................    7.1
              (e)   ......................................    6.14
   Section 316(a)   ......................................    2.10
        (a)(1)(A)   ......................................    6.12
        (a)(1)(B)   ......................................    6.13
              (b)   ......................................    6.8
Section 317(a)(1)   ......................................    6.3
           (a)(2)   ......................................    6.4
              (b)   ......................................    2.5
   Section 318(a)   ......................................    10.1
</TABLE>

Note: This reconciliation and tie shall not, for any purpose, be deemed to be
part of the Indenture.


                                       iv
<PAGE>   6
               Indenture dated as of ___________, 200_ between Aviron, a
Delaware corporation ("Company"), and [Name of Trustee], a ________________
("Trustee").

               Each party agrees as follows for the benefit of the other party
and for the equal and ratable benefit of the Holders of the Securities issued
under this Indenture.

                                   ARTICLE I.
                   DEFINITIONS AND INCORPORATION BY REFERENCE

        Section 1.1. Definitions.

               "Additional Amounts" means any additional amounts which are
required hereby or by any Security, under circumstances specified herein or
therein, to be paid by the Company in respect of certain taxes imposed on
Holders specified therein and which are owing to such Holders.

               "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" (including, with correlative meanings, the terms "controlled by" and
"under common control with"), as used with respect to any person, shall mean the
possession, directly or indirectly, of the power to direct or cause the
direction of the management or policies of such person, whether through the
ownership of voting securities or by agreement or otherwise.

               "Agent" means any Registrar, Paying Agent or Service Agent.

               "Authorized Newspaper" means a newspaper in an official language
of the country of publication customarily published at least once a day for at
least five days in each calendar week and of general circulation in the place in
connection with which the term is used. If it shall be impractical in the
opinion of the Trustee to make any publication of any notice required hereby in
an Authorized Newspaper, any publication or other notice in lieu thereof that is
made or given by the Trustee shall constitute a sufficient publication of such
notice.

               "Bearer" means anyone in possession from time to time of a Bearer
Security.

               "Bearer Security" means any Security, including any interest
coupon appertaining thereto, that does not provide for the identification of the
Holder thereof.

               "Board of Directors" means the Board of Directors of the Company
or any duly authorized committee thereof.

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

               "Business Day" means, unless otherwise provided by Board
Resolution, Officers' Certificate or supplemental indenture hereto for a
particular Series, any day except a Saturday,

<PAGE>   7
Sunday or a legal holiday in The City of New York or the City of San Francisco
on which banking institutions are authorized or required by law, regulation or
executive order to close.

               "Company" means the party named as such above until a successor
replaces it and thereafter means the successor.

               "Company Order" means a written order signed in the name of the
Company by two Officers, one of whom must be the Company's chief executive
officer, chief financial officer or principal accounting officer.

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

               "Corporate Trust Office" means the office of the Trustee at which
at any particular time its corporate trust business shall be principally
administered.

               "Debt" of any person as of any date means, without duplication,
all indebtedness of such person in respect of borrowed money, including all
interest, fees and expenses owed in respect thereto (whether or not the recourse
of the lender is to the whole of the assets of such person or only to a portion
thereof), or evidenced by bonds, notes, debentures or similar instruments.

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

               "Depository" means, with respect to the Securities of any Series
issuable or issued in whole or in part in the form of one or more Global
Securities, the person designated as Depository for such Series by the Company,
which Depository shall be a clearing agency registered under the Exchange Act;
and if at any time there is more than one such person, "Depository" as used with
respect to the Securities of any Series shall mean the Depository with respect
to the Securities of such Series.

               "Discount Security" means any Security that provides for an
amount less than the stated principal amount thereof to be due and payable upon
declaration of acceleration of the maturity thereof pursuant to Section 6.2.

               "Dollars" means the currency of The United States of America.

               "ECU" means the European Currency Unit as determined by the
Commission of the European Union.

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

               "Foreign Currency" means any currency or currency unit issued by
a government other than the government of The United States of America.


                                       2
<PAGE>   8
               "Foreign Government Obligations" means with respect to Securities
of any Series that are denominated in a Foreign Currency, (i) direct obligations
of the government that issued or caused to be issued such currency for the
payment of which obligations its full faith and credit is pledged or (ii)
obligations of a person controlled or supervised by or acting as an agency or
instrumentality of such government the timely payment of which is
unconditionally guaranteed as a full faith and credit obligation by such
government, which, in either case under clauses (i) or (ii), are not callable or
redeemable at the option of the issuer thereof.

               "Global Security" or "Global Securities" means a Security or
Securities, as the case may be, in the form established pursuant to Section 2.2
evidencing all or part of a Series of Securities, issued to the Depository for
such Series or its nominee, and registered in the name of such Depository or
nominee.

               "Holder" or "Securityholder" means a person in whose name a
Security is registered or the holder of a Bearer Security.

               "Indenture" means this Indenture as amended from time to time and
shall include the form and terms of particular Series of Securities established
as contemplated hereunder.

               "interest" with respect to any Discount Security which by its
terms bears interest only after Maturity, means interest payable after Maturity.

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

               "Officer" means the Chairman of the Board, any President, any
Vice-President, the Treasurer, the Secretary, any Assistant Treasurer or any
Assistant Secretary of the Company.

               "Officers' Certificate" means a certificate signed by two
Officers, one of whom must be the Company's principal executive officer,
principal financial officer or principal accounting officer.

               "Opinion of Counsel" means a written opinion of legal counsel who
is acceptable to the Trustee. The counsel may be an employee of or counsel to
the Company.

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

               "principal" of a Security means the principal of the Security
plus, when appropriate, the premium, if any, on, and any Additional Amounts in
respect of, the Security.

               "Responsible Officer" means any officer of the Trustee in its
Corporate Trust Office and also means, with respect to a particular corporate
trust matter, any other officer to whom any corporate trust matter is referred
because of his or her knowledge of and familiarity with a particular subject.


                                       3
<PAGE>   9
               "SEC" means the Securities and Exchange Commission.

               "Securities" means the debentures, notes or other debt
instruments of the Company of any Series authenticated and delivered under this
Indenture.

               "Series" or "Series of Securities" means each series of
debentures, notes or other debt instruments of the Company created pursuant to
Sections 2.1 and 2.2 hereof.

               "Significant Subsidiary" means (i) any direct or indirect
Subsidiary of the Company that would be a "significant subsidiary" as defined in
Article 1, Rule 1-02 of Regulation S-X, promulgated pursuant to the Securities
Act of 1933, as amended, as such regulation is in effect on the date hereof, or
(ii) any group of direct or indirect Subsidiaries of the Company that, taken
together as a group, would be a "significant subsidiary" as defined in Article
1, Rule 1-02 of Regulation S-X, promulgated pursuant to the Securities Act of
1933, as amended, as such regulation is in effect on the date hereof.

               "Stated Maturity" when used with respect to any Security or any
installment of principal thereof or interest thereon, means the date specified
in such Security as the fixed date on which the principal of such Security or
such installment of principal or interest is due and payable.

               "Subsidiary" of any specified person means any corporation of
which at least a majority of the outstanding stock having by the terms thereof
ordinary voting power for the election of directors of such corporation
(irrespective of whether or not at the time stock of any other class or classes
of such corporation shall have or might have voting power by reason of the
happening of any contingency) is at the time directly or indirectly owned by
such person, or by one or more other Subsidiaries, or by such person and one or
more other Subsidiaries.

               "TIA" means the Trust Indenture Act of 1939 (15 U.S. Code
Sections 77aaa-77bbbb) as in effect on the date of this Indenture; provided,
however, that in the event the Trust Indenture Act of 1939 is amended after such
date, "TIA" means, to the extent required by any such amendment, the Trust
Indenture Act 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 or include each person who is then a Trustee hereunder, and
if at any time there is more than one such person, "Trustee" as used with
respect to the Securities of any Series shall mean the Trustee with respect to
Securities of that Series.

               "U.S. Government Obligations" means securities which are (i)
direct obligations of The United States of America for the payment of which its
full faith and credit is pledged or (ii) obligations of a person controlled or
supervised by and acting as an agency or instrumentality of The United States of
America the payment of which is unconditionally guaranteed as a full faith and
credit obligation by The United States of America, and which in the case of (i)
and (ii) are not callable or redeemable at the option of the issuer thereof, and
shall also include a depository receipt issued by a bank or trust company as
custodian with respect to any such U.S. Government Obligation or a specific
payment of interest on or principal of any such U.S.


                                       4
<PAGE>   10
Government Obligation held by such custodian for the account of the holder of a
depository receipt, provided that (except as required by law) such custodian is
not authorized to make any deduction from the amount payable to the holder of
such depository receipt from any amount received by the custodian in respect of
the U.S. Government Obligation evidenced by such depository receipt.

        Section 1.2. Other Definitions.

<TABLE>
<CAPTION>
                                                                    DEFINED IN
TERM                                                                  SECTION
----                                                                -----------
<S>                                                                 <C>
"Bankruptcy Law"                                                        6.1
"Custodian"                                                             6.1
"Event of Default"                                                      6.1
"Journal"                                                              10.15
"Judgment Currency"                                                    10.16
"Legal Holiday"                                                        10.7
"mandatory sinking fund payment"                                       11.1
"Market Exchange Rate"                                                 10.15
"New York Banking Day"                                                 10.16
"optional sinking fund payment"                                        11.1
"Paying Agent"                                                          2.4
"Registrar"                                                             2.4
"Required Currency"                                                    10.16
"Service Agent"                                                         2.4
"successor person"                                                      5.1
</TABLE>

        Section 1.3. Incorporation by Reference of Trust Indenture Act.

               Whenever this Indenture refers to a provision of the TIA, the
provision is incorporated by reference in and made a part of this Indenture. The
following TIA terms used in this Indenture have the following meanings:

               "Commission" means the SEC.

               "indenture securities" means the Securities.

               "indenture security holder" means a Securityholder.

               "indenture to be qualified" means this Indenture.

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

               "obligor" on the indenture securities means the Company and any
               successor obligor upon the Securities.


                                       5
<PAGE>   11
               All other terms used in this Indenture that are defined by the
TIA, defined by TIA reference to another statute or defined by SEC rule under
the TIA and not otherwise defined herein are used herein as so defined.

        Section 1.4. Rules of Construction.

               Unless the context otherwise requires:

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

               (b) an accounting term not otherwise defined has the meaning
        assigned to it in accordance with generally accepted accounting
        principles;

               (c) references to "generally accepted accounting principles"
        shall mean generally accepted accounting principles in effect as of the
        time when and for the period as to which such accounting principles are
        to be applied;

               (d) "or" is not exclusive;

               (e) words in the singular include the plural, and in the plural
        include the singular; and

               (f) provisions apply to successive events and transactions.

                                   ARTICLE II.
                                 THE SECURITIES

        Section 2.1. Issuable in Series.

