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                                                                     EXHIBIT 4.3


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                              WILLBROS GROUP, INC.

                                       AND

                      [                                  ]
                       ----------------------------------
                                   AS TRUSTEE

                                    INDENTURE

                          DATED AS OF           , 200
                                      ----------     --

                             SENIOR DEBT SECURITIES










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                                TABLE OF CONTENTS

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                                            ARTICLE I
                                 DEFINITIONS AND OTHER PROVISIONS
                                      OF GENERAL APPLICATION

SECTION 1.1   DEFINITIONS.......................................................................1
SECTION 1.2   COMPLIANCE CERTIFICATES AND OPINIONS..............................................9
SECTION 1.3   FORM OF DOCUMENTS DELIVERED TO TRUSTEE...........................................10
SECTION 1.4   ACTS OF HOLDERS; RECORD DATES....................................................10
SECTION 1.5   NOTICES, ETC., TO TRUSTEE AND COMPANY............................................13
SECTION 1.6   NOTICE TO HOLDERS; WAIVER. ......................................................13
SECTION 1.7   CONFLICT WITH TRUST INDENTURE ACT................................................14
SECTION 1.8   EFFECT OF HEADINGS AND TABLE OF CONTENTS.........................................14
SECTION 1.9   SUCCESSORS AND ASSIGNS...........................................................14
SECTION 1.10   SEPARABILITY CLAUSE.............................................................14
SECTION 1.11   BENEFITS OF INDENTURE. .........................................................14
SECTION 1.12   GOVERNING LAW...................................................................15
SECTION 1.13   LEGAL HOLIDAYS..................................................................15
SECTION 1.14   INDENTURE AND SECURITIES SOLELY CORPORATE OBLIGATIONS...........................15
SECTION 1.15   INDENTURE MAY BE EXECUTED IN COUNTERPARTS.......................................16

                                           ARTICLE II
                                         SECURITY FORMS

SECTION 2.1   FORMS GENERALLY..................................................................17
SECTION 2.2   FORM OF LEGEND FOR GLOBAL SECURITIES.............................................17
SECTION 2.3   FORM OF TRUSTEE'S CERTIFICATE OF
                       AUTHENTICATION..........................................................18
SECTION 2.4   FORM OF CONVERSION NOTICE........................................................18
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                                           ARTICLE III
                                         THE SECURITIES

SECTION 3.1   AMOUNT UNLIMITED; ISSUABLE IN SERIES.............................................19
SECTION 3.2   DENOMINATIONS....................................................................23
SECTION 3.3   EXECUTION, AUTHENTICATION, DELIVERY AND
                       DATING..................................................................23
SECTION 3.4   TEMPORARY SECURITIES.............................................................25
SECTION 3.5   REGISTRATION; REGISTRATION OF TRANSFER AND
                       EXCHANGE. ..............................................................26
SECTION 3.6   MUTILATED, DESTROYED, LOST AND STOLEN
                       SECURITIES..............................................................28
SECTION 3.7   PAYMENT OF INTEREST; INTEREST RIGHTS
                       PRESERVED...............................................................29
SECTION 3.8  PERSONS DEEMED OWNERS.............................................................31
SECTION 3.9   CANCELLATION.....................................................................31
SECTION 3.10   COMPUTATION OF INTEREST.........................................................31

                                           ARTICLE IV
                                   SATISFACTION AND DISCHARGE

SECTION 4.1   SATISFACTION AND DISCHARGE OF INDENTURE..........................................31
SECTION 4.2   APPLICATION OF TRUST MONEY.......................................................33

                                            ARTICLE V
                                            REMEDIES

SECTION 5.1   EVENTS OF DEFAULT................................................................33
SECTION 5.2   ACCELERATION OF MATURITY; RESCISSION AND
                       ANNULMENT...............................................................35
SECTION 5.3   COLLECTION OF INDEBTEDNESS AND SUITS FOR
                       ENFORCEMENT BY TRUSTEE. ................................................36
SECTION 5.4   TRUSTEE MAY FILE PROOFS OF CLAIM.................................................37
SECTION 5.5   TRUSTEE MAY ENFORCE CLAIMS WITHOUT
                       POSSESSION OF SECURITIES................................................37
SECTION 5.6   APPLICATION OF MONEY COLLECTED...................................................38
SECTION 5.7   LIMITATION ON SUITS..............................................................38
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SECTION 5.8   UNCONDITIONAL RIGHT OF HOLDERS TO RECEIVE PRINCIPAL,
                       PREMIUM AND INTEREST AND TO CONVERT.....................................39
SECTION 5.9   RESTORATION OF RIGHTS AND REMEDIES...............................................39
SECTION 5.10   RIGHTS AND REMEDIES CUMULATIVE..................................................39
SECTION 5.11   DELAY OR OMISSION NOT WAIVER....................................................40
SECTION 5.12   CONTROL BY HOLDERS..............................................................40
SECTION 5.13   WAIVER OF PAST DEFAULTS. .......................................................40
SECTION 5.14   UNDERTAKING FOR COSTS...........................................................41
SECTION 5.15   WAIVER OF USURY, STAY OR EXTENSION LAWS.........................................41

                                           ARTICLE VI
                                           THE TRUSTEE

SECTION 6.1   CERTAIN DUTIES AND RESPONSIBILITIES..............................................42
SECTION 6.2   NOTICE OF DEFAULTS...............................................................42
SECTION 6.3   CERTAIN RIGHTS OF TRUSTEE........................................................42
SECTION 6.4   NOT RESPONSIBLE FOR RECITALS OR ISSUANCE OF
                        SECURITIES.............................................................44
SECTION 6.5   MAY HOLD SECURITIES AND ACT AS TRUSTEE
                        UNDER OTHER INDENTURES.................................................44
SECTION 6.6   MONEY HELD IN TRUST..............................................................44
SECTION 6.7   COMPENSATION AND REIMBURSEMENT...................................................44
SECTION 6.8   CONFLICTING INTERESTS............................................................45
SECTION 6.9   CORPORATE TRUSTEE REQUIRED; ELIGIBILITY..........................................45
SECTION 6.10   RESIGNATION AND REMOVAL; APPOINTMENT
                        OF SUCCESSOR...........................................................46
SECTION 6.11   ACCEPTANCE OF APPOINTMENT BY SUCCESSOR..........................................47
SECTION 6.12   MERGER, CONVERSION, CONSOLIDATION OR
                         SUCCESSION TO BUSINESS................................................48
SECTION 6.13   PREFERENTIAL COLLECTION OF CLAIMS AGAINST
                         COMPANY...............................................................49
SECTION 6.14   APPOINTMENT OF AUTHENTICATING AGENT.............................................49

                                           ARTICLE VII
                        HOLDERS' LISTS AND REPORTS BY TRUSTEE AND COMPANY

SECTION 7.1   COMPANY TO FURNISH TRUSTEE NAMES AND
                        ADDRESSES OF HOLDERS...................................................51
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SECTION 7.2   PRESERVATION OF INFORMATION; COMMUNICATIONS
                        TO HOLDERS.............................................................51
SECTION 7.3   REPORTS BY TRUSTEE...............................................................52
SECTION 7.4   REPORTS BY COMPANY...............................................................52

                                          ARTICLE VIII
                      CONSOLIDATION, MERGER, CONVEYANCE, TRANSFER OR LEASE

SECTION 8.1   COMPANY MAY CONSOLIDATE, ETC., ONLY ON
                      CERTAIN TERMS............................................................52
SECTION 8.2   SUCCESSOR SUBSTITUTED............................................................54

                                           ARTICLE IX
                                     SUPPLEMENTAL INDENTURES

SECTION 9.1   SUPPLEMENTAL INDENTURES WITHOUT CONSENT
                      OF HOLDERS...............................................................54
SECTION 9.2   SUPPLEMENTAL INDENTURES WITH CONSENT
                      OF HOLDERS. .............................................................56
SECTION 9.3   EXECUTION OF SUPPLEMENTAL INDENTURES.............................................57
SECTION 9.4   EFFECT OF SUPPLEMENTAL INDENTURES................................................57
SECTION 9.5   CONFORMITY WITH TRUST INDENTURE ACT..............................................58
SECTION 9.6   REFERENCE IN SECURITIES TO SUPPLEMENTAL
                      INDENTURES...............................................................58

                                            ARTICLE X
                                            COVENANTS

SECTION 10.1   PAYMENT OF PRINCIPAL, PREMIUM AND INTEREST......................................58
SECTION 10.2  MAINTENANCE OF OFFICE OR AGENCY..................................................58
SECTION 10.3   MONEY FOR SECURITIES PAYMENTS TO BE HELD
                        IN TRUST...............................................................59
SECTION 10.4   STATEMENT BY OFFICERS AS TO DEFAULT.............................................60
SECTION 10.5   EXISTENCE.......................................................................60
SECTION 10.6   WAIVER OF CERTAIN COVENANTS.....................................................61
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                                           ARTICLE XI
                                    REDEMPTION OF SECURITIES

SECTION 11.1   APPLICABILITY OF ARTICLE........................................................61
SECTION 11.2   ELECTION TO REDEEM; NOTICE TO TRUSTEE...........................................61
SECTION 11.3   SELECTION BY TRUSTEE OF SECURITIES TO BE
                        REDEEMED. .............................................................62
SECTION 11.4   NOTICE OF REDEMPTION............................................................63
SECTION 11.5   DEPOSIT OF REDEMPTION PRICE.....................................................64
SECTION 11.6   SECURITIES PAYABLE ON REDEMPTION DATE...........................................64
SECTION 11.7   SECURITIES REDEEMED IN PART.....................................................64

                                           ARTICLE XII
                                          SINKING FUNDS

SECTION 12.1   APPLICABILITY OF ARTICLE........................................................65
SECTION 12.2   SATISFACTION OF SINKING FUND PAYMENTS
                       WITH SECURITIES. .......................................................65
SECTION 12.3   REDEMPTION OF SECURITIES FOR SINKING FUND.......................................66

                                          ARTICLE XIII
                               DEFEASANCE AND COVENANT DEFEASANCE

SECTION 13.1   COMPANY'S OPTION TO EFFECT DEFEASANCE
                        OR COVENANT DEFEASANCE.................................................66
SECTION 13.2   DEFEASANCE AND DISCHARGE........................................................66
SECTION 13.3   COVENANT DEFEASANCE.............................................................67
SECTION 13.4   CONDITIONS TO DEFEASANCE OR COVENANT
                        DEFEASANCE.............................................................68
SECTION 13.5   DEPOSITED MONEY AND U.S. GOVERNMENT
                        OBLIGATIONS TO BE HELD IN TRUST;
                        MISCELLANEOUS PROVISIONS...............................................70
SECTION 13.6   REINSTATEMENT...................................................................71

                                           ARTICLE XIV
                                    CONVERSION OF SECURITIES

SECTION 14.1   APPLICABILITY OF ARTICLE........................................................71
SECTION 14.2   EXERCISE OF CONVERSION PRIVILEGE................................................71
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SECTION 14.3   NO FRACTIONAL SHARES............................................................73
SECTION 14.4   ADJUSTMENT OF CONVERSION PRICE..................................................73
SECTION 14.5   NOTICE OF CERTAIN CORPORATE ACTIONS.............................................74
SECTION 14.6   RESERVATION OF SHARES OF COMMON STOCK...........................................75
SECTION 14.7   PAYMENT OF CERTAIN TAXES UPON CONVERSION........................................75
SECTION 14.8   NONASSESSABILITY................................................................75
SECTION 14.9   PROVISION IN CASE OF CONSOLIDATION, MERGER
                        OR SALE OF ASSETS......................................................76
SECTION 14.10   DUTIES OF TRUSTEE REGARDING CONVERSION.........................................77
SECTION 14.11   REPAYMENT OF CERTAIN FUNDS UPON
                         CONVERSION............................................................77
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                           INDENTURE, dated as of ___________, 200__, between
Willbros Group, Inc., a corporation duly organized and existing under the laws
of the Republic of Panama (herein called the "Company"), having its principal
executive office at Plaza Bancomer Building, 50th Street, 8th Floor, Apartado
6307, Panama 5, Republic of Panama, and [___________________], as Trustee
(herein called the "Trustee").


                                  WITNESSETH:

                           WHEREAS, the Company has duly authorized the
execution and delivery of this Indenture to provide for the issuance from time
to time of its unsecured debentures, notes or other evidences of indebtedness
(herein called the "Securities"), to be issued in one or more series as provided
in this Indenture; and

                           WHEREAS, all things necessary to make this Indenture
a valid agreement of the Company, in accordance with its terms, have been done;

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


                                    ARTICLE I

                        DEFINITIONS AND OTHER PROVISIONS
                             OF GENERAL APPLICATION

SECTION 1.1 DEFINITIONS.

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

                                    (1) the terms defined in this Article have
                           the meanings assigned to them in this Article and
                           include the plural as well as the singular;

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



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                  (3) all accounting terms not otherwise defined herein have the
         meanings assigned to them in accordance with generally accepted
         accounting principles, and, except as otherwise herein expressly
         provided, the term "generally accepted accounting principles" with
         respect to any computation required or permitted hereunder shall mean
         such accounting principles as are generally accepted at the date of
         such computation;

                  (4) unless the context otherwise requires, any reference to an
         "Article" or a "Section" refers to an Article or a Section, as the case
         may be, of this Indenture; and

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

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

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

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

         "Board of Directors" means either the board of directors of the Company
or any duly authorized committee of that board empowered to act for it with
respect to this Indenture.

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

         "Business Day," when used with respect to any Place of Payment, means
each Monday, Tuesday, Wednesday, Thursday and Friday which is not a day



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on which banking institutions in that Place of Payment are authorized or
obligated by law or executive order to close.

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

                  "Common Stock" includes any stock of any class of the Company,
which has no preference in respect of dividends or of amounts payable in the
event of any voluntary or involuntary liquidation, dissolution or winding-up of
the Company and which is not subject to redemption by the Company; provided,
however, subject to the provisions of Section 14.9, shares issuable upon
conversion of Securities shall include only shares of the class designated as
Common Stock of the Company at the date of this Indenture or shares of any class
or classes resulting from any reclassification or reclassifications thereof and
which have no preference in respect of dividends or of amounts payable in the
event of any voluntary or involuntary liquidation, dissolution or winding-up of
the Company and which are not subject to redemption by the Company; provided,
further that if at any time there shall be more than one such resulting class,
the shares of each such class then so issuable shall be substantially in the
proportion which the total number of shares of such class resulting from all
such reclassifications bears to the total number of shares of all such classes
resulting from all such reclassifications.

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

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

                  "Constituent Person" has the meaning specified in Section
14.9.

                  "Corporate Trust Office" means the corporate trust office of
the Trustee at [___________________________], Attention: Corporate Trust
Department, or such other office, designated by the Trustee by written notice to
the Company, at which at any particular time its corporate trust business shall
be administered.



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

                  "Covenant Defeasance" has the meaning specified in Section
13.3.

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

                  "Defeasance" has the meaning specified in Section 13.2.

                  "Depositary" means, with respect to Securities of any series
issuable in whole or in part in the form of one or more Global Securities, a
clearing agency registered under the Exchange Act that is designated to act as
Depositary for such Securities as contemplated by Section 3.1.

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

                  "Exchange Act" means the Securities Exchange Act of 1934 and
any statute successor thereto, in each case as amended from time to time.

                  "Expiration Date" has the meaning specified in Section 1.4.

                  "Global Security" means a Security that evidences all or part
of the Securities of any series and bears the legend set forth in Section 2.2
(or such legend as may be specified as contemplated by Section 3.1 for such
Securities).

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

                  "Indenture" means this instrument as originally executed and
as it may from time to time be supplemented or amended by one or more indentures
supplemental hereto entered into pursuant to the applicable provisions hereof,
including, for all purposes of this instrument and any such supplemental
indenture, the provisions of the Trust Indenture Act that are deemed to be a
part of and govern this instrument and any such supplemental indenture,
respectively. The term "Indenture" shall also include the terms of particular
series of Securities established as contemplated by Section 3.1; provided,
however, that if at any time more than one Person is acting as Trustee under
this Indenture due to the appointment of one or more separate Trustees for any
one or more separate series of Securities, "Indenture" shall mean, with respect
to such series of Securities for which any such Person is Trustee, this
instrument as originally executed or as it may from time to time be supplemented
or amended by one or more indentures supplemental hereto entered into pursuant
to the applicable provisions hereof and shall include the terms of

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particular series of Securities for which such Person is Trustee established as
contemplated by Section 3.1, exclusive, however, of any provisions or terms
which relate solely to other series of Securities for which such Person is not
Trustee, regardless of when such terms or provisions were adopted, and exclusive
of any provisions or terms adopted by means of one or more indentures
supplemental hereto executed and delivered after such Person had become such
Trustee, but to which such person, as such Trustee, was not a party; provided,
further that in the event that this Indenture is supplemented or amended by one
or more indentures supplemental hereto which are only applicable to certain
series of Securities, the term "Indenture" for a particular series of Securities
shall only include the supplemental indentures applicable thereto.