               The aggregate principal amount of Securities that may be
authenticated and delivered under this Indenture is unlimited. The Securities
may be issued in one or more Series. All Securities of a Series shall be
identical except as may be set forth in a Board Resolution, a supplemental
indenture or an Officers' Certificate detailing the adoption of the terms
thereof pursuant to the authority granted under a Board Resolution. In the case
of Securities of a Series to be issued from time to time, the Board Resolution,
Officers' Certificate or supplemental indenture may provide for the method by
which specified terms (such as interest rate, maturity date, record date or date
from which interest shall accrue) are to be determined. Securities may differ
between Series in respect of any matters, provided that all Series of Securities
shall be equally and ratably entitled to the benefits of the Indenture.

        Section 2.2.  Establishment of Terms of Series of Securities.

               At or prior to the issuance of any Securities within a Series,
the following shall be established (as to the Series generally, in the case of
Subsection 2.2.1 and either as to such Securities within the Series or as to the
Series generally in the case of Subsections 2.2.2 through 2.2.22) by a Board
Resolution, a supplemental indenture or an Officers' Certificate pursuant to
authority granted under a Board Resolution:

                                       6
<PAGE>   12
               2.2.1. the title of the Series (which shall distinguish the
Securities of that particular Series from the Securities of any other Series);

               2.2.2. the price or prices (expressed as a percentage of the
principal amount thereof) at which the Securities of the Series will be issued;

               2.2.3. any limit upon the aggregate principal amount of the
Securities of the Series which may be authenticated and delivered under this
Indenture (except for Securities authenticated and delivered upon registration
of transfer of, or in exchange for, or in lieu of, other Securities of the
Series pursuant to Section 2.7, 2.8, 2.11, 3.6 or 9.6);

               2.2.4. the date or dates on which the principal of the Securities
of the Series is payable;

               2.2.5. the rate or rates (which may be fixed or variable) per
annum or, if applicable, the method used to determine such rate or rates
(including, but not limited to, any commodity, commodity index, stock exchange
index or financial index) at which the Securities of the Series shall bear
interest, if any, the date or dates from which such interest, if any, shall
accrue, the date or dates on which such interest, if any, shall commence and be
payable and any regular record date for the interest payable on any interest
payment date;

               2.2.6. the place or places where the principal of and interest,
if any, on the Securities of the Series shall be payable, or the method of such
payment, if by wire transfer, mail or other means;

               2.2.7. if applicable, the period or periods within which, the
price or prices at which and the terms and conditions upon which the Securities
of the Series may be redeemed, in whole or in part, at the option of the
Company;

               2.2.8. the obligation, if any, of the Company to redeem or
purchase the Securities of the Series pursuant to any sinking fund or analogous
provisions or at the option of a Holder thereof and the period or periods within
which, the price or prices at which and the terms and conditions upon which
Securities of the Series shall be redeemed or purchased, in whole or in part,
pursuant to such obligation;

               2.2.9. the dates, if any, on which and the price or prices at
which the Securities of the Series will be repurchased by the Company at the
option of the Holders thereof and other detailed terms and provisions of such
repurchase obligations;

               2.2.10. if other than denominations of $1,000 and any integral
multiple thereof, the denominations in which the Securities of the Series shall
be issuable;

               2.2.11. the forms of the Securities of the Series in bearer or
fully registered form (and, if in fully registered form, whether the Securities
will be issuable as Global Securities);


                                       7
<PAGE>   13
               2.2.12. if other than the principal amount thereof, the portion
of the principal amount of the Securities of the Series that shall be payable
upon declaration of acceleration of the maturity thereof pursuant to Section
6.2;

               2.2.13. the currency of denomination of the Securities of the
Series, which may be Dollars or any Foreign Currency, including, but not limited
to, the ECU, and if such currency of denomination is a composite currency other
than the ECU, the agency or organization, if any, responsible for overseeing
such composite currency;

               2.2.14. the designation of the currency, currencies or currency
units in which payment of the principal of and interest, if any, on the
Securities of the Series will be made;

               2.2.15. if payments of principal of or interest, if any, on the
Securities of the Series are to be made in one or more currencies or currency
units other than that or those in which such Securities are denominated, the
manner in which the exchange rate with respect to such payments will be
determined;

               2.2.16. the manner in which the amounts of payment of principal
of or interest, if any, on the Securities of the Series will be determined, if
such amounts may be determined by reference to an index based on a currency or
currencies or by reference to a commodity, commodity index, stock exchange index
or financial index;

               2.2.17. the provisions, if any, relating to any security provided
for the Securities of the Series;

               2.2.18. if the holders of Securities of the Series may convert or
exchange the Securities into or for securities of the Issuer or of other
entities or other property, the period or periods within which, the rate or
rates at which and the terms and conditions upon which Securities of the Series
may be converted or exchanged, in whole or in part;

               2.2.19. any addition to or change in the Events of Default which
applies to any Securities of the Series and any change in the right of the
Trustee or the requisite Holders of such Securities to declare the principal
amount thereof due and payable pursuant to Section 6.2;

               2.2.20. any addition to or change in the covenants set forth in
Articles IV or V which applies to Securities of the Series;

               2.2.21. any other terms of the Securities of the Series (which
terms shall not be inconsistent with the provisions of this Indenture, except as
permitted by Section 9.1, but which may modify or delete any provision of this
Indenture insofar as it applies to such Series); and

               2.2.22. any depositories, interest rate calculation agents,
exchange rate calculation agents or other agents with respect to Securities of
such Series if other than those appointed herein.

               All Securities of any one Series need not be issued at the same
time and may be issued from time to time, consistent with the terms of this
Indenture, if so provided by or pursuant to the Board Resolution, supplemental
indenture or Officers' Certificate referred to above, and the authorized
principal amount of any Series may not be increased to provide for issuances of
additional Securities of such Series, unless otherwise provided in such Board
Resolution, supplemental indenture or Officers' Certificate.

                                       8
<PAGE>   14
        Section 2.3. Execution and Authentication.

               Two Officers shall sign the Securities for the Company by manual
or facsimile signature.

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

               A Security shall not be valid until authenticated by the manual
signature of the Trustee or an authenticating agent. The signature shall be
conclusive evidence that the Security has been authenticated under this
Indenture.

               The Trustee shall at any time, and from time to time,
authenticate Securities for original issue in the principal amount provided in
the Board Resolution, supplemental indenture hereto or Officers' Certificate,
upon receipt by the Trustee of a Company Order. Such Company Order may authorize
authentication and delivery pursuant to oral or electronic instructions from the
Company or its duly authorized agent or agents, which oral instructions shall be
promptly confirmed in writing. Each Security shall be dated the date of its
authentication unless otherwise provided by a Board Resolution, a supplemental
indenture hereto or an Officers' Certificate.

               The aggregate principal amount of Securities of any Series
outstanding at any time may not exceed any limit upon the maximum principal
amount for such Series set forth in the Board Resolution, supplemental indenture
hereto or Officers' Certificate delivered pursuant to Section 2.2, except as
provided in Section 2.8.

               Prior to the issuance of Securities of any Series, the Trustee
shall have received and (subject to Section 7.2) shall be fully protected in
relying on: (a) the Board Resolution, supplemental indenture hereto or Officers'
Certificate establishing the form of the Securities of that Series or of
Securities within that Series and the terms of the Securities of that Series or
of Securities within that Series, (b) an Officers' Certificate complying with
Section 10.4, and (c) an Opinion of Counsel complying with Section 10.4.

               The Trustee shall have the right to decline to authenticate and
deliver any Securities of such Series: (a) if the Trustee, being advised by
counsel, determines that such action may not lawfully be taken; or (b) if the
Trustee in good faith by its board of directors or trustees, executive committee
or a trust committee of directors and/or vice-presidents shall determine that
such action would expose the Trustee to personal liability to Holders of any
then outstanding Series of Securities.

               The Trustee may appoint an authenticating agent acceptable to the
Company to authenticate Securities. An authenticating agent may authenticate
Securities whenever the Trustee may do so. Each reference in this Indenture to
authentication by the Trustee includes authentication by such agent. An
authenticating agent has the same rights as an Agent to deal with the Company or
an Affiliate.


                                       9
<PAGE>   15
        Section 2.4. Registrar and Paying Agent.

               The Company shall maintain, with respect to each Series of
Securities, at the place or places specified with respect to such Series
pursuant to Section 2.2, an office or agency where Securities of such Series may
be presented or surrendered for payment ("Paying Agent"), where Securities of
such Series may be surrendered for registration of transfer or exchange
("Registrar") and where notices and demands to or upon the Company in respect of
the Securities of such Series and this Indenture may be served ("Service
Agent"). The Registrar shall keep a register with respect to each Series of
Securities and to their transfer and exchange. The Company will give prompt
written notice to the Trustee of the name and address, and any change in the
name or address, of each Registrar, Paying Agent or Service Agent. If at any
time the Company shall fail to maintain any such required Registrar, Paying
Agent or Service Agent or shall fail to furnish the Trustee with the name and
address thereof, such presentations, surrenders, notices and demands may be made
or served at the Corporate Trust Office of the Trustee, and the Company hereby
appoints the Trustee as its agent to receive all such presentations, surrenders,
notices and demands.

               The Company may also from time to time designate one or more
co-registrars, additional paying agents or additional service agents and may
from time to time rescind such designations; provided, however, that no such
designation or rescission shall in any manner relieve the Company of its
obligations to maintain a Registrar, Paying Agent and Service Agent in each
place so specified pursuant to Section 2.2 for Securities of any Series for such
purposes. The Company will give prompt written notice to the Trustee of any such
designation or rescission and of any change in the name or address of any such
co-registrar, additional paying agent or additional service agent. The term
"Registrar" includes any co-registrar; the term "Paying Agent" includes any
additional paying agent; and the term "Service Agent" includes any additional
service agent.

               The Company hereby appoints the Trustee the initial Registrar,
Paying Agent and Service Agent for each Series unless another Registrar, Paying
Agent or Service Agent, as the case may be, is appointed prior to the time
Securities of that Series are first issued.

        Section 2.5. Paying Agent to Hold Money in Trust.

               The Company shall require each Paying Agent other than the
Trustee to agree in writing that the Paying Agent will hold in trust, for the
benefit of Securityholders of any Series of Securities, or the Trustee, all
money held by the Paying Agent for the payment of principal of or interest on
the Series of Securities, and will notify the Trustee of any default by the
Company in making any such payment. While any such default continues, the
Trustee may require a Paying Agent to pay all money held by it to the Trustee.
The Company at any time may require a Paying Agent to pay all money held by it
to the Trustee. Upon payment over to the Trustee, the Paying Agent (if other
than the Company or a Subsidiary) shall have no further liability for the money.
If the Company or a Subsidiary acts as Paying Agent, it shall segregate and hold
in a separate trust fund for the benefit of Securityholders of any Series of
Securities all money held by it as Paying Agent.