                  "interest," when used with respect to an Original Issue
Discount Security which by its terms bears interest only after Maturity, means
interest payable after Maturity.

                  "Interest Payment Date," when used with respect to any
Security, means the Stated Maturity of an installment of interest on such
Security.

                  "Investment Company Act" means the Investment Company Act of
1940 and any statute successor thereto, in each case as amended from time to
time.

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

                  "Notice of Default" means a written notice of the kind
specified in Section 5.1(4).

                  "Officers' Certificate" means a certificate signed by the
Chairman of the Board, the President or a Vice President, and by the principal
financial officer, the Treasurer, an Assistant Treasurer, the Secretary or an
Assistant Secretary, of the Company, and delivered to the Trustee. One of the
officers signing an Officers' Certificate given pursuant to Section 10.4 shall
be the principal executive, financial or accounting officer of the Company.

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


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<PAGE>   13

                  "Original Issue Discount Security" means any Security which
provides for an amount less than the principal amount thereof to be due and
payable upon a declaration of acceleration of the Maturity thereof pursuant to
Section 5.2.

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

                           (1) Securities theretofore canceled by the Trustee or
                  delivered to the Trustee for cancellation;

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

                           (3) Securities as to which Defeasance has been
                  effected pursuant to Section 13.2; and

                           (4) Securities which have been paid pursuant to
                  Section 3.6 or in exchange for or in lieu of which other
                  Securities have been authenticated and delivered pursuant to
                  this Indenture, other than any such Securities in respect of
                  which there shall have been presented to the Trustee proof
                  satisfactory to it that such Securities are held by a bona
                  fide purchaser in whose hands such Securities are valid
                  obligations of the Company;

provided, however, that in determining whether the Holders of the requisite
principal amount of the Outstanding Securities have given, made or taken any
request, demand, authorization, direction, notice, consent, waiver or other
action hereunder as of any date, (A) the principal amount of an Original Issue
Discount Security which shall be deemed to be Outstanding shall be the amount of
the principal thereof which would be due and payable as of such date upon
acceleration of the Maturity thereof to such date pursuant to Section 5.2, (B)
if, as of such date, the principal amount payable at the Stated Maturity of a
Security is not determinable, the principal amount of such Security which shall
be deemed to be Outstanding shall be the amount as specified or determined as
contemplated by Section 3.1, (C) the principal amount of a Security denominated
in one or more foreign currencies or currency units which


                                       6
<PAGE>   14

shall be deemed to be Outstanding shall be the U.S. dollar equivalent,
determined as of such date in the manner provided as contemplated by Section
3.1, of the principal amount of such Security (or, in the case of a Security
described in Clause (A) or (B) above, of the amount determined as provided in
such Clause), and (D) Securities owned by the Company or any other obligor upon
the Securities or any Affiliate of the Company or of such other obligor shall be
disregarded and deemed not to be Outstanding, except that, in determining
whether the Trustee shall be protected in relying upon any such request, demand,
authorization, direction, notice, consent, waiver or other action, only
Securities which the Trustee knows to be so owned shall be so disregarded.
Securities so owned which have been pledged in good faith may be regarded as
Outstanding if the pledgee establishes to the satisfaction of the Trustee the
pledgee's right so to act with respect to such Securities and that the pledgee
is not the Company or any other obligor upon the Securities or any Affiliate of
the Company or of such other obligor.

                  "Paying Agent" means any Person authorized by the Company to
pay the principal of or any premium or interest on any Securities on behalf of
the Company.

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

                  "Place of Payment," when used with respect to the Securities
of any series, means the place or places where the principal of and any premium
and interest on the Securities of that series are payable as specified as
contemplated by Section 3.1.

                  "Predecessor Security" of any particular Security means every
previous Security evidencing all or a portion of the same debt as that evidenced
by such particular Security; and, for the purposes of this definition, any
Security authenticated and delivered under Section 3.6 in exchange for or in
lieu of a mutilated, destroyed, lost or stolen Security shall be deemed to
evidence the same debt as the mutilated, destroyed, lost or stolen Security.

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

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



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<PAGE>   15

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

                  "Regular Record Date" for the interest payable on any Interest
Payment Date on the Securities of any series means the date specified for that
purpose as contemplated by Section 3.1.

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

                  "Securities Act" means the Securities Act of 1933 and any
statute successor thereto, in each case as amended from time to time.

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

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

                  "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" means, with respect to any Person, (i) any
corporation or trust of which a majority of the outstanding voting securities is
at the time, and (ii) any partnership of which a majority of the equity capital
or profit interest is at the time, owned, directly or indirectly, by the
Company, by one or more other Subsidiaries or by the Company and one or more
Subsidiaries. For the purposes of this definition, "voting securities" means
securities which ordinarily have voting power for the election of directors,
whether at all times or only so long as no senior class of securities has such
voting power by reason of any contingency.

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

                  "Trustee" means the Person named as the "Trustee" in the first
paragraph of this instrument until a successor Trustee shall have become such

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<PAGE>   16

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 Obligation" has the meaning specified in Section
13.4.

                  "Vice President," when used with respect to the Company or the
Trustee, means any vice president, whether or not designated by a number or a
word or words added before or after the title "vice president."

SECTION 1.2 COMPLIANCE CERTIFICATES AND OPINIONS.

                  Upon any application or request by the Company to the Trustee
to take any action under any provision of this Indenture, the Company shall
furnish to the Trustee such certificates and opinions as may be required under
the Trust Indenture Act. Each such certificate or opinion shall be given in the
form of an Officers' Certificate, if to be given by an officer of the Company,
or an Opinion of Counsel, if to be given by counsel, and shall comply with the
requirements of the Trust Indenture Act and any other requirements set forth in
this Indenture.

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

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

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

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

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



                                       9
<PAGE>   17

SECTION 1.3 FORM OF DOCUMENTS DELIVERED TO TRUSTEE.

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

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

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


SECTION 1.4 ACTS OF HOLDERS; RECORD DATES.

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


                                       10
<PAGE>   18

purpose of this Indenture and (subject to Section 6.1) conclusive in favor of
the Trustee and the Company, if made in the manner provided in this Section.

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

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

                  Any request, demand, authorization, direction, notice,
consent, waiver or other Act of the Holder of any Security shall bind every
future Holder of the same Security and the Holder of every Security issued upon
the registration of transfer thereof or in exchange therefor or in lieu thereof
in respect of anything done, omitted or suffered to be done by the Trustee or
the Company in reliance thereon, whether or not notation of such action is made
upon such Security.

                  The Company may set any day as a record date for the purpose
of determining the Holders of Outstanding Securities of any series entitled to
give, make or take any request, demand, authorization, direction, vote, notice,
consent, waiver or other action provided or permitted by this Indenture to be
given, made or taken by Holders of Securities of such series, provided that the
Company may not set a record date for, and the provisions of this paragraph
shall not apply with respect to, the giving or making of any notice,
declaration, request or direction referred to in the next paragraph. If any
record date is set pursuant to this paragraph, the Holders of Outstanding
Securities of the relevant series on such record date, and no other Holders,
shall be entitled to take the relevant action, whether or not such Holders
remain Holders after such record date; provided that no such action shall be
effective hereunder unless taken on or prior to the applicable Expiration Date
by Holders of the requisite principal amount of Outstanding Securities of such
series on such record date. Nothing in this paragraph shall be construed to
prevent the Company from setting a new record date for any action for which a
record date has previously been set pursuant to this paragraph (whereupon the
record date previously set shall automatically and with no action by any Person
be canceled and of no effect), and nothing in this paragraph shall be construed
to render ineffective any action taken by Holders of the requisite principal
amount of Outstanding Securities of the relevant


                                       11
<PAGE>   19

series on the date such action is taken. Promptly after any record date is set
pursuant to this paragraph, the Company, at its own expense, shall cause notice
of such record date, the proposed action by Holders and the applicable
Expiration Date to be given to the Trustee in writing and to each Holder of
Securities of the relevant series in the manner set forth in Section 1.6.

                  The Trustee may set any day as a record date for the purpose
of determining the Holders of Outstanding Securities of any series entitled to
join in the giving or making of (i) any Notice of Default, (ii) any declaration
of acceleration referred to in Section 5.2, (iii) any request to institute
proceedings referred to in Section 5.7(2) or (iv) any direction referred to in
Section 5.12, in each case with respect to Securities of such series. If any
record date is set pursuant to this paragraph, the Holders of Outstanding
Securities of such series on such record date, and no other Holders, shall be
entitled to join in such notice, declaration, request or direction, whether or
not such Holders remain Holders after such record date; provided that no such
action shall be effective hereunder unless taken on or prior to the applicable
Expiration Date by Holders of the requisite principal amount of Outstanding
Securities of such series on such record date. Nothing in this paragraph shall
be construed to prevent the Trustee from setting a new record date for any
action for which a record date has previously been set pursuant to this
paragraph (whereupon the record date previously set shall automatically and with
no action by any Person be canceled and of no effect), and nothing in this
paragraph shall be construed to render ineffective any action taken by Holders
of the requisite principal amount of Outstanding Securities of the relevant
series on the date such action is taken. Promptly after any record date is set
pursuant to this paragraph, the Trustee, at the Company's expense, shall cause
notice of such record date, the proposed action by Holders and the applicable
Expiration Date to be given to the Company in writing and to each Holder of
Securities of the relevant series in the manner set forth in Section 1.6.

                  With respect to any record date set pursuant to this Section,
the party hereto which sets such record dates may designate any day as the
"Expiration Date" and from time to time may change the Expiration Date to any
earlier or later day; provided that no such change shall be effective unless
notice of the proposed new Expiration Date is given to the other party hereto in
writing, and to each Holder of Securities of the relevant series in the manner
set forth in Section 1.6, on or prior to the existing Expiration Date. If an
Expiration Date is not designated with respect to any record date set pursuant
to this Section, the party hereto which set such record date shall be deemed to
have initially designated the 180th day after such record date as the Expiration
Date with respect thereto, subject to its right to change the Expiration Date as
provided in this paragraph. Notwithstanding the foregoing, no Expiration Date
shall be later than the 180th day after the applicable record date.



                                       12
<PAGE>   20

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

SECTION 1.5 NOTICES, ETC., TO TRUSTEE AND COMPANY.

                  Any request, demand, authorization, direction, notice,
consent, waiver or Act of Holders or other document provided or permitted by
this Indenture to be made upon, given or furnished to, or filed with,

                           (1) the Trustee by any Holder or by the Company shall
                  be sufficient for every purpose hereunder if made, given,
                  furnished or filed in writing (or by facsimile transmissions,
                  provided that oral confirmation of receipt shall have been
                  received) to or with the Trustee at its Corporate Trust
                  Office, Attention: Corporate Trust Department, or

                           (2) the Company by the Trustee or by any Holder shall
                  be sufficient for every purpose hereunder (unless otherwise
                  herein expressly provided) if in writing and mailed,
                  first-class postage prepaid, to the Company addressed to it at
                  the address of its principal office specified in the first
                  paragraph of this instrument or at any other address
                  previously furnished in writing to the Trustee by the Company,
                  Attention: Chief Financial Officer.

SECTION 1.6 NOTICE TO HOLDERS; WAIVER.

                  Where this Indenture provides for notice to Holders of any
event, such notice shall be sufficiently given (unless otherwise herein
expressly provided) if in writing and mailed, first-class postage prepaid, or
delivered by hand or overnight courier to each Holder affected by such event, at
its address as it appears in the Security Register, not later than the latest
date (if any), and not earlier than the earliest date (if any), prescribed for
the giving of such notice. Neither the failure to mail or deliver by hand or
overnight courier any such notice, nor any defect in any such notice so mailed
or delivered by hand or overnight courier, to any particular Holder shall affect
the sufficiency of such notice with respect to other Holders. Where this
Indenture provides for notice in any manner, such notice may be waived in
writing by the Person entitled to receive such notice, either before or after
the event, and such waiver shall be the equivalent of such notice. Waivers of
notice by



                                       13
<PAGE>   21

Holders shall be filed with the Trustee, but such filing shall not be a
condition precedent to the validity of any action taken in reliance upon such
waiver.

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

SECTION 1.7 CONFLICT WITH TRUST INDENTURE ACT.

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

SECTION 1.8 EFFECT OF HEADINGS AND TABLE OF CONTENTS.

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

SECTION 1.9 SUCCESSORS AND ASSIGNS.

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

SECTION 1.10 SEPARABILITY CLAUSE.

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

SECTION 1.11 BENEFITS OF INDENTURE.

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


                                       14
<PAGE>   22

SECTION 1.12 GOVERNING LAW.

                  THIS INDENTURE AND THE SECURITIES SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAW OF THE STATE OF NEW YORK, WITHOUT GIVING
EFFECT TO SUCH STATE'S CONFLICTS OF LAWS PRINCIPLES.

SECTION 1.13 LEGAL HOLIDAYS.

                  In any case where any Interest Payment Date, Redemption Date
or Stated Maturity of any Security or the last date on which a Holder has the
right to convert a Security at a particular conversion price shall not be a
Business Day at any Place of Payment, then (notwithstanding any other provision
of this Indenture or of the Securities (other than a provision of any Security
which specifically states that such provision shall apply in lieu of this
Section)) payment of interest or principal (and premium, if any) or, if
applicable to a particular series of Securities, conversion need not be made at
such Place of Payment on such date, but may be made on the next succeeding
Business Day at such Place of Payment with the same force and effect as if made
on the Interest Payment Date or Redemption Date, at the Stated Maturity or on
such last day for conversion, as the case may be.

SECTION 1.14      INDENTURE AND SECURITIES SOLELY CORPORATE
                  OBLIGATIONS.

                  No recourse for the payment of the principal of or premium, if
any, or interest on any Security, or for any claim based thereon or otherwise in
respect thereof, and no recourse under or upon any obligation, covenant or
agreement of the Company in this Indenture or in any supplemental indenture or
in any Security, or because of the creation of any indebtedness represented
thereby, shall be had against any incorporator, stockholder, employee, agent,
officer, or director or subsidiary, as such, past, present or future, of the
Company or of any successor corporation, either directly or through the Company
or any successor corporation, whether by virtue of any constitution, statute or
rule of law, or by the enforcement of any assessment or penalty or otherwise; it
being expressly understood that all such liability is hereby expressly waived
and released as a condition of, and as a consideration for, the execution of
this Indenture and the issue of the Securities.


                                       15
<PAGE>   23

SECTION 1.15 INDENTURE MAY BE EXECUTED IN COUNTERPARTS.

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


                                       16
<PAGE>   24

                                   ARTICLE II

                                 SECURITY FORMS


SECTION 2.1   FORMS GENERALLY.

               The Securities of each series shall be in substantially the form
set forth in this Article, or in such other form as shall be established by or
pursuant to a Board Resolution or in one or more indentures supplemental hereto,
in each case with such appropriate insertions, omissions, substitutions and
other variations as are required or permitted by this Indenture, and may have
such letters, numbers or other marks of identification and such legends or
endorsements placed thereon as may be required to comply with the rules of any
securities exchange or Depositary therefor or as may, consistently herewith, be
determined by the officers executing such Securities, as evidenced by their
execution thereof. If the form of Securities of any series is established by
action taken pursuant to a Board Resolution, a copy of an appropriate record of
such action shall be certified by the Secretary or an Assistant Secretary of the
Company and delivered to the Trustee at or prior to the delivery of the Company
Order contemplated by Section 3.3 for the authentication and delivery of such
Securities. Any such Board Resolution or record of such action shall have
attached thereto a true and correct copy of the form of Security referred to
therein approved by or pursuant to such Board Resolution.

SECTION 2.2 FORM OF LEGEND FOR GLOBAL SECURITIES.

               Unless otherwise specified as contemplated by Section 3.1 for the
Securities evidenced thereby, every Global Security authenticated and delivered
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 A DEPOSITARY
OR A NOMINEE THEREOF. THIS SECURITY MAY NOT BE EXCHANGED IN WHOLE OR IN PART FOR
A SECURITY REGISTERED, AND NO TRANSFER OF THIS SECURITY IN WHOLE OR IN PART MAY
BE REGISTERED, IN THE NAME OF ANY PERSON OTHER THAN SUCH DEPOSITARY OR A NOMINEE
THEREOF, EXCEPT IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE. FORM OF
TRUSTEE'S CERTIFICATE OF AUTHENTICATION.


                                       17
<PAGE>   25

SECTION 2.3 FORM OF TRUSTEE'S CERTIFICATE OF AUTHENTICATION.

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

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

                            [                     ],
                             ---------------------
                                   as Trustee


                            By:
                                -------------------------
                                     Authorized Officer

SECTION 2.4 FORM OF CONVERSION NOTICE.

               Conversion notices shall be in substantially the following form:

To Willbros Group, Inc.:

               The undersigned owner of this Security hereby irrevocably
exercises the option to convert this Security, or portion hereof (which is
$1,000 or an integral multiple thereof) below designated, into shares of Common
Stock of the Company in accordance with the terms of the Indenture referred to
in this Security, and directs that the shares issuable and deliverable upon the
conversion, together with any check in payment for fractional shares and any
Securities representing any unconverted principal amount hereof, be issued and
delivered to the registered holder hereof unless a different name has been
indicated below. If this Notice is being delivered on a date after the close of
business on a Regular Record Date and prior to the opening of business on the
related Interest Payment Date (unless this Security or the portion thereof being
converted has been called for redemption on a Redemption Date during the period
beginning at the close of business on a Regular Record Date and ending at the
opening of business on the first Business Day after the next succeeding Interest
Payment Date, or if such Interest Payment Date is not a Business Day, the second
such Business Day), this Notice is accompanied by payment, in funds acceptable
to the Company, of an amount equal to the interest payable on such Interest
Payment Date of the principal of this Security to be converted. If shares are to
be issued in the name of a person other than the undersigned, the undersigned
will pay all transfer taxes payable with respect hereto. Any amount required to
be paid by the undersigned on account of interest accompanies this Security.

                                       18
<PAGE>   26

                        Principal Amount to be Converted
              (in an integral multiple of $1,000, if less than all)

U.S. $
      ---------------
Dated:
      ---------------

                              Signature(s) must be guaranteed by an eligible
                              guarantor institution (banks, stock brokers,
                              savings and loan associations and credit unions
                              with membership in an approved signature guarantee
                              medallion program) pursuant to Securities and
                              Exchange Commission Rule 17Ad-15.

                                             -----------------------------------
                                             Signature Guaranty

               Fill in for registration of shares of Common Stock and Security
if to be issued otherwise than to the registered Holder.


--------------------------    ------------------------------------------------
(Name)                        Social Security or Other Taxpayer
                              Identification Number

-------------------------
(Address)


---------------------------------
Please print Name and Address
(including zip code number)

[The above conversion notice is to be modified, as appropriate, for conversion
into other securities or property of the Company.]


                                   ARTICLE III

                                 THE SECURITIES

SECTION 3.1 AMOUNT UNLIMITED; ISSUABLE IN SERIES.

               The aggregate principal amount of Securities which may be
authenticated and delivered under this Indenture is unlimited.


                                       19
<PAGE>   27

               The Securities may be issued in one or more series. There shall
be established in or pursuant to a Board Resolution and, subject to Section 3.3,
set forth, or determined in the manner provided, in an Officers' Certificate, or
established in one or more indentures supplemental hereto, prior to the issuance
of Securities of any series,

                  (1) the title of the Securities of the series (which shall
         distinguish the Securities of the series from Securities of any other
         series);

                  (2) 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 3.4, 3.5, 3.6, 9.6 or 11.7
         and except for any Securities which, pursuant to Section 3.3, are
         deemed never to have been authenticated and delivered hereunder);

                  (3) the Person to whom any interest on a Security of the
         series shall be payable, if other than the Person in whose name that
         Security (or one or more Predecessor Securities) is registered at the
         close of business on the Regular Record Date for such interest;

                  (4) the date or dates on which the principal of any Securities
         of the series is payable;

                  (5) the rate or rates at which any Securities of the series
         shall bear interest, if any, the date or dates from which any such
         interest shall accrue, the Interest Payment Dates on which any such
         interest shall be payable and the Regular Record Date for any such
         interest payable on any Interest Payment Date;

                  (6) the place or places where the principal of and any premium
         and interest on any Securities of the series shall be payable;

                  (7) the period or periods within which, the price or prices at
         which and the terms and conditions upon which any Securities of the
         series may be redeemed, in whole or in part, at the option of the
         Company and, if other than by a Board Resolution, the



                                       20
<PAGE>   28

         manner in which any election by the Company to redeem the Securities
         shall be evidenced;

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

                  (9) if other than denominations of $1,000 and any integral
         multiple thereof, the denominations in which any Securities of the
         series shall be issuable;

                  (10) if the amount of principal of or any premium or interest
         on any Securities of the series may be determined with reference to an
         index or pursuant to a formula, the manner in which such amounts shall
         be determined;

                       (11) if other than the currency of the United States of
        America, the currency, currencies or currency units in which the
        principal of or any premium or interest on any Securities of the series
        shall be payable and the manner of determining the equivalent thereof in
        the currency of the United States of America for any purpose, including
        for purposes of the definition of "Outstanding" in Section 1.1;

                  (12) if the principal of or any premium or interest on any
         Securities of the series is to be payable, at the election of the
         Company or the Holder thereof, in one or more currencies or currency
         units other than that or those in which such Securities are stated to
         be payable, the currency, currencies or currency units in which the
         principal of or any premium or interest on such Securities as to which
         such election is made shall be payable, the periods within which and
         the terms and conditions upon which such election is to be made and the
         amount so payable (or the manner in which such amount shall be
         determined);

                  (13) if other than the entire principal amount thereof, the
         portion of the principal amount of any Securities of the



                                       21
<PAGE>   29

        series which shall be payable upon declaration of acceleration of the
        Maturity thereof pursuant to Section 5.2;

                       (14) if the principal amount payable at the Stated
        Maturity of any Securities of the series will not be determinable as of
        any one or more dates prior to the Stated Maturity, the amount which
        shall be deemed to be the principal amount of such Securities as of any
        such date for any purpose thereunder or hereunder, including the
        principal amount thereof which shall be due and payable upon any
        Maturity other than the Stated Maturity or which shall be deemed to be
        Outstanding as of any date prior to the Stated Maturity (or, in any such
        case, the manner in which such amount deemed to be the principal amount
        shall be determined);

                       (15) if applicable, that the Securities of the series, in
        whole or any specified part, shall be defeasible pursuant to Section
        13.2 or Section 13.3 or both such Sections and, if other than by a Board
        Resolution, the manner in which any election by the Company to defease
        such Securities shall be evidenced;

                       (16) if applicable, the terms of any right to convert
        Securities of the series into shares of Common Stock of the Company or
        other securities or property;

                       (17) if applicable, that any Securities of the series
        shall be issuable in whole or in part in the form of one or more Global
        Securities and, in such case, the respective Depositaries for such
        Global Securities, the form of any legend or legends which shall be
        borne by any such Global Security in addition to or in lieu of that set
        forth in Section 2.2 and any circumstances in addition to or in lieu of
        those set forth in Clause (2) of the last paragraph of Section 3.5 in
        which any such Global Security may be exchanged in whole or in part for
        Securities registered, and any transfer of such Global Security in whole
        or in part may be registered, in the name or names of Persons other than
        the Depositary for such Global Security or a nominee thereof;

                       (18) 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
        5.2;


                                       22
<PAGE>   30

                       (19)   any addition to or change in the covenants set
        forth in Article 10 which applies to Securities of the series; and

                       (20) any other terms of the series (which terms shall not
        be inconsistent with the provisions of this Indenture, except as
        permitted by Section 9.1(5)).

               All Securities of any one series shall be substantially identical
except as to denomination and except as may otherwise be provided in or pursuant
to the Board Resolution referred to above and (subject to Section 3.3) set
forth, or determined in the manner provided, in the Officers' Certificate
referred to above or in any such indenture supplemental hereto.

               If any of the terms of the series are established by action taken
pursuant to a Board Resolution, a copy of an appropriate record of such action
shall be certified by the Secretary or an Assistant Secretary of the Company and
delivered to the Trustee at or prior to the delivery of the Officers'
Certificate setting forth the terms of the series.

SECTION 3.2 DENOMINATIONS.

               The Securities of each series shall be issuable only in
registered form without coupons and only in such denominations as shall be
specified as contemplated by Section 3.1. In the absence of any such specified
denomination with respect to the Securities of any series, the Securities of
such series shall be issuable in denominations of $1,000 and any integral
multiple thereof.

SECTION 3.3 EXECUTION, AUTHENTICATION, DELIVERY AND DATING.

               The Securities shall be executed on behalf of the Company by its
Chairman of the Board, its Chief Executive Officer, its principal financial
officer, its President or one of its Vice Presidents, attested by its Treasurer,
Secretary or one of its Assistant Treasurers or Assistant Secretaries. The
signature of any of these officers on the Securities may be manual or facsimile.

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


                                       23
<PAGE>   31

               At any time and from time to time after the execution and
delivery of this Indenture, the Company may deliver Securities of any series
executed by the Company to the Trustee for authentication, together with a
Company Order for the authentication and delivery of such Securities, and the
Trustee in accordance with the Company Order shall authenticate and deliver such
Securities. If the form or terms of the Securities of the series have been
established by or pursuant to one or more Board Resolutions as permitted by
Sections 2.1 and 3.1, in authenticating such Securities, and accepting the
additional responsibilities under this Indenture in relation to such Securities,
the Trustee shall be entitled to receive, and (subject to Section 6.1) shall be
fully protected in relying upon, a copy of such Board Resolution, the Officers'
Certificate setting forth the terms of the series and an Opinion of Counsel,
with such Opinion of Counsel stating,

                  (1) if the form of such Securities has been established by or
         pursuant to Board Resolution as permitted by Section 2.1, that such
         form has been established in conformity with the provisions of this
         Indenture;

                  (2) if the terms of such Securities have been established by
         or pursuant to Board Resolution as permitted by Section 3.1, that such
         terms have been established in conformity with the provisions of this
         Indenture; and

                  (3) that such Securities, when authenticated and delivered by
         the Trustee and issued by the Company in the manner and subject to any
         conditions specified in such Opinion of Counsel, will constitute valid
         and legally binding obligations of the Company enforceable in
         accordance with their terms, subject to bankruptcy, insolvency,
         fraudulent transfer, reorganization, moratorium and similar laws of
         general applicability relating to or affecting creditors' rights and to
         general equity principles.

               If such form or terms have been so established, the Trustee shall
not be required to authenticate such Securities if the issue of such Securities
pursuant to this Indenture will affect the Trustee's own rights, duties or
immunities under the Securities and this Indenture or otherwise in a manner
which is not reasonably acceptable to the Trustee.

               Notwithstanding the provisions of Section 3.1 and of the
preceding paragraph, if all Securities of a series are not to be originally
issued at one time, it shall not be necessary to deliver the Officers'
Certificate otherwise required pursuant to Section 3.1 or the Company Order and
Opinion of Counsel otherwise required


                                       24
<PAGE>   32

pursuant to such preceding paragraph at or prior to the authentication of each
Security of such series if such documents are delivered at or prior to the
authentication upon original issuance of the first Security of such series to be
issued.

               Each Security shall be dated the date of its authentication.

               No Security shall be entitled to any benefit under this Indenture
or be valid or obligatory for any purpose unless there appears on such Security
a certificate of authentication substantially in the form provided for herein
executed by the Trustee by manual signature, and such certificate upon any
Security shall be conclusive evidence, and the only evidence, that such Security
has been duly authenticated and delivered hereunder. Notwithstanding the
foregoing, if any Security shall have been authenticated and delivered hereunder
but never issued and sold by the Company, and the Company shall deliver such
Security to the Trustee for cancellation as provided in Section 3.9, for all
purposes of this Indenture such Security shall be deemed never to have been
authenticated and delivered hereunder and shall never be entitled to the
benefits of this Indenture.

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

SECTION 3.4 TEMPORARY SECURITIES.

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

               If temporary Securities of any series are issued, the Company
will cause definitive Securities of that series to be prepared without
unreasonable delay. After the preparation of definitive Securities of such
series, the temporary Securities of such series shall be exchangeable for
definitive Securities of such series upon surrender of the temporary Securities
of such series at the office or agency of the Company in a Place of Payment for
that series, without charge to the Holder. Upon



                                       25
<PAGE>   33

surrender for cancellation of any one or more temporary Securities of any
series, the Company shall execute and the Trustee shall authenticate and deliver
in exchange therefor one or more definitive Securities of the same series, of
any authorized denominations and of like tenor and aggregate principal amount.
Until so exchanged, the temporary Securities of any series shall in all respects
be entitled to the same benefits under this Indenture as definitive Securities
of such series and tenor.

SECTION 3.5 REGISTRATION; REGISTRATION OF TRANSFER AND EXCHANGE.

               The Company shall cause to be kept at the Corporate Trust Office
of the Trustee a register (the register maintained in such office and in any
other office or agency of the Company in a Place of Payment being herein
sometimes collectively referred to as the "Security Register") in which, subject
to such reasonable regulations as it may prescribe, the Company shall provide
for the registration of Securities and of transfers of Securities. The Trustee
is hereby appointed "Security Registrar" for the purpose of registering
Securities and transfers of Securities as herein provided.

               Upon surrender for registration of transfer of any Security of a
series at the office or agency of the Company in a Place of Payment for that
series, the Company shall execute, and the Trustee shall authenticate and
deliver, in the name of the designated transferee or transferees, one or more
new Securities of the same series, of any authorized denominations and of like
tenor and aggregate principal amount.

               At the option of the Holder, Securities of any series may be
exchanged for other Securities of the same series, of any authorized
denominations and of like tenor and aggregate principal amount, upon surrender
of the Securities to be exchanged at such office or agency. Whenever any
Securities are so surrendered for exchange, the Company shall execute, and the
Trustee shall authenticate and deliver, the Securities which the Holder making
the exchange is entitled to receive.

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

               Every Security presented or surrendered for registration of
transfer or for exchange shall (if so required by the Company or the Trustee) be
duly endorsed, or be accompanied by a written instrument of transfer in form
satisfactory to the



                                       26
<PAGE>   34

Company and the Security Registrar duly executed, by the Holder thereof or its
attorney duly authorized in writing.

               No service charge shall be made for any registration of transfer
or exchange of Securities, but the Company may require payment of a sum
sufficient to cover any tax or other governmental charge that may be imposed in
connection with any registration of transfer or exchange of Securities, other
than exchanges pursuant to Section 3.4, 9.6 or 11.7 not involving any transfer.

               If the Securities of any series (or of any series and specified
tenor) are to be redeemed in part, the Company shall not be required (A) to
issue, register the transfer of or exchange any Securities of that series (or of
that series and specified tenor, as the case may be) during a period beginning
at the opening of business 15 days before the day of the mailing of a notice of
redemption of any such Securities selected for redemption under Section 11.3 and
ending at the close of business on the day of such mailing, or (B) to register
the transfer of or exchange any Security so selected for redemption in whole or
in part, except the unredeemed portion of any Security being redeemed in part.

               The provisions of Clauses (1), (2), (3) and (4) below shall apply
only to Global Securities:

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

                  (2) Notwithstanding any other provision in this Indenture, no
         Global Security may be exchanged in whole or in part for Securities
         registered, and no transfer of a Global Security in whole or in part
         may be registered, in the name of any Person other than the Depositary
         for such Global Security or a nominee thereof unless (A) such
         Depositary (i) has notified the Company that it is unwilling or unable
         to continue as Depositary for such Global Security or (ii) has ceased
         to be a clearing agency registered under the Exchange Act, (B) there
         shall have occurred and be continuing an Event of Default with respect
         to such Global Security or (C) there shall exist such circumstances, if
         any, in addition to or in lieu of the foregoing as have been specified
         for this purpose as contemplated by Section 3.1.


                                       27
<PAGE>   35

                  (3) Subject to Clause (2) above, any exchange of a Global
         Security for other Securities may be made in whole or in part, and all
         Securities issued in exchange for a Global Security or any portion
         thereof shall be registered in such names as the Depositary for such
         Global Security shall direct.

                  (4) Every Security authenticated and delivered upon
         registration of transfer of, or in exchange for or in lieu of, a Global
         Security or any portion thereof, whether pursuant to this Section,
         Section 3.4, 3.6, 9.6 or 11.7 or otherwise, shall be authenticated and
         delivered in the form of, and shall be, a Global Security, unless such
         Security is registered in the name of a Person other than the
         Depositary for such Global Security or a nominee thereof.

SECTION 3.6 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 the Trustee shall authenticate and
deliver, 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.

               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


                                       28
<PAGE>   36

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 3.7 PAYMENT OF INTEREST; INTEREST RIGHTS PRESERVED.

               Except as otherwise provided as contemplated by Section 3.1 with
respect to any series of Securities, interest on any Security which is payable,
and is punctually paid or duly provided for, on any Interest Payment Date shall
be paid to the Person in whose name that Security (or one or more Predecessor
Securities) is registered at the close of business on the Regular Record Date
for such interest.