                                       10
<PAGE>   16
        Section 2.6. Securityholder Lists.

               The Trustee shall preserve in as current a form as is reasonably
practicable the most recent list available to it of the names and addresses of
Securityholders of each Series of Securities and shall otherwise comply with TIA
Section 312(a). If the Trustee is not the Registrar, the Company shall furnish
to the Trustee at least ten days before each interest payment date and at such
other times as the Trustee may request in writing a list, in such form and as of
such date as the Trustee may reasonably require, of the names and addresses of
Securityholders of each Series of Securities.

        Section 2.7. Transfer and Exchange.

               Where Securities of a Series are presented to the Registrar or a
co-registrar with a request to register a transfer or to exchange them for an
equal principal amount of Securities of the same Series, the Registrar shall
register the transfer or make the exchange if its requirements for such
transactions are met. To permit registrations of transfers and exchanges, the
Trustee shall authenticate Securities at the Registrar's request. No service
charge shall be made for any registration of transfer or exchange (except as
otherwise expressly permitted herein), but the Company may require payment of a
sum sufficient to cover any transfer tax or similar governmental charge payable
in connection therewith (other than any such transfer tax or similar
governmental charge payable upon exchanges pursuant to Sections 2.11, 3.6 or
9.6).

               Neither the Company nor the Registrar shall be required (a) to
issue, register the transfer of, or exchange Securities of any Series for the
period beginning at the opening of business fifteen days immediately preceding
the mailing of a notice of redemption of Securities of that Series selected for
redemption and ending at the close of business on the day of such mailing, or
(b) to register the transfer of or exchange Securities of any Series selected,
called or being called for redemption as a whole or the portion being redeemed
of any such Securities selected, called or being called for redemption in part.

        Section 2.8. Mutilated, Destroyed, Lost and Stolen Securities.

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

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


                                       11
<PAGE>   17
               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
may, instead of issuing a new Security, pay such Security.

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

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

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

        Section 2.9. Outstanding Securities.

               The Securities outstanding at any time are all the Securities
authenticated by the Trustee except for those canceled by it, those delivered to
it for cancellation, those reductions in the interest on a Global Security
effected by the Trustee in accordance with the provisions hereof and those
described in this Section as not outstanding.

               If a Security is replaced pursuant to Section 2.8, it ceases to
be outstanding until the Trustee receives proof satisfactory to it that the
replaced Security is held by a bona fide purchaser.

               If the Paying Agent (other than the Company, a Subsidiary or an
Affiliate of any thereof) holds on the Maturity of Securities of a Series money
sufficient to pay such Securities payable on that date, then on and after that
date such Securities of the Series cease to be outstanding and interest on them
ceases to accrue.

               A Security does not cease to be outstanding because the Company
or an Affiliate holds the Security.

               In determining whether the Holders of the requisite principal
amount of outstanding Securities have given any request, demand, authorization,
direction, notice, consent or waiver hereunder, the principal amount of a
Discount Security that shall be deemed to be outstanding for such purposes shall
be the amount of the principal thereof that would be due and payable as of the
date of such determination upon a declaration of acceleration of the Maturity
thereof pursuant to Section 6.2.


                                       12
<PAGE>   18
        Section 2.10. Treasury Securities.

               In determining whether the Holders of the required principal
amount of Securities of a Series have concurred in any request, demand,
authorization, direction, notice, consent or waiver Securities of a Series owned
by the Company or an Affiliate shall be disregarded, except that for the
purposes of determining whether the Trustee shall be protected in relying on any
such request, demand, authorization, direction, notice, consent or waiver only
Securities of a Series that the Trustee knows are so owned shall be so
disregarded.

        Section 2.11. Temporary Securities.

               Until definitive Securities are ready for delivery, the Company
may prepare and the Trustee shall authenticate temporary Securities upon a
Company Order. Temporary Securities shall be substantially in the form of
definitive Securities but may have variations that the Company considers
appropriate for temporary Securities. Without unreasonable delay, the Company
shall prepare and the Trustee upon request shall authenticate definitive
Securities of the same Series and date of maturity in exchange for temporary
Securities. Until so exchanged, temporary securities shall have the same rights
under this Indenture as the definitive Securities.

        Section 2.12. Cancellation.

               The Company at any time may deliver Securities to the Trustee for
cancellation. The Registrar and the Paying Agent shall forward to the Trustee
any Securities surrendered to them for registration of transfer, exchange or
payment. The Trustee shall cancel all Securities surrendered for transfer,
exchange, payment, replacement or cancellation and shall destroy such canceled
Securities (subject to the record retention requirement of the Exchange Act) and
deliver a certificate of such destruction to the Company, unless the Company
otherwise directs. The Company may not issue new Securities to replace
Securities that it has paid or delivered to the Trustee for cancellation.

        Section 2.13. Defaulted Interest.

               If the Company defaults in a payment of interest on a Series of
Securities, it shall pay the defaulted interest, plus, to the extent permitted
by law, any interest payable on the defaulted interest, to the persons who are
Securityholders of the Series on a subsequent special record date. The Company
shall fix the record date and payment date. At least 30 days before the record
date, the Company shall mail to the Trustee and to each Securityholder of the
Series a notice that states the record date, the payment date and the amount of
interest to be paid. The Company may pay defaulted interest in any other lawful
manner.

        Section 2.14. Global Securities.

               2.14.1. Terms of Securities. A Board Resolution, a supplemental
indenture hereto or an Officers' Certificate shall establish whether the
Securities of a Series shall be issued in whole or in part in the form of one or
more Global Securities and the Depository for such Global Security or
Securities.


                                       13
<PAGE>   19
               2.14.2. Transfer and Exchange. Notwithstanding any provisions to
the contrary contained in Section 2.7 of the Indenture and in addition thereto,
any Global Security shall be exchangeable pursuant to Section 2.7 of the
Indenture for Securities registered in the names of Holders other than the
Depository for such Security or its nominee only if (i) such Depository notifies
the Company that it is unwilling or unable to continue as Depository for such
Global Security or if at any time such Depository ceases to be a clearing agency
registered under the Exchange Act, and, in either case, the Company fails to
appoint a successor Depository within 90 days of such event, (ii) the Company
executes and delivers to the Trustee an Officers' Certificate to the effect that
such Global Security shall be so exchangeable or (iii) an Event of Default with
respect to the Securities represented by such Global Security shall have
happened and be continuing. Any Global Security that is exchangeable pursuant to
the preceding sentence shall be exchangeable for Securities registered in such
names as the Depository shall direct in writing in an aggregate principal amount
equal to the principal amount of the Global Security with like tenor and terms.

               Except as provided in this Section 2.14.2, a Global Security may
not be transferred except as a whole by the Depository with respect to such
Global Security to a nominee of such Depository, by a nominee of such Depository
to such Depository or another nominee of such Depository or by the Depository or
any such nominee to a successor Depository or a nominee of such a successor
Depository.

               2.14.3. Legend. Any Global Security issued hereunder shall bear a
legend in substantially the following form:

               "This Security is a Global Security within the meaning of the
Indenture hereinafter referred to and is registered in the name of the
Depository or a nominee of the Depository. This Security is exchangeable for
Securities registered in the name of a person other than the Depository or its
nominee only in the limited circumstances described in the Indenture, and may
not be transferred except as a whole by the Depository to a nominee of the
Depository, by a nominee of the Depository to the Depository or another nominee
of the Depository or by the Depository or any such nominee to a successor
Depository or a nominee of such a successor Depository."

               2.14.4. Acts of Holders. The Depository, as a Holder, may appoint
agents and otherwise authorize participants to give or take any request, demand,
authorization, direction, notice, consent, waiver or other action which a Holder
is entitled to give or take under the Indenture.

               2.14.5. Payments. Notwithstanding the other provisions of this
Indenture, unless otherwise specified as contemplated by Section 2.2, payment of
the principal of and interest, if any, on any Global Security shall be made to
the Holder thereof.

               2.14.6. Consents, Declaration and Directions. Except as provided
in Section 2.14.5, the Company, the Trustee and any Agent shall treat a person
as the Holder of such principal amount of outstanding Securities of such Series
represented by a Global Security as shall be specified in a written statement of
the Depositary with respect to such Global Security,


                                       14
<PAGE>   20
for purposes of obtaining any consents, declarations, waivers or directions
required to be given by the Holders pursuant to this Indenture.

        Section 2.15. CUSIP Numbers.

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

                                  ARTICLE III.
                                   REDEMPTION

        Section 3.1. Notice to Trustee.

               The Company may, with respect to any Series of Securities,
reserve the right to redeem and pay the Series of Securities or may covenant to
redeem and pay the Series of Securities or any part thereof prior to the Stated
Maturity thereof at such time and on such terms as provided for in such
Securities. If a Series of Securities is redeemable and the Company wants or is
obligated to redeem prior to the Stated Maturity thereof all or part of the
Series of Securities pursuant to the terms of such Securities, it shall notify
the Trustee of the redemption date and the principal amount of Series of
Securities to be redeemed. The Company shall give the notice at least 45 days
before the redemption date (or such shorter notice as may be acceptable to the
Trustee).

        Section 3.2. Selection of Securities to be Redeemed.

               Unless otherwise indicated for a particular Series by a Board
Resolution, a supplemental indenture or an Officers' Certificate, if less than
all the Securities of a Series are to be redeemed, the Trustee shall select the
Securities of the Series to be redeemed in any manner that the Trustee deems
fair and appropriate. The Trustee shall make the selection from Securities of
the Series outstanding not previously called for redemption. The Trustee may
select for redemption portions of the principal of Securities of the Series that
have denominations larger than $1,000. Securities of the Series and portions of
them it selects shall be in amounts of $1,000 or whole multiples of $1,000 or,
with respect to Securities of any Series issuable in other denominations
pursuant to Section 2.2.10, the minimum principal denomination for each Series
and integral multiples thereof. Provisions of this Indenture that apply to
Securities of a Series called for redemption also apply to portions of
Securities of that Series called for redemption.

        Section 3.3. Notice of Redemption.

               Unless otherwise indicated for a particular Series by Board
Resolution, a supplemental indenture hereto or an Officers' Certificate, at
least 30 days but not more than 60 days before a redemption date, the Company
shall mail a notice of redemption by first-class mail


                                       15
<PAGE>   21
to each Holder whose Securities are to be redeemed and if any Bearer Securities
are outstanding, publish on one occasion a notice in an Authorized Newspaper.

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

               (a) the redemption date;

               (b) the redemption price;

               (c) the name and address of the Paying Agent;

               (d) that Securities of the Series called for redemption must be
        surrendered to the Paying Agent to collect the redemption price;

               (e) that interest on Securities of the Series called for
        redemption ceases to accrue on and after the redemption date; and

               (f) any other information as may be required by the terms of the
        particular Series or the Securities of a Series being redeemed.

               At the Company's request, the Trustee shall give the notice of
redemption in the Company's name and at its expense.

        Section 3.4. Effect of Notice of Redemption.

               Once notice of redemption is mailed or published as provided in
Section 3.3, Securities of a Series called for redemption become due and payable
on the redemption date and at the redemption price. A notice of redemption may
not be conditional. Upon surrender to the Paying Agent, such Securities shall be
paid at the redemption price plus accrued interest to the redemption date.

        Section 3.5. Deposit of Redemption Price.

               On or before the redemption date, the Company shall deposit with
the Paying Agent money sufficient to pay the redemption price of and accrued
interest, if any, on all Securities to be redeemed on that date.

        Section 3.6. Securities Redeemed in Part.

               Upon surrender of a Security that is redeemed in part, the
Trustee shall authenticate for the Holder a new Security of the same Series and
the same maturity equal in principal amount to the unredeemed portion of the
Security surrendered.


                                       16
<PAGE>   22
                                   ARTICLE IV.
                                    COVENANTS

        Section 4.1. Payment of Principal and Interest.

               The Company covenants and agrees for the benefit of the Holders
of each Series of Securities that it will duly and punctually pay the principal
of and interest, if any, on the Securities of that Series in accordance with the
terms of such Securities and this Indenture.

        Section 4.2. SEC Reports.

               The Company shall deliver to the Trustee within 15 days after it
files them with the SEC copies of the annual reports and of the information,
documents, and other reports (or copies of such portions of any of the foregoing
as the SEC may by rules and regulations prescribe) which the Company is required
to file with the SEC pursuant to Section 13 or 15(d) of the Exchange Act. The
Company also shall comply with the other provisions of TIA Section 314(a).

        Section 4.3. Compliance Certificate.

               The Company shall deliver to the Trustee, within 90 days after
the end of each fiscal year of the Company, an Officers' Certificate stating
that a review of the activities of the Company and its Subsidiaries during the
preceding fiscal year has been made under the supervision of the signing
Officers with a view to determining whether the Company has kept, observed,
performed and fulfilled its obligations under this Indenture, and further
stating, as to each such Officer signing such certificate, that to the best of
his knowledge the Company has kept, observed, performed and fulfilled each and
every covenant contained in this Indenture and is not in default in the
performance or observance of any of the terms, provisions and conditions hereof
(or, if a Default or Event of Default shall have occurred, describing all such
Defaults or Events of Default of which he may have knowledge).

               The Company will, so long as any of the Securities are
outstanding, deliver to the Trustee, forthwith upon becoming aware of any
Default or Event of Default, an Officers' Certificate specifying such Default or
Event of Default and what action the Company is taking or proposes to take with
respect thereto.

        Section 4.4. Stay, Extension and Usury Laws.

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


                                       17
<PAGE>   23
        Section 4.5. Corporate Existence.

               Subject to Article V, the Company will do or cause to be done all
things necessary to preserve and keep in full force and effect its corporate
existence and the corporate, partnership or other existence of each Significant
Subsidiary in accordance with the respective organizational documents of each
Significant Subsidiary and the rights (charter and statutory), licenses and
franchises of the Company and its Significant Subsidiaries; provided, however,
that the Company shall not be required to preserve any such right, license or
franchise, or the corporate, partnership or other existence of any Significant
Subsidiary, 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
its Subsidiaries taken as a whole and that the loss thereof is not adverse in
any material respect to the Holders.

        Section 4.6. Taxes.

               The Company shall, and shall cause each of its Significant
Subsidiaries to, pay prior to delinquency all taxes, assessments and
governmental levies, except as contested in good faith and by appropriate
proceedings.

                                   ARTICLE V.
                                   SUCCESSORS

        Section 5.1. When Company May Merge, Etc.

               The Company shall not consolidate with or merge into, or convey,
transfer or lease all or substantially all of its properties and assets to, any
person (a "successor person"), and may not permit any person to merge into, or
convey, transfer or lease its properties and assets substantially as an entirety
to, the Company, unless:

               (a) the successor person (if any) is a corporation, partnership,
        trust or other entity organized and validly existing under the laws of
        any U.S. domestic jurisdiction and expressly assumes the Company's
        obligations on the Securities and under this Indenture and

               (b) immediately after giving effect to the transaction, no
        Default or Event of Default, shall have occurred and be continuing.

               The Company shall deliver to the Trustee prior to the
consummation of the proposed transaction an Officers' Certificate to the
foregoing effect and an Opinion of Counsel stating that the proposed transaction
and such supplemental indenture comply with this Indenture.

        Section 5.2. Successor Corporation Substituted.

               Upon any consolidation or merger, or any sale, lease, conveyance
or other disposition of all or substantially all of the assets of the Company in
accordance with Section 5.1, the successor corporation formed by such
consolidation or into or with which the Company is merged or to which such sale,
lease, conveyance or other disposition is made shall succeed to,


                                       18
<PAGE>   24
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 has been
named as the Company herein; provided, however, that the predecessor Company in
the case of a sale, lease, conveyance or other disposition shall not be released
from the obligation to pay the principal of and interest, if any, on the
Securities.

                                   ARTICLE VI.
                              DEFAULTS AND REMEDIES

        Section 6.1. Events of Default.

               "Event of Default," wherever used herein with respect to
Securities of any Series, means any one of the following events, unless in the
establishing Board Resolution, supplemental indenture or Officers' Certificate,
it is provided that such Series shall not have the benefit of said Event of
Default:

               (a) default in the payment of any interest on any Security of
        that Series when it becomes due and payable, and continuance of such
        default for a period of 30 days (unless the entire amount of such
        payment is deposited by the Company with the Trustee or with a Paying
        Agent prior to the expiration of such period of 30 days); or

               (b) default in the payment of the principal of any Security of
        that Series at its Maturity; or

               (c) default in the deposit of any sinking fund payment, when and
        as due in respect of any Security of that Series; or

               (d) default in the performance or breach of any covenant or
        warranty of the Company in this Indenture (other than a covenant or
        warranty that has been included in this Indenture solely for the benefit
        of Series of Securities other than that Series), which default continues
        uncured 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 of that Series a written notice
        specifying such default or breach and requiring it to be remedied and
        stating that such notice is a "Notice of Default" hereunder; or





                                       19
<PAGE>   25

               (f) the Company or any of its Significant Subsidiaries pursuant
        to or within the meaning of any Bankruptcy Law:

                      (i) commences a voluntary case,

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

                      (iii) consents to the appointment of a Custodian of it or
               for all or substantially all of its property,

                      (iv) makes a general assignment for the benefit of its
               creditors, or

                      (v) generally is unable to pay its debts as the same
               become due; or

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

                      (i) is for relief against the Company or any of its
               Significant Subsidiaries in an involuntary case,

                      (ii) appoints a Custodian of the Company or any of its
               Significant Subsidiaries or for all or substantially all of its
               property, or

                      (iii) orders the liquidation of the Company or any of its
               Significant Subsidiaries,

and the order or decree remains unstayed and in effect for 60 days; or

               (h) any other Event of Default provided with respect to
        Securities of that Series, which is specified in a Board Resolution, a
        supplemental indenture hereto or an Officers' Certificate, in accordance
        with Section 2.2.19.

               The term "Bankruptcy Law" means title 11, U.S. Code or any
similar Federal or State law for the relief of debtors. The term "Custodian"
means any receiver, trustee, assignee, liquidator or similar official under any
Bankruptcy Law.

        Section 6.2. Acceleration of Maturity; Rescission and Annulment.

               If an Event of Default with respect to Securities of any Series
at the time outstanding occurs and is continuing (other than an Event of Default
referred to in Section 6.1(e) or (f)) then in every such case the Trustee or the
Holders of not less than 25% in principal amount of the outstanding Securities
of that Series may declare the principal amount (or, if any Securities of that
Series are Discount Securities, such portion of the principal amount as may be
specified in the terms of such Securities) of and accrued and unpaid interest,
if any, on all of the Securities of that Series to be due and payable
immediately, by a notice in writing to the Company (and to the Trustee if given
by Holders), and upon any such declaration such principal amount (or specified
amount) and accrued and unpaid interest, if any, shall become immediately


                                       20
<PAGE>   26

due and payable. If an Event of Default specified in Section 6.1(e) or (f) shall
occur, the principal amount (or specified amount) of and accrued and unpaid
interest, if any, on all outstanding Securities shall ipso facto become and be
immediately due and payable without any declaration or other act on the part of
the Trustee or any Holder.

               At any time after such a declaration of acceleration with respect
to any Series 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
provided, the Holders of a majority in principal amount of the outstanding
Securities of that Series, by written notice to the Company and the Trustee, may
rescind and annul such declaration and its consequences if:

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

                      (i) all overdue interest, if any, on all Securities of
               that Series,

                      (ii) the principal of any Securities of that Series which
               have become due otherwise than by such declaration of
               acceleration and interest thereon at the rate or rates prescribed
               therefor in such Securities,

                      (iii) to the extent that payment of such interest is
               lawful, interest upon any overdue principal and overdue interest
               at the rate or rates prescribed therefor in such Securities, and

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

and

               (b) all Events of Default with respect to Securities of that
        Series, other than the non-payment of the principal of Securities of
        that Series which have become due solely by such declaration of
        acceleration, have been cured or waived as provided in Section 6.13.

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

        Section 6.3. Collection of Indebtedness and Suits for Enforcement by
Trustee.

               The Company covenants that if

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

               (b) default is made in the payment of principal of any Security
        at the Maturity thereof, or


                                       21
<PAGE>   27
               (c) default is made in the deposit of any sinking fund payment
        when and as due by the terms of a Security,

then, 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 and, to the extent that payment of such
interest shall be legally enforceable, interest on any overdue principal or any
overdue interest, at the rate or rates prescribed therefor in such Securities,
and, in addition thereto, such further amount as shall be sufficient to cover
the costs and expenses of collection, including the reasonable compensation,
expenses, disbursements and advances of the Trustee, its agents and 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 such Securities
and collect the moneys adjudged or deemed to be payable in the manner provided
by law out of the property of the Company or any other obligor upon such
Securities, wherever situated.

               If an Event of Default with respect to any Securities of any
Series 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 of
such Series 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 6.4. Trustee May File Proofs of Claim.

               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 their
creditors, the Trustee (irrespective of whether the principal of 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,

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

               (b) to collect and receive any moneys or other property payable
        or deliverable on any such claims and to distribute the same,


                                       22
<PAGE>   28
and any custodian, receiver, assignee, trustee, liquidator, sequestrator or
other similar official in any such judicial proceeding is hereby authorized by
each Holder to make such payments to the Trustee and, in the event that the
Trustee shall consent to the making of such payments directly to the Holders, to
pay to the Trustee any amount due it for the reasonable compensation, expenses,
disbursements and advances of the Trustee, its agents and counsel, and any other
amounts due the Trustee under Section 7.7.