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

                  (1) The Company may elect to make payment of any Defaulted
         Interest to the Persons in whose names the Securities of such series
         (or their respective Predecessor Securities) are registered at the
         close of business on a Special Record Date for the payment of such
         Defaulted Interest, which shall be fixed in the following manner. The
         Company shall notify the Trustee in writing of the amount of Defaulted
         Interest proposed to be paid on each Security of such series and the
         date of the proposed payment, and at the same time the Company shall
         deposit with the Trustee an amount of money equal to the aggregate
         amount proposed to be paid in respect of such Defaulted Interest or
         shall make arrangements satisfactory to the Trustee for such deposit
         prior to the date of the proposed payment, such money when deposited to
         be held in trust for the benefit of the Persons entitled to such
         Defaulted Interest as in this Clause provided. Thereupon the Trustee
         shall fix a Special Record Date for the payment of such Defaulted
         Interest which shall be not more than 15 days and not less than 10 days
         prior to the date of the proposed payment and not less than 10 days
         after the receipt by the Trustee of the notice of the proposed payment.
         The Trustee shall promptly notify the Company of



                                       29
<PAGE>   37

         such Special Record Date and, in the name and at the expense of the
         Company, shall cause notice of the proposed payment of such Defaulted
         Interest and the Special Record Date therefor to be given to each
         Holder of Securities of such series in the manner set forth in Section
         1.6, not less than 10 days prior to such Special Record Date. Notice of
         the proposed payment of such Defaulted Interest and the Special Record
         Date therefor having been so mailed, such Defaulted Interest shall be
         paid to the Persons in whose names the Securities of such series (or
         their respective Predecessor Securities) are registered at the close of
         business on such Special Record Date and shall no longer be payable
         pursuant to the following Clause (2).

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

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

               Subject to the provisions of Section 14.2, in the case of any
Security (or any part thereof) which is converted after any Regular Record Date
and on or prior to the next succeeding Interest Payment Date (other than any
Security the principal of (or premium, if any, on) which shall become due and
payable, whether at Stated Maturity or by declaration of acceleration prior to
such Interest Payment Date), interest whose Stated Maturity is on such Interest
Payment Date shall be payable on such Interest Payment Date notwithstanding such
conversion and such interest (whether or not punctually paid or duly provided
for) shall be paid to the Person in whose name that Security (or any one or more
Predecessor Securities) is registered at the close of business on such Regular
Record Date. Except as otherwise expressly provided in the immediately preceding
sentence or in Section 14.2, in the case of any Security (or any part thereof)
which is converted, interest whose Stated Maturity is after the date of
conversion of such Security (or such part thereof) shall not be payable.


                                       30
<PAGE>   38

SECTION 3.8  PERSONS DEEMED OWNERS.

               Prior to due presentment of a Security for registration of
transfer, the Company, the Trustee and any agent of the Company or the Trustee
may treat the Person in whose name such Security is registered as the owner of
such Security for the purpose of receiving payment of principal of and any
premium and (subject to Section 3.7) any interest on such Security and for all
other purposes whatsoever, whether or not such Security be overdue, and neither
the Company, the Trustee nor any agent of the Company or the Trustee shall be
affected by notice to the contrary.

SECTION 3.9 CANCELLATION.

               All Securities surrendered for payment, redemption, registration
of transfer or exchange or for credit against any sinking fund payment shall, if
surrendered to any Person other than the Trustee, be delivered to the Trustee
and shall be promptly canceled by it. The Company may at any time deliver to the
Trustee for cancellation any Securities previously authenticated and delivered
hereunder which the Company may have acquired in any manner whatsoever, and may
deliver to the Trustee (or to any other Person for delivery to the Trustee) for
cancellation any Securities previously authenticated hereunder which the Company
has not issued and sold, and all Securities so delivered shall be promptly
canceled by the Trustee. No Securities shall be authenticated in lieu of or in
exchange for any Securities canceled as provided in this Section, except as
expressly permitted by this Indenture. All canceled Securities held by the
Trustee shall be disposed of as directed by a Company Order.

SECTION 3.10   COMPUTATION OF INTEREST.

               Except as otherwise specified as contemplated by Section 3.1 for
Securities of any series, interest on the Securities of each series shall be
computed on the basis of a 360-day year of twelve 30-day months.


                                   ARTICLE IV

                           SATISFACTION AND DISCHARGE

SECTION 4.1   SATISFACTION AND DISCHARGE OF INDENTURE.

               This Indenture shall upon Company Request cease to be of further
effect (except as to any surviving rights of registration of transfer or
exchange of Securities herein expressly provided for), and the Trustee, at the
expense of the



                                       31
<PAGE>   39

Company, shall execute proper instruments acknowledging satisfaction and
discharge of this Indenture, when

                  (1) either

                           (A) all Securities theretofore authenticated and
                  delivered (other than (i) Securities which have been
                  destroyed, lost or stolen and which have been replaced or paid
                  as provided in Section 3.6 and (ii) Securities for whose
                  payment money has theretofore been deposited in trust or
                  segregated and held in trust by the Trustee or the Company and
                  thereafter repaid to the Company or discharged from such
                  trust, as provided in Section 10.3) have been delivered to the
                  Trustee for cancellation; or

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

                                    (i) have become due and payable, or

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

                                    (iii) are to be called for redemption within
                           one year under arrangements satisfactory to the
                           Trustee for the giving of notice of redemption by the
                           Trustee in the name, and at the expense, of the
                           Company, and the Company, in the case of (i), (ii) or
                           (iii) above, has deposited or caused to be deposited
                           with the Trustee as trust funds in trust for the
                           purpose of making the following payments, money in an
                           amount sufficient to pay and discharge the entire
                           indebtedness on such Securities not theretofore
                           delivered to the Trustee for cancellation, for
                           principal and any premium and interest to the date of
                           such deposit (in the case of Securities which have
                           become due and payable) or to the Stated Maturity or
                           Redemption Date, as the case may be;

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

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

                                       32
<PAGE>   40


               Notwithstanding the satisfaction and discharge of this Indenture,
the obligations of the Company to the Trustee under Section 6.7, the obligations
of the Trustee to any Authenticating Agent under Section 6.14 and, if money
shall have been deposited with the Trustee pursuant to subclause (B) of Clause
(1) of this Section, the obligations of the Trustee under Section 4.2 and the
last paragraph of Section 10.3 shall survive.

SECTION 4.2 APPLICATION OF TRUST MONEY.

               Subject to the provisions of the last paragraph of Section 10.3,
all money deposited with the Trustee pursuant to Section 4.1 shall be held in
trust and applied by it, in accordance with the provisions of the Securities and
this Indenture, to the payment, either directly or through any Paying Agent
(including the Company acting as its own Paying Agent) as the Trustee may
determine, to the Persons entitled thereto, of the principal and any premium and
interest for whose payment such money has been deposited with the Trustee.


                                    ARTICLE V

                                    REMEDIES

SECTION 5.1 EVENTS OF DEFAULT.

               "Event of Default," wherever used herein with respect to
Securities of any series, means any one of the following events (whatever the
reason for such Event of Default and whether it shall be voluntary or
involuntary or be effected by operation of law or pursuant to any judgment,
decree or order of any court or any order, rule or regulation of any
administrative or governmental body):

                  (1) default in the payment of any interest upon any Security
         of that series when it becomes due and payable, and continuance of such
         default for a period of 30 days; or

                  (2) default in the payment of the principal of or any premium
         on any Security of that series at its Maturity; or

                  (3) default in the deposit of any sinking fund payment, when
         and as due by the terms of a Security of that series; or


                                       33
<PAGE>   41


                  (4) default in the performance, or breach, of any covenant or
         warranty of the Company in this Indenture (other than a covenant or
         warranty a default in whose performance or whose breach is elsewhere in
         this Section specifically dealt with or which has expressly been
         included in this Indenture solely for the benefit of series of
         Securities other than that series), and continuance of such default or
         breach for a period of 60 days after there has been given, by
         registered or certified mail, to the Company by the Trustee or to the
         Company and the Trustee by the Holders of at least 25% in principal
         amount of the Outstanding Securities 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

                  (5) the entry by a court having jurisdiction in the premises
         of a decree or order for relief in respect of the Company in an
         involuntary case or proceeding under any applicable Federal or State
         bankruptcy, insolvency, reorganization or other similar law or (B) a
         decree or order adjudging the company a bankrupt or insolvent, or
         approving as properly filed a petition seeking reorganization,
         arrangement, adjustment or composition of or in respect of the Company
         under any applicable Federal or State law, or appointing a custodian,
         receiver, liquidator, assignee, trustee, equestrator or other similar
         official of the Company or of any substantial part of its property, or
         ordering the winding up or liquidation of its affairs, and the
         continuance of any such decree or order for relief or any such other
         decree or order unstayed and in effect for a period of 90 consecutive
         days; or

                  (6) the commencement by the Company of a voluntary case or
         proceeding under any applicable Federal or State bankruptcy,
         insolvency, reorganization or other similar law or of any other case or
         proceeding to be adjudicated a bankrupt or insolvent, or the consent by
         it to the entry of a decree or order for relief in respect of the
         Company in an involuntary case or proceeding under any applicable
         Federal or State bankruptcy, insolvency, reorganization or other
         similar law or to the commencement of any bankruptcy or insolvency case
         or proceeding against it, or the filing by it of a petition or answer
         or consent seeking reorganization or relief under any applicable
         Federal or State law, or the consent by it to the filing of such
         petition or to the appointment of or taking possession by a custodian,
         receiver, liquidator, assignee, trustee, sequestrator or other similar
         official of the Company or of any substantial part of its



                                       34
<PAGE>   42

         property, or the making by it of an assignment for the benefit of
         creditors, or the admission by it in writing of its inability to pay
         its debts generally as they become due, or the taking of corporate
         action by the Company in furtherance of any such action; or

                  (7) any other Event of Default provided with respect to
         Securities of that series.

SECTION 5.2 ACCELERATION OF MATURITY; RESCISSION AND ANNULMENT.

               If an Event of Default (other than an Event of Default specified
in Section 5.1(5) or 5.1(6)) with respect to Securities of any series at the
time Outstanding occurs and is continuing, then in every such case the Trustee
or the Holders of not less than 25% in principal amount of the Outstanding
Securities of that series may declare the principal amount of all the Securities
of that series (or, if any Securities of that series are Original Issue Discount
Securities, such portion of the principal amount of such Securities as may be
specified by the terms thereof) 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) shall become
immediately due and payable. If an Event of Default specified in Section 5.1(5)
or 5.1(6) with respect to Securities of any series at the time Outstanding
occurs, the principal amount of all the Securities of that series (or, if any
Securities of that series are Original Issue Discount Securities, such portion
of the principal amount of such Securities as may be specified by the terms
thereof) shall automatically, and without any declaration or other action on the
part of the Trustee or any Holder, become immediately due and payable.

               At any time after such a declaration of acceleration with respect
to Securities of 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

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

                           (A) all overdue interest on all Securities of that
                  series,

                           (B) the principal of (and premium, if any, on) any
                  Securities of that series which have become due otherwise



                                       35
<PAGE>   43

                  than by such declaration of acceleration and any interest
                  thereon at the rate or rates prescribed therefor in such
                  Securities,

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

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

                  (2) all Events of Default 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 5.13. No
         such rescission shall affect any subsequent default or impair any right
         consequent thereon.

SECTION 5.3 COLLECTION OF INDEBTEDNESS AND SUITS FOR ENFORCEMENT BY TRUSTEE.

               The Company covenants that if

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

                  (2) default is made in the payment of the principal of (or
         premium, if any, on) any Security at the Maturity thereof, the Company
         will, upon demand of the Trustee, pay to it, for the benefit of the
         Holders of such Securities, the whole amount then due and payable on
         such Securities for principal and any premium and interest and, to the
         extent that payment of such interest shall be legally enforceable,
         interest on any overdue principal and premium and on 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.


                                       36
<PAGE>   44

               If an Event of Default with respect to 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 5.4 TRUSTEE MAY FILE PROOFS OF CLAIM.

               In case of any judicial proceeding relative to the Company (or
any other obligor upon the Securities), its property or its creditors, the
Trustee shall be entitled and empowered, by intervention in such proceeding or
otherwise, to take any and all actions authorized under the Trust Indenture Act
in order to have claims of the Holders and the Trustee allowed in any such
proceeding. In particular, the Trustee shall be authorized to collect and
receive any moneys or other property payable or deliverable on any such claims
and to distribute the same; and any custodian, receiver, assignee, trustee,
liquidator, sequestrator or other similar official in any such judicial
proceeding is hereby authorized by each Holder to make such payments to the
Trustee and, in the event that the Trustee shall consent to the making of such
payments directly to the Holders, to pay to the Trustee any amount due it for
the reasonable compensation, expenses, disbursements and advances of the
Trustee, its agents and counsel, and any other amounts due the Trustee under
Section 6.7.

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

SECTION 5.5 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


                                       37
<PAGE>   45

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

SECTION 5.6 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 any
premium or interest, upon presentation of the Securities and the notation
thereon of the payment if only partially paid and upon surrender thereof if
fully paid:

               FIRST: To the payment of all amounts due the Trustee under
Section 6.7;

               SECOND: To the payment of the amounts then due and unpaid for
principal of and any premium, if any, 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 any premium, if any, and interest,
respectively; and

               THIRD: The balance, if any, to the Company or any other Person or
Persons entitled thereto.

SECTION 5.7 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

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

                  (2) 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;

                  (3) such Holder or Holders have offered to the Trustee
         reasonable indemnity against the costs, expenses and liabilities to be
         incurred in compliance with such request;

                                       38
<PAGE>   46

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

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

SECTION 5.8 UNCONDITIONAL RIGHT OF HOLDERS TO RECEIVE PRINCIPAL, PREMIUM AND
            INTEREST AND TO CONVERT.

               Notwithstanding any other provision in this Indenture, the Holder
of any Security shall have the right, which is absolute and unconditional, to
receive payment of the principal of and any premium and (subject to Section 3.7)
interest on such Security on the respective Stated Maturities expressed in such
Security (or, in the case of redemption, on the Redemption Date), to convert
such Securities in accordance with Article 14 to the extent that such right to
convert is applicable to such Security 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 5.9 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 5.10   RIGHTS AND REMEDIES CUMULATIVE.

               Except as otherwise provided with respect to the replacement or
payment of mutilated, destroyed, lost or stolen Securities in the last paragraph
of Section 3.6, no right or remedy herein conferred upon or reserved to the
Trustee or to the Holders is



                                       39
<PAGE>   47

intended to be exclusive of any other right or remedy, and every right and
remedy shall, to the extent permitted by law, be cumulative and in addition to
every other right and remedy given hereunder or now or hereafter existing at law
or in equity or otherwise. The assertion or employment of any right or remedy
hereunder, or otherwise, shall not prevent the concurrent assertion or
employment of any other appropriate right or remedy.

SECTION 5.11   DELAY OR OMISSION NOT WAIVER.

               No delay or omission of the Trustee or of any Holder of any
Securities to exercise any right or remedy accruing upon any Event of Default
shall impair any such right or remedy or constitute a waiver of any such Event
of Default or an acquiescence therein. Every right and remedy given by this
Article 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 (subject to the
limitations contained in this Indenture) or by the Holders, as the case may be.

SECTION 5.12   CONTROL BY HOLDERS.

               The Holders of a majority in principal amount of the Outstanding
Securities 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:

                  (1) such direction shall not be in conflict with any rule of
         law or with this Indenture and the Trustee shall not have determined
         that the action so directed would be unjustly prejudicial to Holders of
         Securities of that series, or any other series, not taking part in such
         direction; and

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

SECTION 5.13 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:



                                       40
<PAGE>   48

                  (1) a default in the payment of the principal of or any
         premium or interest on any Security of such series; or

                  (2) to the extent such right is applicable to such Security, a
         failure by the Company on request to convert any Security into Common
         Stock; or

                  (3) in respect of a covenant or provision hereof which under
         Article 9 cannot be modified or amended without the consent of the
         Holder of each Outstanding Security of such series affected.

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

SECTION 5.14 UNDERTAKING FOR COSTS.

               In any suit for the enforcement of any right or remedy under this
Indenture, or in any suit against the Trustee for any action taken, suffered or
omitted by it as Trustee, a court may require any party litigant in such suit to
file an undertaking to pay the costs of such suit, and may assess costs against
any such party litigant, in the manner and to the extent provided in the Trust
Indenture Act; provided that neither this Section nor the Trust Indenture Act
shall be deemed to authorize any court to require such an undertaking or to make
such an assessment in any suit instituted by the Company or in any suit for the
enforcement of the right to convert any Security in accordance with Article 14.

SECTION 5.15 WAIVER OF USURY, STAY OR EXTENSION LAWS.