               Nothing herein contained shall be deemed to authorize the Trustee
to authorize or consent to or accept or adopt on behalf of any Holder any plan
of reorganization, arrangement, adjustment or composition affecting the
Securities or the rights of any Holder thereof or to authorize the Trustee to
vote in respect of the claim of any Holder in any such proceeding.

        Section 6.5. 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 counsel, be for the
ratable benefit of the Holders of the Securities in respect of which such
judgment has been recovered.

        Section 6.6. Application of Money Collected.

               Any money collected by the Trustee pursuant to this Article shall
be applied in the following order, at the date or dates fixed by the Trustee
and, in case of the distribution of such money on account of principal or
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 7.7; and

               Second: To the payment of the amounts then due and unpaid for
principal of and interest 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 principal and interest, respectively; and

               Third: To the Company.

        Section 6.7. Limitation on Suits.

               No Holder of any Security of any Series 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

               (a) such Holder has previously given written notice to the
        Trustee of a continuing Event of Default with respect to the Securities
        of that Series;


                                       23
<PAGE>   29
               (b) the Holders of not less than 25% in principal amount of the
        outstanding Securities of that Series 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;

               (c) 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;

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

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

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 to seek to obtain priority or preference over any
other of such Holders or to enforce any right under this Indenture, except in
the manner herein provided and for the equal and ratable benefit of all such
Holders.

        Section 6.8. Unconditional Right of Holders to Receive Principal and
Interest.

               Notwithstanding any other provision in this Indenture, the Holder
of any Security shall have the right, which is absolute and unconditional, to
receive payment of the principal of and interest, if any, on such Security on
the Stated Maturity or Stated Maturities expressed in such Security (or, in the
case of redemption, on the redemption date) and to institute suit for the
enforcement of any such payment, and such rights shall not be impaired without
the consent of such Holder.

        Section 6.9. Restoration of Rights and Remedies.

               If the Trustee or any Holder has instituted any proceeding to
enforce any right or remedy under this Indenture and such proceeding has been
discontinued or abandoned for any reason, or has been determined adversely to
the Trustee or to such Holder, then and in every such case, subject to any
determination in such proceeding, the Company, the Trustee and the Holders shall
be restored severally and respectively to their former positions hereunder and
thereafter all rights and remedies of the Trustee and the Holders shall continue
as though no such proceeding had been instituted.

        Section 6.10. Rights and Remedies Cumulative.

               Except as otherwise provided with respect to the replacement or
payment of mutilated, destroyed, lost or stolen Securities in Section 2.8, no
right or remedy herein conferred upon or reserved to the Trustee or to the
Holders is intended to be exclusive of any other right or remedy, and every
right and remedy shall, to the extent permitted by law, be cumulative and in
addition to every other right and remedy given hereunder or now or hereafter
existing at law or in equity or otherwise. The assertion or employment of any
right or remedy hereunder, or


                                       24
<PAGE>   30
otherwise, shall not prevent the concurrent assertion or employment of any other
appropriate right or remedy.

        Section 6.11. Delay or Omission Not Waiver.

               No delay or omission of the Trustee or of any Holder of any
Securities to exercise any right or remedy accruing upon any Event of Default
shall impair any such right or remedy or constitute a waiver of any such Event
of Default or an acquiescence therein. Every right and remedy given by this
Article or by law to the Trustee or to the Holders may be exercised from time to
time, and as often as may be deemed expedient, by the Trustee or by the Holders,
as the case may be.

        Section 6.12. Control by Holders.

               The Holders of a majority in principal amount of the outstanding
Securities of any Series 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, with respect to the
Securities of such Series, provided that

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

               (b) the Trustee may take any other action deemed proper by the
        Trustee which is not inconsistent with such direction, and

               (c) subject to the provisions of Section 6.1, the Trustee shall
        have the right to decline to follow any such direction if the Trustee in
        good faith shall, by a Responsible Officer of the Trustee, determine
        that the proceeding so directed would involve the Trustee in personal
        liability.

        Section 6.13. Waiver of Past Defaults.

               The Holders of not less than a majority in principal amount of
the outstanding Securities of any Series may on behalf of the Holders of all the
Securities of such Series waive any past Default hereunder with respect to such
Series and its consequences, except a Default in the payment of the principal of
or interest on any Security of such Series (provided, however, that the Holders
of a majority in principal amount of the outstanding Securities of any Series
may rescind an acceleration and its consequences, including any related payment
default that resulted from such acceleration). Upon any such waiver, such
Default shall cease to exist, and any Event of Default arising therefrom shall
be deemed to have been cured, for every purpose of this Indenture; but no such
waiver shall extend to any subsequent or other Default or impair any right
consequent thereon.

        Section 6.14. 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


                                       25
<PAGE>   31
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, 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 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 of any Series,
or to any suit instituted by any Holder for the enforcement of the payment of
the principal of or interest on any Security on or after the Stated Maturity or
Stated Maturities expressed in such Security (or, in the case of redemption, on
the redemption date).

                                  ARTICLE VII.
                                     TRUSTEE

        Section 7.1. Duties of Trustee.

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

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

                      (i) The Trustee need perform only those duties that are
               specifically set forth in this Indenture and no others.

                      (ii) 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 Officers'
               Certificates or Opinions of Counsel furnished to the Trustee and
               conforming to the requirements of this Indenture; however, in the
               case of any such Officers' Certificates or Opinions of Counsel
               which by any provisions hereof are specifically required to be
               furnished to the Trustee, the Trustee shall examine such
               Officers' Certificates and Opinions of Counsel to determine
               whether or not they conform to the requirements of this
               Indenture.

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

                      (i) This paragraph does not limit the effect of paragraph
               (b) of this Section.

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

                      (iii) The Trustee shall not be liable with respect to any
               action taken, suffered or omitted to be taken by it with respect
               to Securities of any Series in


                                       26
<PAGE>   32
               good faith in accordance with the direction of the Holders of a
               majority in principal amount of the outstanding Securities of
               such Series 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 with respect to the Securities of such Series.

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

               (e) The Trustee may refuse to perform any duty or exercise any
        right or power unless it receives indemnity satisfactory to it against
        any loss, liability or expense.

               (f) The Trustee shall not be liable for interest on any money
        received by it except as the Trustee may agree in writing with the
        Company. Money held in trust by the Trustee need not be segregated from
        other funds except to the extent required by law.

               (g) No provision of this Indenture shall require the Trustee to
        risk its own funds or otherwise incur any financial liability in the
        performance of any of its duties, 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 is not
        reasonably assured to it.

               (h) The Paying Agent, the Registrar and any authenticating agent
        shall be entitled to the protections, immunities and standard of care as
        are set forth in paragraphs (a), (b) and (c) of this Section with
        respect to the Trustee.

        Section 7.2. Rights of Trustee.

               (a) The Trustee may rely on and shall be protected in acting or
        refraining from acting upon any document believed by it to be genuine
        and to have been signed or presented by the proper person. The Trustee
        need not investigate any fact or matter stated in the document.

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

               (c) The Trustee may act through agents and shall not be
        responsible for the misconduct or negligence of any agent appointed with
        due care. No Depository shall be deemed an agent of the Trustee and the
        Trustee shall not be responsible for any act or omission by any
        Depository.

               (d) The Trustee shall not be liable for any action it takes or
        omits to take in good faith which it believes to be authorized or within
        its rights or powers.

               (e) The Trustee may consult with counsel and the advice of such
        counsel or any Opinion of Counsel shall be full and complete
        authorization and protection in respect


                                       27
<PAGE>   33
        of any action taken, suffered or omitted by it hereunder in good faith
        and in reliance thereon.

               (f) 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 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.

        Section 7.3. Individual Rights of Trustee.

               The Trustee in its individual or any other capacity may become
the owner or pledgee of Securities and may otherwise deal with the Company or an
Affiliate with the same rights it would have if it were not Trustee. Any Agent
may do the same with like rights. The Trustee is also subject to Sections 7.10
and 7.11.

        Section 7.4. Trustee's Disclaimer.

               The Trustee makes no representation as to the validity or
adequacy of this Indenture or the Securities, it shall not be accountable for
the Company's use of the proceeds from the Securities, and it shall not be
responsible for any statement in the Securities other than its authentication.

        Section 7.5. Notice of Defaults.

               If a Default or Event of Default occurs and is continuing with
respect to the Securities of any Series and if it is known to a Responsible
Officer of the Trustee, the Trustee shall mail to each Securityholder of the
Securities of that Series and, if any Bearer Securities are outstanding, publish
on one occasion in an Authorized Newspaper, notice of a Default or Event of
Default within 90 days after it occurs or, if later, after a Responsible Officer
of the Trustee has knowledge of such Default or Event of Default. Except in the
case of a Default or Event of Default in payment of principal of or interest on
any Security of any Series, the Trustee may withhold the notice if and so long
as its corporate trust committee or a committee of its Responsible Officers in
good faith determines that withholding the notice is in the interests of
Securityholders of that Series.

        Section 7.6. Reports by Trustee to Holders.

               Within 60 days after May 15 in each year, the Trustee shall
transmit by mail to all Securityholders, as their names and addresses appear on
the register kept by the Registrar and, if any Bearer Securities are
outstanding, publish in an Authorized Newspaper, a brief report dated as of such
May 15, in accordance with, and to the extent required under, TIA Section 313.

               A copy of each report at the time of its mailing to
Securityholders of any Series shall be filed with the SEC and each stock
exchange on which the Securities of that Series are listed. The Company shall
promptly notify the Trustee when Securities of any Series are listed on any
stock exchange.


                                       28
<PAGE>   34
        Section 7.7. Compensation and Indemnity.

               The Company shall pay to the Trustee from time to time reasonable
compensation for its services. The Trustee's compensation shall not be limited
by any law on compensation of a trustee of an express trust. The Company shall
reimburse the Trustee upon request for all reasonable out-of-pocket expenses
incurred by it. Such expenses shall include the reasonable compensation and
expenses of the Trustee's agents and counsel.

               The Company shall indemnify the Trustee (including the cost of
defending itself) against any loss, liability or expense incurred by it except
as set forth in the next paragraph in the performance of its duties under this
Indenture as Trustee or Agent. The Trustee shall notify the Company promptly of
any claim for which it may seek indemnity. The Company shall defend the claim
and the Trustee shall cooperate in the defense. The Trustee may have separate
counsel and the Company shall pay the reasonable fees and expenses of such
counsel. The Company need not pay for any settlement made without its consent,
which consent shall not be unreasonably withheld. This indemnification shall
apply to officers, directors, employees, shareholders and agents of the Trustee.

               The Company need not reimburse any expense or indemnify against
any loss or liability incurred by the Trustee or by any officer, director,
employee, shareholder or agent of the Trustee through negligence or bad faith.

               To secure the Company's payment obligations in this Section, the
Trustee shall have a lien prior to the Securities of any Series on all money or
property held or collected by the Trustee, except that held in trust to pay
principal and interest on particular Securities of that Series.

               When the Trustee incurs expenses or renders services after an
Event of Default specified in Section 6.1(e) or (f) occurs, the expenses and the
compensation for the services are intended to constitute expenses of
administration under any Bankruptcy Law.

        Section 7.8. Replacement of Trustee.

               A resignation or removal of the Trustee and appointment of a
successor Trustee shall become effective only upon the successor Trustee's
acceptance of appointment as provided in this Section.

               The Trustee may resign with respect to the Securities of one or
more Series by so notifying the Company. The Holders of a majority in principal
amount of the Securities of any Series may remove the Trustee with respect to
that Series by so notifying the Trustee and the Company. The Company may remove
the Trustee with respect to Securities of one or more Series if:

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

               (b) the Trustee is adjudged a bankrupt or an insolvent or an
        order for relief is entered with respect to the Trustee under any
        Bankruptcy Law;


                                       29
<PAGE>   35
               (c) a Custodian or public officer takes charge of the Trustee or
        its property; or

               (d)    the Trustee becomes incapable of acting.

               If the Trustee resigns or is removed or if a vacancy exists in
the office of Trustee for any reason, the Company shall promptly appoint a
successor Trustee. Within one year after the successor Trustee takes office, the
Holders of a majority in principal amount of the then outstanding Securities may
appoint a successor Trustee to replace the successor Trustee appointed by the
Company.

               If a successor Trustee with respect to the Securities of any one
or more Series does not take office within 60 days after the retiring Trustee
resigns or is removed, the retiring Trustee, the Company or the Holders of at
least 10% in principal amount of the Securities of the applicable Series may
petition any court of competent jurisdiction for the appointment of a successor
Trustee.

               If the Trustee with respect to the Securities of any one or more
Series fails to comply with Section 7.10, any Securityholder of the applicable
Series may petition any court of competent jurisdiction for the removal of the
Trustee and the appointment of a successor Trustee.

               A successor Trustee shall deliver a written acceptance of its
appointment to the retiring Trustee and to the Company. Immediately after that,
the retiring Trustee shall transfer all property held by it as Trustee to the
successor Trustee subject to the lien provided for in Section 7.7, the
resignation or removal of the retiring Trustee shall become effective, and the
successor Trustee shall have all the rights, powers and duties of the Trustee
with respect to each Series of Securities for which it is acting as Trustee
under this Indenture. A successor Trustee shall mail a notice of its succession
to each Securityholder of each such Series and, if any Bearer Securities are
outstanding, publish such notice on one occasion in an Authorized Newspaper.
Notwithstanding replacement of the Trustee pursuant to this Section 7.8, the
Company's obligations under Section 7.7 hereof shall continue for the benefit of
the retiring trustee with respect to expenses and liabilities incurred by it
prior to such replacement.

        Section 7.9. Successor Trustee by Merger, etc.

               If the Trustee consolidates with, merges or converts into, or
transfers all or substantially all of its corporate trust business to, another
corporation, the successor corporation without any further act shall be the
successor Trustee.

        Section 7.10. Eligibility; Disqualification.

               This Indenture shall always have a Trustee who satisfies the
requirements of TIA Section 310(a)(1), (2) and (5). The Trustee shall always
have a combined capital and surplus of at least $25,000,000 as set forth in its
most recent published annual report of condition. The Trustee shall comply with
TIA Section 310(b).


                                       30
<PAGE>   36
        Section 7.11. Preferential Collection of Claims Against Company.

               The Trustee is subject to TIA Section 311(a), excluding any
creditor relationship listed in TIA Section 311(b). A Trustee who has resigned
or been removed shall be subject to TIA Section 311(a) to the extent indicated.

                                  ARTICLE VIII.
                     SATISFACTION AND DISCHARGE; DEFEASANCE

        Section 8.1. Satisfaction and Discharge of Indenture.

               This Indenture shall upon Company Order cease to be of further
effect (except as hereinafter provided in this Section 8.1), and the Trustee, at
the expense of the Company, shall execute proper instruments acknowledging
satisfaction and discharge of this Indenture, when

               (a) either

                      (i) all Securities theretofore authenticated and delivered
               (other than Securities that have been destroyed, lost or stolen
               and that have been replaced or paid) have been delivered to the
               Trustee for cancellation; or

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

                             (1) have become due and payable, or

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

                             (3) 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, or

                             (4) are deemed paid and discharged pursuant to
                      Section 8.3, as applicable;

and the Company, in the case of (1), (2) or (3) above, has deposited or caused
to be deposited with the Trustee as trust funds in trust an amount sufficient
for the purpose of paying and discharging the entire indebtedness on such
Securities not theretofore delivered to the Trustee for cancellation, for
principal and interest to the date of such deposit (in the case of Securities
which have become due and payable on or prior to the date of such deposit) or to
the Stated Maturity or redemption date, as the case may be;

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


                                       31
<PAGE>   37
               (c) 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 7.7, and, if money
shall have been deposited with the Trustee pursuant to clause (a) of this
Section, the provisions of Sections 2.4, 2.7, 2.8, 8.1 8.2 and 8.5 shall
survive.

        Section 8.2. Application of Trust Funds; Indemnification.

               (a) Subject to the provisions of Section 8.5, all money deposited
        with the Trustee pursuant to Section 8.1, all money and U.S. Government
        Obligations or Foreign Government Obligations deposited with the Trustee
        pursuant to Section 8.3 or 8.4 and all money received by the Trustee in
        respect of U.S. Government Obligations or Foreign Government Obligations
        deposited with the Trustee pursuant to Section 8.3 or 8.4, shall be held
        in trust and applied by it, in accordance with the provisions of the
        Securities and this Indenture, to the payment, either directly or
        through any Paying Agent (including the Company acting as its own Paying
        Agent) as the Trustee may determine, to the persons entitled thereto, of
        the principal and interest for whose payment such money has been
        deposited with or received by the Trustee or to make mandatory sinking
        fund payments or analogous payments as contemplated by Sections 8.3 or
        8.4.

               (b) The Company shall pay and shall indemnify the Trustee against
        any tax, fee or other charge imposed on or assessed against U.S.
        Government Obligations or Foreign Government Obligations deposited
        pursuant to Sections 8.3 or 8.4 or the interest and principal received
        in respect of such obligations other than any payable by or on behalf of
        Holders.

               (c) The Trustee shall deliver or pay to the Company from time to
        time upon Company Request any U.S. Government Obligations or Foreign
        Government Obligations or money held by it as provided in Sections 8.3
        or 8.4 which, in the opinion of a nationally recognized firm of
        independent certified public accountants expressed in a written
        certification thereof delivered to the Trustee, are then in excess of
        the amount thereof which then would have been required to be deposited
        for the purpose for which such U.S. Government Obligations or Foreign
        Government Obligations or money were deposited or received. This
        provision shall not authorize the sale by the Trustee of any U.S.
        Government Obligations or Foreign Government Obligations held under this
        Indenture.

        Section 8.3. Legal Defeasance of Securities of any Series.

               Unless this Section 8.3 is otherwise specified, pursuant to
Section 2.2.21, to be inapplicable to Securities of any Series, the Company
shall be deemed to have paid and discharged the entire indebtedness on all the
outstanding Securities of such Series on the 91st day after the date of the
deposit referred to in subparagraph (d) hereof, and the provisions of this
Indenture, as it relates to such outstanding Securities of such Series, shall no
longer be in effect


                                       32
<PAGE>   38
        (and the Trustee, at the expense of the Company, shall, at Company
        Request, execute proper instruments acknowledging the same), except as
        to:

               (a) the rights of Holders of Securities of such Series to
        receive, from the trust funds described in subparagraph (d) hereof, (i)
        payment of the principal of and each installment of principal of and
        interest on the outstanding Securities of such Series on the Stated
        Maturity of such principal or installment of principal or interest and
        (ii) the benefit of any mandatory sinking fund payments applicable to
        the Securities of such Series on the day on which such payments are due
        and payable in accordance with the terms of this Indenture and the
        Securities of such Series;

               (b) the provisions of Sections 2.4, 2.7, 2.8, 8.2, 8.3 and 8.5;
        and

               (c) the rights, powers, trust and immunities of the Trustee
        hereunder;

provided that, the following conditions shall have been satisfied:

               (d) the Company shall have deposited or caused to be deposited
        irrevocably with the Trustee as trust funds in trust for the purpose of
        making the following payments, specifically pledged as security for and
        dedicated solely to the benefit of the Holders of such Securities (i) in
        the case of Securities of such Series denominated in Dollars, cash in
        Dollars (or such other money or currencies as shall then be legal tender
        in the United States) and/or U.S. Government Obligations, or (ii) in the
        case of Securities of such Series denominated in a Foreign Currency
        (other than a composite currency), money and/or Foreign Government
        Obligations, which through the payment of interest and principal in
        respect thereof, in accordance with their terms, will provide (and
        without reinvestment and assuming no tax liability will be imposed on
        such Trustee), not later than one day before the due date of any payment
        of money, an amount in cash, sufficient, in the opinion of a nationally
        recognized firm of independent public accountants expressed in a written
        certification thereof delivered to the Trustee, to pay and discharge
        each installment of principal (including mandatory sinking fund or
        analogous payments) of and interest, if any, on all the Securities of
        such Series on the dates such installments of interest or principal are
        due;

               (e) such deposit will not result in a breach or violation of, or
        constitute a default under, this Indenture or any other agreement or
        instrument to which the Company is a party or by which it is bound;

               (f) no Default or Event of Default with respect to the Securities
        of such Series shall have occurred and be continuing on the date of such
        deposit or during the period ending on the 91st day after such date;

               (g) the Company shall have delivered to the Trustee an Officers'
        Certificate and an Opinion of Counsel to the effect that (i) the Company
        has received from, or there has been published by, the Internal Revenue
        Service a ruling, or (ii) since the date of execution of this Indenture,
        there has been a change in the applicable Federal income tax law, in
        either case to the effect that, and based thereon such Opinion of
        Counsel shall confirm that, the Holders of the Securities of such Series
        will not recognize income, gain


                                       33
<PAGE>   39
        or loss for Federal income tax purposes as a result of such deposit,
        defeasance and discharge and will be subject to Federal income tax on
        the same amount and in the same manner and at the same times as would
        have been the case if such deposit, defeasance and discharge had not
        occurred;

               (h) the Company shall have delivered to the Trustee an Officers'
        Certificate stating that the deposit was not made by the Company with
        the intent of preferring the Holders of the Securities of such Series
        over any other creditors of the company or with the intent of defeating,
        hindering, delaying or defrauding any other creditors of the Company;

               (i) such deposit shall not result in the trust arising from such
        deposit constituting an investment company (as defined in the Investment
        Company Act of 1940, as amended), or such trust shall be qualified under
        such Act or exempt from regulation thereunder; and

               (j) the Company shall have delivered to the Trustee an Officers'
        Certificate and an Opinion of Counsel, each stating that all conditions
        precedent provided for relating to the defeasance contemplated by this
        Section have been complied with.