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


                                       41
<PAGE>   49

                                   ARTICLE VI

                                   THE TRUSTEE

SECTION 6.1 CERTAIN DUTIES AND RESPONSIBILITIES.

               The duties and responsibilities of the Trustee shall be as
provided by the Trust Indenture Act. Notwithstanding the foregoing, no provision
of this Indenture shall require the Trustee to expend or risk its own funds or
otherwise incur any financial liability in the performance of any of its duties
hereunder, or in the exercise of any of its rights or powers if it shall have
reasonable grounds for believing that repayment of such funds or adequate
indemnity against such risk or liability is not reasonably assured to it.
Whether or not therein expressly so provided, every provision of this Indenture
relating to the conduct or affecting the liability of or affording protection to
the Trustee shall be subject to the provisions of this Section.

SECTION 6.2 NOTICE OF DEFAULTS.

               If a default occurs hereunder with respect to Securities of any
series, the Trustee shall give the Holders of Securities of such series notice
of such default as and to the extent provided by the Trust Indenture Act;
provided, however, that in the case of any default of the character specified in
Section 5.1(4) with respect to Securities of such series, no such notice to
Holders shall be given until at least 30 days after the occurrence thereof. For
the purpose of this Section, the term "default" means any event which is, or
after notice or lapse of time or both would become, an Event of Default with
respect to Securities of such series.

SECTION 6.3 CERTAIN RIGHTS OF TRUSTEE.

               Subject to the provisions of Section 6.1:

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

                  (2) any request or direction of the Company mentioned herein
         shall be sufficiently evidenced by a Company Request


                                       42
<PAGE>   50

         or Company Order, and any resolution of the Board of Directors shall be
         sufficiently evidenced by a Board Resolution;

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

                  (4) the Trustee may consult with counsel and the written
         advice of such counsel or any Opinion of Counsel shall be full and
         complete authorization and protection in respect of any action taken,
         suffered or omitted by it hereunder in good faith and in reliance
         thereon;

                  (5) the Trustee shall be under no obligation to exercise any
         of the rights or powers vested in it by this Indenture at the request
         or direction of any of the Holders pursuant to this Indenture, unless
         such Holders shall have offered to the Trustee reasonable security or
         indemnity against the costs, expenses and liabilities which might be
         incurred by it in compliance with such request or direction;

                  (6) the Trustee shall not be bound to make any investigation
         into the facts or matters stated in any resolution, certificate,
         statement, instrument, opinion, report, notice, request, direction,
         consent, order, bond, debenture, note, other evidence of indebtedness
         or other paper or document, but the Trustee, in its discretion, may
         make such further inquiry or investigation into such facts or matters
         as it may see fit, and, if the Trustee shall determine to make such
         further inquiry or investigation, it shall be entitled to examine the
         books, records and premises of the Company, personally or by agent or
         attorney; and

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



                                       43
<PAGE>   51

SECTION 6.4 NOT RESPONSIBLE FOR RECITALS OR ISSUANCE OF SECURITIES.

               The recitals contained herein and in the Securities, except the
Trustee's certificates of authentication, shall be taken as the statements of
the Company, and neither the Trustee nor any Authenticating Agent assumes any
responsibility for their correctness. The Trustee makes no representations as to
the validity, sufficiency or priority of this Indenture or of the Securities.
Neither the Trustee nor any Authenticating Agent shall be accountable for the
use or application by the Company of Securities or the proceeds thereof.

SECTION 6.5 MAY HOLD SECURITIES AND ACT AS TRUSTEE UNDER OTHER INDENTURES.

               The Trustee, any Authenticating Agent, any Paying Agent, any
Security Registrar or any other agent of the Company, in its individual or any
other capacity, may become the owner or pledgee of Securities and, subject to
Sections 6.8 and 6.13, may otherwise deal with the Company with the same rights
it would have if it were not Trustee, Authenticating Agent, Paying Agent,
Security Registrar or such other agent.

               Subject to the limitations imposed by the Trust Indenture Act,
nothing in this Indenture shall prohibit the Trustee from becoming and acting as
trustee under other indentures under which other securities, or certificates of
interest of participation in other securities, of the Company are outstanding in
the same manner as if it were not Trustee hereunder.

SECTION 6.6 MONEY HELD IN TRUST.

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

SECTION 6.7 COMPENSATION AND REIMBURSEMENT.

               The Company agrees:

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

                  (2) except as otherwise expressly provided herein, to
         reimburse the Trustee upon its request for all reasonable expenses,
         disbursements and advances incurred or made by the Trustee in


                                       44
<PAGE>   52

         accordance with any provision of this Indenture (including the
         reasonable compensation and the expenses and disbursements of its
         agents and counsel), except any such expense, disbursement or advance
         as may be attributable to its negligence or bad faith; and

                  (3) to indemnify the Trustee for, and to hold it harmless
         against, any loss, liability or expense incurred without negligence or
         bad faith on its part, arising out of or in connection with the
         acceptance or administration of the trust or trusts hereunder,
         including the costs and expenses of defending itself against any claim
         or liability in connection with the exercise or performance of any of
         its powers or duties hereunder.

SECTION 6.8 CONFLICTING INTERESTS.

               If the Trustee has or shall acquire a conflicting interest within
the meaning of the Trust Indenture Act, the Trustee shall either eliminate such
interest or resign, to the extent and in the manner provided by, and subject to
the provisions of, the Trust Indenture Act and this Indenture. To the extent
permitted by such Act, the Trustee shall not be deemed to have a conflicting
interest by virtue of being a trustee under this Indenture with respect to
Securities of more than one series.

SECTION 6.9 CORPORATE TRUSTEE REQUIRED; ELIGIBILITY.

               There shall at all times be one (and only one) Trustee hereunder
with respect to the Securities of each series, which may be Trustee hereunder
for Securities of one or more other series. Each Trustee shall be a Person that
is eligible pursuant to the Trust Indenture Act to act as such and has (or if
the Trustee is a member of a bank holding company system, its bank holding
company has) a combined capital and surplus of at least $50,000,000. If any such
Person or bank holding company publishes reports of condition at least annually,
pursuant to law or to the requirements of its supervising or examining
authority, then for the purposes of this Section and to the extent permitted by
the Trust Indenture Act, the combined capital and surplus of such Person or bank
holding company shall be deemed to be its combined capital and surplus as set
forth in its most recent report of condition so published. If at any time the
Trustee with respect to the Securities of any series shall cease to be eligible
in accordance with the provisions of this Section, it shall resign immediately
in the manner and with the effect hereinafter specified in this Article.


                                       45
<PAGE>   53

SECTION 6.10 RESIGNATION AND REMOVAL; APPOINTMENT OF SUCCESSOR.

                  No resignation or removal of the Trustee and no appointment of
a successor Trustee pursuant to this Article shall become effective until the
acceptance of appointment by the successor Trustee in accordance with the
applicable requirements of Section 6.11.

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

                  The Trustee may be removed at any time with respect to the
Securities of any series by Act of the Holders of a majority in principal amount
of the Outstanding Securities of such series, delivered to the Trustee and to
the Company.

                  If at any time:

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

                           (2) the Trustee shall cease to be eligible under
         Section 6.9 and shall fail to resign after written request therefor by
         the Company or by any such Holder, or

                           (3) the Trustee shall become incapable of acting or
         shall be adjudged a bankrupt or insolvent or a receiver of the Trustee
         or of its property shall be appointed or any public officer shall take
         charge or control of the Trustee or of its property or affairs for the
         purpose of rehabilitation, conservation or liquidation, then, in any
         such case, (A) the Company by a Board Resolution may remove the Trustee
         with respect to all Securities, or (B) subject to Section 5.14, any
         Holder who has been a bona fide Holder of a Security for at least six
         months may, on behalf of himself and all others similarly situated,
         petition any court of competent jurisdiction for the removal of the
         Trustee with respect to all Securities and the appointment of a
         successor Trustee or Trustees.

                  If the Trustee shall resign, be removed or become incapable of
acting, or if a vacancy shall occur in the office of Trustee for any cause, with
respect to the Securities of one or more series, the Company, by a Board
Resolution, shall promptly appoint a successor Trustee or Trustees with respect
to the Securities of that or those



                                       46
<PAGE>   54

series (it being understood that any such successor Trustee may be appointed
with respect to the Securities of one or more or all of such series and that at
any time there shall be only one Trustee with respect to the Securities of any
particular series) and shall comply with the applicable requirements of Section
6.11. If, within one year after such resignation, removal or incapability, or
the occurrence of such vacancy, a successor Trustee with respect to the
Securities of any series shall be appointed by Act of the Holders of a majority
in principal amount of the Outstanding Securities of such series delivered to
the Company and the retiring Trustee, the successor Trustee so appointed shall,
forthwith upon its acceptance of such appointment in accordance with the
applicable requirements of Section 6.11, become the successor Trustee with
respect to the Securities of such series and to that extent supersede the
successor Trustee appointed by the Company. If no successor Trustee with respect
to the Securities of any series shall have been so appointed by the Company or
the Holders and accepted appointment in the manner required by Section 6.11, the
retiring Trustee may petition, or any Holder who has been a bona fide Holder of
a Security of such series for at least six months may, on behalf of himself and
all others similarly situated, petition any court of competent jurisdiction for
the appointment of a successor Trustee with respect to the Securities of such
series.

                  The Company shall give notice of each resignation and each
removal of the Trustee with respect to the Securities of any series and each
appointment of a successor Trustee with respect to the Securities of any series
to all Holders of Securities of such series in the manner provided in Section
1.6. Each notice shall include the name of the successor Trustee with respect to
the Securities of such series and the address of its Corporate Trust Office.

SECTION 6.11 ACCEPTANCE OF APPOINTMENT BY SUCCESSOR.

                  In case of the appointment hereunder of a successor Trustee
with respect to all Securities, every such successor Trustee so appointed shall
execute, acknowledge and deliver to the Company and to the retiring Trustee an
instrument accepting such appointment, and thereupon the resignation or removal
of the retiring Trustee shall become effective and such successor Trustee,
without any further act, deed or conveyance, shall become vested with all the
rights, powers, trusts and duties of the retiring Trustee; but, on the request
of the Company or the successor Trustee, such retiring Trustee shall, upon
payment of its charges, execute and deliver an instrument transferring to such
successor Trustee all the rights, powers and trusts of the retiring Trustee and
shall duly assign, transfer and deliver to such successor Trustee all property
and money held by such retiring Trustee hereunder.

                  In case of the appointment hereunder of a successor Trustee
with respect to the Securities of one or more (but not all) series, the Company,
the retiring Trustee



                                       47
<PAGE>   55

and each successor Trustee with respect to the Securities of one or more series
shall execute and deliver an indenture supplemental hereto wherein each
successor Trustee shall accept such appointment and which (1) shall contain such
provisions as shall be necessary or desirable to transfer and confirm to, and to
vest in, each successor Trustee all the rights, powers, trusts and duties of the
retiring Trustee with respect to the Securities of that or those series to which
the appointment of such successor Trustee relates, (2) if the retiring Trustee
is not retiring with respect to all Securities, shall contain such provisions as
shall be deemed necessary or desirable to confirm that all the rights, powers,
trusts and duties of the retiring Trustee with respect to the Securities of that
or those series as to which the retiring Trustee is not retiring shall continue
to be vested in the retiring Trustee, and (3) shall 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, it being
understood that nothing herein or in such supplemental indenture shall
constitute such Trustees co-trustees of the same trust and that each such
Trustee shall be trustee of a trust or trusts hereunder separate and apart from
any trust or trusts hereunder administered by any other such Trustee; and upon
the execution and delivery of such supplemental indenture the resignation or
removal of the retiring Trustee shall become effective to the extent provided
therein and each such successor Trustee, without any further act, deed or
conveyance, shall become vested with all the rights, powers, trusts and duties
of the retiring Trustee with respect to the Securities of that or those series
to which the appointment of such successor Trustee relates; but, on request of
the Company or any successor Trustee, such retiring Trustee shall duly assign,
transfer and deliver to such successor Trustee all property and money held by
such retiring Trustee hereunder with respect to the Securities of that or those
series to which the appointment of such successor Trustee relates.

                  Upon request of any such successor Trustee, the Company shall
execute any and all instruments for more fully and certainly vesting in and
confirming to such successor Trustee all such rights, powers and trusts referred
to in the first or second preceding paragraph, as the case may be.

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

SECTION 6.12 MERGER, CONVERSION, CONSOLIDATION OR SUCCESSION TO BUSINESS.

                  Any corporation into which the Trustee may be merged or
converted or with which it may be consolidated, or any corporation resulting
from any merger, conversion or consolidation to which the Trustee shall be a
party, or any corporation succeeding to all or substantially all the corporate
trust business of the Trustee, shall be



                                       48
<PAGE>   56

the successor of the Trustee hereunder, provided such corporation shall be
otherwise qualified and eligible under this Article, without the execution or
filing of any paper or any further act on the part of any of the parties hereto.
In case any Securities shall have been authenticated, but not delivered, by the
Trustee then in office, any successor by merger, conversion or consolidation to
such authenticating Trustee may adopt such authentication and deliver the
Securities so authenticated with the same effect as if such successor Trustee
had itself authenticated such Securities.

SECTION 6.13 PREFERENTIAL COLLECTION OF CLAIMS AGAINST COMPANY.

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

SECTION 6.14 APPOINTMENT OF AUTHENTICATING AGENT.

                  The Trustee may appoint an Authenticating Agent or Agents with
respect to one or more series of Securities which shall be authorized to act on
behalf of the Trustee to authenticate Securities of such series issued upon
original issue and upon exchange, registration of transfer or partial redemption
thereof or pursuant to Section 3.6, and Securities so authenticated shall be
entitled to the benefits of this Indenture and shall be valid and obligatory for
all purposes as if authenticated by the Trustee hereunder. Wherever reference is
made in this Indenture to the authentication and delivery of Securities by the
Trustee or the Trustee's certificate of authentication, such reference shall be
deemed to include authentication and delivery on behalf of the Trustee by an
Authenticating Agent and a certificate of authentication executed on behalf of
the Trustee by an Authenticating Agent. Each Authenticating Agent shall be
acceptable to the Company and shall at all times be a corporation organized and
doing business under the laws of the United States of America, any State thereof
or the District of Columbia, authorized under such laws to act as Authenticating
Agent, having (or if the Authenticating Agent is a member of a bank holding
company system, its bank holding company has) a combined capital and surplus of
not less than $50,000,000 and subject to supervision or examination by Federal
or State authority. If such Authenticating Agent publishes reports of condition
at least annually, pursuant to law or to the requirements of said supervising or
examining authority, then for the purposes of this Section, the combined capital
and surplus of such Authenticating Agent shall be deemed to be its combined
capital and surplus as set forth in its most recent report of condition so
published. If at any time an Authenticating Agent shall cease to be eligible in
accordance with the provisions of this Section, such Authenticating Agent shall
resign immediately in the manner and with the effect specified in this Section.



                                       49
<PAGE>   57

                  Any corporation into which an Authenticating Agent may be
merged or converted or with which it may be consolidated, or any corporation
resulting from any merger, conversion or consolidation to which such
Authenticating Agent shall be a party, or any corporation succeeding to the
corporate agency or corporate trust business of an Authenticating Agent, shall
continue to be an Authenticating Agent, provided such corporation shall be
otherwise eligible under this Section, without the execution or filing of any
paper or any further act on the part of the Trustee or the Authenticating Agent.

                  An Authenticating Agent may resign at any time by giving
written notice thereof to the Trustee and to the Company. The Trustee may at any
time terminate the agency of an Authenticating Agent by giving written notice
thereof to such Authenticating Agent and to the Company. Upon receiving such a
notice of resignation or upon such a termination, or in case at any time such
Authenticating Agent shall cease to be eligible in accordance with the
provisions of this Section, the Trustee may appoint a successor Authenticating
Agent which shall be acceptable to the Company and shall give notice of such
appointment in the manner provided in Section 1.6 to all Holders of Securities
of the series with respect to which such Authenticating Agent will serve. Any
successor Authenticating Agent upon acceptance of its appointment hereunder
shall become vested with all the rights, powers and duties of its predecessor
hereunder, with like effect as if originally named as an Authenticating Agent.
No successor Authenticating Agent shall be appointed unless eligible under the
provisions of this Section.

                  The Trustee agrees to pay to each Authenticating Agent from
time to time reasonable compensation for its services under this Section, and
the Trustee shall be entitled to be reimbursed for such payments, subject to the
provisions of Section 6.7.

                  If an appointment with respect to one or more series is made
pursuant to this Section 6.12, the Securities of such series may have endorsed
thereon, in addition to the Trustee's certificate of authentication, an
alternative certificate of authentication in the following form:

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

                                       [                     ],
                                        ---------------------
                                       as Trustee

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

                                       By:
                                          -----------------------
                                          Authorized Officer



                                       50
<PAGE>   58

                                   ARTICLE VII

                HOLDERS' LISTS AND REPORTS BY TRUSTEE AND COMPANY

SECTION 7.1 COMPANY TO FURNISH TRUSTEE NAMES AND ADDRESSES OF HOLDERS.

                  The Company will furnish or cause to be furnished to the
Trustee:

                           (1) semi-annually, not later than 15 days after the
         Regular Record Date, a list, in such form as the Trustee may reasonably
         require, of the names and addresses of the Holders of Securities of
         each series as of such Regular Record Date, as the case may be; and

                           (2) at such other times as the Trustee may request in
         writing, within 30 days after the receipt by the Company of any such
         request, a list of similar form and content as of a date not more than
         15 days prior to the time such list is furnished; provided that no such
         list need be furnished by the Company to the Trustee so long as the
         Trustee is acting as Security Registrar.

SECTION 7.2 PRESERVATION OF INFORMATION; COMMUNICATIONS TO HOLDERS.

                  The Trustee shall preserve, in as current a form as is
reasonably practicable, the names and addresses of Holders contained in the most
recent list furnished to the Trustee as provided in Section 7.1 and the names
and addresses of Holders received by the Trustee in its capacity as Security
Registrar. The Trustee may destroy any list furnished to it as provided in
Section 7.1 upon receipt of a new list so furnished.

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

                  Every Holder of Securities, by receiving and holding the same,
agrees with the Company and the Trustee that neither the Company nor the Trustee
nor any agent of either of them shall be held accountable by reason of any
disclosure of



                                       51
<PAGE>   59

information as to names and addresses of Holders made pursuant to the Trust
Indenture Act.

SECTION 7.3 REPORTS BY TRUSTEE.

                  The Trustee shall transmit to Holders such reports concerning
the Trustee and its actions under this Indenture as may be required pursuant to
the Trust Indenture Act at the times and in the manner provided pursuant
thereto.

                  Reports so required to be transmitted at stated intervals of
not more than 12 months shall be transmitted no later than July 1 in each
calendar year, commencing with the first July 1 after the first issuance of
Securities pursuant to this Indenture.

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

SECTION 7.4 REPORTS BY COMPANY.

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


                                  ARTICLE VIII

              CONSOLIDATION, MERGER, CONVEYANCE, TRANSFER OR LEASE

SECTION 8.1 COMPANY MAY CONSOLIDATE, ETC., ONLY ON CERTAIN TERMS.

                  The Company shall not consolidate with or merge into any other
Person (in a transaction in which the Company is not the surviving corporation)
or convey, transfer or lease its properties and assets substantially as an
entirety to any Person, unless:



                                       52
<PAGE>   60

                           (1) in case the Company shall consolidate with or
         merge into another Person (in a transaction in which the Company is not
         the surviving corporation) or convey, transfer or lease its properties
         and assets substantially as an entirety to any Person, the Person
         formed by such consolidation or into which the Company is merged or the
         Person which acquires by conveyance or transfer, or which leases, the
         properties and assets of the Company substantially as an entirety shall
         be a corporation, limited liability company, partnership or trust,
         shall be organized and validly existing under the laws of the United
         States of America, any State thereof or the District of Columbia and
         shall expressly assume, by an indenture supplemental hereto, executed
         and delivered to the Trustee, in form satisfactory to the Trustee, the
         due and punctual payment of the principal of and any premium and
         interest on all the Securities and the performance or observance of
         every covenant of this Indenture on the part of the Company to be
         performed or observed and the conversion rights shall be provided for
         in accordance with Article 14, if applicable, or as otherwise specified
         pursuant to Section 3.1, by supplemental indenture satisfactory in form
         to the Trustee, executed and delivered to the Trustee, by the Person
         (if other than the Company) formed by such consolidation or into which
         the Company shall have been merged or by the Person which shall have
         acquired the Company's assets;

                           (2) immediately after giving effect to such
         transaction and treating any indebtedness which becomes an obligation
         of the Company or any Subsidiary as a result of such transaction as
         having been incurred by the Company or such Subsidiary at the time of
         such transaction, no Event of Default, and no event which, after notice
         or lapse of time or both, would become an Event of Default, shall have
         happened and be continuing; and

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



                                       53
<PAGE>   61

SECTION 8.2 SUCCESSOR SUBSTITUTED.

                  Upon any consolidation of the Company with, or merger of the
Company into, any other Person or any conveyance, transfer or lease of the
properties and assets of the Company substantially as an entirety in accordance
with Section 8.1, the successor Person formed by such consolidation or into
which the Company is merged or to which such conveyance, transfer or lease is
made shall succeed to, and be substituted for, and may exercise every right and
power of, the Company under this Indenture with the same effect as if such
successor Person had been named as the Company herein, and thereafter, except in
the case of a lease, the predecessor Person shall be relieved of all obligations
and covenants under this Indenture and the Securities.

                                   ARTICLE IX

                             SUPPLEMENTAL INDENTURES

SECTION 9.1 SUPPLEMENTAL INDENTURES WITHOUT CONSENT OF HOLDERS.

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

                           (1) to evidence the succession of another Person to
         the Company, or successive successions, and the assumption by any such
         successor of the covenants of the Company herein and in the Securities;
         or

                           (2) to add to the covenants of the Company for the
         benefit of the Holders of all or any series of Securities (and if such
         covenants are to be for the benefit of less than all series of
         Securities, stating that such covenants are expressly being included
         solely for the benefit of such series) or to surrender any right or
         power herein conferred upon the Company; or

                           (3) to add any additional Events of Default for the
         benefit of the Holders of all or any series of Securities (and if such
         additional Events of Default are to be for the benefit of less than all
         series of Securities, stating that such additional Events of Default
         are expressly being included solely for the benefit of such series); or



                                       54
<PAGE>   62

                           (4) to add to or change any of the provisions of this
         Indenture to such extent as shall be necessary to permit or facilitate
         the issuance of Securities in bearer form, registrable or not
         registrable as to principal, and with or without interest coupons, or
         to permit or facilitate the issuance of Securities in uncertificated
         form; or

                           (5) to add to, change or eliminate any of the
         provisions of this Indenture in respect of one or more series of
         Securities, provided that any such addition, change or elimination (A)
         shall neither (i) apply to any Security of any series created prior to
         the execution of such supplemental indenture and entitled to the
         benefit of such provision nor (ii) modify the rights of the Holder of
         any such Security with respect to such provision or (B) shall become
         effective only when there is no such Security Outstanding; or

                           (6) to secure the Securities; or

                           (7) to establish the form or terms of Securities of
         any series as permitted by Sections 2.1 and 3.1; or

                           (8) 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, pursuant to the requirements of Section 6.11; or

                           (9) to make provision with respect to the conversion
         rights of Holders pursuant to the requirements of Article 14, including
         providing for the conversion of the securities into any security (other
         than the Common Stock of the Company) or property of the Company; or

                           (10) to cure any ambiguity, to correct or supplement
         any provision herein which may be defective or inconsistent with any
         other provision herein, or to make any other provisions with respect to
         matters or questions arising under this Indenture, provided that such
         action pursuant to this Clause (10) shall not adversely affect the
         interests of the Holders of Securities of any series in any material
         respect; or

                           (11) to supplement any of the provisions of the
         Indenture to such extent as shall be necessary to permit or facilitate
         the



                                       55
<PAGE>   63

         defeasance and discharge of any series of Securities pursuant to
         Articles Four and Thirteen, provided that any such action shall not
         adversely affect the interests of the Holders of Securities of such
         series or any other series of Securities in any material respect.

SECTION 9.2 SUPPLEMENTAL INDENTURES WITH CONSENT OF HOLDERS.

                  With the consent of the Holders of a majority in principal
amount of the Outstanding Securities of each series affected by such
supplemental indenture, by Act of said Holders delivered to the Company and the
Trustee, the Company, when authorized by a Board Resolution, and the Trustee may
enter into an indenture or indentures supplemental hereto for the purpose of
adding any provisions to or changing in any manner or eliminating any of the
provisions of this Indenture or of modifying in any manner the rights of the
Holders of Securities of such series under this Indenture; provided, however,
that no such supplemental indenture shall, without the consent of the Holder of
each Outstanding Security affected thereby,

                           (1) change the Stated Maturity of the principal of,
         or any installment of principal of or interest on, any Security, or
         reduce the principal amount thereof or the rate of interest thereon or
         any premium payable upon the redemption thereof, or reduce the amount
         of the principal of an Original Issue Discount Security or any other
         Security which would be due and payable upon a declaration of
         acceleration of the Maturity thereof pursuant to Section 5.2, or change
         any Place of Payment where, or the coin or currency in which, any
         Security or any premium or interest thereon is payable, or impair the
         right to institute suit for the enforcement of any such payment on or
         after the Stated Maturity thereof (or, in the case of redemption, on or
         after the Redemption Date), or

                           (2) reduce the percentage in principal amount of the
         Outstanding Securities of any series, the consent of whose Holders is
         required for any such supplemental indenture, or the consent of whose
         Holders is required for any waiver (of compliance with certain
         provisions of this Indenture or certain defaults hereunder and their
         consequences) provided for in this Indenture, or

                           (3) modify any of the provisions of this Section,
         Section 5.13 or Section 10.06, except to increase any such percentage
         or to provide that certain other provisions of this Indenture cannot be
         modified or waived without the consent of the Holder of each
         Outstanding Security affected thereby; provided, however, that this
         clause shall not be deemed to require the consent of any Holder with



                                       56
<PAGE>   64

         respect to changes in the references to "the Trustee" and concomitant
         changes in this Section and Section 10.6, or the deletion of this
         proviso, in accordance with the requirements of Sections 6.11 and
         9.1(8), or

                           (4) if applicable, make any change that adversely
         affects the right to convert any security as provided in Article 14 or
         pursuant to Section 3.1 (except as permitted by Section 9.1(9)) or
         decrease the conversion rate or increase the conversion price of any
         such security. A supplemental indenture which changes or eliminates any
         covenant or other provision of this Indenture which has expressly been
         included solely for the benefit of one or more particular series of
         Securities, or which modifies the rights of the Holders of Securities
         of such series with respect to such covenant or other provision, shall
         be deemed not to affect the rights under this Indenture of the Holders
         of Securities of any other series.

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

SECTION 9.3 EXECUTION OF SUPPLEMENTAL INDENTURES.

                  In executing, or accepting the additional trusts created by,
any supplemental indenture permitted by this Article or the modifications
thereby of the trusts created by this Indenture, the Trustee shall be entitled
to receive, and (subject to Sections 6.1 and 6.3) shall be fully protected in
relying upon, an Opinion of Counsel stating that the execution of such
supplemental indenture is authorized or permitted by this Indenture. The Trustee
may, but shall not be obligated to, enter into any such supplemental indenture
which affects the Trustee's own rights, duties or immunities under this
Indenture or otherwise.

SECTION 9.4 EFFECT OF SUPPLEMENTAL INDENTURES.

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



                                       57
<PAGE>   65

SECTION 9.5 CONFORMITY WITH TRUST INDENTURE ACT.

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

SECTION 9.6 REFERENCE IN SECURITIES TO SUPPLEMENTAL INDENTURES.

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


                                    ARTICLE X

                                    COVENANTS

SECTION 10.1 PAYMENT OF PRINCIPAL, PREMIUM AND INTEREST.

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

SECTION 10.2 MAINTENANCE OF OFFICE OR AGENCY.

                  The Company will maintain in each Place of Payment for any
series of Securities an office or agency where Securities of that series may be
presented or surrendered for payment, where Securities of that series may be
surrendered for registration of transfer or exchange, where Securities of that
series may be surrendered for conversion and where notices and demands to or
upon the Company in respect of the Securities of that series and this Indenture
may be served. The Company will give prompt written notice to the Trustee of the
location, and any change in the location, of such office or agency. If at any
time the Company shall fail to maintain any such required office or agency or
shall fail to furnish the Trustee with the address thereof, such presentations,
surrenders, notices and demands may be made or served at the Corporate Trust
Office of the Trustee, and the Company hereby appoints the Trustee as its agent
to receive all such presentations, surrenders, notices and demands. Unless
otherwise provided in a supplemental indenture or pursuant to Section 3.1
hereof, the



                                       58
<PAGE>   66

Place of Payment for any series of Securities shall be the Corporate Trust
Office of the Trustee.

                  The Company may also from time to time designate one or more
other offices or agencies where the Securities of one or more series may be
presented or surrendered for any or all such purposes and may from time to time
rescind such designations; provided, however, that no such designation or
rescission shall in any manner relieve the Company of its obligation to maintain
an office or agency in each Place of Payment 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 location of any such
other office or agency.

SECTION 10.3 MONEY FOR SECURITIES PAYMENTS TO BE HELD IN TRUST.

                  If the Company shall at any time act as its own Paying Agent
with respect to any series of Securities, it will, on or before each due date of
the principal of or any premium or interest on any of the Securities of that
series, segregate and hold in trust for the benefit of the Persons entitled
thereto a sum sufficient to pay the principal and any premium and interest so
becoming due until such sums shall be paid to such Persons or otherwise disposed
of as herein provided and will promptly notify the Trustee of its action or
failure so to act.

                  Whenever the Company shall have one or more Paying Agents for
any series of Securities, it will, on or prior to each due date of the principal
of or any premium or interest on any Securities of that series, deposit with a
Paying Agent a sum sufficient to pay such amount, such sum to be held as
provided by the Trust Indenture Act, and (unless such Paying Agent is the
Trustee) the Company will promptly notify the Trustee of its action or failure
so to act.

                  The Company will cause each Paying Agent for any series of
Securities other than the Trustee to execute and deliver to the Trustee an
instrument in which such Paying Agent shall agree with the Trustee, subject to
the provisions of this Section, that such Paying Agent will (1) comply with the
provisions of the Trust Indenture Act applicable to it as a Paying Agent and (2)
during the continuance of any default by the Company (or any other obligor upon
the Securities of that series) in the making of any payment in respect of the
Securities of that series, upon the written request of the Trustee, forthwith
pay to the Trustee all sums held in trust by such Paying Agent for payment in
respect of the Securities of that series.

                  The Company may at any time, for the purpose of obtaining the
satisfaction and discharge of this Indenture or for any other purpose, pay, or
by



                                       59
<PAGE>   67

Company Order direct any Paying Agent to pay, to the Trustee all sums held in
trust by the Company or such Paying Agent, such sums to be held by the Trustee
upon the same trusts as those upon which such sums were held by the Company or
such Paying Agent; and, upon such payment by any Paying Agent to the Trustee,
such Paying Agent shall be released from all further liability with respect to
such money.

                  Any money deposited with the Trustee or any Paying Agent, or
then held by the Company, in trust for the payment of the principal of or any
premium or interest on any Security of any series and remaining unclaimed for a
period ending on the earlier of the date that is ten Business Days prior to the
date such money would escheat to the State or two years after such principal,
premium or interest has become due and payable shall be paid to the Company on
Company Request, or (if then held by the Company) shall be discharged from such
trust; and the Holder of such Security shall thereafter, as an unsecured general
creditor, look only to the Company for payment thereof, and all liability of the
Trustee or such Paying Agent with respect to such trust money, and all liability
of the Company as trustee thereof, shall thereupon cease; provided, however,
that the Trustee or such Paying Agent, before being required to make any such
repayment, may at the expense of the Company cause to be published once, in a
newspaper published in the English language, customarily published on each
Business Day and of general circulation in each Place of Payment, notice that
such money remains unclaimed and that, after a date specified therein, which
shall not be less than 30 days from the date of such publication, any unclaimed
balance of such money then remaining will be repaid to the Company.

SECTION 10.4 STATEMENT BY OFFICERS AS TO DEFAULT.

                  The Company will deliver to the Trustee, within 120 days after
the end of each fiscal year of the Company ending after the date hereof, an
Officers' Certificate, stating whether or not to the best knowledge of the
signers thereof the Company is in default in the performance and observance of
any of the terms, provisions and conditions of this Indenture (without regard to
any period of grace or requirement of notice provided hereunder) and, if the
Company shall be in default, specifying all such defaults and the nature and
status thereof of which they may have knowledge. The fiscal year of the Company
currently ends on December 31; and the Company will give the Trustee prompt
written notice of any change of its fiscal year.

SECTION 10.5 EXISTENCE.

                  Subject to Article 8, the Company will do or cause to be done
all things necessary to preserve and keep in full force and effect its
existence.



                                       60
<PAGE>   68

SECTION 10.6 WAIVER OF CERTAIN COVENANTS.

                  Except as otherwise specified as contemplated by Section 3.1
for Securities of such series, the Company may, with respect to the Securities
of any series, omit in any particular instance to comply with any term,
provision or condition set forth in any covenant provided pursuant to Section
3.1(19) or 9.1(2) for the benefit of the Holders of such series if before the
time for such compliance the Holders of at least a majority in principal amount
of the Outstanding Securities of such series shall, by Act of such Holders,
either waive such compliance in such instance or generally waive compliance with
such term, provision or condition, but no such waiver shall extend to or affect
such term, provision or condition except to the extent so expressly waived, and,
until such waiver shall become effective, the obligations of the Company and the
duties of the Trustee in respect of any such term, provision or condition shall
remain in full force and effect.


                                   ARTICLE XI

                            REDEMPTION OF SECURITIES

SECTION 11.1 APPLICABILITY OF ARTICLE.

                  Securities of any series which are redeemable before their
Stated Maturity shall be redeemable in accordance with their terms and (except
as otherwise specified as contemplated by Section 3.1 for such Securities) in
accordance with this Article.

SECTION 11.2 ELECTION TO REDEEM; NOTICE TO TRUSTEE.

                  The election of the Company to redeem any Securities shall be
evidenced by a Board Resolution or in another manner specified as contemplated
by Section 3.1 for such Securities. In case of any redemption at the election of
the Company of less than all the Securities of any series (including any such
redemption affecting only a single Security), the Company shall, at least 45
days prior to the Redemption Date fixed by the Company (unless a shorter notice
shall be satisfactory to the Trustee), notify the Trustee of such Redemption
Date, of the principal amount of Securities of such series to be redeemed and,
if applicable, of the tenor of the Securities to be redeemed. In the case of any
redemption of Securities prior to the expiration of any restriction on such
redemption provided in the terms of such Securities or elsewhere in this
Indenture, the Company shall furnish the Trustee with an Officers' Certificate
evidencing compliance with such restriction.



                                       61
<PAGE>   69

SECTION 11.3 SELECTION BY TRUSTEE OF SECURITIES TO BE REDEEMED.

                  If less than all the Securities of any series are to be
redeemed (unless all the Securities of such series and of a specified tenor are
to be redeemed or unless such redemption affects only a single Security), the
particular Securities to be redeemed shall be selected not more than 45 days
prior to the Redemption Date by the Trustee, from the Outstanding Securities of
such series not previously called for redemption, by lot, or in the Trustee's
discretion, on a pro-rata basis, provided that the unredeemed portion of the
principal amount of any Security shall be in an authorized denomination (which
shall not be less than the minimum authorized denomination) for such Security.
If less than all the Securities of such series and of a specified tenor are to
be redeemed (unless such redemption affects only a single Security), the
particular Securities to be redeemed shall be selected not more than 45 days
prior to the Redemption Date by the Trustee, from the Outstanding Securities of
such series and specified tenor not previously called for redemption in
accordance with the preceding sentence.

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

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

                  The provisions of the two preceding paragraphs shall not apply
with respect to any redemption affecting only a single Security, whether such
Security is to be redeemed in whole or in part. In the case of any such
redemption in part, the unredeemed portion of the principal amount of the
Security shall be in an authorized denomination (which shall not be less than
the minimum authorized denomination) for such Security.

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



                                       62
<PAGE>   70

SECTION 11.4   NOTICE OF REDEMPTION.

                  Notice of redemption shall be given by first-class mail,
postage prepaid, mailed not less than 30 nor more than 60 days prior to the
Redemption Date, unless a shorter period is specified in the Securities to be
redeemed, to each Holder of Securities to be redeemed, at its address appearing
in the Security Register.

                  All notices of redemption shall state:

                           (1) the Redemption Date,

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

                           (3) if less than all the Outstanding Securities of
         any series consisting of more than a single Security are to be
         redeemed, the identification (and, in the case of partial redemption of
         any such Securities, the principal amounts) of the particular
         Securities to be redeemed and, if less than all the Outstanding
         Securities of any series consisting of a single Security are to be
         redeemed, the principal amount of the particular Security to be
         redeemed,

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

                           (5) the place or places where each such Security is
         to be surrendered for payment of the Redemption Price,

                           (6) if applicable, the conversion price, the date on
         which the right to convert the principal of the Securities or the
         portions thereof to be redeemed will terminate, and the place or places
         where such Securities may be surrendered for conversion, and

                           (7) that the redemption is for a sinking fund, if
         such is the case.

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



                                       63
<PAGE>   71

SECTION 11.5 DEPOSIT OF REDEMPTION PRICE.

                  On or prior to any Redemption Date, the Company shall deposit
with the Trustee or with a Paying Agent (or, if the Company is acting as its own
Paying Agent, segregate and hold in trust as provided in Section 10.3) an amount
of money sufficient to pay the Redemption Price of, and (except if the
Redemption Date shall be an Interest Payment Date) accrued interest on, all the
Securities which are to be redeemed on that date.

                  If any Security called for redemption is converted, any money
deposited with the Trustee or with a Paying Agent or so segregated and held in
trust for the redemption of such Security shall (subject to the right of any
Holder of such Security to receive interest as provided in the last paragraph of
Section 3.7) be paid to the Company on Company Request, or if then held by the
Company, shall be discharged from such trust.

SECTION 11.6 SECURITIES PAYABLE ON REDEMPTION DATE.

                  Notice of redemption having been given as aforesaid, the
Securities so to be redeemed shall, on the Redemption Date, become due and
payable at the Redemption Price therein specified, and from and after such date
(unless the Company shall default in the payment of the Redemption Price and
accrued interest) such Securities shall cease to bear interest. Upon surrender
of any such Security for redemption in accordance with said notice, such
Security shall be paid by the Company at the Redemption Price, together with
accrued interest to the Redemption Date; provided, however, that, unless
otherwise specified as contemplated by Section 3.1, installments of interest
whose Stated Maturity is on or prior to the Redemption Date will be payable to
the Holders of such Securities, or one or more Predecessor Securities,
registered as such at the close of business on the relevant Record Dates
according to their terms and the provisions of Section 3.7.

                  If any Security called for redemption shall not be so paid
upon surrender thereof for redemption, the principal and any premium shall,
until paid, bear interest from the Redemption Date at the rate prescribed
therefor in the Security.

SECTION 11.7 SECURITIES REDEEMED IN PART.

                  Any Security which is to be redeemed only in part shall be
surrendered at a Place of Payment therefor (with, if the Company or the Trustee
so requires, due endorsement by, or a written instrument of transfer in form
satisfactory to the Company and the Trustee duly executed by, the Holder thereof
or its attorney duly authorized in writing), and the Company shall execute, and
the Trustee shall authenticate and deliver to the Holder of such Security
without service charge, a new Security or Securities of the same series and of
like tenor, of any authorized denomination as requested by such



                                       64
<PAGE>   72

Holder, in aggregate principal amount equal to and in exchange for the
unredeemed portion of the principal of the Security so surrendered.

                                   ARTICLE XII

                                  SINKING FUNDS

SECTION 12.1 APPLICABILITY OF ARTICLE.

                  The provisions of this Article shall be applicable to any
sinking fund for the retirement of Securities of any series except as otherwise
specified as contemplated by Section 3.1 for such Securities.

                  The minimum amount of any sinking fund payment provided for by
the terms of any Securities is herein referred to as a "mandatory sinking fund
payment," and any payment in excess of such minimum amount provided for by the
terms of such Securities is herein referred to as an "optional sinking fund
payment." If provided for by the terms of any Securities, the cash amount of any
sinking fund payment may be subject to reduction as provided in Section 12.2.
Each sinking fund payment shall be applied to the redemption of Securities as
provided for by the terms of such Securities.

SECTION 12.2 SATISFACTION OF SINKING FUND PAYMENTS WITH SECURITIES.

                  The Company (1) may deliver Outstanding Securities of a series
(other than any previously called for redemption) and (2) may apply as a credit
Securities of a series which have been redeemed either at the election of the
Company pursuant to the terms of such Securities or through the application of
permitted optional sinking fund payments pursuant to the terms of such
Securities, in each case in satisfaction of all or any part of any sinking fund
payment with respect to any Securities of such series required to be made
pursuant to the terms of such Securities as and to the extent provided for by
the terms of such Securities; provided that the Securities to be so credited
have not been previously so credited. The Securities to be so credited shall be
received and credited for such purpose by the Trustee at the Redemption Price,
as specified in the Securities so to be redeemed, for redemption through
operation of the sinking fund and the amount of such sinking fund payment shall
be reduced accordingly.



                                       65
<PAGE>   73

SECTION 12.3 REDEMPTION OF SECURITIES FOR SINKING FUND.

                  Not less than 60 days prior to each sinking fund payment date
for any Securities, the Company will deliver to the Trustee an Officers'
Certificate specifying the amount of the next ensuing sinking fund payment for
such Securities pursuant to the terms of such Securities, 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 Securities pursuant to
Section 12.2 and will also deliver to the Trustee any Securities to be so
delivered. Not less than 30 days prior to 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 11.3 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 11.4. Such notice having been duly given, the
redemption of such Securities shall be made upon the terms and in the manner
stated in Sections 11.6 and 11.7.


                                  ARTICLE XIII

                       DEFEASANCE AND COVENANT DEFEASANCE

SECTION 13.1 COMPANY'S OPTION TO EFFECT DEFEASANCE OR COVENANT DEFEASANCE.

                  The Company may elect, at its option at any time, to have
Section 13.2 or Section 13.3 applied to any Securities or any series of
Securities, as the case may be, designated pursuant to Section 3.1 as being
defeasible pursuant to such Section 13.2 or 13.3, in accordance with any
applicable requirements provided pursuant to Section 3.1 and upon compliance
with the conditions set forth below in this Article. Any such election shall be
evidenced by a Board Resolution or in another manner specified as contemplated
by Section 3.1 for such Securities.

SECTION 13.2 DEFEASANCE AND DISCHARGE.

                  Upon the Company's exercise of its option (if any) to have
this Section applied to any Securities or any series of Securities, as the case
may be, the Company shall be deemed to have been discharged from its obligations
with respect to such Securities as provided in this Section on and after the
date the conditions set forth in Section 13.4 are satisfied (hereinafter called
"Defeasance"). For this purpose, such Defeasance means that the Company shall be
deemed to have paid and discharged the entire indebtedness represented by such
Securities and to have satisfied all its other obligations under such Securities
and this Indenture insofar as such Securities are



                                       66
<PAGE>   74

concerned (and the Trustee, at the expense of the Company, shall execute proper
instruments acknowledging the same), subject to the following which shall
survive until otherwise terminated or discharged hereunder:

                           (1) the rights of Holders of such Securities to
                  receive, solely from the trust fund described in Section 13.4
                  and as more fully set forth in such Section, payments in
                  respect of the principal of and any premium and interest on
                  such Securities when payments are due;

                           (2) the Company's obligations with respect to such
                  Securities under Sections 3.4, 3.5, 3.6, 10.2 and 10.3, and,
                  if applicable, Article 14;

                           (3) the rights, powers, trusts, duties and immunities
                  of the Trustee hereunder; and

                           (4) this Article.

                  Subject to compliance with this Article, the Company may
exercise its option (if any) to have this Section applied to any Securities
notwithstanding the prior exercise of its option (if any) to have Section 13.3
applied to such Securities.

SECTION 13.3 COVENANT DEFEASANCE.

                  Upon the Company's exercise of its option (if any) to have
this Section applied to any Securities or any series of Securities, as the case
may be:

                           (1) the Company shall be released from its
         obligations under any covenants provided pursuant to Section 3.1(19) or
         9.1(2) or for the benefit of the Holders of such Securities; and

                           (2) the occurrence of any event specified in any
         covenants provided pursuant to Section 3.1(19) or 9.1(2) shall be
         deemed not to be or result in an Event of Default,

in each case with respect to such Securities as provided in this Section on and
after the date the conditions set forth in Section 13.4 are satisfied
(hereinafter called "Covenant Defeasance"). For this purpose, such Covenant
Defeasance means that, with respect to such Securities, the Company may omit to
comply with and shall have no liability in respect of any term, condition or
limitation set forth in any such specified Section (to the extent so specified
in the case of Section 5.1(4)), whether directly or indirectly by reason of any



                                       67
<PAGE>   75

reference elsewhere herein to any such Section or by reason of any reference in
any such Section to any other provision herein or in any other document, but the
remainder of this Indenture and such Securities shall be unaffected thereby.

SECTION 13.4 CONDITIONS TO DEFEASANCE OR COVENANT DEFEASANCE.

                  The following shall be the conditions to the application of
Section 13.2 or Section 13.3 to any Securities or any series of Securities, as
the case may be:

                           (1) The Company shall irrevocably have deposited or
         caused to be deposited with the Trustee (or another trustee which
         satisfies the requirements contemplated by Section 6.9 and agrees to
         comply with the provisions of this Article applicable to it) as trust
         funds in trust for the purpose of making the following payments,
         specifically pledged as security for, and dedicated solely to, the
         benefits of the Holders of such Securities, (A) money in an amount, or
         (B) U.S. Government Obligations which through the scheduled payment of
         principal and interest in respect thereof in accordance with their
         terms will provide, not later than one day before the due date of any
         payment, money in an amount, or (C) a combination thereof, in each case
         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, and which shall
         be applied by the Trustee (or any such other qualifying trustee) to pay
         and discharge, the principal of and any premium and interest on such
         Securities on the respective Stated Maturities, in accordance with the
         terms of this Indenture and such Securities. As used herein, "U.S.
         Government Obligation" means (x) any security which is (i) a direct
         obligation of the United States of America for the payment of which the
         full faith and credit of the United States of America is pledged or
         (ii) an obligation of a Person controlled or supervised by and acting
         as an agency or instrumentality of the United States of America the
         payment of which is unconditionally guaranteed as a full faith and
         credit obligation by the United States of America, which, in either
         case (i) or (ii), is not callable or redeemable at the option of the
         issuer thereof, and (y) any depositary receipt issued by a bank (as
         defined in Section 3(a)(2) of the Securities Act) as custodian with
         respect to any U.S. Government Obligation which is specified in Clause
         (x) above and held by such bank for the account of the holder of such
         depositary receipt, or with respect to any specific payment of
         principal of or interest on any U.S. Government Obligation which is so
         specified and held, provided that



                                       68
<PAGE>   76

         (except as required by law) such custodian is not authorized to make
         any deduction from the amount payable to the holder of such depositary
         receipt from any amount received by the custodian in respect of the
         U.S. Government Obligation or the specific payment of principal or
         interest evidenced by such depositary receipt.

                           (2) In the event of an election to have Section 13.2
         apply to any Securities or any series of Securities, as the case may
         be, the Company shall have delivered to the Trustee an Opinion of
         Counsel stating that (A) the Company has received from, or there has
         been published by, the Internal Revenue Service a ruling or (B) since
         the date of this instrument, there has been a change in the applicable
         Federal income tax law, in either case (A) or (B) to the effect that,
         and based thereon such opinion shall confirm that, the Holders of such
         Securities will not recognize gain or loss for Federal income tax
         purposes as a result of the deposit, Defeasance and discharge to be
         effected with respect to such Securities and will be subject to Federal
         income tax on the same amount, in the same manner and at the same times
         as would be the case if such deposit, Defeasance and discharge were not
         to occur.

                           (3) In the event of an election to have Section 13.3
         apply to any Securities or any series of Securities, as the case may
         be, the Company shall have delivered to the Trustee an Opinion of
         Counsel to the effect that the Holders of such Securities will not
         recognize gain or loss for Federal income tax purposes as a result of
         the deposit and Covenant Defeasance to be effected with respect to such
         Securities and will be subject to Federal income tax on the same
         amount, in the same manner and at the same times as would be the case
         if such deposit and Covenant Defeasance were not to occur.

                           (4) The Company shall have delivered to the Trustee
         an Officers' Certificate to the effect that neither such Securities nor
         any other Securities of the same series, if then listed on any
         securities exchange, will be delisted as a result of such deposit.

                           (5) No event which is, or after notice or lapse of
         time or both would become, an Event of Default with respect to such
         Securities or any other Securities shall have occurred and be
         continuing at the time of such deposit or, with regard to any such
         event specified in Sections 5.1(5) and (6), at any time on or prior to
         the 90th day after the date of such deposit (it being understood that
         this condition shall not be deemed satisfied until after such 90th
         day).



                                       69
<PAGE>   77

                           (6) Such Defeasance or Covenant Defeasance shall not
         cause the Trustee to have a conflicting interest within the meaning of
         the Trust Indenture Act (assuming all Securities are in default within
         the meaning of such Act).

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

                           (8) Such Defeasance or Covenant Defeasance shall not
         result in the trust arising from such deposit constituting an
         investment company within the meaning of the Investment Company Act
         unless such trust shall be registered under such Act or exempt from
         registration thereunder.

                           (9) The Company shall have delivered to the Trustee
         an Officers' Certificate and an Opinion of Counsel, each stating that
         all conditions precedent with respect to such Defeasance or Covenant
         Defeasance have been complied with.

SECTION 13.5 DEPOSITED MONEY AND U.S. GOVERNMENT OBLIGATIONS TO BE HELD IN
             TRUST; MISCELLANEOUS PROVISIONS.

                  Subject to the provisions of the last paragraph of Section
10.3, all money and U.S. Government Obligations (including the proceeds thereof)
deposited with the Trustee or other qualifying trustee (solely for purposes of
this Section and Section 13.6, the Trustee and any such other trustee are
referred to collectively as the "Trustee") pursuant to Section 13.4 in respect
of any Securities shall be held in trust and applied by the Trustee, in
accordance with the provisions of such Securities and this Indenture, to the
payment, either directly or through any such Paying Agent (including the Company
acting as its own Paying Agent) as the Trustee may determine, to the Holders of
such Securities, of all sums due and to become due thereon in respect of
principal and any premium and interest, but money so held in trust need not be
segregated from other funds except to the extent required by law.

                  The Company shall pay and indemnify the Trustee against any
tax, fee or other charge imposed on or assessed against the U.S. Government
Obligations deposited pursuant to Section 13.4 or the principal and interest
received in respect thereof other than any such tax, fee or other charge which
by law is for the account of the Holders of Outstanding Securities.



                                       70
<PAGE>   78

                  Anything in this Article to the contrary notwithstanding, the
Trustee shall deliver or pay to the Company from time to time upon Company
Request any money or U.S. Government Obligations held by it as provided in
Section 13.4 with respect to any Securities which, in the opinion of a
nationally recognized firm of independent public accountants expressed in a
written certification thereof delivered to the Trustee, are in excess of the
amount thereof which would then be required to be deposited to effect the
Defeasance or Covenant Defeasance, as the case may be, with respect to such
Securities.

SECTION 13.6 REINSTATEMENT.

                  If the Trustee or the Paying Agent is unable to apply any
money in accordance with this Article with respect to any Securities by reason
of any order or judgment of any court or governmental authority enjoining,
restraining or otherwise prohibiting such application, then the obligations
under this Indenture and such Securities from which the Company has been
discharged or released pursuant to Section 13.2 or 13.3 shall be revived and
reinstated as though no deposit had occurred pursuant to this Article with
respect to such Securities, until such time as the Trustee or Paying Agent is
permitted to apply all money held in trust pursuant to Section 13.5 with respect
to such Securities in accordance with this Article; provided, however, that if
the Company makes any payment of principal of or any premium or interest on any
such Security following such reinstatement of its obligations, the Company shall
be subrogated to the rights (if any) of the Holders of such Securities to
receive such payment from the money so held in trust.


                                   ARTICLE XIV

                            CONVERSION OF SECURITIES

SECTION 14.1 APPLICABILITY OF ARTICLE.

                  The provisions of this Article shall be applicable to the
Securities of any series which are convertible into shares of Common Stock of
the Company, and the issuance of such shares of Common Stock upon the conversion
of such Securities, except as otherwise specified as contemplated by Section 3.1
for the Securities of such series.

SECTION 14.2 EXERCISE OF CONVERSION PRIVILEGE.

                  In order to exercise a conversion privilege, the Holder of a
Security of a series with such a privilege shall surrender such Security to the
Company at the office or agency maintained for that purpose pursuant to Section
10.2, accompanied by a duly



                                       71
<PAGE>   79

executed conversion notice to the Company substantially in the form set forth in
Section 2.6 stating that the Holder elects to convert such Security or a
specified portion thereof. Such notice shall also state, if different from the
name and address of such Holder, the name or names (with address) in which the
certificate or certificates for shares of Common Stock which shall be issuable
on such conversion shall be issued. Securities surrendered for conversion shall
(if so required by the Company or the Trustee) be duly endorsed by or
accompanied by instruments of transfer in forms satisfactory to the Company and
the Trustee duly executed by the registered Holder or its attorney duly
authorized in writing; and Securities so surrendered for conversion (in whole or
in part) during the period from the close of business on any Regular Record Date
to the opening of business on the next succeeding Interest Payment Date
(excluding Securities or portions thereof called for redemption during the
period beginning at the close of business on a Regular Record Date and ending at
the opening of business on the first Business Day after the next succeeding
Interest Payment Date, or if such Interest Payment Date is not a Business Day,
the second such Business Day) shall also be accompanied by payment in funds
acceptable to the Company of an amount equal to the interest payable on such
Interest Payment Date on the principal amount of such Security then being
converted, and such interest shall be payable to such registered Holder
notwithstanding the conversion of such Security, subject to the provisions of
Section 3.7 relating to the payment of Defaulted Interest by the Company. As
promptly as practicable after the receipt of such notice and of any payment
required pursuant to a Board Resolution and, subject to Section 3.3, set forth,
or determined in the manner provided, in an Officers' Certificate, or
established in one or more indentures supplemental hereto setting forth the
terms of such series of Security, and the surrender of such Security in
accordance with such reasonable regulations as the Company may prescribe, the
Company shall issue and shall deliver, at the office or agency at which such
Security is surrendered, to such Holder or on its written order, a certificate
or certificates for the number of full shares of Common Stock issuable upon the
conversion of such Security (or specified portion thereof), in accordance with
the provisions of such Board Resolution, Officers' Certificate or supplemental
indenture, and cash as provided therein in respect of any fractional share of
such Common Stock otherwise issuable upon such conversion. Such conversion shall
be deemed to have been effected immediately prior to the close of business on
the date on which such notice and such payment, if required, shall have been
received in proper order for conversion by the Company and such Security shall
have been surrendered as aforesaid (unless such Holder shall have so surrendered
such Security and shall have instructed the Company to effect the conversion on
a particular date following such surrender and such Holder shall be entitled to
convert such Security on such date, in which case such conversion shall be
deemed to be effected immediately prior to the close of business on such date)
and at such time the rights of the Holder of such Security as such Security
Holder shall cease and the person or persons in whose name or names any
certificate or certificates for shares of Common Stock of the Company shall be
issuable upon such



                                       72
<PAGE>   80

conversion shall be deemed to have become the Holder or Holders of record of the
shares represented thereby. Except as set forth above and subject to the final
paragraph of Section 3.7, no payment or adjustment shall be made upon any
conversion on account of any interest accrued on the Securities (or any part
thereof) surrendered for conversion or on account of any dividends on the Common
Stock of the Company issued upon such conversion. In the case of any Security
which is converted in part only, upon such conversion the Company shall execute
and the Trustee shall authenticate and deliver to or on the order of the Holder
thereof, at the expense of the Company, a new Security or Securities of the same
series, of authorized denominations, in aggregate principal amount equal to the
unconverted portion of such Security.

SECTION 14.3 NO FRACTIONAL SHARES.

                  No fractional share of Common Stock of the Company shall be
issued upon conversions of Securities of any series. If more than one Security
shall be surrendered for conversion at one time by the same Holder, the number
of full shares which shall be issuable upon conversion shall be computed on the
basis of the aggregate principal amount of the Securities (or specified portions
thereof to the extent permitted hereby) so surrendered. If, except for the
provisions of this Section 14.3, any Holder of a Security or Securities would be
entitled to a fractional share of Common Stock of the Company upon the
conversion of such Security or Securities, or specified portions thereof, the
Company shall pay to such Holder an amount in cash equal to the current market
value of such fractional share computed, (i) if such Common Stock is listed or
admitted to unlisted trading privileges on a national securities exchange or
market, on the basis of the last reported sale price on such exchange or market
on the last trading day prior to the date of conversion upon which such a sale
shall have been effected, or (ii) if such Common Stock is not at the time so
listed or admitted to unlisted trading privileges on a national securities
exchange or market, on the basis of the average of the bid and asked prices of
such Common Stock in the over-the-counter market, on the last trading day prior
to the date of conversion, as reported by the National Quotation Bureau,
Incorporated or similar organization if the National Quotation Bureau,
Incorporated is no longer reporting such information, or if not so available,
the fair market price as determined by the Board of Directors. For purposes of
this Section, "trading day" shall mean each Monday, Tuesday, Wednesday, Thursday
and Friday other than any day on which the Common Stock is not traded on the New
York Stock Exchange, or if the Common Stock is not traded on the New York Stock
Exchange, on the principal exchange or market on which the Common Stock is
traded or quoted.

SECTION 14.4 ADJUSTMENT OF CONVERSION PRICE.

                  The conversion price of Securities of any series that is
convertible into Common Stock of the Company shall be adjusted for any stock
dividends, stock splits,



                                       73
<PAGE>   81

reclassifications, combinations or similar transactions in accordance with the
terms of the supplemental indenture or Board Resolutions setting forth the terms
of the Securities of such series. Whenever the conversion price is adjusted, the
Company shall compute the adjusted conversion price in accordance with terms of
the applicable Board Resolution or supplemental indenture and shall prepare an
Officers' Certificate setting forth the adjusted conversion price and showing in
reasonable detail the facts upon which such adjustment is based, and such
certificate shall forthwith be filed at each office or agency maintained for the
purpose of conversion of Securities pursuant to Section 10.2 and, if different,
with the Trustee. The Company shall forthwith cause a notice setting forth the
adjusted conversion price to be mailed, first class postage prepaid, to each
Holder of Securities of such series at its address appearing on the Security
Register and to any conversion agent other than the Trustee.

SECTION 14.5 NOTICE OF CERTAIN CORPORATE ACTIONS.

                  In case:

                           (1) the Company shall declare a dividend (or any
         other distribution) on its Common Stock payable otherwise than in cash
         out of its retained earnings (other than a dividend for which approval
         of any shareholders of the Company is required) that would require an
         adjustment pursuant to Section 14.4; or

                           (2) the Company shall authorize the granting to all
         or substantially all of the holders of its Common Stock of rights,
         options or warrants to subscribe for or purchase any shares of capital
         stock of any class or of any other rights (other than any such grant
         for which approval of any shareholders of the Company is required); or

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

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

then the Company shall cause to be filed with the Trustee, and shall cause to be
mailed to all Holders at their last addresses as they shall appear in the
Security Register, at least 20 days (or 10 days in any case specified in Clause
(1) or (2) above) prior to the



                                       74
<PAGE>   82

applicable record date hereinafter specified, a notice stating (i) the date on
which a record is to be taken for the purpose of such dividend, distribution,
rights, options or warrants, or, if a record is not to be taken, the date as of
which the holders of Common Stock of Record to be entitled to such dividend,
distribution, rights, options or warrants are to be determined, or (ii) the date
on which such reclassification, consolidation, merger, share exchange, sale,
dissolution, liquidation or winding up is expected to become effective, and the
date as of which it is expected that holders of Common Stock of record shall be
entitled to exchange their shares of Common Stock for securities, cash or other
property deliverable upon such reclassification, consolidation, merger, share
exchange, sale, dissolution, liquidation or winding up. If at any time the
Trustee shall not be the conversion agent, a copy of such notice shall also
forthwith be filed by the Company with the Trustee.

SECTION 14.6 RESERVATION OF SHARES OF COMMON STOCK.

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

SECTION 14.7 PAYMENT OF CERTAIN TAXES UPON CONVERSION.

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

SECTION 14.8 NONASSESSABILITY.

                  The Company covenants that all shares of its Common Stock
which may be issued upon conversion of Securities will upon issue in accordance
with the terms hereof be duly and validly issued and fully paid and
nonassessable.



                                       75
<PAGE>   83

SECTION 14.9 PROVISION IN CASE OF CONSOLIDATION, MERGER OR SALE OF ASSETS.

                  In case of any consolidation or merger of the Company with or
into any other Person, any merger of another Person with or into the Company
(other than a merger which does not result in any reclassification, conversion,
exchange or cancellation of outstanding shares of Common Stock of the Company)
or any conveyance, sale, transfer or lease of all or substantially all of the
assets of the Company, the Person formed by such consolidation or resulting from
such merger or which acquires such assets, as the case may be, shall execute and
deliver to the Trustee a supplemental indenture providing that the Holder of
each Security of a series then Outstanding that is convertible into Common Stock
of the Company shall have the right thereafter (which right shall be the
exclusive conversion right thereafter available to said Holder), during the
period such Security shall be convertible, to convert such Security only into
the kind and amount of securities, cash and other property receivable upon such
consolidation, merger, conveyance, sale, transfer or lease by a holder of the
number of shares of Common Stock of the Company into which such Security might
have been converted immediately prior to such consolidation, merger, conveyance,
sale, transfer or lease, assuming such holder of Common Stock of the Company (i)
is not a Person with which the Company consolidated or merged with or into or
which merged into or with the Company or to which such conveyance, sale,
transfer or lease was made, as the case may be (a "Constituent Person"), or an
Affiliate of a Constituent Person and (ii) failed to exercise his rights of
election, if any, as to the kind or amount of securities, cash and other
property receivable upon such consolidation, merger, conveyance, sale, transfer
or lease (provided that if the kind or amount of securities, cash and other
property receivable upon such consolidation, merger, conveyance, sale, transfer,
or lease is not the same for each share of Common Stock of the Company held
immediately prior to such consolidation, merger, conveyance, sale, transfer or
lease by others than a Constituent Person or an Affiliate thereof and in respect
of which such rights of election shall not have been exercised ("Non-electing
Share"), then for the purpose of this Section 14.9 the kind and amount of
securities, cash and other property receivable upon such consolidation, merger,
conveyance, sale, transfer or lease by the holders of each Non-electing Share
shall be deemed to be the kind and amount so receivable per share by a plurality
of the Non-electing Shares). Such supplemental indenture shall provide for
adjustments which, for events subsequent to the effective date of such
supplemental indenture, shall be as nearly equivalent as may be practicable to
the adjustments provided for in this Article or in accordance with the terms of
the supplemental indenture or Board Resolutions setting forth the terms of such
adjustments. The above provisions of this Section 14.9 shall similarly apply to
successive consolidations, mergers, conveyances, sales, transfers or leases.
Notice of the execution of such a supplemental indenture shall be given by the
Company to the Holder of each Security of a series that is convertible into
Common Stock of the



                                       76
<PAGE>   84

Company as provided in Section 1.6 promptly upon such execution. Neither the
Trustee nor any conversion agent, if any, shall be under any responsibility to
determine the correctness of any provisions contained in any such supplemental
indenture relating either to the kind or amount of shares of stock or other
securities or property or cash receivable by Holders of Securities of a series
convertible into Common Stock of the Company upon the conversion of their
Securities after any such consolidation, merger, conveyance, transfer, sale or
lease or to any such adjustment, but may accept as conclusive evidence of the
correctness of any such provisions, and shall be protected in relying upon, an
Opinion of Counsel with respect thereto, which the Company shall cause to be
furnished to the Trustee upon request.

SECTION 14.10 DUTIES OF TRUSTEE REGARDING CONVERSION.

                  Neither the Trustee nor any conversion agent shall at any time
be under any duty or responsibility to any Holder of Securities of any series
that is convertible into Common Stock of the Company to determine whether any
facts exist which may require any adjustment of the conversion price, or with
respect to the nature or extent of any such adjustment when made, or with
respect to the method employed, whether herein or in any supplemental indenture,
any resolutions of the Board of Directors or written instrument executed by one
or more officers of the Company provided to be employed in making the same.
Neither the Trustee nor any conversion agent shall be accountable with respect
to the validity or value (or the kind or amount) of any shares of Common Stock
of the Company, or of any securities or property, which may at any time be
issued or delivered upon the conversion of any Securities and neither the
Trustee nor any conversion agent makes any representation with respect thereto.
Subject to the provisions of Section 6.1, neither the Trustee nor any conversion
agent shall be responsible for any failure of the Company to issue, transfer or
deliver any shares of its Common Stock or stock certificates or other securities
or property upon the surrender of any Security for the purpose of conversion or
to comply with any of the covenants of the Company contained in this Article 14
or in the applicable supplemental indenture, resolutions of the Board of
Directors or written instrument executed by one or more duly authorized officers
of the Company.

SECTION 14.11 REPAYMENT OF CERTAIN FUNDS UPON CONVERSION.

                  Any funds which at any time shall have been deposited by the
Company or on its behalf with the Trustee or any other paying agent for the
purpose of paying the principal of and any premium and interest on any of the
Securities (including, but not limited to, funds deposited for the sinking fund
referred to in Article 12 hereof and funds deposited pursuant to Article 13
hereof) and which shall not be required for such purposes because of the
conversion of such Securities as provided in this Article 14 shall after such
conversion be repaid to the Company by the Trustee upon the Company's written
request.



                                       77
<PAGE>   85

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

                                       WILLBROS GROUP, INC.


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



                                       ATTEST:

                                       [                     ],
                                        ---------------------
                                             as Trustee

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



                                       78