        Section 8.4. Covenant Defeasance.

               Unless this Section 8.4 is otherwise specified pursuant to
Section 2.2.21 to be inapplicable to Securities of any Series, on and after the
91st day after the date of the deposit referred to in subparagraph (a) hereof,
the Company may omit to comply with any term, provision or condition set forth
under Sections 4.2, 4.3, 4.4, 4.5, 4.6, and 5.1 as well as any additional
covenants contained in a supplemental indenture hereto for a particular Series
of Securities or a Board Resolution or an Officers' Certificate delivered
pursuant to Section 2.2.21 (and the failure to comply with any such covenants
shall not constitute a Default or Event of Default under Section 6.1) and the
occurrence of any event described in clause (e) of Section 6.1 shall not
constitute a Default or Event of Default hereunder, with respect to the
Securities of such Series, provided that the following conditions shall have
been satisfied:

               (a) With reference to this Section 8.4, the Company has deposited
        or caused to be irrevocably deposited (except as provided in Section
        8.2(c)) with the Trustee as trust funds in trust, specifically pledged
        as security for, and dedicated solely to, the benefit of the Holders of
        such Securities (i) in the case of Securities of such Series denominated
        in Dollars, cash in Dollars (or such other money or currencies as shall
        then be legal tender in the United States) and/or U.S. Government
        Obligations, or (ii) in the case of Securities of such Series
        denominated in a Foreign Currency (other than a composite currency),
        money and/or Foreign Government Obligations, which through the payment
        of interest and principal in respect thereof, in accordance with their
        terms, will provide (and without reinvestment and assuming no tax
        liability will be imposed on such Trustee), not later than one day
        before the due date of any payment of money, an amount in cash,
        sufficient, in the opinion of a nationally recognized firm of
        independent certified public accountants expressed in a written
        certification thereof delivered to the Trustee, to


                                       34
<PAGE>   40
        pay principal and interest, if any, on and any mandatory sinking fund in
        respect of the Securities of such Series on the dates such installments
        of interest or principal are due;

               (b) Such deposit will not result in a breach or violation of, or
        constitute a default under, this Indenture or any other agreement or
        instrument to which the Company is a party or by which it is bound;

               (c) No Default or Event of Default with respect to the Securities
        of such Series shall have occurred and be continuing on the date of such
        deposit or during the period ending on the 91st day after such date;

               (d) the Company shall have delivered to the Trustee an Opinion of
        Counsel confirming that Holders of the Securities of such Series will
        not recognize income, gain or loss for federal income tax purposes as a
        result of such deposit and defeasance and will be subject to federal
        income tax on the same amounts, in the same manner and at the same times
        as would have been the case if such deposit and defeasance had not
        occurred;

               (e) the Company shall have delivered to the Trustee an Officers'
        Certificate stating the deposit was not made by the Company with the
        intent of preferring the Holders of the Securities of such Series over
        any other creditors of the Company or with the intent of defeating,
        hindering, delaying or defrauding any other creditors of the Company;
        and

               (f) The Company shall have delivered to the Trustee an Officers'
        Certificate and an Opinion of Counsel, each stating that all conditions
        precedent herein provided for relating to the defeasance contemplated by
        this Section have been complied with.

        Section 8.5. Repayment to Company.

               The Trustee and the Paying Agent shall pay to the Company upon
request any money held by them for the payment of principal and interest that
remains unclaimed for two years. After that, Securityholders entitled to the
money must look to the Company for payment as general creditors unless an
applicable abandoned property law designates another person.

                                   ARTICLE IX.
                             AMENDMENTS AND WAIVERS

        Section 9.1. Without Consent of Holders.

               The Company and the Trustee may amend or supplement this
Indenture or the Securities of one or more Series without the consent of any
Securityholder:

               (a) to cure any ambiguity, defect or inconsistency;

               (b) to comply with Article V;

               (c) to provide for uncertificated Securities in addition to or in
        place of certificated Securities;


                                       35
<PAGE>   41
               (d) to make any change that does not adversely affect the rights
        of any Securityholder;

               (e) to provide for the issuance of and establish the form and
        terms and conditions of Securities of any Series as permitted by this
        Indenture;

               (f) to evidence and provide for the acceptance of appointment
        hereunder by a successor Trustee with respect to the Securities of one
        or more Series and to add to or change any of the provisions of this
        Indenture as shall be necessary to provide for or facilitate the
        administration of the trusts hereunder by more than one Trustee; or

               (g) to comply with requirements of the SEC in order to effect or
        maintain the qualification of this Indenture under the TIA.

        Section 9.2. With Consent of Holders.

               The Company and the Trustee may enter into a supplemental
indenture with the written consent of the Holders of at least a majority in
principal amount of the outstanding Securities of each Series affected by such
supplemental indenture (including consents obtained in connection with a tender
offer or exchange offer for the Securities of such Series), for the purpose of
adding any provisions to or changing in any manner or eliminating any of the
provisions of this Indenture or of any supplemental indenture or of modifying in
any manner the rights of the Securityholders of each such Series. Except as
provided in Section 6.13, the Holders of at least a majority in principal amount
of the outstanding Securities of each Series affected by such waiver by notice
to the Trustee (including consents obtained in connection with a tender offer or
exchange offer for the Securities of such Series) may waive compliance by the
Company with any provision of this Indenture or the Securities with respect to
such Series.

               It shall not be necessary for the consent of the Holders of
Securities under this Section 9.2 to approve the particular form of any proposed
supplemental indenture or waiver, but it shall be sufficient if such consent
approves the substance thereof. After a supplemental indenture or waiver under
this section becomes effective, the Company shall mail to the Holders of
Securities affected thereby and, if any Bearer Securities affected thereby are
outstanding, publish on one occasion in an Authorized Newspaper, a notice
briefly describing the supplemental indenture or waiver. Any failure by the
Company to mail or publish such notice, or any defect therein, shall not,
however, in any way impair or affect the validity of any such supplemental
indenture or waiver.

        Section 9.3. Limitations.

               Without the consent of each Securityholder affected, an amendment
or waiver may not:

               (a) change the amount of Securities whose Holders must consent to
        an amendment, supplement or waiver;

               (b) reduce the rate of or extend the time for payment of interest
        (including default interest) on any Security;


                                       36
<PAGE>   42
               (c) reduce the principal or change the Stated Maturity of any
        Security or reduce the amount of, or postpone the date fixed for, the
        payment of any sinking fund or analogous obligation;

               (d) reduce the principal amount of Discount Securities payable
        upon acceleration of the maturity thereof;

               (e) waive a Default or Event of Default in the payment of the
        principal of or interest, if any, on any Security (except a rescission
        of acceleration of the Securities of any Series by the Holders of at
        least a majority in principal amount of the outstanding Securities of
        such Series and a waiver of the payment default that resulted from such
        acceleration);

               (f) make the principal of or interest, if any, on any Security
        payable in any currency other than that stated in the Security;

               (g) make any change in Sections 6.8, 6.13, 9.3 (this sentence),
        10.15 or 10.16; or

               (h) waive a redemption payment with respect to any Security or
        change any of the provisions with respect to the redemption of any
        Securities.

        Section 9.4. Compliance with Trust Indenture Act.

               Every amendment to this Indenture or the Securities of one or
more Series shall be set forth in a supplemental indenture hereto that complies
with the TIA as then in effect.

        Section 9.5. Revocation and Effect of Consents.

               Until an amendment or waiver becomes effective, a consent to it
by a Holder of a Security is a continuing consent by the Holder and every
subsequent Holder of a Security or portion of a Security that evidences the same
debt as the consenting Holder's Security, even if notation of the consent is not
made on any Security. However, any such Holder or subsequent Holder may revoke
the consent as to his Security or portion of a Security if the Trustee receives
the notice of revocation before the date the amendment or waiver becomes
effective.

               Any amendment or waiver once effective shall bind every
Securityholder of each Series affected by such amendment or waiver unless it is
of the type described in any of clauses (a) through (g) of Section 9.3. In that
case, the amendment or waiver shall bind each Holder of a Security who has
consented to it and every subsequent Holder of a Security or portion of a
Security that evidences the same debt as the consenting Holder's Security.

        Section 9.6. Notation on or Exchange of Securities.

               The Trustee may place an appropriate notation about an amendment
or waiver on any Security of any Series thereafter authenticated. The Company in
exchange for Securities of that Series may issue and the Trustee shall
authenticate upon request new Securities of that Series that reflect the
amendment or waiver.


                                       37
<PAGE>   43
        Section 9.7. Trustee Protected.

               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 Section 7.1) 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. The Trustee shall sign all
supplemental indentures, except that the Trustee need not sign any supplemental
indenture that adversely affects its rights.

                                   ARTICLE X.
                                  MISCELLANEOUS

        Section 10.1. Trust Indenture Act Controls.

               If any provision of this Indenture limits, qualifies, or
conflicts with another provision which is required or deemed to be included in
this Indenture by the TIA, such required or deemed provision shall control.

        Section 10.2. Notices.

               Any notice or communication by the Company or the Trustee to the
other is duly given if in writing and delivered in person or mailed by
first-class mail:

if to the Company:

Aviron
297 North Bernardo Avenue
Mountain View, CA 94043
Attention: General Counsel

if to the Trustee:

[Name of Trustee]
[Address]

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

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

Attention:
           ---------------

               The Company or the Trustee by notice to the other may designate
additional or different addresses for subsequent notices or communications.

               Any notice or communication to a Securityholder shall be mailed
by first-class mail to his address shown on the register kept by the Registrar
and, if any Bearer Securities are outstanding, published in an Authorized
Newspaper. Failure to mail a notice or communication to a Securityholder of any
Series or any defect in it shall not affect its sufficiency with respect to
other Securityholders of that or any other Series.


                                       38
<PAGE>   44
               If a notice or communication is mailed or published in the manner
provided above, within the time prescribed, it is duly given, whether or not the
Securityholder receives it.

               If the Company mails a notice or communication to
Securityholders, it shall mail a copy to the Trustee and each Agent at the same
time.

        Section 10.3. Communication by Holders with Other Holders.

               Securityholders of any Series may communicate pursuant to TIA
Section 312(b) with other Securityholders of that Series or any other Series
with respect to their rights under this Indenture or the Securities of that
Series or all Series. The Company, the Trustee, the Registrar and anyone else
shall have the protection of TIA Section 312(c).

        Section 10.4. Certificate and Opinion as to Conditions Precedent.

               Upon any request or application by the Company to the Trustee to
take any action under this Indenture, the Company shall furnish to the Trustee:

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

               (b) an Opinion of Counsel stating that, in the opinion of such
        counsel, all such conditions precedent have been complied with.

        Section 10.5. Statements Required in Certificate or Opinion.

               Each certificate or opinion with respect to compliance with a
condition or covenant provided for in this Indenture (other than a certificate
provided pursuant to TIA Section 314(a)(4)) shall comply with the provisions of
TIA Section 314(e) and shall include:

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

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

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

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

        Section 10.6. Rules by Trustee and Agents.


                                       39
<PAGE>   45
               The Trustee may make reasonable rules for action by or a meeting
of Securityholders of one or more Series. Any Agent may make reasonable rules
and set reasonable requirements for its functions.

        Section 10.7. Legal Holidays.

               Unless otherwise provided by Board Resolution, Officers'
Certificate or supplemental indenture for a particular Series, a "Legal Holiday"
is any day that is not a Business Day. If a payment date is a Legal Holiday at a
place of payment, payment may be made at that place on the next succeeding day
that is not a Legal Holiday, and no interest shall accrue for the intervening
period.

        Section 10.8. No Recourse Against Others.

               A 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 the Indenture or for any claim based on, in respect of or by
reason of such obligations or their creation. Each Securityholder by accepting a
Security waives and releases all such liability. The waiver and release are part
of the consideration for the issue of the Securities.

        Section 10.9. Counterparts.

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

        Section 10.10. Governing Laws.

               THIS INDENTURE AND THE SECURITIES SHALL BE GOVERNED BY THE LAWS
OF THE STATE OF NEW YORK APPLICABLE TO AGREEMENTS MADE AND TO BE PERFORMED IN
SUCH STATE, WITHOUT REGARD TO THE CONFLICT OF LAWS PROVISIONS THEREOF.

        Section 10.11. No Adverse Interpretation of Other Agreements.

               This Indenture may not be used to interpret another indenture,
loan or debt agreement of the Company or a Subsidiary. Any such indenture, loan
or debt agreement may not be used to interpret this Indenture.

        Section 10.12. Successors.

               All agreements of the Company in this Indenture and the
Securities shall bind its successor. All agreements of the Trustee in this
Indenture shall bind its successor.


                                       40
<PAGE>   46
        Section 10.13. Severability.

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

        Section 10.14. Table of Contents, Headings, Etc.

               The Table of Contents, Cross Reference Table, and headings of the
Articles and Sections of this Indenture have been inserted for convenience of
reference only, are not to be considered a part hereof, and shall in no way
modify or restrict any of the terms or provisions hereof.

        Section 10.15. Securities in a Foreign Currency or in ECU.

               Unless otherwise specified in a Board Resolution, a supplemental
indenture hereto or an Officers' Certificate delivered pursuant to Section 2.2
of this Indenture with respect to a particular Series of Securities, whenever
for purposes of this Indenture any action may be taken by the Holders of a
specified percentage in aggregate principal amount of Securities of all Series
or all Series affected by a particular action at the time outstanding and, at
such time, there are outstanding Securities of any Series which are denominated
in a coin or currency other than Dollars (including ECUs), then the principal
amount of Securities of such Series which shall be deemed to be outstanding for
the purpose of taking such action shall be that amount of Dollars that could be
obtained for such amount at the Market Exchange Rate at such time. For purposes
of this Section 10.15, "Market Exchange Rate" shall mean the noon Dollar buying
rate in New York City for cable transfers of that currency as published by the
Federal Reserve Bank of New York; provided, however, in the case of ECUs, Market
Exchange Rate shall mean the rate of exchange determined by the Commission of
the European Union (or any successor thereto) as published in the Official
Journal of the European Union (such publication or any successor publication,
the "Journal"). If such Market Exchange Rate is not available for any reason
with respect to such currency, the Trustee shall use, in its sole discretion and
without liability on its part, such quotation of the Federal Reserve Bank of New
York or, in the case of ECUs, the rate of exchange as published in the Journal,
as of the most recent available date, or quotations or, in the case of ECUs,
rates of exchange from one or more major banks in The City of New York or in the
country of issue of the currency in question or, in the case of ECUs, in
Luxembourg or such other quotations or, in the case of ECUs, rates of exchange
as the Trustee, upon consultation with the Company, shall deem appropriate. The
provisions of this paragraph shall apply in determining the equivalent principal
amount in respect of Securities of a Series denominated in currency other than
Dollars in connection with any action taken by Holders of Securities pursuant to
the terms of this Indenture.

               All decisions and determinations of the Trustee regarding the
Market Exchange Rate or any alternative determination provided for in the
preceding paragraph shall be in its sole discretion and shall, in the absence of
manifest error, be conclusive to the extent permitted by law for all purposes
and irrevocably binding upon the Company and all Holders.


                                       41
<PAGE>   47
        Section 10.16. Judgment Currency.

               The Company agrees, to the fullest extent that it may effectively
do so under applicable law, that (a) if for the purpose of obtaining judgment in
any court it is necessary to convert the sum due in respect of the principal of
or interest or other amount on the Securities of any Series (the "Required
Currency") into a currency in which a judgment will be rendered (the "Judgment
Currency"), the rate of exchange used shall be the rate at which in accordance
with normal banking procedures the Trustee could purchase in The City of New
York the Required Currency with the Judgment Currency on the day on which final
unappealable judgment is entered, unless such day is not a New York Banking Day,
then, the rate of exchange used shall be the rate at which in accordance with
normal banking procedures the Trustee could purchase in The City of New York the
Required Currency with the Judgment Currency on the New York Banking Day
preceding the day on which final unappealable judgment is entered and (b) its
obligations under this Indenture to make payments in the Required Currency (i)
shall not be discharged or satisfied by any tender, any recovery pursuant to any
judgment (whether or not entered in accordance with subsection (a)), in any
currency other than the Required Currency, except to the extent that such tender
or recovery shall result in the actual receipt, by the payee, of the full amount
of the Required Currency expressed to be payable in respect of such payments,
(ii) shall be enforceable as an alternative or additional cause of action for
the purpose of recovering in the Required Currency the amount, if any, by which
such actual receipt shall fall short of the full amount of the Required Currency
so expressed to be payable, and (iii) shall not be affected by judgment being
obtained for any other sum due under this Indenture. For purposes of the
foregoing, "New York Banking Day" means any day except a Saturday, Sunday or a
legal holiday in The City of New York on which banking institutions are
authorized or required by law, regulation or executive order to close.

                                   ARTICLE XI.
                                  SINKING FUNDS

        Section 11.1. Applicability of Article.

               The provisions of this Article shall be applicable to any sinking
fund for the retirement of the Securities of a Series, except as otherwise
permitted or required by any form of Security of such Series issued pursuant to
this Indenture.

               The minimum amount of any sinking fund payment provided for by
the terms of the Securities of any Series is herein referred to as a "mandatory
sinking fund payment" and any other amount provided for by the terms of
Securities of such Series is herein referred to as an "optional sinking fund
payment." If provided for by the terms of Securities of any Series, the cash
amount of any sinking fund payment may be subject to reduction as provided in
Section 11.2. Each sinking fund payment shall be applied to the redemption of
Securities of any Series as provided for by the terms of the Securities of such
Series.

        Section 11.2. Satisfaction of Sinking Fund Payments with Securities.

               The Company may, in satisfaction of all or any part of any
sinking fund payment with respect to the Securities of any Series to be made
pursuant to the terms of such Securities


                                       42
<PAGE>   48
(1) deliver outstanding Securities of such Series to which such sinking fund
payment is applicable (other than any of such Securities previously called for
mandatory sinking fund redemption) and (2) apply as credit Securities of such
Series to which such sinking fund payment is applicable and which have been
redeemed either at the election of the Company pursuant to the terms of such
Series of Securities (except pursuant to any mandatory sinking fund) or through
the application of permitted optional sinking fund payments or other optional
redemptions pursuant to the terms of such Securities, provided that such
Securities have not been previously so credited. Such Securities shall be
received by the Trustee, together with an Officers' Certificate with respect
thereto, not later than 15 days prior to the date on which the Trustee begins
the process of selecting Securities for redemption, and shall be credited for
such purpose by the Trustee at the price specified in such Securities for
redemption through operation of the sinking fund and the amount of such sinking
fund payment shall be reduced accordingly. If as a result of the delivery or
credit of Securities in lieu of cash payments pursuant to this Section 11.2, the
principal amount of Securities of such Series to be redeemed in order to exhaust
the aforesaid cash payment shall be less than $100,000, the Trustee need not
call Securities of such Series for redemption, except upon receipt of a Company
Order that such action be taken, and such cash payment shall be held by the
Trustee or a Paying Agent and applied to the next succeeding sinking fund
payment, provided, however, that the Trustee or such Paying Agent shall from
time to time upon receipt of a Company Order pay over and deliver to the Company
any cash payment so being held by the Trustee or such Paying Agent upon delivery
by the Company to the Trustee of Securities of that Series purchased by the
Company having an unpaid principal amount equal to the cash payment required to
be released to the Company.

        Section 11.3. Redemption of Securities for Sinking Fund.

               Not less than 45 days (unless otherwise indicated in the Board
Resolution, supplemental indenture hereto or Officers' Certificate in respect of
a particular Series of Securities) prior to each sinking fund payment date for
any Series of Securities, the Company will deliver to the Trustee an Officers'
Certificate specifying the amount of the next ensuing mandatory sinking fund
payment for that Series pursuant to the terms of that Series, the portion
thereof, if any, which is to be satisfied by payment of cash and the portion
thereof, if any, which is to be satisfied by delivering and crediting of
Securities of that Series pursuant to Section 11.2, and the optional amount, if
any, to be added in cash to the next ensuing mandatory sinking fund payment, and
the Company shall thereupon be obligated to pay the amount therein specified.
Not less than 30 days (unless otherwise indicated in the Board Resolution,
Officers' Certificate or supplemental indenture in respect of a particular
Series of Securities) before each such sinking fund payment date the Trustee
shall select the Securities to be redeemed upon such sinking fund payment date
in the manner specified in Section 3.2 and cause notice of the redemption
thereof to be given in the name of and at the expense of the Company in the
manner provided in Section 3.3. Such notice having been duly given, the
redemption of such Securities shall be made upon the terms and in the manner
stated in Sections 3.4, 3.5 and 3.6.


                                       43
<PAGE>   49
               IN WITNESS WHEREOF, the parties hereto have caused this Indenture
to be duly executed as of the day and year first above written.

                                        AVIRON

                                        By:
                                           -------------------------------------
                                           Name:
                                           Its:

                                        [Name of Trustee]

                                        By:
                                           -------------------------------------
                                           Name:
                                           Its: