<PAGE>
 
                                                                     EXHIBIT 4.6

 
                          PLATINUM technology, inc.,

                                    ISSUER,

                                      AND

             AMERICAN NATIONAL BANK AND TRUST COMPANY OF CHICAGO,

                                  AS TRUSTEE,

                                   INDENTURE

                         Dated as of December 15, 1997


                              Up to $172,500,000


                 6.25% Convertible Subordinated Notes due 2002
<PAGE>
 
                             CROSS-REFERENCE TABLE


<TABLE>
<CAPTION>
  TIA                                             INDENTURE
SECTION                                           SECTION
-------                                           ---------
<S>                                               <C>
310 (a) (1)...................................... 7.10
    (a) (2)...................................... 7.10
    (a) (3)...................................... N.A.
    (a) (4)...................................... N.A.
    (a) (5)...................................... 7.10
    (b).......................................... 7.8; 7.10; 13.2
    (c).......................................... N.A.
311 (a).......................................... 7.11
    (b).......................................... 7.11
    (c).......................................... N.A.
312 (a).......................................... 2.5
    (b).......................................... 13.3
    (c).......................................... 13.3
313 (a).......................................... 7.6
    (b) (1)...................................... N.A.
    (b) (2)...................................... 7.6
    (c).......................................... 7.6; 13.2
    (d).......................................... 7.6
314 (a).......................................... 4.7; 13.2
    (b).......................................... N.A.
    (c) (1)...................................... 2.2; 7.2; 13.4
    (c) (2)...................................... 7.2; 13.4
    (c) (33)..................................... N.A.
    (d).......................................... N.A.
    (e).......................................... 13.5
    (f).......................................... N.A.
315 (a).......................................... 7.1(b)
    (b).......................................... 7.5; 13.2
    (c).......................................... 7.1(a)
    (d).......................................... 6.11; 7.1(b); 7.1(c); 7.2(c)
    (e).......................................... 6.13
316 (a) (last sentence).......................... 2.9
    (a) (1) (A).................................. 6.11
    (a) (1) (B).................................. 6.12
    (a) (2)...................................... N.A.
    (b).......................................... 6.12; 6.7
317 (a) (1)...................................... 6.3
    (a) (2)...................................... 6.4
    (b).......................................... 2.4
318 (a).......................................... 13.1
</TABLE>
------------ 
N.A. Means Not Applicable.
Note: This Cross-Reference Table shall not, for any purpose, be deemed to be a
part of the Indenture.
<PAGE>
 



                               TABLE OF CONTENTS

<TABLE>
<CAPTION>

                                                                       Page
                                                                       ----
<S>        <C>                                                         <C>

ARTICLE 1  DEFINITIONS AND INCORPORATION BY REFERENCE................... 1

   Section 1.1    Definitions........................................... 1
   Section 1.2    Incorporation By Reference of TIA..................... 9
   Section 1.3    Rules of Construction.................................10

ARTICLE 2  THE SECURITIES...............................................11

   Section 2.1    Form and Dating.......................................11
   Section 2.2    Execution and Authentication..........................11
   Section 2.3    Registrar, Paying Agent And Depositary................12
   Section 2.4    Paying Agent To Hold Assets In Trust..................12
   Section 2.5    Security Holder Lists.................................13
   Section 2.6    Transfer and Exchange; Restrictions on Transfer.......13
   Section 2.7    Replacement Securities................................19
   Section 2.8    Outstanding Securities................................20
   Section 2.9    Treasury Securities...................................20
   Section 2.10   Temporary Securities..................................21
   Section 2.11   Cancellation..........................................21
   Section 2.12   Defaulted Interest....................................21

ARTICLE 3  REDEMPTION...................................................22

   Section 3.1    Right of Redemption...................................22
   Section 3.2    Notices To Trustee....................................23
   Section 3.3    Selection of Securities To Be Redeemed................23
   Section 3.4    Notice of Redemption..................................23
   Section 3.5    Effect of Notice of Redemption........................24
   Section 3.6    Deposit of Redemption Price...........................25
   Section 3.7    Securities Redeemed in Part...........................25
   Section 3.8    Conversion Arrangement on Call for Redemption ........25

ARTICLE 4  COVENANTS....................................................26

   Section 4.1    Payment Of Securities.................................26
   Section 4.2    Maintenance Of Office Or Agency.......................27
   Section 4.3    Corporate Existence...................................27
   Section 4.4    Payment Of Taxes And Other Claims.....................27
   Section 4.5    Maintenance Of Properties And Insurance...............28
   Section 4.6    Compliance Certificate; Notice Of Default.............28
   Section 4.7    Reports...............................................29
   Section 4.8    Limitation On Status As Investment Company............29
   Section 4.9    Waiver Of Stay, Extension Or Usury Laws...............29
   Section 4.10   Additional Amounts....................................29
   Section 4.11   Delivery of Certain Information.......................30
</TABLE>

                                      -i-





<PAGE>
 
                               TABLE OF CONTENTS
                                 (continued) 
<TABLE>
<CAPTION> 
                                                                            Page
                                                                            ----
<S>                                                                         <C> 
ARTICLE 5  SUCCESSOR CORPORATION..............................................30

  Section 5.1    Limitation On Merger, Sale Or Consolidation..................30
  Section 5.2    Successor Corporation Substituted............................31

ARTICLE 6  EVENTS OF DEFAULT AND REMEDIES.....................................31

  Section 6.1    Events Of Default............................................31
  Section 6.2    Acceleration Of Maturity Date; Rescission And Annulment......33
  Section 6.3    Collection Of Indebtedness And Suits For Enforcement By 
                 Trustee......................................................34
  Section 6.4    Trustee May File Proofs Of Claim.............................35
  Section 6.5    Trustee May Enforce Claims Without Possession Of Securities..36
  Section 6.6    Priorities...................................................36
  Section 6.7    Limitation On Suits..........................................36
  Section 6.8    Unconditional Right Of Holders To Receive Principal, 
                 Premium And Interest.........................................37
  Section 6.9    Rights And Remedies Cumulative...............................37
  Section 6.10   Delay Or Omission Not Waiver.................................37
  Section 6.11   Control By Holders...........................................38
  Section 6.12   Waiver Of Past Default.......................................38
  Section 6.13   Undertaking For Costs........................................38
  Section 6.14   Restoration Of Rights And Remedies...........................39

ARTICLE 7 TRUSTEE.............................................................39

  Section 7.1    Duties Of Trustee............................................39
  Section 7.2    Rights Of Trustee............................................40
  Section 7.3    Individual Rights Of Trustee.................................41
  Section 7.4    Trustee's Disclaimer.........................................41
  Section 7.5    Notice Of Default............................................41
  Section 7.6    Reports By Trustee To Holders................................42
  Section 7.7    Compensation And Indemnity...................................42
  Section 7.8    Replacement Of Trustee.......................................43
  Section 7.9    Successor Trustee By Merger, Etc.............................44
  Section 7.10   Eligibility; Disqualification................................44
  Section 7.11   Preferential Collection Of Claims Against Company............44

ARTICLE 8  SATISFACTION AND DISCHARGE.........................................44

  Section 8.1    Satisfaction And Discharge Of Indenture......................44
  Section 8.2    Payment To The Company.......................................45

ARTICLE 9  AMENDMENTS, SUPPLEMENTS AND WAIVERS................................45

  Section 9.1    Supplemental Indentures Without Consent of Holders...........45
</TABLE>
                                     -ii-


<PAGE>
 
                               TABLE OF CONTENTS
                                 (continued) 
<TABLE>
<CAPTION> 
                                                                            Page
                                                                            ----
<S>                                                                         <C>
  Section 9.2    Amendments, Supplemental Indentures And Waivers With 
                 Consent Of Holders...........................................46
  Section 9.3    Compliance With TIA..........................................47
  Section 9.4    Revocation And Effect Of Consents............................47
  Section 9.5    Notation On Or Exchange Of Securities........................48
  Section 9.6    Trustee To Sign Amendments, Etc..............................48

 
ARTICLE 10  RIGHT TO REQUIRE REPURCHASE UPON A CHANGE OF CONTROL..............48

  Section 10.1   Repurchase Of Securities At Option Of The Holder Upon A 
                 Change Of Control............................................48

ARTICLE 11  SUBORDINATION.....................................................51

  Section 11.1   Securities Subordinated To Senior Indebtedness...............51
  Section 11.2   No Payment On Securities In Certain Circumstances............51
  Section 11.3   Securities Subordinated To Prior Payment Of All Senior 
                 Indebtedness On Dissolution, Liquidation Or Reorganization...52
  Section 11.4   Security Holders To Be Subrogated To Rights Of Holders 
                 Of Senior Indebtedness.......................................53
  Section 11.5   Obligations Of The Company Unconditional.....................54
  Section 11.6   Trustee Entitled To Assume Payments Not Prohibited In 
                 Absence of Notice............................................54
  Section 11.7   Application By Trustee Of Assets Deposited With It...........55
  Section 11.8   Subordination Rights Not Impaired By Acts Or Omissions 
                 Of The Company Or Holders Of Senior Indebtedness.............55
  Section 11.9   Security Holders Authorize Trustee To Effectuate 
                 Subordination Of Securities..................................55
  Section 11.10  Right Of Trustee To Hold Senior Indebtedness.................56
  Section 11.11  Article 11 Not To Prevent Events Of Default..................56
  Section 11.12  No Fiduciary Duty Of Trustee To Holders Of Senior 
                 Indebtedness.................................................56

ARTICLE 12  CONVERSION OF SECURITIES..........................................56

  Section 12.1   Conversion Privilege.........................................56
  Section 12.2   Exercise Of Conversion Privilege.............................57
  Section 12.3   Fractional Interests.........................................58
  Section 12.4   Conversion Price.............................................58
  Section 12.5   Adjustment Of Conversion Price...............................59
  Section 12.6   Continuation Of Conversion Privilege In Case
                 Of Reclassification, Change,
                 Merger, Consolidation Or Sale Of Assets......................64
  Section 12.7   Notice Of Certain Events.....................................65
  Section 12.8   Taxes On Conversion..........................................66
  Section 12.9   Company To Provide Stock.....................................66
  Section 12.10  Disclaimer Of Responsibility For Certain Matters.............67
</TABLE>

                                     -iii-
<PAGE>
 
                               TABLE OF CONTENTS
                                  (continued) 
<TABLE>
<CAPTION> 
                                                                                       Page
                                                                                       ----
<S>                <C>                                                                 <C>  
   Section 12.11   Return Of Funds Deposited For Redemption Of Converted Securities...  67
 
ARTICLE 13  MISCELLANEOUS.............................................................  67

   Section 13.1    TIA Controls.......................................................  67
   Section 13.2    Notices............................................................  68
   Section 13.3    Communications By Holders With Other Holders.......................  68
   Section 13.4    Certificate And Opinion As To Conditions Precedent.................  69
   Section 13.5    Statements Required In Certificate Or Opinion......................  69
   Section 13.6    Rules By Trustee, Paying Agent, Registrar..........................  69
   Section 13.7    Legal Holidays.....................................................  69
   Section 13.8    Governing Law......................................................  70
   Section 13.9    No Adverse Interpretation Of Other Agreements......................  70
   Section 13.10   No Recourse Against Others.........................................  70
   Section 13.11   Successors.........................................................  71
   Section 13.12   Duplicate Originals................................................  71
   Section 13.13   Severability.......................................................  71
   Section 13.14   Table Of Contents, Headings, Etc...................................  71
   Section 13.15   Qualification Of Indenture.........................................  71

Exhibit A   Form of Security
 
</TABLE>

                                     -iv-
<PAGE>
 
     INDENTURE, dated as of December 15, 1997 between PLATINUM technology, inc.,
a Delaware corporation (the "Company"), and American National Bank and Trust
Company of Chicago, a national banking association organized under the laws of
the United States of America, as trustee (The "Trustee").

     Each party hereto agrees as follows for the benefit of each other party and
for the equal and ratable benefit of the Holders of the Company's 6.25%
Convertible Subordinated Notes due 2002:


                                   ARTICLE I

                   DEFINITIONS AND INCORPORATION BY REFERENCE

Section 1.1  Definitions.
             ----------- 

     "Acceleration Notice" shall have the meaning specified in Section 6.2.

     "Additional Amounts" shall have the meaning specified in Paragraph 6 in the
form of Security attached hereto as Exhibit A.

     "Additional Interest" shall have the meaning specified in the Registration
Rights Agreement.

     "Affiliate" means (i) any person directly or indirectly controlling or
controlled by or under direct or indirect common control with the Company, (ii)
any spouse, immediate family member, or other relative who has the same
principal residence of any person described in clause (i) above, and (iii) any
trust in which any person described in clause (i) or (ii) above has a beneficial
interest. For purposes of this definition, the term "control" means the power to
direct the management and policies of a person, directly or through one or more
intermediaries, whether through the ownership of voting securities, by contract,
or otherwise.

     "Agent" means any Registrar, Paying Agent or co-Registrar.

     "Bankruptcy Law" means Title 11, U.S. Code, or any similar Federal, state
or foreign law for the relief of debtors.
 
     "Board of Directors" means, with respect to any Person, the Board of
Directors of such Person or any committee of the Board of Directors of such
person authorized, with respect to any particular matter, to exercise the power
of the Board of Directors of such Person.

     "Board Resolution" means, with respect to any person, a duly adopted
resolution of the Board of Directors of such Person.
<PAGE>
 
     "Business Day" means each Monday, Tuesday, Wednesday, Thursday and Friday
that is not a day on which banking institutions in New York, New York are
authorized or obligated by law or executive order to close.

     "Capitalized Lease Obligations" means rental obligations under a lease that
are required to be capitalized for financial reporting purposes in accordance
with GAAP, and the amount of Indebtedness represented by such obligations shall
be the capitalized amount of such obligations, as determined in accordance with
GAAP.

     "Capital Stock" means, with respect to any corporation, any and all shares,
interest, rights to purchase (other than convertible or exchangeable
Indebtedness), warrants, options, participations or other equivalents of or
interests (however designated) in stock issued by that corporation.

     "Cash" means such coin or currency of the United States of America as at
the time of payment shall be legal tender for the payment of public and private
debts.

     "Cedel" means Cedel Bank, societe anonyme.

     "Change of Control" occurs upon the occurrence of any of the following
events: (i) upon any merger or consolidation of the Company with or into any
Person or any sale, transfer or other conveyance, whether direct or indirect, of
all or substantially all of the assets of the Company, on a consolidated basis,
in one transaction or a series of related transactions, if, immediately after
giving effect to such transaction, any "person" or "group" other than the
Company is or becomes the "beneficial owner," directly or indirectly, of more
than 50% of the voting power in the aggregate normally entitled to vote in the
election of directors, managers, or trustees, as applicable, of the transferee
or surviving entity, (ii) when any "person" or "group" is or becomes the
"beneficial owner," directly or indirectly, of more than 50% of the voting power
in the aggregate normally entitled to vote in the election of directors of the
Company, (iii) when, during any period of 12 consecutive months after the Issue
Date, individuals who at the beginning of any such 12-month period constituted
the Board of Directors of the Company (together with any new directors whose
election by such Board or whose nomination for election by the stockholders of
the Company was approved by a vote of a majority of the directors then still in
office who were either directors at the beginning of such period or whose
election or nomination for election was previously so approved) cease for any
reason to constitute a majority of the Board of Directors of the Company then in
office, or (iv) the pro rata distribution by the Company to its stockholders of
substantially all of its assets.

     For purposes of this definition, (i) the terms "person" and "group" shall
have the meaning used for purposes of Rules 13d-3 and 13d-5 of the Exchange Act
as in effect on the Issue Date, whether or not applicable; and (ii) the term
"beneficial owner" shall have the meaning used in Rules 13d-3 and 13d-5 under
the Exchange Act as in effect on the Issue Date, whether or not applicable,
except that a "person" shall be deemed to have "beneficial ownership" of all
shares that any such person has the right to acquire, whether such right is
exercisable immediately or only after the passage of time or upon the occurrence
of certain events.


                                      -2-
<PAGE>
 
     "Change of Control Notice" shall have the meaning specified in Section 10.1

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

     "Common Stock" means the Company's common stock, par value $.001 per share,
or as such stock may be reconstituted from time to time.

     "Company" means PLATINUM technology, inc. until a successor replaces it
pursuant to the Indenture, and thereafter means such successor.

     "Conversion Price" shall have the meaning specified in Section 12.4.

     "Conversion Shares" shall have the meaning specified in Section 12.1.

     "Custodian" means any receiver, trustee, assignee, liquidator, sequestrator
or similar official under any Bankruptcy Law.

     "Date of Conversion" shall have the meaning specified in Section 12.2.

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

     "Defaulted Interest" shall have the meaning specified in Section 2.12.

     "Depositary" means the sole holder of the Global Security, as specified in
Section 2.3 until a successor shall have been appointed and become such pursuant
to the applicable provision of this Indenture, and, thereafter, "Depositary"
shall mean or include such successor.

     "Designated Senior Indebtedness" means any particular Senior Indebtedness
in which the instrument creating or evidencing the same or the assumption or
guarantee thereof (or related agreements or documents to which the Company is a
party) expressly provides that such Senior Indebtedness shall be "Designated
Senior Indebtedness" for purposes of this Indenture (provided that such
instrument agreement or other document may place limitations and conditions on
the right of such Senior Indebtedness to exercise the rights of Designated
Senior Indebtedness).

     "Disqualified Capital Stock" means (a) except as set forth in (b), with
respect to any Person, Capital Stock of such Person that, by its terms or by the
terms of any security into which it is convertible, exercisable or exchangeable,
is, or upon the happening of an event or the passage of time would be, required
to be redeemed or repurchased (including at the option of the holder thereof) by
such Person or any of its Subsidiaries, in whole or in part, on or prior to the
Stated Maturity of the Securities and (b) with respect to any Subsidiary of such
Person (including with respect to any Subsidiary of the Company), any Capital
Stock other than any common stock with no preference, privileges, or redemption
or repayment provisions.

                                      -3-
<PAGE>
 
     "Distribution Date" shall have the meaning specified in Section 12.5.

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

     "Euroclear" means the Euroclear System.

     "Event of Default" shall have the meaning specified in Section 6.1.

     "Exchange Act" means the Securities Exchange Act of 1934, as amended, and
the rules and regulations promulgated by the SEC thereunder.

     "Expiration Time" shall have the meaning specified in Section 12.5.

     "GAAP" means United States generally accepted accounting principles set
forth in the opinions and pronouncements of the Accounting Principles Board of
the American Institute of Certified Public Accountants and statements and
pronouncements of the Financial Accounting Standards Board ("FASB") or in such
other statements by such other entity as approved by a significant segment of
the accounting profession which are in effect in the United States; provided,
however, that for purposes of determining compliance with covenants in this
Indenture, "GAAP" means such generally accepted accounting principles which are
in effect as of the Issue Date.

     "Global Security" means a Security held by the Depositary for the benefit
of beneficial owners, and which contains the paragraph referred to in footnote 1
and the schedule referred to in footnote 2 of the form of Security attached
hereto as Exhibit A.

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

     "Indebtedness" of any Person means, without duplication, (a) all
liabilities and obligations, contingent or otherwise, of any such Person, (i) in
respect of borrowed money (whether or not the recourse of the lender is to the
whole of the assets of such Person or only to a portion thereof), (ii) evidenced
by bonds, notes, debentures or similar instruments, (iii) representing the
balance deferred and unpaid of the purchase price of any property or services,
except such as would constitute trade payables to trade creditors in the
ordinary course of business that are not more than ninety (90) days past their
original due date, (iv) evidenced by bankers' acceptances or similar instruments
issued or accepted by banks, (v) for the payment of money relating to a
Capitalized Lease Obligation, or (vi) evidenced by a letter of credit or a
reimbursement obligation of such Person with respect to any letter of credit;
(b) all net obligations of such Person under Interest Swap and Hedging
Obligations; (c) all liabilities of others of the kind described in the
preceding clause (a) or (b) that such person has guaranteed or that is otherwise
its legal liability and all obligations to purchase, redeem or acquire any
Capital Stock; and (d) any and all deferrals, renewals, extensions,
refinancings, refundings (whether direct or indirect) of any liability of the
kind described in any of the preceding clauses (a), (b) or (c), or this clause
(d), whether or not between or among the same parties.

                                      -4-
<PAGE>
 
     "Indenture" means this indenture, as amended or supplemented from time to
time in accordance with the terms hereof.

     "Initial Purchasers" means Deutsche Morgan Grenfell Inc. and Donaldson,
Lufkin & Jenrette Securities Corporation.

     "Interest Payment Date" means the stated due date of an installment of
interest on the Securities.

     "Interest Swap And Hedging Obligations" means any obligation of any Person
pursuant to any interest rate swap agreement, interest rate cap agreement,
interest rate collar agreement, interest rate exchange agreement, currency
exchange agreement or any other agreement or arrangement designed to protect
against fluctuations in interest rates or currency values, including, without
limitation, any arrangement whereby, directly or indirectly, such Person is
entitled to receive from time to time periodic payments calculated by applying
either a fixed or floating rate of interest on a stated notional amount in
exchange for periodic payment made by such Person calculated by applying a fixed
or floating rate of interest on the same notional amount.

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

     "Junior Security" of any Person means any Qualified Capital Stock and any
Indebtedness of such Person that is subordinated in right of payment to the
Securities and has no scheduled installment of principal due, by redemption,
sinking fund payment or otherwise, on or prior to the Stated Maturity of the
Securities.

     "Last Sale Price" shall have the meaning specified in Section 12.3.

     "Legal Holiday" shall have the meaning specified in Section 13.7.

     "Lien" means any mortgage, lien, pledge, charge, security interest or other
encumbrance of any kind, whether or not filed, recorded or otherwise perfected
under applicable law (including any conditional sale or other title retention
agreement and any lease deemed to constitute a security interest and any option
or other agreement to give any security interest).

     "Non-Electing Share" shall have the meaning specified in Section 12.6.

     "Non-U.S. Holder" means any Holder other than a U.S. Holder.

     "Notice of Default" shall have the meaning specified in Section 6.1(3).

     "Offer" shall have the meaning specified in Section 12.5(e).


                                      -5-
<PAGE>
 
     "Officer" means, with respect to the Company, the Chief Executive Officer,
the President, any Vice President, the Chief Financial Officer, the Treasurer,
the Controller, or the Secretary of the Company.

     "Officers' Certificate" means, with respect to the Company, a certificate
signed by two Officers or by an Officer and an Assistant Secretary of the
Company and otherwise complying with the requirements of Sections 13.4 and 13.5.

     "Opinion of Counsel" means a written opinion from legal counsel who is
reasonably acceptable to the Trustee and which complies with the requirements of
Sections 13.4 and 13.5.

     "Paying Agent" shall have the meaning specified in Section 2.3.

     "Payment Blockage Period" shall have the meaning specified in Section
11.2(b).

     "Payment Default" shall have the meaning specified in Section 11.2(a).

     "Payment Notice" shall have the meaning specified in Section 11.2(b).

     "Person" means any corporation, individual, limited liability company,
joint stock company, joint venture, partnership, unincorporated association,
governmental regulatory entity, country, state or political subdivision thereof,
trust, municipality or other entity.

     "principal" of any Indebtedness means the principal of such Indebtedness
plus, without duplication, any applicable premium, if any, on such Indebtedness.

     "Principal Amount" shall have the meaning specified in Section 2.6(b).

     "Property" means any right or interest in or to property or assets of any
kind whatsoever, whether real, personal or mixed and whether tangible or
intangible.

     "Purchase Agreement" means that certain Purchase Agreement, dated December
11, 1997, by and between the Company and the Initial Purchasers, as such
agreement may be amended, modified or supplemented from time to time in
accordance with the terms thereof.

     "Purchased Shares" shall have the meaning specified in Section 12.5(e).

     "QIB" shall mean a "qualified institutional buyer" as defined in Rule 144A.

     "Qualified Capital Stock" means any Capital Stock of the Company that is
not Disqualified Capital Stock.

     "Record Date" means a Record Date specified in the Securities whether or
not such Record Date is a Business Day.


                                      -6-
<PAGE>
 
     "Redemption Date," when used with respect to any Security to be redeemed,
means the date fixed for such redemption pursuant to Paragraph 5 or Paragraph 7,
as the case may be, of the form of Security attached hereto as Exhibit A and
Article 3 of this Indenture.

     "Redemption Price," when used with respect to any Security to be redeemed,
means the redemption price for such redemption pursuant to Paragraph 5 or
Paragraph 7, as the case may be, in the form of Security attached hereto as
Exhibit A, which shall include, without duplication, in each case, accrued and
unpaid interest (including any Additional Amounts and Additional Interest), if
any, to the Redemption Date.

     "Registrar" shall have the meaning specified in Section 2.3.

     "Registration Rights Agreement" means the Registration Rights Agreement,
dated as of December 15, 1997, between the Company and the Initial Purchasers,
as such agreement may be amended from time to time.

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

     "Regulation S Global Security" shall have the meaning specified in Section
2.6(b).

     "Repurchase Date" shall have the meaning specified in Section 10.1(a).

     "Repurchase Offer" shall have the meaning specified in Section 10.1(a).

     "Repurchase Price" shall have the meaning specified in Section 10.1(a).

     "Repurchase Put Date" shall have the meaning specified in Section 10.1(b).

     "Restricted Security" shall have the meaning specified in Section 2.6(d).

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

     "Rule 144A Global Security" shall have the meaning specified in Section
2.6(b).

     "Rule 144A Information" shall have the meaning specified in Section 4.11.

     "SEC" means the Securities and Exchange Commission.

     "Securities" means, collectively, the unsecured 6.25% Convertible
Subordinated Notes due 2002 issued by the Company under this Indenture, as
supplemented from time to time in accordance with the terms hereof, limited in
aggregate principal amount to $150,000,000 ($172,500,000 if the Initial
Purchasers' over-allotment option is exercised in full).


                                      -7-
<PAGE>
 
     "Securities Act" means the Securities Act of 1933, as amended, and the
rules and regulations of the SEC promulgated thereunder.

     "Securities Custodian" means the Trustee, as custodian with respect to the
Global Security, or any successor entity thereto.

     "Senior Indebtedness" means any Indebtedness of the Company, whether
outstanding on the date of the Indenture or thereafter created, incurred,
assumed, guaranteed or in effect guaranteed by the Company, unless the
instrument creating or evidencing such Indebtedness provides that such
Indebtedness is not senior or superior, in right of payment, to the Securities
or to other Indebtedness which is pari passu with, or subordinated to, the
Securities; provided, that in no event shall Senior Indebtedness include (a)
Indebtedness of the Company owed or owing to any Subsidiary of the Company or
any officer, director or employee of the Company or any Subsidiary of the
Company, (b) Indebtedness to trade creditors, (c) any liability for taxes owed
or owing by the Company or (d) any Indebtedness of the Company with respect to
the Company's 6 3/4% Convertible Subordinated Notes Due 2001 (the "6 3/4%
Notes").

     "Significant Subsidiary" means any Subsidiary which is a "significant
subsidiary" of the Company within the meaning of Rule 1-02(w) of Regulation S-X
promulgated by the SEC as in effect on the date of this Indenture.

     "Special Record Date" for payment of any Defaulted Interest means a date
fixed by the Trustee pursuant to Section 2.12.

     "Stated Maturity," when used with respect to any Security, means December
15, 2002.

     "Subsidiary" with respect to any Person, means (i) a corporation a majority
of whose Capital Stock with voting power normally entitled to vote in the
election of directors is at the time, directly or indirectly, owned by such
Person, by such Person and one or more Subsidiaries of such Person or by one or
more Subsidiaries of such Person, (ii) a partnership in which such Person or a
Subsidiary of such Person is, at the time, a general partner and owns alone or
together with one or more Subsidiaries of such Person a majority of the
partnership interests, or (iii) any other Person (other than a corporation or
partnership) in which such Person, one or more Subsidiaries of such Person, or
such Person and one or more Subsidiaries of such Person, directly or indirectly,
at the date of determination thereof has at least majority ownership interest.

     "Tax Affected Security" means any Security in respect of which, as a result
of any Tax Law Change, the Company has or will become obligated to pay
Additional Amounts.

     "Taxing Jurisdiction" shall have the meaning specified in Paragraph 6 of
the form of Security attached hereto as Exhibit A.

     "Tax Law Change" means any change in, or amendment to, the laws,
regulations, treaties or rulings prevailing in the United States or any
political subdivision or taxing authority thereof or 


                                      -8-
<PAGE>
 
therein, which change or amendment becomes effective on or after the date hereof
or any application or judicial, legislative or administrative interpretation of
such laws, regulations, treaties or rulings.

     "TIA" means the Trust Indenture Act of 1939 (15 U.S. Code Sections 77aaa-
77bbbb) as in effect on the date of the execution of this Indenture.

     "Trading Day" means each Monday, Tuesday, Wednesday, Thursday and Friday,
other than any day on which securities are not traded on the Nasdaq National
Market.

     "Trustee" means American National Bank and Trust Company of Chicago, as
trustee, until a successor replaces it in accordance with the provisions of this
Indenture and thereafter means such successor.

     "Trust Officer" means any officer within the corporate trust division (or
any successor group) of the Trustee or any other officer of the Trustee
customarily performing functions similar to those performed by the Persons who
at that time shall be such officers, and also means, with respect to a
particular corporate trust matter, any other officer of the Trustee to whom such
trust matter is referred because of his or her knowledge of and familiarity with
the particular subject.

     "United States" means the United States of America (including the States
and the District of Columbia), its territories, its possessions and other areas
subject to its jurisdiction (its "possessions" including Puerto Rico, the U.S.
Virgin Islands, Guam, American Samoa, Wake Island and the Northern Mariana
Islands).

     "U.S. Holder" means the beneficial holder of a Security or Common Stock
that for United States federal income tax purposes is (i) a citizen or resident
(as defined in Section 7701(b) of the Code) of the United States, (ii) a
corporation, partnership or other entity formed under the laws of the United
States or any political subdivision thereof, (iii) an estate the income of which
is subject to U.S. federal income taxation regardless of its source, and (iv) in
general, a trust subject to the primary supervision of a court within the United
States and the control of a United States fiduciary as described in Section
7701(a)(30) of the Code and (v) any other person whose income or gain with
respect to a Security or gain with respect to a Security or Common Stock is
effectively connected with the conduct of a United States trade or business.

     "U.S. Government Obligations" means direct non-callable obligations of, or
non-callable obligations guaranteed by, the United States of America for the
payment of which obligation or guarantee the full faith and credit of the United
States of America is pledged.

Section 1.2  Incorporation By Reference of TIA.

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


                                      -9-
<PAGE>
 
     "Commission" means the SEC.

     "Indenture Securities" means the Securities.

     "Indenture Security Holder" means a Holder or a Security Holder.

     "Indenture To Be Qualified" means this Indenture.

     "Indenture Trustee" or "Institutional Trustee" means the Trustee.

     "Obligor" on the Securities means the Company and any other obligor on the
Securities.

     All other TIA terms used in this Indenture that are defined by the TIA,
defined by TIA reference to another statute or defined by SEC rule and not
otherwise defined herein have the meanings assigned to them thereby.

Section 1.3  Rules of Construction.
             --------------------- 

     Unless the context otherwise requires:

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

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

          (3)  "or" is not exclusive;

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

          (5)  provisions apply to successive events and transactions;

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

          (7)  references to Sections or Articles means reference to such
               Sections or Articles in this Indenture, unless stated otherwise.


                                     -10-
<PAGE>
 
                                   ARTICLE 2

                                 THE SECURITIES

Section 2.1  Form and Dating.
             --------------- 

     The Securities and the Trustee's certificate of authentication, in respect
thereof, shall be substantially in the form of Exhibit A hereto, which Exhibit
is part of this Indenture. The Securities may have notations, legends or
endorsements required by law, stock exchange or market rule or usage. The
Company shall approve the form of the Securities and any notation, legend or
endorsement on them. Any such notations, legends or endorsements not contained
in the form of Security attached as Exhibit A hereto shall be delivered in
writing to the Trustee. Each Security shall be dated the date of its
authentication.

     The terms and provisions contained in the forms of Securities shall
constitute, and are hereby expressly made, a part of this Indenture, and, to the
extent applicable, the Company and the Trustee, by their execution and delivery
of this Indenture, expressly agree to such terms and provisions and to be bound
thereby.

Section 2.2  Execution and Authentication.
             ---------------------------- 

     Two Officers shall sign, or one Officer shall sign and one Officer shall
attest to, the Security for the Company by manual or facsimile signature. The
Company's seal shall be impressed, affixed, imprinted or reproduced on the
Securities and may be in facsimile form.

     If an Officer whose signature is on a Security was an Officer at the time
of such execution but no longer holds that office at the time the Trustee
authenticates the Security, the Security shall be valid nevertheless and the
Company shall nevertheless be bound by the terms of the Securities and this
Indenture.

     A Security shall not be valid until an authorized signatory of the Trustee
manually signs the certificate of authentication on the Security, but such
signature shall be conclusive evidence that the Security has been authenticated
pursuant to the terms of this Indenture. Notwithstanding anything herein to the
contrary, if any Security shall have been authenticated and delivered hereunder
but never issued or sold by the Company, and the Company shall deliver such
Security to the Trustee for cancellation, 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.

     The Trustee shall authenticate the Securities for original issue in the
aggregate principal amount of up to $172,500,000 upon a written order of the
Company in the form of an Officers' Certificate. The Officers' Certificate shall
specify the amount of Securities to be authenticated and the date the Securities
are to be authenticated. The aggregate principal amount of Securities
outstanding at any time may not exceed $172,500,000 except as provided in
Section 2.7; provided, that Securities in excess of $150,000,000 shall not be
issued other than upon exercise of the 


                                     -11-
<PAGE>
 
over-allotment option granted by the Company to the Initial Purchasers as
provided in the Purchase Agreement, or pursuant to Section 2.7. Upon the written
order of the Company in the form of an Officers' Certificate, the Trustee shall
authenticate Securities in substitution of Securities originally issued to
reflect any name change of the Company.

     The Trustee may appoint an authenticating agent acceptable to the Company
to authenticate Securities. Unless otherwise provided in the appointment, an
authenticating agent may authenticate Securities whenever the Trustee may do so.
Each reference in this Indenture to authentication by the Trustee includes
authentication by such agent. An authenticating agent has the same rights as an
Agent to deal with the Company, any Affiliate of the Company, or any of their
respective Subsidiaries.

     Securities shall be issuable only in registered form without coupons in
denominations of $1,000 and any integral multiple thereof.

Section 2.3  Registrar, Paying Agent And Depositary.
             -------------------------------------- 

     The Company shall maintain an office or agency in the Borough of Manhattan,
The City of New York, where Securities may be presented for registration of
transfer or for exchange ("Registrar") and an office or agency where Securities
may be presented for payment ("Paying Agent") and where notices and demands to
or upon the Company in respect of the Securities may be served. The Company may
act as Registrar or Paying Agent, except that, for the purposes of Articles 3, 8
and 10 and as otherwise specified in the Indenture, neither the Company nor any
Affiliate of the Company shall act as Paying Agent. The Registrar shall keep a
register of the Securities and of their transfer and exchange. The Company may
have one or more co-Registrars and one or more additional Paying Agents. The
term "Paying Agent" includes any additional Paying Agent.  The Trustee, at its
office located at 14 Wall Street, New York, New York 10005 is initially
designated as Registrar and Paying Agent.

     The Company shall enter into an appropriate written agency agreement with
any Agent, other than the Trustee, which is not an Affiliate, which agreement
shall implement the provisions of this Indenture that relate to such Agent. The
Company shall promptly notify the Trustee in writing of the name and address of
any such Agent. If the Company fails to maintain a Registrar or Paying Agent,
the Trustee shall act as such.

     The Company initially appoints the DTC to act as Depositary with respect to
the Global Securities.

Section 2.4  Paying Agent To Hold Assets In Trust.
             ------------------------------------ 

     The Company shall require each Paying Agent other than the Trustee to agree
in writing that such Paying Agent shall hold in trust for the benefit of Holders
or the Trustee all assets held by the Paying Agent for the payment of principal
of, premium, if any, and interest on the Securities (whether such assets have
been distributed to it by the Company or any other obligor on the 


                                     -12-
<PAGE>
 
Securities), and shall notify the Trustee in writing of any Default in making
any such payment. If either of the Company or a Subsidiary of the Company acts
as Paying Agent, it shall segregate such assets and hold them as a separate
trust for the benefit of the Holders or the Trustee. The Company at any time may
require a Paying Agent to distribute all assets held by it to the Trustee and
account for any assets distributed and the Trustee may at any time during the
continuance of any Payment Default, upon written request to a Paying Agent,
require such Paying Agent to distribute all assets held by it to the Trustee and
to account for any assets distributed. Upon distribution to the Trustee of all
assets that shall have been delivered by the Company to the Paying Agent, the
Paying Agent (if other than the Company or an Affiliate of the Company) shall
have no further liability for such assets.

Section 2.5  Security Holder Lists.
             ----------------------

     The Trustee shall preserve in as current a form as is reasonably
practicable the most recent list available to it of the names and addresses of
Holders. If the Trustee is not the Registrar, the Company shall furnish to the
Trustee on or before the third Business Day preceding each Interest Payment Date
and at such other times as the Trustee may request in writing a list in such
form and as of such date as the Trustee reasonably may require of the names and
addresses of Holders.

Section 2.6  Transfer and Exchange; Restrictions on Transfer.
             ----------------------------------------------- 

     (a) (i)    To permit registrations of transfers and exchanges, the 
Company shall execute and the Trustee shall authenticate definitive Securities
and Global Securities at the Registrar's or co-Registrar's request.

         (ii)   No service charge shall be made for any registration of 
transfer or exchange, but the Company may require payment of a sum sufficient to
cover any transfer taxes, assessments, or similar governmental charge payable in
connection therewith (other than any such transfer taxes, assessments, or
similar governmental charge payable upon exchanges or transfers pursuant to
Section 2.2 (fourth paragraph), 2.10, 3.7, 9.5, or 10.1 (final paragraph)).

         (iii)  The Registrar or co-Registrar shall not be required to 
register the transfer of or exchange of (a) any definitive Security selected for
redemption in whole or in part pursuant to Article 3, except the unredeemed
portion of any definitive Security being redeemed in part, or (b) in the event
that the Trustee has been notified of an offer to repurchase Securities pursuant
to Article 10 hereof or of a redemption of Securities pursuant to Article 3
hereof, any Security for a period beginning 15 days before the mailing of a
notice of an offer to repurchase or the mailing of a notice of redemption and
ending at the close of business on the day of such mailing.

     (b) So long as the Securities are eligible for book-entry settlement with 
the Depositary, or unless otherwise required by law, all Securities that are so
eligible may be represented by one or more Global Securities registered in the
name of the Depositary or the nominee of the Depositary, except as otherwise
specified below. The transfer and exchange of beneficial interests in any such


                                     -13-
<PAGE>
 
Global Security shall be effected through the Depositary in accordance with this
Indenture and the procedures of the Depositary therefor.

     Securities that upon initial issuance are beneficially owned by QIBs will
be represented by a Global Security (the "Rule 144A Global Security") and
Securities that upon initial issuance are beneficially owned by Non-U.S. Persons
will be represented by another Global Security (the "Regulation S Global
Security").  Transfers of interests in the Securities between the Rule 144A
Global Security and the Regulation S Global Security will be made in accordance
with the standing instructions and procedures of the Depositary and its
participants.  The Trustee shall make appropriate endorsements to reflect
increases or decreases in the principal amounts of such Global Securities as set
forth on the face of the Security ("Principal Amount") to reflect any such
transfers. Except as provided below, beneficial owners of a Global Security
shall not be entitled to have certificates registered in their names, will not
receive or be entitled to receive physical delivery of certificates in
definitive form and will not be considered Holders of such Global Securities.

     (c) So long as the Securities are eligible for book-entry settlement, or 
unless otherwise required by law, upon any transfer of a definitive Security to
a QIB in accordance with Rule 144A or to a Non-U.S. Person in accordance with
Regulation S, and upon receipt of the definitive Security or Securities being so
transferred, together with a certification, substantially in the form on the
reverse of the Security, from the transferor that the transfer is being made in
compliance with Rule 144A or Regulation S, as the case may be (or other evidence
satisfactory to the Trustee), the Trustee shall make an endorsement on the Rule
144A Global Security or the Regulation S Global Security, as the case may be, to
reflect an increase in the aggregate Principal Amount of the Securities
represented by such Global Security, the Trustee shall cancel such definitive
Security or Securities in accordance with the standing instructions and
procedures of the Depositary, the aggregate Principal Amount of Securities
represented by such Global Security to be increased accordingly; provided that
no definitive Security, or portion thereof, in respect of which the Company or
an Affiliate of the Company held any beneficial interest shall be included in
such Global Security until such definitive Security is freely tradable in
accordance with Rule 144(k); provided further that the Trustee shall issue
Securities in definitive form upon any transfer of a beneficial interest in the
Global Security to the Company or any Affiliate of the Company.

     Any Global Security may be endorsed with or have incorporated in the text
thereof such legends or recitals or changes not inconsistent with the provisions
of this Indenture as may be required by the Securities Custodian, the Depositary
or by the National Association of Securities Dealers, Inc. in order for the
Securities to be tradeable on The Portal Market or as may be required for the
Securities to be tradeable on any other market developed for trading of
securities pursuant to Rule 144A or Regulation S or required to comply with any
applicable law or any regulation thereunder or with the rules and regulations of
Euroclear, Cedel or any securities exchange or automated quotation system upon
which the Securities may be listed or traded or to conform with any usage with
respect thereto, or to indicate any special limitations or restrictions to which
any particular Securities are subject.


                                     -14-
<PAGE>
 
     (d) Every Security that bears or is required under this Section 2.6(d) to 
bear the legend set forth in this Section 2.6(d) (together with any Common Stock
issued upon conversion of the Securities and required to bear the legend set
forth in Section 2.6(e), collectively, the "Restricted Securities") shall be
subject to the restrictions on transfer set fort in this Section 2.6(d)
(including those set forth in the legend set forth below) unless such
restrictions on transfer shall be waived by written consent of the Company; and
the Holder of each such Restricted Security, by such Holder's acceptance
thereof, agrees to be bound by all such restrictions on transfer. As used in
Sections 2.6(d) and 2.6(e), the term "transfer" encompasses any sale, pledge,
transfer or other disposition whatsoever of any Restricted Security.

     Until the expiration of the holding period applicable to sales thereof
under Rule 144(k) under the Securities Act (or any successor provision), any
certificate evidencing such Security (and all securities issued in exchange
therefor or substitution thereof, other than Common Stock, if any, issued upon
conversion thereof, which shall bear the legend set forth in Section 2.6(e), if
applicable) shall bear a legend in substantially the following form, unless such
Security has been sold pursuant to a registration statement that has been
declared effective under the Securities Act (and which continues to be effective
at the time of such transfer), or unless otherwise agreed by the Company in
writing, with written notice thereof to the Trustee:

     THE SECURITY EVIDENCED HEREBY HAS NOT BEEN REGISTERED UNDER THE U.S.
     SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR ANY STATE
     SECURITIES LAWS, AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD WITHIN THE
     UNITED STATES OR TO, OR FOR THE ACCOUNT OR BENEFIT OF, U.S. PERSONS EXCEPT
     AS SET FORTH IN THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF, THE
     HOLDER (1) REPRESENTS THAT (A) IT IS A "QUALIFIED INSTITUTIONAL BUYER" (AS
     DEFINED IN RULE 144A UNDER THE SECURITIES ACT) OR (B) IT IS NOT A U.S.
     PERSON AND IS ACQUIRING THE SECURITY EVIDENCED HEREBY IN AN OFFSHORE
     TRANSACTION; (2) AGREES THAT IT WILL NOT, PRIOR TO EXPIRATION OF THE
     HOLDING PERIOD APPLICABLE TO SALES OF THE SECURITY EVIDENCED HEREBY UNDER
     RULE 144(K) UNDER THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION), RESELL
     OR OTHERWISE TRANSFER THE SECURITY EVIDENCED HEREBY OR THE COMMON STOCK
     ISSUABLE UPON CONVERSION OF SUCH SECURITY EXCEPT (A) TO PLATINUM
     TECHNOLOGY, INC. OR ANY SUBSIDIARY THEREOF, (B) INSIDE THE UNITED STATES TO
     A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE
     SECURITIES ACT, (C) OUTSIDE THE UNITED STATES IN COMPLIANCE WITH RULE 904
     UNDER THE SECURITIES ACT, (D) PURSUANT TO THE EXEMPTION FROM

                                     -15-
<PAGE>
 
     REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT (IF AVAILABLE),
     (E) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BEEN DECLARED EFFECTIVE
     UNDER THE SECURITIES ACT (AND WHICH CONTINUES TO BE EFFECTIVE AT THE TIME
     OF SUCH TRANSFER), OR (F) PURSUANT TO ANOTHER AVAILABLE EXEMPTION FROM THE
     REGISTRATION REQUIREMENTS OF THE SECURITIES ACT; (3) PRIOR TO SUCH TRANSFER
     (OTHER THAN A TRANSFER PURSUANT TO CLAUSE 2(E) ABOVE), IT WILL FURNISH TO
     AMERICAN NATIONAL BANK AND TRUST COMPANY OF CHICAGO, AS TRUSTEE (OR A
     SUCCESSOR TRUSTEE, AS APPLICABLE), SUCH CERTIFICATIONS, LEGAL OPINIONS OR
     OTHER INFORMATION AS IT MAY REASONABLY REQUIRE TO CONFIRM THAT SUCH
     TRANSFER IS BEING MADE PURSUANT TO AN EXEMPTION FROM, OR IN A TRANSACTION
     NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND (4)
     AGREES THAT IT WILL DELIVER TO EACH PERSON TO WHOM THE SECURITY EVIDENCED
     HEREBY IS TRANSFERRED A NOTICE SUBSTANTIALLY TO THE EFFECT OF THIS LEGEND.
     IN CONNECTION WITH ANY TRANSFER OF THE SECURITY EVIDENCED HEREBY PRIOR TO
     THE EXPIRATION OF THE HOLDING PERIOD APPLICABLE TO SALES OF THE SECURITY
     EVIDENCED HEREBY UNDER RULE 144(K) UNDER THE SECURITIES ACT (OR ANY
     SUCCESSOR PROVISION), THE HOLDER MUST CHECK THE APPROPRIATE BOX SET FORTH
     ON THE REVERSE HEREOF RELATING TO THE MANNER OF SUCH TRANSFER AND SUBMIT
     THIS CERTIFICATE TO AMERICAN NATIONAL BANK AND TRUST COMPANY OF CHICAGO, AS
     TRUSTEE (OR A SUCCESSOR TRUSTEE, AS APPLICABLE). THIS LEGEND WILL BE
     REMOVED UPON THE TRANSFER OF THE SECURITY EVIDENCED HEREBY PURSUANT TO
     CLAUSE 2(D) OR 2(E) ABOVE. AS USED HEREIN, THE TERMS "OFFSHORE
     TRANSACTION," "UNITED STATES" AND "U.S. PERSON" HAVE THE MEANINGS GIVEN TO
     THEM BY REGULATION S UNDER THE SECURITIES ACT.

     Any Security (or Successor Security issued in exchange or substitution
therefor) as to which such restrictions on transfer shall have expired in
accordance with their terms or as to the conditions for removal of the foregoing
legend set forth therein have been satisfied may, upon surrender of such
Security for exchange to the Registrar in accordance with the provisions of this
Section 2.6, be exchanged for a new Security or Securities of like tenor and
aggregate principal amount, which shall not bear the restrictive legend required
by this Section 2.6(d).

                                     -16-
<PAGE>
 
     Notwithstanding any other provisions of this Indenture (other than the
provisions set forth in the second paragraph of Section 2.6(b) and in this
Section 2.6(d)), a Global Security may not be transferred as a whole or in part
except by the Depositary to a nominee of the Depositary or by a nominee of the
Depositary to the Depositary or another nominee of the Depositary or by the
Depositary or any such nominee to a successor Depositary or a nominee of such
successor Depositary.

     The Depositary shall be a clearing agency registered under the Exchange
Act.  The Company initially appoints DTC to act as Depositary with respect to
the Global Securities.  Initially, the Rule 144A Global Security and the
Regulation S Global Security shall be issued to the Depositary, registered in
the name of Cede & Co., as the nominee of the Depositary, and deposited with the
Securities Custodian for Cede & Co.

     If at any time the Depositary for a Global Security notifies the Company
that it is unwilling or unable to continue as Depositary for such Global
Security, the Company may appoint a successor Depositary with respect to such
Global Security.  If a successor Depositary is not appointed by the Company
within ninety (90) days after the Company receives such notice, the Company will
execute, and the Trustee, upon receipt of an Officers' Certificate for the
authentication and delivery of Securities, will authenticate and deliver,
Securities in certificated form, in aggregate principal amount equal to the
Principal Amount of such Global Security, in exchange for such Global Security.

     If a Security in certificated form is issued in exchange for any portion of
a Global Security after the close of business at the office or agency where such
exchange occurs on any Record Date and before the opening of business at such
office or agency on the next succeeding Interest Payment Date, interest will not
be payable on such Interest Payment Date in respect of such certificated
Security, but will be payable on such Interest Payment Date, subject to the
provisions of Section 2.12, only to the Person to whom interest in respect of
such portion of such Global Security is payable in accordance with the
provisions of this Indenture.

     Securities in certificated form issued in exchange for all or a part of a
Global Security pursuant to this Section 2.6 shall be registered in such names
and in such authorized denominations as the Depositary, pursuant to instructions
from its direct or indirect participants or otherwise, shall instruct the
Trustee.  Upon execution and authentication, the Trustee shall deliver such
Securities in certificated form to the Persons in whose names such Securities in
certificated form are so registered.

     At such time as all interests in a Global Security have been redeemed,
repurchased, converted, canceled, exchanged for Securities in certificated form,
or transferred to a transferee who receives Securities in certificated form
thereof, such Global Security shall, upon receipt thereof, be canceled by the
Trustee in accordance with standing procedures and instructions existing between
the Depositary and the Securities Custodian.  At any time prior to such
cancellation, if any interest in a Global Security is exchanged for Securities
in certificated form, redeemed, converted, repurchased or canceled, exchanged
for Securities in certificated form or transferred to a transferee who receives
Securities in certificated form therefor or any Security in certificated form is
exchanged or 

                                     -17-
<PAGE>
 
transferred for part of a Global Security, the principal amount of
such Security shall, in accordance with the standing procedures and instructions
existing between the Depositary and the Securities Custodian, be appropriately
reduced or increased, as the case may be, and an endorsement shall be made on
such Global Security, by the Trustee or the Securities Custodian, at the
direction of the Trustee, to reflect such reduction or increase.

     (e) Until the expiration of the holding period applicable to sales thereof
under Rule 144(k) under the Securities Act (or any successor provision), any
stock certificate representing Common Stock issued upon conversion of such
Security shall bear a legend in substantially the following form, unless such
Common Stock has been sold pursuant to a registration statement that has been
declared effective under the Securities Act (and which continues to be effective
at the time of such transfer) or such Common Stock has been issued upon
conversion of Securities that have been transferred pursuant to a registration
statement that has been declared effective under the Securities Act, or unless
otherwise agreed by the Company in writing with written notice thereof to the
Common Stock transfer agent:

     THE COMMON STOCK EVIDENCED HEREBY HAS NOT BEEN REGISTERED UNDER THE U.S.
     SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR ANY STATE
     SECURITIES LAWS, AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD WITHIN THE
     UNITED STATES OR TO, OR FOR THE ACCOUNT OR BENEFIT OF, U.S. PERSONS EXCEPT
     AS SET FORTH IN THE FOLLOWING SENTENCE. THE HOLDER HEREOF AGREES THAT UNTIL
     THE EXPIRATION OF THE HOLDING PERIOD APPLICABLE TO SALES OF THE SECURITY
     EVIDENCED HEREBY UNDER RULE 144(K) UNDER THE SECURITIES ACT (OR ANY
     SUCCESSOR PROVISION), (1) IT WILL NOT RESELL OR OTHERWISE TRANSFER THE
     COMMON STOCK EVIDENCED HEREBY EXCEPT (A) TO PLATINUM TECHNOLOGY, INC. OR
     ANY SUBSIDIARY THEREOF, (B) INSIDE THE UNITED STATES TO A "QUALIFIED
     INSTITUTIONAL BUYER" (AS DEFINED IN RULE 144A UNDER THE SECURITIES ACT) IN
     COMPLIANCE WITH RULE 144A, (C) OUTSIDE THE UNITED STATES IN COMPLIANCE WITH
     RULE 904 UNDER THE SECURITIES ACT, (D) PURSUANT TO THE EXEMPTION FROM
     REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT (IF AVAILABLE),
     (E) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BEEN DECLARED EFFECTIVE
     UNDER THE SECURITIES ACT (AND WHICH CONTINUES TO BE EFFECTIVE AT THE TIME
     OF SUCH TRANSFER) OR (F) PURSUANT TO ANOTHER AVAILABLE EXEMPTION FROM THE
     REGISTRATION REQUIREMENTS OF THE SECURITIES; (2) PRIOR TO SUCH TRANSFER
     (OTHER THAN A TRANSFER PURSUANT TO

                                     -18-
<PAGE>
 
     CLAUSE 1(E) ABOVE), IT WILL FURNISH TO HARRIS TRUST AND SAVINGS BANK, AS
     TRANSFER AGENT (OR A SUCCESSOR TRANSFER AGENT, AS APPLICABLE), SUCH
     CERTIFICATIONS, LEGAL OPINIONS OR OTHER INFORMATION AS IT MAY REASONABLY
     REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING MADE PURSUANT TO AN
     EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION
     REQUIREMENTS OF THE SECURITIES ACT AND (3) AGREES IT WILL DELIVER TO EACH
     PERSON TO WHOM THE COMMON STOCK EVIDENCED HEREBY IS TRANSFERRED A NOTICE
     SUBSTANTIALLY TO THE EFFECT OF THIS LEGEND. IN CONNECTION WITH ANY TRANSFER
     OF THE COMMON STOCK EVIDENCED HEREBY PRIOR TO THE EXPIRATION OF THE HOLDING
     PERIOD APPLICABLE TO SALES OF THE COMMON STOCK EVIDENCED HEREBY UNDER RULE
     144(K) UNDER THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION), THE HOLDER
     MUST SUBMIT THIS CERTIFICATE TO HARRIS TRUST AND SAVINGS BANK, AS TRANSFER
     AGENT (OR A SUCCESSOR TRANSFER AGENT, AS APPLICABLE). THIS LEGEND WILL BE
     REMOVED UPON THE TRANSFER OF THE COMMON STOCK EVIDENCED HEREBY PURSUANT TO
     CLAUSE 1(D) OR 1(E) ABOVE. AS USED HEREIN, THE TERMS "OFFSHORE
     TRANSACTION," "UNITED STATES" AND "U.S. PERSON" HAVE THE MEANINGS GIVEN TO
     THEM BY REGULATION S UNDER THE SECURITIES ACT.

     Any such Common Stock as to which such restrictions on transfer shall have
expired in accordance with their terms or as to which the conditions for removal
of the foregoing legend set forth therein have been satisfied may, upon
surrender of the certificates representing such shares of Common Stock for
exchange in accordance with the procedures of the transfer agent for the Common
Stock, be exchanged for a new certificate or certificates for a like number of
shares of Common Stock, which shall not bear the restrictive legend required by
this Section 2.6.

     (f) Any Security or Common Stock issued upon the conversion or exchange of 
a Security that, prior to the expiration of the holding period applicable to
sales thereof under Rule 144(k) under the Securities Act (or any successor
provision), is purchased or owned by the Company or any Affiliate thereof may
not be resold by the Company or such Affiliate unless registered under the
Securities Act or resold pursuant to an exemption from the registration
requirements of the Securities Act in a transaction which results in such
Securities or Common Stock, as the case may be, no longer being "restricted
securities" (as defined under Rule 144).


                                     -19-
<PAGE>
 
Section 2.7  Replacement Securities.
             ---------------------- 

     If a mutilated Security is surrendered to the Trustee or if the Holder of a
Security claims and submits an affidavit or other evidence, satisfactory to the
Trustee, to the Trustee to the effect that the Security has been lost, destroyed
or wrongfully taken, the Company shall issue and the Trustee shall authenticate
a replacement Security if the Trustee's requirements are met. If required by the
Trustee or the Company, such Holder must provide an indemnity bond or other
indemnity, sufficient in the judgment of both the Company and the Trustee, to
protect the Company, the Trustee or any Agent from any loss which any of them
may suffer if a Security is replaced. The Company may charge such Holder for its
reasonable, out-of-pocket expenses in replacing a Security. In case any such
mutilated, destroyed, lost or stolen Security has become or is about to become
due, the Company, in its discretion, may instead of issuing a new Security, pay
such Security.

     Every replacement Security is an additional obligation of the Company.

     The provisions of this Section 2.7 are exclusive and, to the extent lawful,
preclude other rights and remedies with respect to replacement or payment of
mutilated, destroyed, lost or stolen Securities.

Section 2.8   Outstanding Securities.
              ---------------------- 

     Securities outstanding at any time are all of the Securities that have been
authenticated by the Trustee (including any Security represented by a Global
Security) except those canceled by it, those delivered to it for cancellation,
those reductions in the interest in a Global Security effected by the Trustee
hereunder and those described in this Section 2.8 as not outstanding. A Security
does not cease to be outstanding because the Company or an Affiliate of the
Company holds the Security, except as provided in Section 2.9.



     If a Security is replaced pursuant to Section 2.7 (other than a mutilated
Security surrendered for replacement), it ceases to be outstanding unless the
Trustee receives proof satisfactory to it that the replaced Security is held by
a bona fide purchaser. A mutilated Security ceases to be outstanding upon
surrender of such Security and replacement thereof pursuant to Section 2.7.

     If on a Redemption Date the Paying Agent (other than the Company or an
Affiliate of the Company) holds Cash or U.S. Government Obligations sufficient
to pay all of the principal and interest due on the Securities payable on that
date in accordance with Section 3.6 hereof and payment of the Securities called
for redemption is not otherwise prohibited pursuant to Article 11 hereof or
otherwise, then on and after that date such Securities cease to be outstanding
and interest on them ceases to accrue.

Section 2.9  Treasury Securities.
             ------------------- 

     In determining whether the Holders of the required principal amount of
Securities have concurred in any direction, amendment, supplement, waiver or
consent, Securities owned by the 

                                     -20-
<PAGE>
 
Company or an Affiliate of the Company shall be disregarded, except that, for
the purposes of determining whether the Trustee shall be protected in relying on
any such direction, amendment, supplement, waiver or consent, only Securities
that the Trustee knows are so owned shall be disregarded.

Section 2.10  Temporary Securities.
              -------------------- 

     Until the Securities are ready for delivery in their definitive form, the
Company may prepare and the Trustee shall authenticate, temporary Securities.
Temporary Securities shall be substantially in the form of definitive Securities
but may have variations that the Company reasonably and in good faith considers
appropriate for temporary Securities. Without unreasonable delay, the Company
shall prepare and the Trustee shall authenticate Securities in their definitive
form in exchange for temporary Securities. Until so exchanged, the temporary
Securities shall in all respects be entitled to the same benefits under this
Indenture as Securities in their definitive form authenticated and delivered
hereunder.

Section 2.11  Cancellation.
              ------------ 

     The Company at any time may deliver Securities to the Trustee for
cancellation.  The Registrar and the Paying Agent shall forward to the Trustee
any Securities surrendered to them for transfer, exchange, payment, conversion
or cancellation.  The Trustee, or at the direction of the Trustee, the Registrar
or the Paying Agent (other than the Company or an Affiliate of the Company), and
no one else, shall cancel and, at the written direction of the Company, shall
dispose of all Securities surrendered for transfer, exchange, payment or
cancellation and shall deliver a cancellation certificate to the Company.
Subject to Section 2.7, the Company may not issue new Securities to replace
Securities that have been paid or delivered to the Trustee for cancellation.  No
Securities shall be authenticated in lieu of or in exchange for any Securities
canceled as provided in this Section 2.11, except as expressly permitted in the
form of Securities and as permitted by this Indenture.

Section 2.12  Defaulted Interest.
              ------------------ 

     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 the Security (or one or more predecessor Securities) is registered at the
close of business on the Record Date for such interest.

     Any interest on any Security which is payable, but is not punctually paid
or duly provided for, on any Interest Payment Date plus, to the extent lawful,
any interest payable on the defaulted interest (herein called "Defaulted
Interest") shall forthwith cease to be payable to the registered holder on the
relevant Record Date, and such Defaulted Interest may be paid by the Company at
its election as provided in clause (1) or (2) below:

     (1)  The Company may elect to make payment of any Defaulted Interest to the
persons in whose names the Securities (or their respective predecessor
Securities) are registered at the close of business on a Special Record Date for
the payment of such
                                     -21-
<PAGE>
 
     Defaulted Interest, which shall be fixed in the following manner. The
     Company shall notify the Trustee in writing of the amount of Defaulted
     Interest proposed to be paid on each Security and the date of the proposed
     payment, and at the same time the Company shall deposit with the Trustee an
     amount of Cash 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
     Cash when deposited to be held in trust for the benefit of the persons
     entitled to such Defaulted Interest as provided in this clause (1).
     Thereupon the Trustee shall fix a Special Record Date for the payment of
     such Defaulted Interest which shall be not more than 15 days and not less
     than 10 days prior to the date of the proposed payment and not less than 10
     days after the receipt by the Trustee of the notice of the proposed
     payment. The Trustee shall promptly notify the Company of such Special
     Record Date and, in the name and at the expense of the Company, shall cause
     notice of the proposed payment of such Defaulted Interest and the Special
     Record Date therefor to be mailed, first-class postage prepaid, to each
     Holder at his address shown upon the registry books of the Registrar not
     less than 10 days prior to such Special Record Date. Notice of the proposed
     payment of such Defaulted Interest and the Special Record Date therefor
     having been mailed as aforesaid, such Defaulted Interest shall be paid to
     the persons in whose names the Securities (or their respective predecessor
     Securities) are registered on such Special Record Date and shall no longer
     be payable pursuant to the following clause (2).

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

     Subject to the foregoing provisions of this Section 2.12, each Security
delivered under this Indenture upon 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.


                                   ARTICLE 3

                                  REDEMPTION

Section 3.1  Right of Redemption.
             ------------------- 

          Redemption of Securities, as permitted by any provision of this
Indenture, shall be made in accordance with the provisions of Paragraphs 5 and 7
of the form of Securities attached as Exhibit A and this Article 3. Subject to
Paragraph 7 of the form of Securities attached as Exhibit A, the Company will
not have the right to redeem any Securities prior to December 15, 2000.  At any
time on or after December 15, 2000, upon not less than 30 nor more than 60 days
notice to each Holder of Securities, the Company will have the right to redeem
all or any part of the Securities at the Redemption Prices specified in
Paragraph 5 therein under the caption "Redemption", in each case 


                                     -22-
<PAGE>
 
including accrued and unpaid interest (including any Additional Amounts or
Additional Interest) to the Redemption Date.

Section 3.2  Notices To Trustee.
             ------------------ 

          If the Company elects to redeem Securities pursuant to the form of
Securities attached as Exhibit A, it shall notify the Trustee in writing of the
Redemption Date and the principal amount of Securities to be redeemed and
whether it wants the Trustee to give notice of redemption to the Holders.

          If the Company elects to reduce the principal amount of Securities to
be redeemed pursuant to the form of Securities attached as Exhibit A by
crediting against any such redemption Securities in its possession, which it has
not previously delivered to the Trustee for cancellation, it shall so notify the
Trustee of the amount of the reduction and deliver such Securities with such
notice.

          The Company shall give each notice provided for in this Section 3.2 to
the Trustee at least 45 days before the Redemption Date (unless a shorter notice
shall be satisfactory to the Trustee). Any such notice may be canceled at any
time prior to notice of such redemption being mailed to any Holder and shall
thereby be void and of no effect.

Section 3.3  Selection of Securities To Be Redeemed.
             -------------------------------------- 

          If less than all of the Securities are to be redeemed pursuant to the
form of Securities attached hereto as Exhibit A, the Trustee shall promptly
redeem the Securities to be redeemed on a pro rata basis, in such manner as the
Trustee shall determine to be fair and appropriate and in such manner as
complies with any applicable Depositary, legal and stock exchange requirements.

          The Trustee shall make the selection from the Securities outstanding
and not previously called for redemption and shall promptly notify the Company
in writing of the Securities selected for redemption and, in the case of any
Security selected for partial redemption, the principal amount thereof to be
redeemed. Securities in denominations of $1,000 may be redeemed only in whole.
The Trustee may select for redemption portions (equal to $1,000 or any integral
multiple thereof) of the principal of Securities that have denominations larger
than $1,000. Provisions of this Indenture that apply to Securities called for
redemption also apply to portions of Securities called for redemption. If any
Security selected for partial redemption is thereafter converted in part before
termination of the conversion right as provided by Section 12.1 hereof, the
portion of the Security so converted shall be deemed to have been a part of the
portion selected for redemption such that only the excess, if any, of the amount
selected for partial redemption over the amount so converted, shall be redeemed.

Section 3.4  Notice of Redemption.
             -------------------- 

          At least 30 days but not more than 60 days before a Redemption Date,
the Company shall mail a notice of redemption by first-class mail, postage
prepaid, to the Trustee and each Holder whose Securities are to be redeemed. At
the Company's request, the Trustee shall give the notice of 


                                     -23-
<PAGE>
 
redemption in the Company's name and at the Company's expense. Each notice for
redemption shall identify the Securities to be redeemed and shall state:

          (1)  the Redemption Date, and that the Securities called for
     redemption may not be converted after the Business Day prior to the
     Redemption Date;

          (2)  the Redemption Price, including the amount of accrued and unpaid
     interest, if any, to be paid upon such redemption;

          (3)  the name, address and telephone number of the Paying Agent;

          (4)  that Securities called for redemption must be surrendered to the
     Paying Agent at the address specified in such notice to collect the
     Redemption Price;

          (5)  that, unless (a) the Company defaults in its obligation to
     deposit Cash with the Paying Agent in accordance with Section 3.6 hereof or
     (b) such redemption is prohibited pursuant to Article 11 hereof or
     otherwise, interest on the Securities called for redemption ceases to
     accrue on and after the Redemption Date and the only remaining right of the
     Holders of such Securities is to receive payment of the Redemption Price,
     including accrued and unpaid interest, if any, to the Redemption Date, upon
     surrender to the Paying Agent of the Securities called for redemption and
     to be redeemed;

          (6)  if any Security is being redeemed in part, the portion of the
     principal amount, equal to $1,000 or any integral multiple thereof, of such
     Security to be redeemed and that, after the Redemption Date, and that upon
     surrender of such Security, a new Security or Securities in aggregate
     principal amount equal to the unredeemed portion thereof will be issued;

          (7)  if less than all the Securities are to be redeemed, the
     identification of the particular Securities (or portion thereof) to be
     redeemed, as well as the aggregate principal amount of such Securities to
     be redeemed and the aggregate principal amount of Securities to be
     outstanding after such partial redemption;

          (8)  the CUSIP number of the Securities to be redeemed;

          (9)  that the notice is being sent pursuant to this Section 3.4 and
     pursuant to the redemption provisions in the form of Securities attached as
     Exhibit A; and

          (10) in the case of a redemption pursuant to Paragraph 7 of the form
     of Securities attached as Exhibit A, a form of written certification of
     each beneficial owner of a Security as to such beneficial owner's
     entitlement to Additional Amounts.

                                     -24-
<PAGE>
 
Section 3.5  Effect of Notice of Redemption.
             ------------------------------ 

     Once notice of redemption is mailed in accordance with Section 3.4,
Securities called for redemption become due and payable on the Redemption Date
and at the Redemption Price, including accrued and unpaid interest (including
any Additional Amounts or Additional Interest), if any, to the Redemption Date.
Upon surrender to the Trustee or Paying Agent, such Securities called for
redemption shall be paid at the Redemption Price, including accrued and unpaid
interest, if any, to the Redemption Date; provided that if the Redemption Date
is after a regular Record Date and on or prior to the corresponding Interest
Payment Date, the accrued interest, if any, shall be payable to the Holder of
the redeemed Securities registered on the relevant Record Date; and provided,
further, that if a Redemption Date is a Legal Holiday, payment shall be made on
the next succeeding Business Day and no interest shall accrue for the period
from such Redemption Date to such succeeding Business Day.

Section 3.6  Deposit of Redemption Price.
             --------------------------- 

     On or prior to the Redemption Date, the Company shall deposit with the
Paying Agent (other than the Company or an Affiliate of the Company) Cash
sufficient to pay the Redemption Price of, including accrued and unpaid interest
on, all Securities to be redeemed on such Redemption Date (other than Securities
or portions thereof called for redemption on that date that have been delivered
by the Company to the Trustee for cancellation). The Paying Agent shall promptly
return to the Company any Cash so deposited which is not required for that
purpose upon the written request of the Company.

     If the Company complies with the preceding paragraph and the other
provisions of this Article 3 and payment of the Securities called for redemption
is not prohibited under Article 11 or otherwise, interest on the Securities to
be redeemed will cease to accrue on the applicable Redemption Date, whether or
not such Securities are presented for payment. Notwithstanding anything herein
to the contrary, if any Security surrendered for redemption in the manner
provided in the Securities shall not be so paid upon surrender for redemption
because of the failure of the Company to comply with the preceding paragraph,
interest shall continue to accrue and be paid from the Redemption Date until
such payment is made on the unpaid principal, and, to the extent lawful, on any
interest not paid on such unpaid principal, in each case at the rate and in the
manner provided in Section 4.1 hereof and the Security.

Section 3.7  Securities Redeemed in Part.
             --------------------------- 

     Upon surrender of a Security that is to be redeemed in part, the Company
shall execute and the Trustee shall authenticate and deliver to the Holder,
without service charge to the Holder, a new Security or Securities equal in
principal amount to the unredeemed portion of the Security surrendered.

Section 3.8  Conversion Arrangement on Call for Redemption.
             --------------------------------------------- 

                                     -25-
<PAGE>
 
     In connection with any redemption of Securities, the Company may arrange
for the purchase and conversion of any Securities by an agreement with one or
more investment bankers or other purchasers (the "Purchasers") to purchase such
securities by paying to the Trustee in trust for the Holders, on or before the
Redemption Date, an amount not less than the applicable Redemption Price,
together with interest accrued to the Redemption Date, of such Securities.
Notwithstanding anything to the contrary contained in this Article 3, the
obligation of the Company to pay the Redemption Price, together with interest
accrued to, but excluding, the Redemption Date, shall be deemed to be satisfied
and discharged to the extent such amount is so paid by such Purchasers. If such
an agreement is entered into (a copy of which shall be filed with the Trustee
prior to the close of business on the Business Day immediately prior to the
Redemption Date), any Securities called for redemption that are not duly
surrendered for conversion by the Holders thereof may, at the option of the
Company, be deemed, to the fullest extent permitted by law, and consistent with
any agreement or agreements with such Purchasers, to be acquired by such
Purchasers from such Holders and (notwithstanding anything to the contrary
contained in Article 12) surrendered by such Purchasers for conversion, all as
of immediately prior to the close of business on the Redemption Date (and the
right to convert any such Securities shall be extended though such time),
subject to payment of the above amount as aforesaid. At the direction of the
Company, the Trustee shall hold and dispose of any such amount paid to it to the
Holders in the same manner as it would monies deposited with it by the Company
for the redemption of Securities. Without the Trustee's prior written consent,
no arrangement between the Company and such Purchasers for the purchase and
conversion of any Securities shall increase or otherwise affect any of the
powers, duties, responsibilities or obligations of the Trustee as set forth in
this Indenture, and the Company agrees to indemnify the Trustee from, and hold
it harmless against, any loss, liability or expense arising out of or in
connection with any such arrangement for the purchase and conversion of any
Securities between the Company and such Purchasers, including the costs and
expenses, including reasonable legal fees, incurred by the Trustee in the
defense of any claim or liability arising out of or in connection with the
exercise or performance of any of its powers, duties, responsibilities or
obligations under this Indenture.


                                   ARTICLE 4

                                   COVENANTS

Section 4.1  Payment Of Securities.
             --------------------- 

     The Company shall pay the principal of and interest (including Additional
Amounts, if any, or Additional Interest, if any) on the Securities on the dates
and in the manner provided in the Securities and this Indenture. An installment
of principal of or interest (including Additional Amounts, if any, or Additional
Interest, if any) on the Securities shall be considered paid on the date it is
due if the Trustee or Paying Agent (other than the Company or an Affiliate of
the Company) holds for the benefit of the Holders, on or before 10:00 a.m. New
York City time on that date, Cash deposited and designated for and sufficient to
pay the installment.

                                     -26-
<PAGE>
 
          The Company shall pay interest on overdue principal and on overdue
installments of interest  (including Additional Amounts, if any, or Additional
Interest, if any) at the rate specified in the Securities, compounded semi-
annually, to the extent lawful.


Section 4.2  Maintenance Of Office Or Agency.
             ------------------------------- 

          The Company shall maintain in the Borough of Manhattan, The City of
New York, an office or agency where Securities may be presented or surrendered
for payment, where Securities may be surrendered for registration of transfer or
exchange and for conversion and where notices and demands to or upon the Company
in respect of the Securities and this Indenture may be served. The Company shall
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 address of the Trustee set forth in Section 13.2.

          The Company may also from time to time designate one or more other
offices or agencies where the Securities may be presented or surrendered for any
or all such purposes and may from time to time rescind such designations;
provided, however, that no such designation or rescission shall in any manner
relieve the Company of its obligation to maintain an office or agency in the
Borough of Manhattan, The City of New York, for such purposes. The Company shall
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. The office
of the Trustee located at 14 Wall Street, New York, New York 10005 is initially
designated as such office.

Section 4.3  Corporate Existence.
             ------------------- 

          Subject to Article 5, the Company shall do or cause to be done all
things necessary to preserve and keep in full force and effect its corporate
existence and the corporate or other existence of each of its Subsidiaries in
accordance with the respective organizational documents of each of them and the
rights (charter and statutory) and corporate franchises of the Company and each
of its Subsidiaries; provided, however, that the Company shall not be required
to preserve, with respect to itself, any right or franchise, and with respect to
any of its Subsidiaries, any such existence, right or franchise, if the Company
shall determine (a) that the preservation thereof is no longer desirable in the
conduct of the business of such entity and (b) the loss thereof is not
disadvantageous in any material respect to the Holders.

Section 4.4  Payment Of Taxes And Other Claims.
             --------------------------------- 

          Except with respect to immaterial items, the Company shall, and shall
cause each of its Subsidiaries to, pay or discharge or cause to be paid or
discharged, before the same shall become 

                                     -27-
<PAGE>
 
delinquent, (i) all taxes, assessments and governmental charges (including
withholding taxes and any penalties, interest and additions to taxes) levied or
imposed upon the Company or any of its Subsidiaries or any of their respective
properties and assets and (ii) all lawful claims, whether for labor, materials,
supplies, services or anything else, which have become due and payable and which
by law have or may become a Lien upon the property and assets of the Company or
any of its Subsidiaries; provided, however, that neither the Company nor any
Subsidiary shall be required to pay or discharge or cause to be paid or
discharged any such tax, assessment, charge or claim whose amount, applicability
or validity is being contested in good faith by appropriate proceedings and for
which disputed amounts adequate reserves have been established in accordance
with GAAP.

Section 4.5   Maintenance Of Properties And Insurance.
              --------------------------------------- 

          The Company shall cause all material properties used or useful to the
conduct of its business and the business of each of its Subsidiaries to be
maintained and kept in good condition, repair and working order (reasonable wear
and tear excepted) and supplied with all necessary equipment and shall cause to
be made all necessary repairs, renewals, replacements, betterments and
improvements thereof, all as in their reasonable judgment may be necessary, so
that the business carried on in connection therewith may be properly conducted
at all times; provided, however, that nothing in this Section 4.5 shall prevent
the Company or any Subsidiary from discontinuing any operation or maintenance of
any of such properties, or disposing of any of them, if such discontinuance or
disposal is in the judgment of the Company, (a) desirable in the conduct of the
business of such entity and (b) not disadvantageous in any material respect to
the Holders.

          The Company shall provide, or cause to be provided, for itself and
each of its Subsidiaries, insurance (including appropriate self-insurance)
against loss or damage of the kinds that, in the reasonable, good faith opinion
of the Company is adequate and appropriate for the conduct of the business of
the Company and such Subsidiaries in a prudent manner, with (except for self-
insurance) reputable insurers or with the government of the United States of
America or an agency or instrumentality thereof, in such amounts, with such
deductibles, and by such methods as shall, in the reasonable, good faith opinion
of the Company, be customary, and adequate and appropriate for the conduct of
the business of the Company and such Subsidiaries in a prudent manner for
entities similarly situated in the industry, unless failure to provide such
insurance (together with all other such failures) would not have a material
adverse effect on the financial condition or results of operations of the
Company or such Subsidiary.

Section 4.6   Compliance Certificate; Notice Of Default.
              ----------------------------------------- 

      (a) The Company shall deliver to the Trustee within 120 days after the end
of its fiscal year an Officers' Certificate complying with Section 314(a)(4) of
the TIA and stating that a review of its activities and the activities of its
Subsidiaries during the preceding fiscal year has been made under the
supervision of the signing Officers with a view to determining whether the
Company has kept, observed, performed and fulfilled its obligations under this
Indenture and further stating, as to each such Officer signing such certificate,
whether or not the signer knows of any failure by the Company or any Subsidiary
of the Company to comply with any conditions or covenants in this 


                                     -28-
<PAGE>
 
Indenture and, if such signor does know of such a failure to comply, the
certificate shall describe such failure with particularity. The Officers'
Certificate shall also notify the Trustee should the relevant fiscal year end on
any date other than the current fiscal year end date.

          (b) The Company shall, so long as any of the Securities are
outstanding, deliver to the Trustee, promptly upon becoming aware of any
Default, Event of Default or fact which would prohibit the making of any payment
to or by the Trustee in respect of the Securities, an Officers' Certificate
specifying such Default, Event of Default or fact and what action the Company is
taking or proposes to take with respect thereto. The Trustee shall not be deemed
to have knowledge of any Default, any Event of Default or any such fact unless
one of its Trust Officers receives notice thereof from the Company or any of the
Holders.

Section 4.7  Reports.
             ------- 

          Whether or not the Company is subject to the reporting requirements of
Section 13 or 15(d) of the Exchange Act, the Company shall deliver to the
Trustee and to each Holder, within 30 days after it is or would have been
required to file such with the SEC, annual and quarterly consolidated financial
statements substantially equivalent to financial statements that would have been
included in reports filed with the SEC if the Company was subject to the
requirements of Section 13 or 15(d) of the Exchange Act, including, with respect
to annual information only, a report thereon by the Company's certified
independent public accountants as such would be required in such reports to the
SEC and, in each case, together with a management's discussion and analysis of
financial condition and results of operations which would be so required.

Section 4.8  Limitation On Status As Investment Company.
             ------------------------------------------ 

          Neither the Company nor any of its Subsidiaries shall become an
"investment company" (as that term is defined in the Investment Company Act of
1940, as amended).

Section 4.9  Waiver Of Stay, Extension Or Usury Laws.
             --------------------------------------- 

          The Company covenants (to the extent that it may lawfully do so) that
it will not at any time insist upon, plead, or in any manner whatsoever claim or
take the benefit or advantage of, any stay or extension law or any usury law or
other law which would prohibit or forgive the Company from paying all or any
portion of the principal of, premium of, or interest on, the Securities as
contemplated herein, wherever enacted, now or at any time hereafter in force, or
which may affect the covenants or the performance of this Indenture; and (to the
extent that it may lawfully do so) the Company 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.

                                      -29-
<PAGE>
 
Section 4.10   Additional Amounts.
               ------------------ 

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

          At least 10 days prior to June 15, 1998, or an earlier Redemption Date
or Repurchase Date (and at least 10 days prior to each date of payment of
principal, premium, if any, or interest after June 15, 1998, or such earlier
Redemption Date or Repurchase Date), the Company shall furnish the Trustee, the
office or agency of the Trustee in the Borough of Manhattan and the office or
agency of the Paying Agent in the Borough of Manhattan, The City of New York, if
other than the Trustee or an agent thereof, with an Officers' Certificate
instructing the Trustee and such Paying Agent whether or not such payment of
principal of, premium, if any, or interest on the Securities shall be made to
the Holders of Securities subject to withholding or deduction. If any
withholding or deduction shall be required, such Officers' Certificate shall
specify the amount required to be withheld or deducted with respect to such
payments to such Holders of Securities and the Company will pay to the Trustee
or the applicable Paying Agent the Additional Amounts, if any, required to be
paid as set forth in the first sentence of this Section 4.10. The Company
covenants to indemnify the Trustee and any Paying Agent for, and to hold them
harmless against, any loss, liability or expense reasonably incurred without
negligence, bad faith or willful misconduct arising out of or in connection with
actions taken or omitted by any of them in reliance on any Officers' Certificate
furnished pursuant to this Section. In the absence of any such Officers'
Certificates with respect to withholding, the Trustee can conclusively rely on
the fact that there is no such withholding.

Section 4.11   Delivery of Certain Information.
               ------------------------------- 

          At any time when the Company is not subject to Section 13 or 15(d) of
the Exchange Act, upon the request of a holder of a Restricted Security, the
Company will promptly furnish or cause to be furnished Rule 144A Information (as
defined below) to such holder of Restricted Securities, or to a prospective
purchaser of any such security designated by any such holder, as the case may
be, to the extent required to permit compliance by such holder with Rule 144A
under the Securities Act (or any successor provision thereto) in connection with
the resale of any such security; provided, however, that the Company shall not
be required to furnish such information in connection with any request made on
or after the date which is two years from the later of (i) the date such a
Security (or any predecessor Security) was last acquired from the Company or
(ii) the date such a Security (or any predecessor Security) was last acquired
from an "affiliate" of the Company within the meaning of Rule 144 under the
Securities Act (or any successor provision thereto). "Rule 144A Information"
shall be such information as is specified pursuant to Rule 144A(d)(4) under the
Securities Act (or any successor provision thereto).

                                      -30
<PAGE>
 
                                    ARTICLE 5

                             SUCCESSOR CORPORATION

Section 5.1   Limitation On Merger, Sale Or Consolidation.
              ------------------------------------------- 

      (a) The Company shall not, directly or indirectly, consolidate with or
merge with or into another Person or sell, lease, convey or transfer all or
substantially all of its assets (computed on a consolidated basis), whether in a
single transaction or a series of related transactions, to another Person or
group of affiliated Persons, unless (i) either (a) in the case of a merger or
consolidation, the Company is the surviving entity or (b) the resulting,
surviving or transferee entity is a corporation organized under the laws of the
United States, any state thereof or the District of Columbia and expressly
assumes by supplemental indenture the due and punctual payment of the principal
of and interest (including Additional Amounts, if any, or Additional Interest,
if any) on all of the Securities and all of the obligations of the Company in
connection with the Securities and the Indenture; (ii) no Default or Event of
Default shall exist or shall occur immediately before or after giving effect on
a pro forma basis to such transaction; (iii) the Company has delivered to the
Trustee an Officers' Certificate and an Opinion of Counsel, each stating that
such consolidation, merger or transfer and, if a supplemental indenture is
required, such supplemental indenture comply with the Indenture and that all
conditions precedent relating to such transactions have been satisfied; and (iv)
the resulting, surviving or transferee entity, unless it is a Subsidiary,
immediately thereafter has a consolidated net worth not less than that of the
Company immediately prior thereto.

      (b) For purposes of clause (a) of this Section 5.1, the sale, lease,
conveyance, assignment, transfer, or other disposition of all or substantially
all of the properties and assets of one or more Subsidiaries of the Company,
which properties and assets, if held by the Company instead of such
Subsidiaries, would constitute all or substantially all of the properties and
assets of the Company on a consolidated basis, shall be deemed to be the
transfer of all or substantially all of the properties and assets of the
Company.

Section 5.2  Successor Corporation Substituted.
             --------------------------------- 

          Upon any consolidation or merger or any sale, lease, conveyance or
transfer of all or substantially all of the assets of the Company in accordance
with the foregoing, the successor corporation formed by such consolidation or
into which the Company is merged or to which such sale, lease, conveyance or
transfer is made (the "Successor Corporation"), shall succeed to, and be
substituted for, and may exercise every right and power of, the Company under
the Indenture with the same effect as if such successor corporation had been
named herein as the Company, and when a successor corporation duly assumes all
of the obligations of the Company pursuant hereto and pursuant to the
Securities, the predecessor shall be released from such obligations (except with
respect to any obligations that arise from or as a result of such transaction);
provided, however, that if the Successor Corporation is a Subsidiary, the
consolidated net worth of which is less than that of 


                                     -31-
<PAGE>
 
the Company immediately prior to such merger, consolidation, sale, lease,
conveyance or transfer, the Company shall not be released from such obligations
but shall remain jointly and severally liable therefor with the Successor
Corporation.


                                   ARTICLE 6

                        EVENTS OF DEFAULT AND REMEDIES

Section 6.1  Events Of Default.
             ----------------- 

     "Event of Default," wherever used herein, means any one of the following
events (whatever the reason for such Event of Default and whether it shall be
caused voluntarily or involuntarily or effected, without limitation, 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)  failure to pay any installment of interest (including Additional
     Amounts, if any, or Additional Interest, if any) on the Securities as and
     when the same becomes due and payable, and the continuance of such default
     for a period of 30 days, whether or not such payment is prohibited by
     Article 11;

          (2)  failure to perform any conversion of the Securities required
     under this Indenture and the continuance of such default for a period of 30
     days;

          (3)  failure to pay all or any part of the principal of, or premium,
     if any on the Securities when and as the same become due and payable at
     maturity, redemption, by acceleration or otherwise, including, without
     limitation, default in the payment of the Repurchase Price on the
     Repurchase Date in accordance with Article 10, whether or not such payment
     is prohibited by Article 11;

          (4)  failure by the Company to observe or perform any covenant,
     agreement or warranty contained in the Securities or this Indenture (other
     than a default in the performance of any covenant, agreement or warranty
     which is specifically dealt with elsewhere in this Section 6.1), and
     continuance of such failure 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 Holders of at least 25% in aggregate
     principal amount of the then outstanding Securities, a written notice
     specifying such default or breach, requesting it to be remedied and stating
     that such notice is a "Notice of Default" hereunder;

          (5)  a default under Indebtedness of the Company or any of its
     Subsidiaries with an aggregate principal amount, individually or in the
     aggregate, in excess of $25,000,000 (a) resulting from the failure to pay
     principal at maturity or (b) as a result of which the maturity of such
     Indebtedness has been accelerated prior to its stated maturity;

                                     -32-
<PAGE>
 
          (6)  a decree, judgment, or order by a court of competent jurisdiction
     shall have been entered adjudging the Company or any of its Significant
     Subsidiaries as bankrupt or insolvent, or approving as properly filed a
     petition seeking reorganization of the Company or any of its Significant
     Subsidiaries under any bankruptcy or similar law, and such decree or order
     shall have continued undischarged and unstayed for a period of 75 days; or
     a decree or order of a court of competent jurisdiction over the appointment
     of a receiver, liquidator, trustee, or assignee in bankruptcy or insolvency
     of the Company, any of its Significant Subsidiaries, or of the property of
     any such Person, or for the winding up or liquidation of the affairs of any
     such Person, shall have been entered, and such decree, judgment, or order
     shall have remained in force undischarged and unstayed for a period of 75
     days;

          (7)  the Company or any of its Significant Subsidiaries shall
     institute proceedings to be adjudicated a voluntary bankrupt, or shall
     consent to the filing of a bankruptcy proceeding against it, or shall file
     a petition or answer or consent seeking reorganization under any bankruptcy
     or similar law or similar statute, or shall consent to the filing of any
     such petition, or shall consent to the appointment of a Custodian,
     receiver, liquidator, trustee, or assignee in bankruptcy or insolvency of
     it or any of its assets or property, or shall make a general assignment for
     the benefit of its creditors, or shall admit in writing its inability to
     pay its debts generally as they become due, or shall, within the meaning of
     any Bankruptcy Law, become insolvent, fail generally to pay its debts as
     they become due, or take any corporate action in furtherance of or to
     facilitate, conditionally or otherwise, any of the foregoing; or

          Notwithstanding the 60-day period and notice requirement contained in
Section 6.1(4) above, with respect to a default under Article 10 the 60-day
period referred to in Section 6.1(4) shall be deemed to have begun as of the
date the Change of Control Notice is required to be sent in the event that the
Company has not complied with the provisions of Section 10.1 and the Trustee or
Holders of at least 25% in principal amount of the outstanding Securities
thereafter give the Notice of Default referred to in Section 6.1(4) to the
Company and, if applicable, the Trustee; provided, however, that if the breach
or default is a result of a default in the payment when due of the Repurchase
Price on the Repurchase Date, such Event of Default shall be deemed, for
purposes of this Section 6.1, to arise no later than on the Repurchase Date.

          If a Default occurs and is continuing and if it is known to the
Trustee, the Trustee shall, within 90 days after the occurrence of such default,
give to the Holders notice of such default.

Section 6.2    Acceleration Of Maturity Date; Rescission And Annulment.
               ------------------------------------------------------- 

          If an Event of Default (other than an Event of Default specified in
Section 6.1(6) or (7) relating to the Company) occurs and is continuing, then,
and in every such case, unless the principal of all of the Securities shall have
already become due and payable, either the Trustee or the Holders of not less
than 25% in aggregate principal amount of then outstanding Securities, by a
notice in writing to the Company (and to the Trustee if given by Holders) (an
"Acceleration Notice"), may declare all of the principal of the Securities (or
the Repurchase Price if the Event of Default includes failure to pay the
Repurchase Price, determined as set forth below), including in each case accrued


                                     -33-
<PAGE>
 
interest thereon, to be due and payable immediately. If an Event of Default
specified in Section 6.1(6) or (7) relating to the Company occurs, all principal
and accrued interest (including Additional Amounts, if any, or accrued
Additional Interest, if any) thereon will be immediately due and payable on all
outstanding Securities without any declaration or other act on the part of
Trustee or the Holders.

     At any time after such a declaration of acceleration has been made and
before a judgment or decree for payment of the money due has been obtained by
the Trustee as hereinafter provided in this Article 6, the Holders of no less
than a majority in aggregate principal amount of then outstanding Securities, by
written notice to the Company and the Trustee, may rescind, on behalf of all
Holders, any such declaration of acceleration if:

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

               (i)   all overdue interest (including Additional Amounts, if any,
          or accrued Additional Interest, if any) on all Securities,

               (ii)  the principal of (and premium, if any, applicable to) any
          Securities which would then be due otherwise than by such declaration
          of acceleration, and interest thereon at the rate borne by the
          Securities, 

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

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

          (2)  all Events of Default, other than the non-payment of the
     principal of, premium, if any, and interest (including Additional Amounts,
     if any, or accrued Additional Interest, if any) on Securities that have
     become due solely by such declaration of acceleration, have been cured or
     waived as provided in Section 6.12, including, if applicable, any Event of
     Default relating to the covenants contained in Section 10.1.

     Notwithstanding the previous sentence of this Section 6.2, no waiver shall
be effective against any Holder for any Event of Default or event which with
notice or lapse of time or both would be an Event of Default with respect to any
covenant or provision which cannot be modified or amended without the consent of
the Holder of each outstanding Security affected thereby, unless such affected
Holder agrees, in writing, to waive any subsequent Default or Event or Default
or impair any right consequent thereon.

Section 6.3  Collection Of Indebtedness And Suits For Enforcement By Trustee.
             --------------------------------------------------------------- 

                                     -34-
<PAGE>
 
     The Company covenants that if an Event of Default in payment of principal,
premium or interest (including any Additional Amounts and Additional Interest)
specified in clause (1) or (3) of Section 6.1 occurs and is continuing, the
Company shall, 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, premium (if any), interest (including any Additional
Amounts and Additional Interest) and, to the extent that payment of such
interest shall be legally enforceable, interest on any overdue principal (and
premium, if any) and on any overdue interest (including any Additional Amounts
and Additional Interest), at the rate borne by the Securities, and, in addition
thereto, such further amount as shall be sufficient to cover the costs and
expenses of collection, including compensation to, and expenses, disbursements
and advances of, the Trustee, its agents and counsel.

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

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

Section 6.4   Trustee May File Proofs Of Claim.
              -------------------------------- 

     In case of the pendency of any receivership, insolvency, liquidation,
bankruptcy, reorganization, arrangement, adjustment, composition or other
judicial proceeding relative to the Company or any other obligor upon the
Securities or the property of the Company or of such obligor or their creditors,
the Trustee (irrespective of whether the principal of the Securities shall then
be due and payable as therein expressed or by declaration or otherwise and
irrespective of whether the Trustee shall have made any demand on the Company
for the payment of overdue principal or interest) shall be entitled and
empowered, by intervention in such proceeding or otherwise to take any and all
actions under the TIA, including:

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


                                     -35-
<PAGE>
 
               (2) 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 7.7.

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

Section 6.5  Trustee May Enforce Claims Without Possession Of Securities.
             ----------------------------------------------------------- 

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

Section 6.6  Priorities.
             ---------- 

          Any money collected by the Trustee pursuant to this Article 6 shall be
applied in the following order, at the date or dates fixed by the Trustee and,
in case of the distribution of such money on account of principal, premium (if
any) or interest, upon presentation of the Securities and the notation thereon
of the payment if only partially paid and upon surrender thereof if fully paid:

            FIRST: To the Trustee in payment of all amounts due pursuant to
            Section 7.7;

            SECOND: To the holders of the Senior Indebtedness of the Company to
            the extent provided in Article 11;

            THIRD: To the Holders in payment of the amounts then due and unpaid
            for principal of, premium (if any), and interest (including any
            Additional Amounts and Additional Interest) on, the Securities in
            respect 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,
            premium (if any) and interest (including any Additional Amounts and
            Additional Interest), respectively; and

            FOURTH: To whomsoever may be lawfully entitled thereto, the
            remainder, if any.


                                     -36- 
<PAGE>
 
Section 6.7  Limitation On Suits.
             ------------------- 

          No Holder of any Security shall have any right to order or direct the
Trustee to institute any proceeding, judicial or otherwise, with respect to this
Indenture, or for the appointment of a receiver or trustee, or for any other
remedy hereunder, unless

               (A) such Holder has previously given written notice to the
          Trustee of a continuing Event of Default;

               (B) the Holders of not less than 25% in principal amount of then
          outstanding Securities shall have made written request to the Trustee
          to institute proceedings in respect of such Event of Default in its
          own name as Trustee hereunder;
          
               (C) such Holder or Holders have offered to the Trustee reasonable
          security or indemnity against the costs, expenses and liabilities to
          be incurred or reasonably probable to be incurred in compliance with
          such request;

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

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

it being understood and intended that no one or more Holders may 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 Holders or to
obtain or to seek to obtain priority or preference over any other Holders or to
enforce any right under this Indenture, except in the manner herein provided and
for the equal and ratable benefit of all the Holders.

Section 6.8  Unconditional Right Of Holders To Receive Principal, Premium And
             ----------------------------------------------------------------
Interest.
-------- 

          Notwithstanding any other provision of this Indenture, the Holder of
any Security shall have the right, which is absolute and unconditional, to
receive payment of the principal of, and premium (if any) and interest on, such
Security when due (including, in the case of redemption, the Redemption Price on
the applicable Redemption Date, and in the case of the Repurchase Price, on the
applicable Repurchase Date) and to institute suit for the enforcement of any
such payment after such respective dates, and such rights shall not be impaired
without the consent of such Holder.

Section 6.9  Rights And Remedies Cumulative.
             ------------------------------ 

          Except as otherwise provided with respect to the replacement or
payment of mutilated, destroyed, lost or stolen Securities in Section 2.7, no
right or remedy herein conferred upon or reserved to the Trustee or to the
Holders is intended to be exclusive of any other right or remedy, and 


                                     -37-
<PAGE>
 
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   6.10  Delay Or Omission Not Waiver.
                ---------------------------- 

          No delay or omission by the Trustee or by any Holder of any Security
to exercise any right or remedy arising upon any Event of Default shall impair
the exercise of any such right or remedy or constitute a waiver of any such
Event of Default. Every right and remedy given by this Article 6, or by law to
the Trustee or to the Holders may be exercised from time to time, and as often
as may be deemed expedient, by the Trustee or by the Holders, as the case may
be.

Section   6.11  Control By Holders.
                ------------------ 

          The Holder or Holders of no less than a majority in aggregate
principal amount of then outstanding Securities shall have the right to direct
the time, method and place of conducting any proceeding for any remedy available
to the Trustee or exercising any trust or power conferred upon the Trustee,
provided that

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

          (2) the Trustee shall not determine that the action so directed would
     be unjustly prejudicial to the Holders not taking part in such direction,
     and

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

Section   6.12  Waiver Of Past Default.
                ---------------------- 
 
          Subject to Section 6.8, the Holder or Holders of not less than a
majority in aggregate principal amount of then outstanding Securities may, on
behalf of all Holders, prior to the declaration of acceleration of the maturity
of the Securities, waive any past Default hereunder and its consequences, except
a Default

               (A) in the payment of the principal of, premium, if any, or
          interest (including any Additional Amounts) on, any Security not yet
          cured as specified in clauses (1) and (3) of Section 6.1, or

               (B) 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 affected.

                                     -38-
<PAGE>
 
          Upon any such waiver, such Default shall cease to exist, and any Event
of Default arising from such a Default 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 the exercise of any right arresting
therefrom.

Section 6.13  Undertaking For Costs.
              --------------------- 

          All parties to this Indenture agree, and each Holder of any Security
by his acceptance thereof shall be deemed to have agreed, that any court may in
its discretion require, in any suit for the enforcement of any right or remedy
under this Indenture, or in any suit against the Trustee for any action taken,
suffered or omitted to be taken by it as Trustee, the filing by any party
litigant in such suit of an undertaking to pay the costs of such suit, and that
such court may in its discretion assess reasonable costs, including reasonable
attorneys' fees, against any party litigant in such suit, having due regard to
the merits and good faith of the claims or defenses made by such party litigant;
but the provisions of this Section 6.13 shall not apply to any suit instituted
by the Company, to any suit instituted by the Trustee, to any suit instituted by
any Holder, or group of Holders, holding in the aggregate more than 10% in
aggregate principal amount of then outstanding Securities, or to any suit
instituted by any Holder for enforcement of the payment of principal of, premium
(if any) or interest on, any Security on or after the respective Stated Maturity
of such Security (including, in the case of redemption, on or after the
Redemption Date).

Section 6.14  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 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.


                                    ARTICLE

                                    TRUSTEE

          The Trustee hereby accepts the trust imposed upon it by this Indenture
and covenants and agrees to perform the same, as herein expressed.

Section 7.1  Duties Of Trustee.
             ----------------- 

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

                                     -39-
<PAGE>
 
     (b)  Except during the continuance of a Default or an Event of Default:

          (i)  The Trustee need perform only those duties as are specifically
set forth in this Indenture and no others, and no covenants or obligations shall
be implied in or read into this Indenture which are adverse to the Trustee.

          (ii)  In the absence of bad faith on its part, the Trustee may
conclusively rely, as to the truth of the statements and the correctness of the
opinions expressed therein, upon certificates or opinions furnished to the
Trustee and conforming to the requirements of this Indenture. However, the
Trustee shall examine the certificates and opinions to determine whether or not
they conform to the requirements of this Indenture.

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

          (i)  This paragraph does not limit the effect of paragraph (b) of
this Section 7.1.

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

          (iii)  The Trustee shall not be liable with respect to any action it
takes or omits to take in good faith in accordance with a direction received by
it pursuant to Section 6.11.

     (d)  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 to take or omit to take any action under this
Indenture or at the request, order or direction of the Holders 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.

     (e)  Every provision of this Indenture that in any way relates to the
Trustee is subject to paragraphs (a), (b), (c), (d) and (f) of this Section 7.1.

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

Section   7.2  Rights Of Trustee.
               ----------------- 

          Subject to Section 7.1:

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

                                     -40-
<PAGE>
 
     (b)  Before the Trustee acts or refrains from acting, it may consult with
counsel and may require an Officers' Certificate on or Opinion of Counsel, which
shall conform to Sections 13.4 and 13.5. The Trustee shall not be liable for any
action it takes or omits to take in good faith in reliance on such Officers'
Certificate or Opinion of Counsel.

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

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

     (e)  The Trustee shall not be bound to make any investigation into the
facts or matters stated in any resolution, certificate, statement, instrument,
opinion, notice, request, direction, consent, order, bond, debenture, 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.

     (f)  The Trustee shall be under no obligation to exercise any of the rights
or powers vested in it by this Indenture at the request, order or direction of
any of the Holders, pursuant to the provisions of this Indenture, unless such
Holders shall have offered to the Trustee reasonable security or indemnity
against the costs, expenses and liabilities which may be incurred therein or
thereby.

     (g)  Unless otherwise specifically provided for in this Indenture, any
demand, request, direction or notice from the Company shall be sufficient if
signed by an Officer of the Company.

     (h)  The Trustee shall have no duty to inquire as to the performance of the
Company's covenants in Article 4 hereof. In addition, the Trustee shall not be
deemed to have knowledge of any Default or Event of Default except (i) any Event
of Default occurring pursuant to Sections 6.1(1), 6.1(2) or 6.1(3), or (ii) any
Default or Event of Default of which the Trustee shall have received written
notification or obtained actual knowledge.

Section   7.3  Individual Rights Of Trustee.
               ---------------------------- 

     The Trustee in its individual or any other capacity may become the
owner or pledgee of Securities and may otherwise deal with the Company, any of
its Subsidiaries, or their respective affiliates with the same rights it would
have it if were not Trustee. Any Agent may do the same with like rights.
However, the Trustee must comply with Section 7.10 and 7.11.

Section   7.4  Trustee's Disclaimer.
               -------------------- 

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

                                     -41-
<PAGE>
 
of authentication, or the use or application of any funds received by a Paying
Agent other than the Trustee.

Section   7.5  Notice Of Default.
               ----------------- 

          If a Default or an Event of Default occurs and is continuing and if it
is known to the Trustee, the Trustee shall mail to each Security Holder notice
of the uncured Default or Event of Default within 90 days after such Default or
Event of Default occurs.  Except in the case of a Default or an Event of Default
in payment of principal (or premium, if any), or interest (including any
Additional Amounts or Additional Interest) on, any Security (including the
payment of the Repurchase Price on the Repurchase Date and the payment of the
Redemption Price on the Redemption Date), the Trustee may withhold the notice if
and so long as a Trust Officer in good faith determines that withholding the
notice is in the interest of the Security Holders.

Section   7.6  Reports By Trustee To Holders.
               ----------------------------- 

          Within 60 days after each November 15 beginning with the November 15
following the date of this Indenture, the Trustee shall, if required by law,
mail to each Security Holder a brief report dated as of such November 15 that
complies with the TIA Section 313(a). The Trustee also shall comply with TIA
Sections 313(b) and 313(c).

          The Company shall promptly notify the Trustee in writing if the
Securities become listed on any stock exchange, market or automatic quotation
system.

          A copy of each report at the time of its mailing to Security Holders
shall be mailed to the Company and filed, if required, with the SEC and each
stock exchange or market, if any, on which the Securities are listed.

Section   7.7  Compensation And Indemnity.
               -------------------------- 

          The Company agrees to pay to the Trustee from time to time reasonable
compensation for its services.  The Trustee's compensation shall not be limited
by any law on compensation of a trustee of an express trust.  The Company shall
reimburse the Trustee upon request for all reasonable disbursements, expenses
and advances incurred or made by it.  Such expenses shall include the reasonable
compensation, disbursements and expenses of the Trustee's agents, accountants,
experts and counsel.

          The Company agrees to indemnify each of the Trustee (in its capacity
as Trustee) and its officers, directors, attorneys-in-fact and agents for, and
hold it harmless against, any claim, demand, expense (including but not limited
to reasonable compensation, disbursements and expenses of the Trustee's agents
and counsel), loss or liability incurred by it without negligence, bad faith or
willful misconduct on its part, arising out of or in connection with the
administration of this Indenture and its rights or duties hereunder including
the reasonable 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 

                                     -42-
<PAGE>
 
hereunder. The Trustee shall notify the Company promptly of any claim asserted
against the Trustee for which it may seek indemnity under this Section 7.7. The
Company shall defend the claim and the Trustee shall provide reasonable
cooperation at the Company's expense in the defense. The Trustee may have
separate counsel and the Company shall pay the reasonable fees and expenses of
such counsel; provided, that the Company will not be required to pay such fees
and expenses if it assumes the Trustee's defense and in the opinion of the
Trustee there is no conflict of interest between the Company and the Trustee in
connection with such defense. The Company need not pay for any settlement made
without its written consent. The Company need not reimburse any expense or
indemnify against any loss or liability to the extent incurred by the Trustee
through its negligence, bad faith or willful misconduct.

          To secure the Company's payment obligations in this Section 7.7, the
Trustee shall have a lien prior to the Securities on all assets held or
collected by the Trustee, in its capacity as Trustee, except assets held in
trust to pay principal of, and premium, if any, or interest on particular
Securities.

          When the Trustee incurs expenses or renders services after an Event of
Default specified in Section 6.1(6) or (7) occurs, the expenses and the
compensation for the services are intended to constitute expenses of
administration under any Bankruptcy Law.

          The Company's obligations under this Section 7.7 and any lien arising
hereunder shall survive the resignation or removal of the Trustee, the discharge
of the Company's obligations pursuant to Article 8 of this Indenture and any
rejection or termination of this Indenture, including without limitation any
rejection or termination under any Bankruptcy Law.

Section   7.8  Replacement Of Trustee
               ----------------------

          The Trustee may resign by so notifying the Company in writing. The
Holder or Holders of a majority in principal amount of then outstanding
Securities may remove the Trustee by so notifying the Company and the Trustee in
writing and may appoint a successor trustee with the Company's consent. The
Company may remove the Trustee if

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

               (b)  the Trustee is adjudged bankrupt or insolvent;

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

               (d)  the Trustee becomes incapable of acting.

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

                                     -43-
<PAGE>
 
Securities may appoint a successor Trustee to replace the successor Trustee
appointed by the Company.

          A successor Trustee shall deliver a written acceptance of its
appointment to the retiring Trustee and to the Company. Immediately after such
delivery and provided that all sums owing to the retiring Trustee provided for
in Section 7.7 have been paid, the retiring Trustee shall transfer all property
held by it as trustee to the successor Trustee, subject to the lien provided in
Section 7.7, the resignation or removal of the retiring Trustee shall become
effective, and the successor Trustee shall have all the rights, powers and
duties of the Trustee under this Indenture. A successor Trustee shall mail
notice of its succession to each Holder.

          If a successor Trustee does not take office within 60 days after the
retiring Trustee resigns or is removed, the retiring Trustee, the Company or the
Holder or Holders of at least 10% in principal amount of then outstanding
Securities may petition any court of competent jurisdiction for the appointment
of a successor Trustee.

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

          Notwithstanding replacement of the Trustee pursuant to this Section
7.8, the Company's obligations under Section 7.7 shall continue for the benefit
of the retiring Trustee.

Section   7.9  Successor Trustee By Merger, Etc.
               ---------------------------------

          If the Trustee consolidates with, merges or converts into, or
transfers all or substantially all of its corporate trust business to, another
corporation, the resulting, surviving or transferee corporation without any
further act shall, if such resulting surviving or transferee corporation is
otherwise eligible hereunder, be the successor Trustee.

Section   7.10  Eligibility; Disqualification.
                ----------------------------- 

          The Trustee shall at all times satisfy the requirements of TIA Section
310(a)(1), (2) and (5).  The Trustee shall have a combined capital and surplus
of at least $100,000,000 as set forth in its most recent published annual report
of condition.  The Trustee shall comply with TIA Section 310(b).

Section   7.11  Preferential Collection Of Claims Against Company.
                ------------------------------------------------- 

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

                                     -44-
<PAGE>
 
                                   ARTICLE 8

                          SATISFACTION AND DISCHARGE

Section 8.1  Satisfaction And Discharge Of Indenture.
             --------------------------------------- 

          The Company may terminate its obligations under this Indenture
(subject to the provisions of this Article 8) when it shall have delivered to
the Trustee for cancellation all Securities theretofore authenticated (other
than any Securities which shall have been destroyed, lost or stolen and which
shall have been replaced or paid as provided in Article 2 hereof) and the
following conditions shall be satisfied:

          (1) The Company has paid all sums payable under the Indenture; and

          (2) The Company shall have delivered to the Trustee an Officers'
Certificate and an Opinion of Counsel, each stating that all conditions
precedent have been complied with as contemplated by this Section 8.1.

Section 8.2  Payment To The Company.
             ---------------------- 

          Any money deposited with the Trustee or any Paying Agent, or then held
by the Company, for the payment of the principal of, premium, if any, or
interest on any Security and remaining unclaimed for two years after such
principal, premium, if any, or interest has become due and payable shall be paid
to the Company on its request; and the Holder of such Security shall thereafter
look only to the Company for payment thereof, and all liability of the Trustee
or such Paying Agent with respect to such trust money shall thereupon cease.


                                   ARTICLE 9

                      AMENDMENTS, SUPPLEMENTS AND WAIVERS

Section 9.1  Supplemental Indentures Without Consent Of Holders.
             -------------------------------------------------- 

          Without the consent of any Holder, the Company, when authorized by
Board Resolutions, 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 cure any ambiguity, defect, or inconsistency, or to make any
other provisions with respect to matters or questions arising under this
Indenture which shall not be inconsistent with the provisions of this Indenture,
provided that such action pursuant to this clause (1) does not adversely affect
the interests of any Holder in any respect;

                                     -45-
<PAGE>
 
     (2)  to create additional covenants of the Company for the benefit of the
Holders, or to surrender any right or power herein conferred upon the Company or
to make any other change that does not adversely affect the rights of any
Holder, provided, that the Company has delivered to the Trustee an Opinion of
Counsel stating that such change pursuant to this clause (2) does not adversely
affect the rights of any Holder;

     (3)  to provide for collateral for, or guarantors of, the Securities;

     (4)  to evidence the succession of another Person to the Company and the
assumption by any such successor of the obligations of the Company herein and in
the Securities in accordance with Article 5;

     (5)  to comply with the TIA; or

     (6)  to qualify the Securities for listing for trading on the Luxembourg
Stock Exchange.

Section   9.2  Amendments, Supplemental Indentures And Waivers With Consent Of
               ---------------------------------------------------------------
Holders.
------- 

          Subject to Section 6.8 and the last sentence of this paragraph, with
the consent of the Holders of not less than a majority in aggregate principal
amount of then outstanding Securities, by written act of said Holders delivered
to the Company and the Trustee, the Company, when authorized by Board
Resolutions, and the Trustee may amend or supplement this Indenture or the
Securities or 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 the Securities or of modifying in any
manner the rights of the Holders under this Indenture or the Securities. Subject
to Section 6.8 and the last sentence of this paragraph, the Holder or Holders of
not less than a majority in aggregate principal amount of then outstanding
Securities may, in writing, waive compliance by the Company with any provision
of this Indenture or the Securities. Notwithstanding any of the above, however,
no such amendment, supplemental indenture or waiver shall, without the consent
of the Holder of each outstanding Security affected thereby:

          (1)  change the Stated Maturity of any Security or reduce the
     principal amount thereof or the rate (or extend the time for payment) of
     interest thereon or any premium payable upon the redemption thereof, or
     change the obligation of the Company to pay Additional Amounts in a manner
     adverse to the Holders, or change the place of payment where, or the coin
     or currency in which, any Security or any premium or the interest thereon
     is payable, or impair the right to institute suit for the enforcement of
     any such payment or the conversion of any Security on or after the due date
     thereof (including, in the case of redemption, on or after the Redemption
     Date), or reduce the Repurchase Price, or alter the Repurchase Offer or
     redemption provisions in a manner adverse to the Holders;

                                     -46-
<PAGE>
 
     (2)  reduce the percentage in principal amount of the outstanding
Securities, the consent of whose Holders is required for any such amendment,
supplemental indenture or waiver provided for in the Indenture;

     (3)  adversely affect the right of such Holder to convert Securities; or

     (4)  modify any of the waiver provisions, except to increase any required
percentage or to provide that certain other provisions of the Indenture cannot
be modified or waived without the consent of the Holder of each outstanding
Security affected thereby.

          It shall not be necessary for the consent of the Holders under this
Section 9.2 to approve the particular form of any proposed amendment, supplement
or waiver, but it shall be sufficient if such consent approves the substance
thereof.

          After an amendment, supplement or waiver under this Section 9.2
becomes effective, the Company shall mail to the Holders affected thereby a
notice briefly describing the amendment, supplement or waiver. Any failure of
the Company to mail such notice, or any defect therein, shall not, however, in
any way impair or affect the validity of any such supplemental indenture or
waiver.

          After an amendment, supplement or waiver under this Section 9.2
becomes effective, it shall bind each Holder.

          In connection with any amendment, supplement or waiver under this
Article 9, the Company may, but shall not be obligated to, offer to any Holder
who consents to such amendment, supplement or waiver, or (at the option of the
Company) to all Holders, consideration for consent to such amendment, supplement
or waiver.

Section 9.3  Compliance With TIA.
             ------------------- 

          Every amendment, waiver or supplement of this Indenture or the
Securities shall comply with the TIA as then in effect; provided that this
Section 9.3 shall not require such supplemental indenture or the Trustee to be
qualified under the TIA prior to the time such qualification is in fact required
under the terms of the TIA or the Indenture has been qualified under the TIA,
nor shall it constitute any admission or acknowledgment by any party to such
supplemental indenture that any such qualification is required prior to the time
such qualification is in fact required under the terms of the TIA or the
Indenture has been qualified under the TIA.

Section 9.4  Revocation And Effect Of Consents.
             --------------------------------- 

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

                                     -47-
<PAGE>
 
as to his Security or portion of his Security by written notice to the Company
or the Person designated by the Company as the Person to whom consents should be
sent if such revocation is received by the Company or such Person before the
date on which the Trustee receives an Officers' Certificate certifying that the
Holders of the requisite principal amount of Securities have consented (and not
theretofore revoked such consent) to the amendment, supplement or waiver.

          The Company may, but shall not be obligated to, fix a record date for
the purpose of determining the Holders entitled to consent to any amendment,
supplement or waiver, which record date shall be the date so fixed by the
Company notwithstanding the provisions of the TIA. If a record date is fixed,
then notwithstanding the last sentence of the immediately preceding paragraph,
those Persons who were Holders at such record date, and only those Persons (or
their duly designated proxies), shall be entitled to revoke any consent
previously given, whether or not such Persons continue to be Holders after such
record date. No such consent shall be valid or effective for more than 90 days
after such record date.

          After an amendment, supplement or waiver becomes effective pursuant to
this Section 9.4, it shall bind every Security Holder, unless it makes a change
described in any of clauses (1) through (4) of Section 9.2, in which case, the
amendment, supplement or waiver shall bind only each Holder of a Security who
has consented to it and every subsequent Holder of a Security or portion of a
Security that evidences the same debt as the consenting Holder's Security.

Section 9.5  Notation On Or Exchange Of Securities.
             ------------------------------------- 

          If an amendment, supplement or waiver changes the terms of a Security,
the Trustee may require the Holder of the Security to deliver it to the Trustee
or require the Holder to put an appropriate notation on the Security. The
Trustee may place an appropriate notation on the Security about the changed
terms and return it to the Holder. Alternatively, if the Company or the Trustee
so determines, the Company in exchange for the Security shall issue and the
Trustee shall authenticate a new Security that reflects the changed terms. Any
failure to make the appropriate notation or to issue a new Security shall not
affect the validity of such amendment, supplement or waiver.

Section 9.6  Trustee To Sign Amendments, Etc.
             --------------------------------

          The Trustee shall execute any amendment, supplement or waiver
authorized pursuant to this Article 9; provided, however, that the Trustee may,
but shall not be obligated to, execute any such amendment, supplement or waiver
which affects the Trustee's own rights, duties or immunities under this
Indenture. The Trustee shall be entitled to receive, and shall be fully
protected in relying upon, an Opinion of Counsel stating that the execution of
any amendment, supplement or waiver authorized pursuant to this Article 9 is
authorized or permitted by this Indenture.

                                     -48-
<PAGE>
 
                                    ARTICLE

             RIGHT TO REQUIRE REPURCHASE UPON A CHANGE OF CONTROL

Section 10.1  Repurchase Of Securities At Option Of The Holder Upon A Change Of
              -----------------------------------------------------------------
              Control.
              ------- 

     (a)  In the event that a Change of Control occurs, each Holder shall have
the right, at such Holder's option, subject to the terms and conditions of this
Indenture, to require the Company to repurchase all or any part of such Holder's
Securities (provided, that the principal amount of such Securities must be
$1,000 or an integral multiple thereof) on the date (the "Repurchase Date") that
is no later than 45 Business Days after the occurrence of such Change of
Control, at a cash price (the "Repurchase Price") equal to 100% of the principal
amount thereof, together with accrued and unpaid interest (including any
Additional Amounts or Additional Interest) to the Repurchase Date.

     (b)  In the event of a Change of Control, the Company shall be required to
commence an irrevocable and unconditional offer to purchase Securities (a
"Repurchase Offer"), and the Company shall follow the procedures set forth in
this Section 10.1 as follows:

          (1)  the Repurchase Offer shall commence within 30 Business Days
     following a Change of Control;

          (2)  the Repurchase Offer shall remain open for 15 Business Days
     following its commencement, except to the extent that a longer period is
     required by applicable law, but in any case not more than 45 Business Days
     following the Change of Control (the "Repurchase Offer Period");

          (3)  upon the expiration of a Repurchase Offer, the Company shall
     purchase all Securities tendered in response to the Repurchase Offer;

          (4)  if the Repurchase Date is on or after an interest payment record
     date and on or before the related Interest Payment Date, any accrued
     interest will be paid to the Person in whose name a Security is registered
     at the close of business on such record date, and no additional interest
     will be payable to Security Holders who tender Securities pursuant to the
     Repurchase Offer;

          (5)  the Company shall provide the Trustee with notice of the
     Repurchase Offer at least 5 Business Days before the commencement of any
     Repurchase Offer; and

          (6)  on or before the commencement of any Repurchase Offer, the
     Company or the Trustee (upon the request and at the expense of the Company)
     shall send, by first-class mail, a notice (a "Change of Control Notice") to
     each of the

                                     -49-
<PAGE>
 
Security Holders, which (to the extent consistent with this Indenture) shall
govern the terms of the Repurchase Offer and shall state:

               (i)   that the Repurchase Offer is being made pursuant to such
          Change of Control Notice and this Section 10.1 and that all
          Securities, or portions thereof, tendered will be accepted for
          payment;

               (ii)  the Repurchase Price (including the amount of accrued and
          unpaid interest, if any), the Repurchase Date and the Repurchase Put
          Date;

               (iii) that any Security, or portion thereof, not tendered or
          accepted for payment will continue to accrue interest, if any;

               (vi)  that, unless the Company defaults in depositing Cash with
          the Paying Agent in accordance with the last paragraph of this clause
          (b) or such payment is prevented pursuant to Article 11, any Security,
          or portion thereof, accepted for payment pursuant to the Repurchase
          Offer shall cease to accrue interest after the Repurchase Date;

               (v)   that Holders electing to have a Security, or portion
          thereof, purchased pursuant to a Repurchase Offer will be required to
          surrender the Security, with the form entitled "Option of Holder to
          Elect Purchase" on the reverse of the Security completed, to the
          Paying Agent (which may not for purposes of this Section 10.1,
          notwithstanding anything in this Indenture to the contrary, be the
          Company or any Affiliate of the Company) at the address specified in
          the Change of Control Notice prior to the close of business on the
          earlier of (a) the third Business Day prior to the Repurchase Date and
          (b) the third Business Day following the expiration of the Repurchase
          Offer (such earlier date being the "Repurchase Put Date");

               (vi)  that Holders will be entitled to withdraw their election,
         in whole or in part, if the Paying Agent (which may not for purposes of
         this Section 10.1, notwithstanding anything in this Indenture to the
         contrary, be the Company or any Affiliate of the Company) receives, up
         to the close of business on the Repurchase Put Date, a telegram,
         facsimile transmission or letter setting forth the name of the Holder,
         the principal amount of the Securities the Holder is withdrawing and a
         statement that such Holder is withdrawing his election to have such
         principal amount of Securities purchased; and

               (vii) a brief description of the events resulting in such Change
         of Control.


                                     -50-
<PAGE>
 
          Any such Repurchase Offer shall comply with all applicable provisions
of Federal and state laws, including those regulating tender offers, if
applicable, and any provisions of this Indenture which conflict with such laws
shall be deemed to be superseded by the provisions of such laws.

          On or before the Repurchase Date, the Company shall (i) accept for
payment Securities or portions thereof properly tendered pursuant to the
Repurchase Offer on or before the Repurchase Put Date, (ii) deposit with the
Paying Agent Cash sufficient to pay the Repurchase Price (together with accrued
and unpaid interest (including any Additional Amounts and Additional Interest),
if any) of all Securities or portions thereof so tendered and (iii) deliver to
the Trustee Securities so accepted together with an Officers' Certificate
listing the Securities or portions thereof being purchased by the Company. The
Paying Agent shall promptly mail to Holders of Securities so accepted payment in
an amount equal to the Repurchase Price (together with accrued and unpaid
interest (including any Additional Amounts and Additional Interest), if any),
and the Trustee shall promptly authenticate and mail or deliver to such Holders
a new Security or Securities equal in principal amount to any unpurchased
portion of the Securities surrendered. Any Securities not so accepted shall be
promptly mailed or delivered by the Company to the Holder thereof. The Company
will publicly announce the results of the Repurchase Offer on or as soon as
practicable after the Repurchase Date.

                                  ARTICLE 11

                                 SUBORDINATION

Section 11.1  Securities Subordinated To Senior Indebtedness.
              ---------------------------------------------- 

          The Company and each Holder, by its acceptance of Securities, agree
that (a) the payment of the principal of, premium, if any, and interest
(including any Additional Amounts or Additional Interest) on the Securities and
(b) any other payment in respect of the Securities, including on account of the
acquisition or redemption of the Securities by the Company (including, without
limitation, pursuant to Article 10) is subordinated, to the extent and in the
manner provided in this Article 11, to the prior payment in full of all Senior
Indebtedness of the Company, whether outstanding at the date of this Indenture
or thereafter created, incurred, assumed or guaranteed, and that these
subordination provisions are for the benefit of the holders of Senior
Indebtedness.

          Payments by the Company on the Securities are not senior or superior
in right of payments by the Company on the 6 3/4% Notes.

          This Article 11 shall constitute a continuing offer to all Persons
who, in reliance upon such provisions, become holders of, or continue to hold,
Senior Indebtedness, and such provisions are made for the benefit of the holders
of Senior Indebtedness, and such holders are made obligees hereunder and any one
or more of them may enforce such provisions.

                                     -51-
<PAGE>
 
Section 11.2  No Payment On Securities In Certain Circumstances.
              ------------------------------------------------- 

     (a)  No payment may be made by the Company on account of the principal of,
premium, if any, or interest (including any Additional Amounts or Additional
Interest) on, the Securities, or to acquire any of the Securities (including
repurchases of Securities at the option of the Holder) for cash or property
(other than Junior Securities), or on account of the redemption provisions of
the Securities, (i) upon the maturity of any Senior Indebtedness of the Company
by lapse of time, acceleration (unless waived) or otherwise, unless and until
all principal of, premium, if any, and interest on such Senior Indebtedness are
first paid in full (or such payment is duly provided for), or (ii) in the event
of default in the payment of any principal of, premium, if any, or interest on
any Senior Indebtedness of the Company when it becomes due and payable, whether
at maturity or at a date fixed for prepayment or by acceleration or otherwise (a
"Payment Default"), unless and until such Payment Default has been cured or
waived or otherwise has ceased to exist.

     (b)  Upon (i) the happening of an event of default (other than a Payment
Default) that permits the holders of Designated Senior Indebtedness or their
representative immediately to accelerate its maturity and (ii) written notice of
such event of default given to the Company and the Trustee by the holders of an
aggregate of at least $5,000,000 principal amount outstanding of such Designated
Senior Indebtedness or their representative (a "Payment Notice"), then, unless
and until such event of default has been cured or waived or otherwise has ceased
to exist, no payment (by set-off or otherwise) may be made by or on behalf of
the Company on account of the principal of, premium, if any, or interest
(including any Additional Amounts or Additional Interest) on, the Securities, or
to acquire or repurchase any of the Securities for cash or property, or on
account of the redemption provisions of the Securities, in any such case other
than payments made with Junior Securities of the Company. Notwithstanding the
foregoing, unless (i) the Designated Senior Indebtedness in respect of which
such event of default exists has been declared due and payable in its entirety
within 179 days after the Payment Notice is delivered as set forth above (the
"Payment Blockage Period"), and (ii) such declaration has not been rescinded or
waived, at the end of the Payment Blockage Period, the Company shall be required
to pay all sums not paid to the Holders of the Securities during the Payment
Blockage Period due to the foregoing prohibitions and to resume all other
payments as and when due on the Securities. Any number of Payment Notices may be
given; provided, however, that (i) not more than one Payment Notice shall be
given within a period of any 360 consecutive days, and (ii) no default that
existed upon the date of such Payment Notice or the commencement of such Payment
Blockage Period (whether or not such event of default is on the same issue of
Senior Indebtedness) shall be made the basis for the commencement of any other
Payment Blockage Period.

     (c)  In furtherance of the provisions of Section 11.1, in the event that,
notwithstanding the foregoing provisions of this Section 11.2, any payment or
distribution of assets of the Company (other than Junior Securities) shall be
received by the Trustee or the Holders at a time when such payment or
distribution is prohibited by the provisions of this Section 11.2, then such
payment or distribution (subject to the provisions of Section 11.7) shall be
received and held in trust by the Trustee or such Holder or Paying Agent for the
benefit of the holders of Senior Indebtedness of the Company, and shall be paid
or delivered by the Trustee or such Holders or such Paying Agent, as the


                                     -52-
<PAGE>
 
case may be, to the holders of Senior Indebtedness of the Company remaining
unpaid or unprovided for, or their representative or representatives, or to the
trustee or trustees under any indenture pursuant to which any instruments
evidencing any of such Senior Indebtedness of the Company may have been issued,
ratably according to the aggregate amounts remaining unpaid on account of the
Senior Indebtedness of the Company held or represented by each, for application
to the payment of all Senior Indebtedness of the Company in full after giving
effect to any concurrent payment and distribution to the holders of such Senior
Indebtedness.

Section 11.3   Securities Subordinated To Prior Payment Of All Senior
               ------------------------------------------------------ 
               Indebtedness On Dissolution, Liquidation Or Reorganization.
               ----------------------------------------------------------

     Upon any distribution of assets of the Company upon any dissolution,
winding up, total or partial liquidation or reorganization of the Company,
whether voluntary or involuntary, in bankruptcy, insolvency, receivership or a
similar proceeding or upon assignment for the benefit of creditors or any
marshaling of assets or liabilities:

     (a)  the holders of all Senior Indebtedness of the Company shall first be
entitled to receive payments in full (or have such payment duly provided for)
before the Holders are entitled to receive any payment on account of the
principal of, premium, if any, and interest (including any Additional Amounts or
Additional Interest) on, the Securities (other than payment in Junior
Securities);

     (b)  any payment or distribution of assets of the Company of any kind or
character, whether in cash, property or securities (other than payment in Junior
Securities) to which the Holders or the Trustee on behalf of the Holders would
be entitled (by setoff or otherwise), except for the provisions of this Article
11, shall be paid by the liquidating trustee or agent or other Person making
such a payment or distribution directly to the holders of Senior Indebtedness of
the Company or their representatives ratably according to the respective amounts
of such Senior Indebtedness held or represented by each, to the extent necessary
to make payment in full of all such Senior Indebtedness remaining unpaid, after
giving effect to any concurrent payment or distribution to the holders of such
Senior Indebtedness; and

     (c)  in the event that, notwithstanding the foregoing, any payment or
distribution of assets of the Company of any kind or character, whether in cash,
property or securities (other than Junior Securities), shall be received by the
Trustee or the Holders or any Paying Agent (or, if the Company or any Affiliate
of the Company is acting as its own Paying Agent, money for any such payment or
distribution shall be segregated or held in trust) on account of the principal
of or interest (including any Additional Amounts or Additional Interest) on the
Securities before all Senior Indebtedness of the Company is paid in full, such
payment or distribution (subject to the provisions of Section 11.7) shall be
received and held in trust by the Trustee or such Holder or Paying Agent for the
benefit of the holders of such Senior Indebtedness, or their respective
representatives, ratably according to the respective amounts of such Senior
Indebtedness held or represented by each, to the extent necessary to make
payment as provided herein of all such Senior Indebtedness remaining unpaid
after giving effect to all concurrent payments and distributions and all
provisions therefor to or for the holders of such Senior Indebtedness, but only
to the extent that as to any holder of such Senior Indebtedness, as


                                     -53-
<PAGE>
 
promptly as practical following notice from the Trustee to the holders of such
Senior Indebtedness that such prohibited payment has been received by the
Trustee, Holder(s) or Paying Agent (or has been segregated as provided above),
such holder (or a representative therefor) notifies the Trustee of the amounts
then due and owing on such Senior Indebtedness, if any, held by such holder, and
only the amounts specified in such notices to the Trustee shall be paid to the
holders of such Senior Indebtedness.

Section 11.4   Security Holders To Be Subrogated To Rights Of Holders Of Senior
               ----------------------------------------------------------------
               Indebtedness.
               ------------ 

     Subject to the payment in full of all Senior Indebtedness of the Company as
provided herein, the Holders of Securities shall be subrogated to the rights of
the holders of such Senior Indebtedness to receive payments or distributions of
assets of the Company applicable to the Senior Indebtedness until all amounts
owing on the Securities shall be paid in full, and for the purpose of such
subrogation no such payments or distributions to the holders of such Senior
Indebtedness by the Company, or by or on behalf of the Holders by virtue of this
Article 11, which otherwise would have been made to the Holders shall, as
between the Company and the Holders, be deemed to be payment by the Company or
on account of such Senior Indebtedness, it being understood that the provisions
of this Article 11 are and are intended solely for the purpose of defining the
relative rights of the Holders, on the one hand, and the holders of such Senior
Indebtedness, on the other hand.

     If any payment or distribution to which the Holders would otherwise have
been entitled but for the provisions of this Article 11 shall have been applied,
pursuant to the provisions of this Article 11, to the payment of amounts payable
under Senior Indebtedness of the Company, then the Holders shall be entitled to
receive from the holders of such Senior Indebtedness any payments or
distributions received by such holders of Senior Indebtedness in excess of the
amount sufficient to pay all amounts payable under, or in respect of, such
Senior Indebtedness in full.

Section 11.5   Obligations Of The Company Unconditional.
               ---------------------------------------- 

     Nothing contained in this Article 11 or elsewhere in this Indenture or in
the Securities is intended to or shall impair, as between the Company and the
Holders, the obligation of each such Person, which obligation is absolute and
unconditional, to pay to the Holders the principal of, premium, if any, and
interest on, the Securities as and when the same shall become due and payable in
accordance with their terms, or is intended to or shall affect the relative
rights of the Holders and creditors of the Company other than the holders of the
Senior Indebtedness, nor shall anything herein or therein prevent the Trustee or
any Holder from exercising all remedies otherwise permitted by applicable law
upon default under this Indenture, subject to the rights, if any, under this
Article 11, of the holders of Senior Indebtedness in respect of cash, property
or securities of the Company received upon the exercise of any such remedy.
Notwithstanding anything to the contrary in this Article 11 or elsewhere in this
Indenture or in the Securities, upon any distribution of assets of the Company
referred to in this Article 11, the Trustee, subject to the provisions of
Sections 7.1 and 7.2, and the Holders shall be entitled to rely upon any order
or decree made by any court of competent jurisdiction in which such dissolution,
winding up, liquidation or reorganization proceedings are


                                     -54-
<PAGE>
 
pending, or a certificate of the liquidating trustee or agent or other Person
making any distribution to the Trustee or to the Holders for the purpose of
ascertaining the Persons entitled to participate in such distribution, the
holders of the Senior Indebtedness and other Indebtedness of the Company, the
amount thereof or payable thereon, the amount or amounts paid or distributed
thereon and all other facts pertinent thereto or to this Article 11 so long as
such court has been apprised of the provisions of, or the order, decree or
certificate makes reference to, the provisions of this Article 11. Nothing in
this Section 11.5 shall apply to the claims of, or payments to, the Trustee
under or pursuant to Section 7.7.

Section 11.6  Trustee Entitled To Assume Payments Not Prohibited In Absence of
              ----------------------------------------------------------------
              Notice.
              ------ 

          The Trustee shall not at any time be charged with knowledge of the
existence of any facts which would prohibit the making of any payment to or by
the Trustee unless and until a Trust Officer of the Trustee or any Paying Agent
shall have received, no later than one Business Day prior to such payment,
written notice thereof from the Company or from one or more holders of Senior
Indebtedness or from any representative therefor, and, prior to the receipt of
any such written notice, the Trustee, subject to the provisions of Sections 7.1
and 7.2, shall be entitled in all respects conclusively to assume that no such
fact exists.

Section 11.7  Application By Trustee Of Assets Deposited With It.
              -------------------------------------------------- 

          Any deposit of assets with the Trustee or the Agent (whether or not in
trust) for the payment of principal of or interest on any Securities shall be
subject to the provisions of Sections 11.1, 11.2, 11.3 and 11.4; provided, that,
if prior to one Business Day preceding the date on which by the terms of this
Indenture any such assets may become distributable for any purpose (including,
without limitation, the payment of either principal of or interest on any
Security) the Trustee or such Paying Agent shall not have received with respect
to such assets the written notice provided for in Section 11.6, then the Trustee
or such Paying Agent shall have full power and authority to receive such assets
and to apply the same to the purpose for which they were received, and shall not
be affected by any notice to the contrary which may be received by it on or
after such date.

Section 11.8  Subordination Rights Not Impaired By Acts Or Omissions Of The
              -------------------------------------------------------------
              Company Or Holders Of Senior Indebtedness.
              ----------------------------------------- 

          No right of any present or future holders of any Senior Indebtedness
to enforce subordination provisions contained in this Article 11 shall at any
time in any way be prejudiced or impaired by any act or failure to act on the
part of the Company or by any act or failure to act, in good faith, by any such
holder, or by any noncompliance by the Company with the terms of this Indenture,
regardless of any knowledge thereof which any such holder may have or be
otherwise charged with. The holders of Senior Indebtedness may extend, renew,
modify or amend the terms of the Senior Indebtedness or any security therefor
and release, sell or exchange such security and otherwise deal freely with the
Company, all without affecting the liabilities and obligations of the parties to
the Indenture or the Holders.

                                     -55-
<PAGE>
 
Section 11.9  Security Holders Authorize Trustee To Effectuate Subordination Of
              -----------------------------------------------------------------
              Securities.
              ---------- 

          Each Holder of the Securities by his acceptance thereof authorizes and
expressly directs the Trustee on his behalf to take such action as may be
necessary or appropriate to effectuate the subordination provisions contained in
this Article 11 and to protect the rights of the Holders pursuant to this
Indenture, and appoints the Trustee his attorney-in-fact for such purpose,
including, in the event of any dissolution, winding up, liquidation or
reorganization of the Company (whether in bankruptcy, insolvency or receivership
proceedings or upon an assignment for the benefit of creditors of the Company),
the immediate filing of a claim for the unpaid balance of his Securities in the
form required in said proceedings and causing said claim to be approved. If the
Trustee does not file a proper claim or proof of debt in the form required in
such proceeding prior to 30 days before the expiration of the time to file such
claim or claims, then the holders of the Senior Indebtedness or their
representative are or is hereby authorized to have the right to file and are or
is hereby authorized to file an appropriate claim for and on behalf of the
Holders of said Securities. Nothing herein contained shall be deemed to
authorize the Trustee or the holders of Senior Indebtedness or their
representative to authorize or consent to or accept or adopt on behalf of any
Security Holder any plan of reorganization, arrangement, adjustment or
composition affecting the Securities or the rights of any Holder thereof, or to
authorize the Trustee or the holders of Senior Indebtedness or their
representative to vote in respect of the claim of any Security Holder in any
such proceeding.

Section 11.10  Right Of Trustee To Hold Senior Indebtedness.
               -------------------------------------------- 

          The Trustee shall be entitled to all of the rights set forth in this
Article 11 in respect of any Senior Indebtedness to the same extent as any other
holder of Senior Indebtedness, and nothing in this Indenture shall be construed
to deprive the Trustee of any of its rights as such holder.

Section 11.11  Article 11 Not To Prevent Events Of Default
               -------------------------------------------  

          The failure to make a payment on account of principal of, premium, if
any, or interest on, the Securities by reason of any provision of this Article
11 shall not be construed as preventing the occurrence of a Default or an Event
of Default under Section 6.1 or in any way preventing the Holders from
exercising any right hereunder, other than the right to receive payment on the
Securities.

Section 11.12  No Fiduciary Duty Of Trustee To Holders Of Senior Indebtedness.
               -------------------------------------------------------------- 

          The Trustee shall not be deemed to owe any fiduciary duty to the
holders of Senior Indebtedness, and shall not be liable to any such holders
(other than for its willful misconduct or negligence) if it shall in good faith
mistakenly pay over or distribute to the Holders of Securities or the Company or
any other Person, cash, property or securities to which any holders of Senior
Indebtedness shall be entitled by virtue of this Article 11 or otherwise.
Nothing in this Section 11.12 shall affect the obligation of any other such
Person to hold such payment for the benefit of, and to pay such payment over to,
the holders of Senior Indebtedness or their representatives.

                                     -56-
<PAGE>
 
                                    ARTICLE 12

                            CONVERSION OF SECURITIES

Section 12.1  Conversion Privilege.
              -------------------- 

          Subject to and upon compliance with the provisions of this Article 12,
at the option of the Holder thereof, any Security may at any time be converted,
in whole, or in part in multiples of $1,000 principal amount, into fully paid
and non-assessable shares of Common Stock issuable upon conversion of the
Securities (the "Conversion Shares"), at the conversion price in effect at the
Date of Conversion, until and including, but not after the close of business on,
the Stated Maturity, or unless such Security or some portion thereof shall have
been called for redemption or delivered for repurchase prior to such date and no
Default is made in making due provision for the payment of the Redemption Price
or Repurchase Price in accordance with the terms of this Indenture, in which
case, with respect to such Security or portion thereof as has been so called for
redemption or delivered for repurchase, such Security or portion thereof may be
so converted until and including, but not after the close of business on, the
Business Day prior to the Redemption Date or Repurchase Date, as applicable for
such Security, unless the Company subsequently fails to pay the applicable
Redemption Price or Repurchase Price, as the case may be.

Section 12.2  Exercise Of Conversion Privilege.
              -------------------------------- 

          In order to exercise the conversion privilege, the Holder of any
Security to be converted shall surrender such Security to the Company at any
time during usual business hours at its office or agency maintained for the
purpose as provided in this Indenture, accompanied by a fully executed written
notice, in substantially the form set forth on the reverse of the Security, that
the Holder elects to convert such Security or a stated portion thereof
constituting an integral multiple of a $1,000 principal amount, and, if such
Security is surrendered for conversion during the period between the close of
business of any Record Date and the opening of business on the next following
Interest Payment Date and has not been called for redemption on a Redemption
Date which occurs within such period, accompanied also by payment of an amount
equal to the interest payable on such Interest Payment Date on the principal
amount of the Security being surrendered for conversion, notwithstanding such
conversion. The Holder of any Security at the close of business on a Record Date
will be entitled to receive the interest payable on such Security on the
corresponding Interest Payment Date notwithstanding the conversion thereof after
such Record Date. Holders will receive the interest payment due on December 15,
2000 whether or not they surrender Securities for conversion as a result of the
Company's exercise of its right to redeem Securities on or after December 15,
2000. Such notice of conversion shall also state the name or names (with
address) in which the certificate or certificates for shares of Common shall be
issued. Securities surrendered for conversion shall (if reasonably required by
the Company or the Trustee) be duly endorsed by, or be accompanied by a written
instrument or instruments of transfer in form satisfactory to the Company, duly
executed by the Holder or his attorney duly authorized in writing. As promptly
as practicable after the receipt of such notice and the surrender of such
Security as aforesaid, the Company shall, subject to the provisions of Section
12.8 hereof, issue and deliver at such office or agency to such


                                     -57-
<PAGE>
 
Holder, or on his written order, a certificate or certificates for the number of
full shares of Common Stock issuable on such conversion of Securities in
accordance with the provisions of this Article 12 and Cash, as provided in
Section 12.3 hereof, in respect of any fraction of a share of 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 (herein
called the "Date of Conversion") on which such Security shall have been
surrendered as aforesaid, the person or persons in whose name or names any
certificate or certificates for shares of Common Stock shall be issuable upon
such conversion shall be deemed to have become on the Date of Conversion the
holder or holders of record of the shares represented thereby; provided,
however, that any such surrender on any date when the stock transfer books of
the Company shall be closed shall cause the person or persons in whose name or
names the certificate or certificates for such shares are to be issued to be
deemed to have become the record holder or holders thereof for all purposes at
the opening of business on the next succeeding day on which such stock transfer
books are open but such conversion shall nevertheless be at the conversion price
in effect at the close of business on the date when such Security shall have
been so surrendered with the conversion notice. In the case of conversion of a
portion, but less than all, of a Security, the Company shall as promptly as
practicable execute, and the Trustee shall authenticate and deliver to the
Holder thereof, at the expense of the Company, a Security or Securities in the
aggregate principal amount of the unconverted portion of the Security
surrendered. Except as otherwise expressly provided in this Indenture, no
payment or adjustment shall be made for interest accrued on any Security (or
portion thereof) converted or for dividends or distributions on any Common Stock
issued upon conversion of any Security.

     All shares of Common Stock delivered upon such conversion of Securities
that are Restricted Securities shall, if required, bear restrictive legends set
forth in Section 2.6(e) and shall be subject to the restrictions on transfer
provided in such legends. Neither the Trustee nor any agent maintained for the
purpose of such conversion shall have any responsibility for the inclusion or
content of any such restrictive legends on such shares of Common Stock;
provided, however, that the Trustee shall have provided, to the Company or to
the transfer agent for such shares of Common Stock, prior to or concurrently
with a request to the Company to deliver such shares of Common Stock, written
notice that the Securities delivered for conversion are Restricted Securities.


Section 12.3  Fractional Interests.
              -------------------- 

     No fractions of shares or scrip representing fractions of shares shall be
issued upon conversion of Securities. If more than one Security shall be
surrendered for conversion at one time by the same Holder, the number of full
shares which shall be issuable upon conversion thereof shall be basis of the
aggregate principal amount of the Securities so surrendered. If any fraction of
a share of Common Stock would, except for the foregoing provisions of this
Section 12.3, be issuable on the conversion of any Security or Securities, the
Company shall make payment in lieu thereof in an amount of Cash equal to the
value of such fraction computed on the basis of the last sale price of the
Common Stock as reported on the Nasdaq National Market (or if not listed for
trading thereon, then on the principal national securities exchange or market on
which the Common Stock is listed or admitted to trading) at the close of
business on the Date of Conversion or if no such sale takes place

                                     -58-
<PAGE>
 
on such day, the last sale price for such day shall be the average of the
closing bid and asked prices regular way on the Nasdaq National Market (or if
not listed for trading thereon, on the principal national securities exchange or
market on which the Common Stock is listed or admitted to trading) (such last
sale price being hereinafter referred to as the "Last Sale Price"). If on such
Trading Day the Common Stock is not quoted by any such organization, the fair
value of such Common Stock on such day, as reasonably determined in good faith
by the Board of Directors of the Company, shall be used.

Section 12.4  Conversion Price.
              ----------------
 
     The conversion price per share of Common Stock issuable upon conversion of
the Securities (the "Conversion Price") shall initially be $36.0525, subject to
adjustment pursuant to Section 12.5.

Section 12.5  Adjustment Of Conversion Price.
              ------------------------------

     The Conversion Price shall be subject to adjustment from time to time as
follows:
 
     (a) In case the Company shall (i) make or pay a dividend (or other
distribution) in shares of Common Stock on any class of Capital Stock of the
Company, (ii) subdivide its outstanding shares of Common Stock into a greater
number of shares or (iii) combine or reclassify its outstanding shares of Common
Stock into a smaller number of shares, the Conversion Price in effect
immediately prior to such action shall be adjusted so that the Holder of any
Security thereafter surrendered for conversion shall be entitled to receive the
number of shares of Common Stock that he would have owned immediately following
such action had such Security been converted immediately prior thereto. An
adjustment made pursuant to this subsection (a) shall become effective
immediately, except as provided in subsection (h) below, after the record date
in the case of a dividend or distribution and shall become effective immediately
after the effective date in the case of a subdivision or combination.

     (b) In case the Company shall issue rights, options or warrants to all
holders of Common Stock entitling them to subscribe for or purchase shares of
Common Stock at a price per share less than the then current market price per
share of the Common Stock (as determined pursuant to subsection (f) below) on
the record date mentioned below, the Conversion Price shall be adjusted to a
price, computed to the nearest cent, so that the same shall equal the price
determined by multiplying:

          (i) the Conversion Price in effect immediately prior to the date of
issuance of such rights or warrants by a fraction, of which

          (ii) the numerator shall be (A) the number of shares of Common Stock
outstanding on the date of issuance of such rights, options or warrants,
immediately prior to such issuance, plus (B) the number of shares which the
aggregate offering price of the total number of shares so offered for
subscription or purchase would purchase at such current market price 

                                     -59-
<PAGE>
 
(determined by multiplying such total number of shares by the exercise price of
such rights, options or warrants and dividing the product so obtained by such
current market price), and of which

          (iii) the denominator shall be (A) the number of shares of Common
Stock outstanding on the date of issuance of such rights, options or warrants,
immediately prior to such issuance, plus (B) the number of additional shares of
Common Stock which are so offered for subscription or purchase.

     Such adjustment shall become effective immediately, except as provided in
subsection (h) below, after the record date for the determination of holders
entitled to receive such rights, options or warrants; provided, however, that if
any such rights, options or warrants issued by the Company as described in this
subsection (b) are only exercisable upon the occurrence of certain triggering
events relating to control and provided for in shareholder rights plans, then
the Conversion Price will be adjusted only as provided in the following
paragraphs.

     Each share of Common Stock issued upon conversion of Securities pursuant to
this Article 12 shall be entitled to receive the appropriate number of Rights
(as defined in the Rights Agreement) and the certificates representing the
Common Stock issued upon such conversion shall bear such legends, if any, in
each case as may be provided by the terms of the Rights Agreement between the
Company and Harris Trust and Savings Bank (the "Rights Agreement"). Provided
that such Rights Agreement requires that each share of Common Stock issued upon
conversion of Securities shall be entitled to receive such Rights, then,
notwithstanding anything else to the contrary in this Section, there shall not
be any adjustment to the conversion privilege or Conversion Price as a result of
the issuance of such Rights, the distribution of separate certificates
representing such Rights, the exercise or redemption of such Rights in
accordance with any such Rights Agreement, or the termination or invalidation of
such Rights. In addition, in the event the Company amends the Rights Agreement
or implements a replacement or successor stockholders' rights plan, such
successor or amended rights plan must provide that upon conversion of the
Securities the Holders will receive, in addition to the Common Stock issuable
upon such conversion, such rights whether or not such rights have separated from
the Common Stock at the time of such conversion.

     Rights or warrants distributed by the Company to all holders of Common
Stock entitling the holders thereof to subscribe for or purchase shares of the
Company's capital stock (either initially or under certain circumstances), which
rights or warrants, until the occurrence of a specified event or events
("Trigger Event"):

           (i) are deemed to be transferred with such shares of Common Stock,

           (ii) are not exercisable, and

           (iii) are also issued in respect of future issuances of Common Stock,

shall not be deemed distributed for purposes of this Section until the
occurrence of the earliest Trigger Event.  In addition, in the event of any
distribution of rights or warrants, or any Trigger 

                                     -60-
<PAGE>
 
Event with respect thereto, that shall have resulted in an adjustment to the
Conversion Price under this Section, (1) in the case of any such rights or
warrants which shall all have been redeemed or repurchased without exercise by
any holders thereof, the Conversion Price shall be readjusted upon such final
redemption or repurchase to give effect to such distribution or Trigger Event,
as the case may be, as thought it were a cash distribution, equal to the per
share redemption or repurchase price received by a holder of Common Stock with
respect to such rights or warrants (assuming such holder had retained such
rights or warrants), made to all holders of Common Stock as of the date of such
redemption or repurchase, and (2) in the case of any such rights or warrants all
of which shall have expired without exercise by any holder thereof, the
Conversion Price shall be readjusted as if such issuance had not occurred.

     (c) In case the Company or any subsidiary of the Company shall distribute
to all holders of Common Stock, any of its assets, evidences of indebtedness,
cash or other assets or shares of Capital Stock other than Common Stock
(including securities, but other than (x) dividends or distributions exclusively
in cash or (y) any dividend or distribution for which an adjustment is required
to be made in accordance with subsection (a) or (b) above) then in each such
case the Conversion Price shall be adjusted so that the same shall equal the
price determined by multiplying the Conversion Price in effect immediately prior
to the date of such distribution by a fraction of which the numerator shall be
the then current market price per share of the Common Stock (determined as
provided in subsection (f) below) on the record date mentioned below less the
then fair market value (as reasonably determined in good faith by the Board of
Directors of the Company) of the portion of the assets so distributed applicable
to one share of Common Stock, and of which the denominator shall be such current
market price per share of the Common Stock. Such adjustment shall become
effective immediately, except as provided in subsection (h) below, after the
record date for the determination of stockholders entitled to receive such
distribution.

     (d) In case the Company or any subsidiary of the Company shall make any
distribution consisting exclusively of cash (excluding any cash portion of
distributions for which an adjustment is required to be made in accordance with
(c) above, or cash distributed upon a merger or consolidation to which Section
12.6 applies) to all holders of Common Stock in an aggregate amount that,
combined together with (i) all other such all-cash distributions made within the
then preceding 12 months in respect of which no adjustment has been made and
(ii) any cash and the fair market value of other consideration paid or payable
in respect of any tender offer by the Company or any of its Subsidiaries for
Common Stock concluded within the preceding 12 months in respect of which no
adjustment has been made, exceeds 10% of the Company's market capitalization
(defined as being the product of the then current market price of the Common
Stock (determined as provided in subsection (f) below) times the number of
shares of Common Stock then outstanding) on the record date of such
distribution, in each such case the Conversion Price shall be adjusted so that
the same shall equal the price determined by multiplying the Conversion Price in
effect immediately prior to the date of such distribution by a fraction of which
the numerator shall be the then current market price per share of the Common
Stock on such record date less the amount of the cash so distributed applicable
to one share of Common Stock, and of which the denominator shall be such current
market price per share of the Common Stock. Such adjustment shall become
effective immediately, 

                                     -61-
<PAGE>
 
except as provided in subsection (h) below, after the record date for the
determination of stockholders entitled to receive such distribution.

     (e) In case there shall be completed a tender or exchange offer made by
the Company or any Subsidiary of the Company for all or any portion of the
Common Stock (any such tender or exchange offer being referred to as an "Offer")
that involves an aggregate consideration having a fair market value as of the
expiration of such Offer (the "Expiration Time") that, together with (i) any
cash and the fair market value of any other consideration payable in respect of
any other Offer, as of the expiration of such other Offer, expiring within the
12 months preceding the expiration of such Offer and in respect for which no
Conversion Price adjustment pursuant to this subsection (e) has been made and
(ii) the aggregate amount of any all-cash distributions referred to in
subsection (d) of this Section 12.5 to all holders of Common Stock within the 12
months preceding the expiration of such Offer for which no Conversion Price
adjustment, pursuant to such subsection (d), has been made, exceeds 10% of the
Company's market capitalization (defined as being the product of the then
current market price per share (determined as provided in subsection (f) below)
of the Common Stock on the Expiration Time times the number of shares of Common
Stock outstanding (including any tendered shares)) at the Expiration Time, the
Conversion Price shall be reduced by multiplying such Conversion Price in effect
immediately prior to the Expiration Time by a fraction of which the numerator
shall be (i) the product of the then current market price per share (determined
as provided in subsection (f) below) at the Expiration Time times the number of
shares of Common Stock outstanding (including any tendered shares) at the
Expiration Time minus (ii) the fair market value of the aggregate consideration
payable to stockholders based on the acceptance (up to any maximum specified in
the terms of the Offer) of all shares validly tendered and not withdrawn as of
the Expiration Time (the shares deemed so accepted being referred to as the
"Purchased Shares") and the denominator shall be the product of (i) such current
market price per share at the Expiration Time times (ii) such number of
outstanding shares at the Expiration Time less the number of Purchased Shares,
such reduction to become effective immediately prior to the opening of business
on the day following the Expiration Time.

     For purposes of this subsection (e), the fair market value of any
consideration with respect to an Offer shall be reasonably determined in good
faith by the Board of Directors of the Company and described in a Board
Resolution.

     (f) For the purpose of any computation under subsections (b), (c), (d) and
(e) above, the current market price per share of Common Stock on any date shall
be deemed to be the average of the Last Sale Prices of a share of Common Stock
for the five consecutive Trading Days selected by the Company commencing not
more than 20 Trading Days before, and ending not later than, the earlier of the
date in question and the date before the "ex date," with respect to the
issuance, distribution or Offer requiring such computation. If on any such
Trading Day the Common Stock is not quoted by any organization referred to in
the definition of Last Sale Price in Section 12.3 hereof, the fair value of the
Common Stock on such day, as reasonably determined in good faith by the Board of
Directors of the Company, shall be used. For purposes of this paragraph, the
term "ex date," when used with respect to any issuance, distribution or payments
with respect to an Offer, means the first date on which the Common Stock trades
regular way on the Nasdaq National Market (or if not 

                                     -62-
<PAGE>
 
listed or admitted to trading thereon, then on the principal market or exchange
on which the Common Stock is listed or admitted to trading) without the right to
receive such issuance, distribution or Offer.

     (g) In addition to the foregoing adjustments in subsections (a), (b), (c),
(d) and (e) above, the Company will be permitted to make such reductions in the
Conversion Price as it considers to be advisable. In the event the Company
elects to make such a reduction in the Conversion Price, the Company will comply
with the requirements of Rule 14e-1 of the Exchange Act and any other Federal
and state laws and regulations thereunder if and to the extent that such laws
and regulations are applicable in connection with the reduction of the price of
the Notes; provided, that any provisions of this Indenture which conflict with
such laws shall be deemed superseded by the provisions of such laws.

     (h) In any case in which this Section 12.5 shall require that an
adjustment (including by reason of the last sentence of subsection (a) or (c)
above) be made immediately following a record date, the Company may elect to
defer the effectiveness of such adjustment (but in no event until a date later
than the effective time of the event giving rise to such adjustment), in which
case the Company shall, with respect to any Security converted after such record
date and on and before such adjustment shall have become effective (i) defer
paying any Cash payment pursuant to Section 12.3 hereof or issuing to the Holder
of such Security the number of shares of Common Stock and other Capital Stock of
the Company (or other assets or securities) issuable upon such conversion in
excess of the number of shares of Common Stock and other Capital Stock of the
Company issuable thereupon only on the basis of the Conversion Price prior to
adjustment, and (ii) not later than five Business Days after such adjustment
shall become effective, pay to such Holder the appropriate Cash payment pursuant
to Section 12.3 hereof and issue to such Holder the additional shares of Common
Stock and other Capital Stock of the Company issuable on such Conversion.

     (i) No adjustment in the Conversion price shall be required unless such
adjustment would require an increase or decrease of at least 1.0% of the
Conversion Price; provided that any adjustments which by reason of this
subsection (i) are not required to be made shall be carried forward and taken
into account in any subsequent adjustment. All calculations under this Article
12 shall be made to the nearest cent or to the nearest one-hundredth of a share,
as the case may be.

     (j) Whenever the Conversion Price is adjusted as herein provided, the
Company shall promptly (i) file with the Trustee and the Registrar an Officers'
Certificate setting forth the Conversion Price after such adjustment and setting
forth a brief statement of the facts requiring such adjustment, which
certificate shall be conclusive evidence of the correctness of such adjustment,
and (ii) mail or cause to be mailed a notice of such adjustment to each Security
Holder at his address as the same appears on the registry books of the
Registrar.

     (k) In the event that the Company distributes rights or warrants (other
than those referred to in subsection (b) above) pro rata to holders of Common
Stock, so long as any such rights or warrants have not expired or been redeemed
by the Company, the Company shall make proper provision so that the Holder of
any Security surrendered for conversion will be entitled to receive 

                                     -63-
<PAGE>
 
upon such conversion, in addition to the Conversion Shares, a number of rights
and warrants to be determined as follows: (i) if such conversion occurs on or
prior to the date for the distribution to the holders of rights or warrants of
separate certificates evidencing such rights or warrants (the "Distribution
Date"), the same number of rights or warrants to which a holder of a number of
shares of Common Stock equal to the number of Conversion Shares is entitled at
the time of such conversion in accordance with the terms and provisions of and
applicable to the rights or warrants, and (ii) if such conversion occurs after
such Distribution Date, the same number of rights or warrants to which a holder
of the number of shares of Common Stock into which the principal amount of such
Security so converted was convertible immediately prior to such Distribution
Date would have been entitled on such Distribution Date in accordance with the
terms and provisions of, and applicable to, the rights or warrants.

Section 12.6  Continuation Of Conversion Privilege In Case Of Reclassification,
              -----------------------------------------------------------------
              Change, Merger, Consolidation Or Sale Of Assets.
              -----------------------------------------------

     If any of the following shall occur, namely: (a) any reclassification or
change of outstanding shares of Common Stock issuable upon conversion of the
Securities (other than a change in par value, or from par value to no par value,
or from no par value, to par value, or as a result of a subdivision or
combination), (b) any consolidation or merger of the Company with or into any
other Person, or the merger of any other Person with or into the Company (other
than a merger which does not result in any reclassification, change, conversion,
exchange or cancellation of outstanding shares of Common Stock) or (c) any sale,
transfer or conveyance of all or substantially all of the assets of the Company
(computed on a consolidated basis), then the Company, or such successor or
purchasing entity, as the case may be, shall, as a condition precedent to such
reclassification, change, consolidation, merger, sale or conveyance, execute and
deliver to the Trustee a supplemental indenture providing that the Holder of
each Security then outstanding shall have the right to convert such Security
only into the kind and amount of shares of stock and other securities and
property (including cash) receivable upon such reclassification, change,
consolidation, merger, sale, transfer or conveyance by a holder of the number of
shares of Common Stock issuable upon conversion of such Security immediately
prior to such reclassification, change, consolidation, merger, sale, transfer or
conveyance assuming such holder of Common Stock of the Company failed to
exercise his rights of an election, if any, as to the kind or amount of cash and
other property receivable upon such reclassification, change, consolidation,
merger, sale, transfer or conveyance (provided that if the kind or amount of
securities, cash and other property receivable upon such reclassification,
change, consolidation, merger, sale, transfer or conveyance is not the same for
each share of Common Stock of the Company held immediately prior to such
reclassification, change, consolidation, merger, sale, transfer or conveyance in
respect of which such rights of election shall not have been exercised ("Non-
Electing Shares"), then for the purpose of this Section 12.6, the kind and
amount of securities, cash and other property receivable upon such
reclassification, change, consolidation, merger, sale, transfer or conveyance by
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 shall be as nearly equivalent as
may be practicable to the adjustments provided for in this Article 12. If, in
the case of any such consolidation, merger, sale or conveyance, the stock or
other securities and property (including cash) receivable thereupon by a holder
of shares

                                     -64-
<PAGE>
 
of Common Stock includes shares of stock or other securities and property
(including cash) of a corporation other than the successor or purchasing
corporation, as the case may be, in such consolidation, merger, sale or
conveyance, then such supplemental indenture shall also be executed by such
other corporation and shall contain such additional provisions to protect the
interests of the Holders of the Securities as the Board of Directors of the
Company shall reasonably consider necessary by reason of the foregoing. The
provisions of this Section 12.6 shall similarly apply to successive
consolidations, mergers, sales or conveyances.

     Notice of the execution of each such supplemental indenture shall be mailed
to each Holder of Securities at his address as the same appears on the registry
books of the Company.

     Neither the Trustee nor any agent shall be under any responsibility to
determine the correctness of any provisions contained in any such supplemental
indenture relating either to the kind or amount of shares of stock or securities
or property (including cash) receivable by Holders of Securities upon the
conversion of their Securities after any such reclassification, change,
consolidation, merger, sale or conveyance or to any adjustment to be made with
respect thereto, but, subject to the provisions of Article 7.1 and 7.2 hereof,
may accept as conclusive evidence of the correctness of any such provisions, and
shall be protected in relying upon, the Officers' Certificate (which the Company
shall be obligated to file with the Trustee prior to the execution of any such
supplemental indenture) with respect thereto.

Section 12.7  Notice Of Certain Events.
              ------------------------

     In case:

     (a) the Company shall declare a dividend (or any other distribution)
payable to the holders of Common Stock (other than cash dividends);

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

     (c) the Company shall authorize any reclassification or change of the
Common Stock (including a subdivision or combination of its outstanding shares
of Common Stock), or any consolidation or merger to which the Company is a party
and for which approval of any stockholders of the Company is required, or the
sale or conveyance of all or substantially all the property or business of the
Company;

     (d) there shall be proposed any voluntary or involuntary dissolution,
liquidation or winding-up of the Company; or

                                     -65-
<PAGE>
 
     (e) the Company or any of its Subsidiaries shall complete an Offer;

then, the Company shall cause to be filed at the office or agency maintained for
the purpose of conversion of the Securities as provided in Section 4.2 hereof,
and shall cause to be mailed to each Holder of Securities, at its address as it
shall appear on the registry books of the Company, at least 20 days before the
date hereinafter specified (or the earlier of the dates hereinafter specified,
in the event that more than one date is specified), a notice stating the date on
which (1) a record is expected to be taken for the purpose of such dividend,
distribution, rights, warrants or options or Offer, or if a record is not to be
taken, the date as of which the holders of Common Stock of record to be entitled
to such dividend, distribution, rights, warrants or options or to participate in
such Offer are to be determined, or (2) such reclassification, change,
consolidation, merger, sale, conveyance, dissolution, liquidation or winding-up
is expected to become effective and the date, if any is to be fixed, 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 or other property
deliverable upon such reclassification, change, consolidation, merger, sale,
conveyance, dissolution, liquidation or winding-up. Neither the failure to give
notice nor any defect therein shall affect the legality or validity of the
events described in clauses (a) through (e) of this Section 12.7.

Section 12.8  Taxes On Conversion.
              -------------------

     The Company will pay any and all documentary, stamp or similar taxes 
payable to the United States of America or any political subdivision or taxing
authority thereof or therein in respect of the issue or delivery of shares of
Common Stock on conversion of Securities pursuant thereto; provided, however,
that the Company shall not be required to pay any tax which may be payable in
respect of any transfer involved in the issue or delivery of shares of Common
Stock in a name other than that of the Holder of the Securities to be converted
and no such issue or delivery shall be made unless and until the person
requesting such issue or delivery 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. The Company extends no protection with respect to any other taxes
imposed in connection with conversion of Securities.

Section 12.9  Company To Provide Stock.
              ------------------------

     The Company shall reserve, free from preemptive rights, out of its
authorized but unissued shares, sufficient shares to provide for the conversion
of the Securities from time to time as such Securities are presented for
conversion, provided, that nothing contained herein shall be construed to
preclude the Company from satisfying its obligations in respect of the
conversion of Securities by delivery of repurchased shares of Common Stock which
are held in the treasury of the Company.

     If any shares of Common Stock to be reserved for the purpose of conversion
of Securities hereunder require registration with or approval of any
governmental authority under any Federal or state law before such shares may be
validly issued or delivered upon conversion, then the Company covenants that it
will in good faith and as expeditiously as possible use its best efforts to
secure such

                                     -66-
<PAGE>
 
registration or approval, as the case may be, provided, however, that nothing in
this Section 12.9 shall be deemed to limit in any way the obligations of the
Company provided in this Article 12.

     Before taking any action which would cause an adjustment reducing the
Conversion Price below the then par value, if any, of the Common Stock, the
Company will take all corporate action which may, in the Opinion of Counsel, be
necessary in order that the Company may validly and legally issue fully paid and
non-assessable shares of Common Stock at such adjusted Conversion Price.

     The Company covenants that all shares of Common Stock which may be issued
upon conversion of Securities will upon issue be fully paid and non-assessable
by the Company and free of preemptive rights.

Section 12.10  Disclaimer Of Responsibility For Certain Matters.
               ------------------------------------------------

     Neither the Trustee nor any agent of the Trustee shall at any time be under
any duty or responsibility to any Holder of Securities to determine whether any
facts exist which may require any adjustment of the Conversion Price, or with
respect to the Officers' Certificate referred to in Section 12.5(j) hereof, or
with respect to the nature or extent of any such adjustment when made, or with
respect to the method employed, herein or in any supplemental indenture 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, or of any securities or property
(including cash), which may at any time be issued or delivered upon the
conversion of any Security; and neither the Trustee nor any conversion agent
makes any representation with respect thereto. Neither the Trustee nor any
conversion agent shall be responsible for any failure of the Company to issue,
register the transfer of or deliver any shares of Common Stock or stock
certificates or other securities or property (including cash) upon the surrender
of any Security for the purpose of conversion or, subject to Article 7 hereof,
to comply with any of the covenants of the Company contained in this Article 12.

Section 12.11  Return Of Funds Deposited For Redemption Of Converted Securities.
               ----------------------------------------------------------------

     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 interest on any of the Securities and which shall not be
required for such purposes because of the conversion of such Securities, as
provided in this Article 12, shall after such conversion be repaid to the
Company by the Trustee or such other Paying Agent. All Securities delivered for
conversion to the Trustee will be canceled by or at the direction of the
Trustee.

                                     -67-
<PAGE>
 
                                  ARTICLE 13

                                 MISCELLANEOUS

Section 13.1   TIA Controls.
               ------------
 
     If any provision of this Indenture limits, qualifies, or conflicts with the
duties imposed by operation of the TIA, the imposed duties, upon qualification
of this Indenture under the TIA, shall control; provided that this Section 13.1
shall not require such supplemental indenture or the Trustee to be qualified
under the TIA prior to the time such qualification is in fact required under the
terms of the TIA or the Indenture has been qualified under the TIA, nor shall it
constitute any admission or acknowledgment by any party to such supplemental
indenture that any such qualification is required prior to the time such
qualification is in fact required under the terms of the TIA or the Indenture
has been qualified under the TIA.


Section 13.2   Notices.
               ------- 

     Any notices or other communications to the Company or the Trustee required
or permitted hereunder shall be in writing, and shall be sufficiently given if
made by hand delivery, by overnight courier, by telecopier or registered or
certified mail, postage prepaid, return receipt requested, addressed as follows:

     if to the Company:

               PLATINUM technology, inc.
               1815 South Meyers Road
               Oakbrook Terrace, Illinois 60181
               Attention:  Chief Financial Officer Telecopy:(630) 691-0710
                           with a copy to General Counsel at (630)691-0454

     if to the Trustee:

               American National Bank and Trust Company of Chicago
               33 North LaSalle Street, 13th Floor   Chicago, IL 60690
               Attention:  Corporate Trust Division
               Telecopy: (312) 661-6491

     Any party by notice to each other party may designate additional or
different addresses as shall be furnished in writing by such party. Any notice
or communication to any party shall be deemed to have been given or made as of
the date so delivered, if personally delivered; the next Business Day, if by
overnight courier; when receipt is acknowledged, if telecopied; and five
Business


                                     -68-
<PAGE>
 
Days after mailing if sent by registered or certified mail, postage prepaid
(except that a notice of change of address shall not be deemed to have been
given until actually received by the addressee).

     Any notice or communication mailed to a Security Holder shall be mailed to
him by first class mail or other equivalent means at his address as it appears
on the registry books of the Registrar and shall be sufficiently given to him if
so mailed within the time prescribed.

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

Section 13.3   Communications By Holders With Other Holders.
               --------------------------------------------

     Security Holders may communicate pursuant to TIA Section 312(b) with other
Security Holders with respect to their rights under this Indenture or the
Securities. The Company, the Trustee, the Registrar and any other Person shall
have the protection of TIA Section 312(c).

Section 13.4   Certificate And Opinion As To Conditions Precedent.
               --------------------------------------------------

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

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

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

Section 13.5   Statements Required In Certificate Or Opinion.
               ---------------------------------------------

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

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

          (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;


                                     -69-
<PAGE>
 
          (3)  A statement that, in opinion of such Person, he has made such
     examination or investigation as is necessary to enable him to express an
     informed opinion as to whether or not such covenant or condition has been
     complied with; and

          (4)  a statement as to whether or not, in the opinion of each such
     Person, such condition or covenant has been complied with; provided,
     however, that with respect to matters of fact an Opinion of Counsel may
     rely on an Officers' Certificate or certificates of public officials.

Section 13.6   Rules By Trustee, Paying Agent, Registrar.
               -----------------------------------------

     The Trustee may make reasonable rules for action by or at a meeting of
Security Holders. The Paying Agent or Registrar may make reasonable rules for
its functions.

Section 13.7   Legal Holidays.
               --------------

     A "Legal Holiday" is a Saturday, a Sunday or a day on which banking
institutions in New York, New York are authorized or obligated by law or
executive order to close. If a payment date is a Legal Holiday at such place,
payment may be made at such place on the next succeeding day that is not a Legal
Holiday, and no interest shall accrue for the intervening period.

Section 13.8   Governing Law.
               -------------

     THIS INDENTURE AND THE SECURITIES SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, AS APPLIED TO CONTRACTS MADE
AND PERFORMED WITHIN THE STATE OF NEW YORK. THE COMPANY HEREBY IRREVOCABLY
SUBMITS TO THE JURISDICTION OF ANY NEW YORK STATE COURT SITTING IN THE BOROUGH
OF MANHATTAN IN THE CITY OF NEW YORK OR ANY FEDERAL COURT SITTING IN THE BOROUGH
OF MANHATTAN IN THE CITY OF NEW YORK IN RESPECT OF ANY SUIT, ACTION OR
PROCEEDING ARISING OUT OF OR RELATING TO THIS INDENTURE AND THE SECURITIES, AND
IRREVOCABLY ACCEPTS FOR ITSELF AND IN RESPECT OF ITS PROPERTY, GENERALLY AND
UNCONDITIONALLY, JURISDICTION OF THE AFORESAID COURTS. THE COMPANY IRREVOCABLY
WAIVES, TO THE FULLEST EXTENT IT MAY EFFECTIVELY DO SO UNDER APPLICABLE LAW, ANY
OBJECTION WHICH IT MAY NOW OR HEREAFTER HAVE TO THE LAYING OF THE VENUE OF ANY
SUCH SUIT, ACTION OR PROCEEDING BROUGHT IN ANY SUCH COURT AND ANY CLAIM THAT ANY
SUCH SUIT, ACTION OR PROCEEDING BROUGHT IN ANY SUCH COURT HAS BEEN BROUGHT IN AN
INCONVENIENT FORUM. NOTHING HEREIN SHALL AFFECT THE RIGHT OF THE TRUSTEE OR ANY
SECURITY HOLDER TO SERVE PROCESS IN ANY OTHER MANNER PERMITTED BY LAW OR TO
COMMENCE LEGAL PROCEEDINGS OR OTHERWISE PROCEED AGAINST THE COMPANY IN ANY OTHER
JURISDICTION.


                                     -70-
<PAGE>
 
Section 13.9   No Adverse Interpretation Of Other Agreements.
               ---------------------------------------------

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

Section 13.10  No Recourse Against Others.
               --------------------------  

     No direct or indirect partner, employee, stockholder, director or officer,
as such, past, present or future of the Company or any successor corporation,
shall have any personal liability in respect of the obligations of the Company
under the Securities or this Indenture by reason of his, her or its status as
such partner, stockholder, employee, director or officer. Each Holder of a
Security waives and releases all such liability. Such waiver and release are
part of the consideration for the issuance of the Securities.

Section 13.11  Successors.
               ----------

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

Section 13.12  Duplicate Originals.
               -------------------

     All parties may sign any number of copies or counterparts of this
Indenture. Each signed copy or counterpart shall be an original, but all of them
together shall represent the same agreement.

Section 13.13  Severability.
               ------------

     In case any one or more of the provisions in this Indenture or in the
Securities shall be held invalid, illegal or unenforceable, in any respect for
any reason, the validity, legality and enforceability of any such provision in
every other respect and of the remaining provisions shall not in any way be
affected or impaired thereby, it being intended that all of the provisions
hereof shall be enforceable to the full extent permitted by law.

Section 13.14  Table Of Contents, Headings, Etc.
               ---------------------------------

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

Section 13.15  Qualification Of Indenture.
               --------------------------

     If required by the TIA, the Company shall qualify this Indenture under the
TIA and shall pay all costs and expenses (including attorneys' fees for the
Company and the Trustee) incurred in connection therewith, including, but not
limited to, costs and expenses of qualification of the


                                     -71-
<PAGE>
 
Indenture and the Securities and printing this Indenture and the Securities. The
Trustee shall be entitled to receive from the Company any such Officers'
Certificates, Opinions of Counsel or other documentation as it may reasonably
request in connection with any such qualification of this Indenture under the
TIA. Notwithstanding anything to the contrary contained herein, the parties
hereto shall be required to comply with the provisions of the TIA only to the
extent required thereby.


                                     -72-
<PAGE>
 
                                  SIGNATURES


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

                                  PLATINUM technology, inc.,
                                  a Delaware Corporation



                                  By: /s/ Andrew J. Filipowski
                                      ----------------------------------
                                  Name:   Andrew J. Filipowski
                                        --------------------------------
                                  Title:  President, CEO & CHAIRMAN
                                         -------------------------------
Attest: /s/ Larry Freedman
        --------------------
        Secretary


                                  American National Bank and Trust Company of
                                  Chicago, a national banking association

                                  as Trustee

                                  By:
                                      ----------------------------------
                                  Name:
                                        --------------------------------
                                  Title:
                                         ------------------------------- 
<PAGE>
 
                                   EXHIBIT A

[For Global Security only:

     UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (55 WATER STREET, NEW YORK, NEW
YORK) (THE "DEPOSITARY," WHICH TERM INCLUDES ANY SUCCESSOR DEPOSITARY FOR THE
CERTIFICATES) TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE
OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO.
OR IN SUCH OTHER NAME AS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DEPOSITARY
AND ANY PAYMENT HEREON IS MADE TO CEDE & CO. (OR TO SUCH OTHER ENTITY AS IS
REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITARY), ANY TRANSFER,
PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS
WRONGFUL SINCE THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.]

     THE SECURITY EVIDENCED HEREBY HAS NOT BEEN REGISTERED UNDER THE U.S.
SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR ANY STATE
SECURITIES LAWS, AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD WITHIN THE UNITED
STATES OR TO, OR FOR THE ACCOUNT OR BENEFIT OF, U.S. PERSONS EXCEPT AS SET FORTH
IN THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF, THE HOLDER (1) REPRESENTS
THAT (A) IT IS A "QUALIFIED INSTITUTIONAL BUYER" (AS DEFINED IN RULE 144A UNDER
THE SECURITIES ACT) OR (B) IT IS NOT A U.S. PERSON AND IS ACQUIRING THE SECURITY
EVIDENCED HEREBY IN AN OFFSHORE TRANSACTION; (2) AGREES THAT IT WILL NOT, PRIOR
TO EXPIRATION OF THE HOLDING PERIOD APPLICABLE TO SALES OF THE SECURITY
EVIDENCED HEREBY UNDER RULE 144(K) UNDER THE SECURITIES ACT (OR ANY SUCCESSOR
PROVISION), RESELL OR OTHERWISE TRANSFER THE SECURITY EVIDENCED HEREBY OR THE
COMMON STOCK ISSUABLE UPON CONVERSION OF SUCH SECURITY EXCEPT (A) TO PLATINUM
TECHNOLOGY, INC. OR ANY SUBSIDIARY THEREOF, (B) INSIDE THE UNITED STATES TO A
QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES
ACT, (C) OUTSIDE THE UNITED STATES IN COMPLIANCE WITH RULE 904 UNDER THE
SECURITIES ACT, (D) PURSUANT TO THE EXEMPTION FROM REGISTRATION PROVIDED BY RULE
144 UNDER THE SECURITIES ACT (IF AVAILABLE), (E) PURSUANT TO A REGISTRATION
STATEMENT WHICH HAS BEEN DECLARED EFFECTIVE UNDER THE SECURITIES ACT (AND WHICH
CONTINUES TO BE EFFECTIVE AT THE TIME OF SUCH TRANSFER), OR (F) PURSUANT TO
ANOTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES
ACT; (3) PRIOR TO SUCH TRANSFER (OTHER THAN A TRANSFER PURSUANT TO CLAUSE 2(E)
ABOVE), IT WILL FURNISH TO AMERICAN NATIONAL BANK AND TRUST COMPANY OF
<PAGE>
 
CHICAGO, AS TRUSTEE (OR A SUCCESSOR TRUSTEE, AS APPLICABLE), SUCH
CERTIFICATIONS, LEGAL OPINIONS OR OTHER INFORMATION AS IT MAY REASONABLY REQUIRE
TO CONFIRM THAT SUCH TRANSFER IS BEING MADE PURSUANT TO AN EXEMPTION FROM, OR IN
A TRANSACTION NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE SECURITIES
ACT AND (4) AGREES THAT IT WILL DELIVER TO EACH PERSON TO WHOM THE SECURITY
EVIDENCED HEREBY IS TRANSFERRED A NOTICE SUBSTANTIALLY TO THE EFFECT OF THIS
LEGEND. IN CONNECTION WITH ANY TRANSFER OF THE SECURITY EVIDENCED HEREBY PRIOR
TO THE EXPIRATION OF THE HOLDING PERIOD APPLICABLE TO SALES OF THE SECURITY
EVIDENCED HEREBY UNDER RULE 144(K) UNDER THE SECURITIES ACT (OR ANY SUCCESSOR
PROVISION), THE HOLDER MUST CHECK THE APPROPRIATE BOX SET FORTH ON THE REVERSE
HEREOF RELATING TO THE MANNER OF SUCH TRANSFER AND SUBMIT THIS CERTIFICATE TO
AMERICAN NATIONAL BANK AND TRUST COMPANY OF CHICAGO, AS TRUSTEE (OR A SUCCESSOR
TRUSTEE, AS APPLICABLE). THIS LEGEND WILL BE REMOVED UPON THE TRANSFER OF THE
SECURITY EVIDENCED HEREBY PURSUANT TO CLAUSE 2(D) OR 2(E) ABOVE. AS USED HEREIN,
THE TERMS "OFFSHORE TRANSACTION," "UNITED STATES" AND "U.S. PERSON" HAVE THE
MEANINGS GIVEN TO THEM BY REGULATION S UNDER THE SECURITIES ACT.


                                      -2-
<PAGE>
 
                              [FORM OF SECURITY]

                           PLATINUM technology, inc.

                 6.25% CONVERTIBLE SUBORDINATED NOTE DUE 2002

No.                                                      CUSIP No.______________
                                                                    $___________

     PLATINUM technology, inc., a Delaware corporation (hereinafter called the
"Company," which term includes any successors under the Indenture hereinafter
referred to), for value received, hereby promises to pay to
__________________________, or registered assigns, the principal sum of
________________ Dollars, on December 15, 2002.

     Interest Payment Dates: June 15 and December 15; commencing June 15, 1998.

     Record Dates:  June 1 and December 1.

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


                                      -3-
<PAGE>
 
     IN WITNESS WHEREOF, the Company has caused this Instrument to be duly
executed under its corporate seal.

Dated:

                               PLATINUM technology, inc., a Delaware Corporation

[seal]
                               By:
                                   ------------------------------    
                               Name:
                               Title:
 

Attest


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


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


Dated:


AMERICAN NATIONAL BANK AND TRUST COMPANY OF CHICAGO,
a national banking association, as Trustee


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


                                      -4-
<PAGE>
 
                           PLATINUM technology, inc.

                  6.25% CONVERTIBLE SUBORDINATED NOTE DUE 2001

     [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. Unless and until it is exchanged in whole or in part for
Securities in definitive form, this Security may not be transferred except as a
whole by the Depositary to a nominee of the Depositary or by a nominee of the
Depositary to the Depositary or another nominee of the Depositary or by the
Depositary or any such nominee to a successor Depositary or a nominee of such
successor Depositary. Unless this certificate is presented by an authorized
representative of The Depository Trust Company, a New York corporation ("DTC"),
to the Company or its agent for registration of transfer, exchange or payment,
and any certificate issued is registered in the name of Cede & Co. or in such
other name as is requested by an authorized representative of DTC (and any
payment is made to Cede & Co. or to such other entity as is requested by an
authorized representative of DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR
VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL inasmuch as the registered
owner hereof, Cede & Co., has an interest herein./1/]

1.   INTEREST.
  
     PLATINUM technology, inc., a Delaware corporation (hereinafter called the
"Company," which term includes any successors under the Indenture hereinafter
referred to), promises to pay interest on the principal amount of this Security
at the rate of 6.25% per annum. To the extent it is lawful, the Company promises
to pay interest on any interest payment due but unpaid on such principal amount
at a rate of 6.25% per annum compounded semi-annually.

     The Company will pay interest semi-annually on June 15 and December 15 of
each year (each, an "Interest Payment Date"), commencing June 15, 1998, until
maturity, redemption, repurchase or conversion pursuant to the Indenture (as
hereinafter defined). Interest on the Securities will accrue from the most
recent date to which interest has been paid or, if no interest has been paid on
the Securities, from December 16, 1997. Interest will be computed on the basis
of a 360-day year consisting of twelve 30-day months.

2.   METHOD OF PAYMENT.

     The Company shall pay interest on the Securities (except defaulted
interest) to the Persons who are the registered Holders at the close of business
on the Record Date immediately preceding the Interest Payment Date. Any such
interest not so punctually paid, and defaulted interest relating thereto, may be
paid to the Persons who are registered Holders at the close of business on a
Special Record Date for the payment of such defaulted interest, as more fully
provided in the Indenture referred to below. Except as provided below, the
Company shall pay principal and interest in such

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

/1/This paragraph should only be added if the Security is issued in global form.
<PAGE>
 
coin or currency of the United States of America as at the time of payment shall
be legal tender for payment of public and private debts ("U.S. Legal Tender").
The Securities will be payable as to principal, premium and interest at the
office or agency of the Company maintained for such purpose within or without
the City and State of New York, or at the option of the Company, payment of
principal, premium and interest may be made by check mailed to the Holders at
their addresses set forth in the registry of Holders, and provided that payment
by wire transfer of immediately available funds will be required with respect to
principal of, premium and interest on Global Securities and all other Securities
the Holders of which shall have provided wire transfer instructions to the
Company or the Paying Agent. Holders must surrender Securities to a Paying Agent
to collect principal payments.

3.   PAYING AGENT AND REGISTRAR.

     Initially, American National Bank and Trust Company, a national banking
association (the "Trustee"), at its office located at 14 Wall Street, New York,
New York 10005, will act as Paying Agent and Registrar. The Company may change
any Paying Agent, Registrar or Co-Registrar without notice to the Holders. The
Company or any of its Subsidiaries may, subject to certain exceptions, act as
Paying Agent, Registrar or Co-Registrar.

4.   INDENTURE.

     The Company issued the Securities under an Indenture, dated as of December
15, 1997 (the "Indenture"), between the Company and the Trustee. Capitalized
terms herein are used as defined in the Indenture unless otherwise defined
herein. The terms of the Securities include those stated in the Indenture and
those made part of the Indenture by reference to the Trust Indenture Act, as in
effect on the date of the Indenture. The Securities are subject to all such
terms, and Holders of Securities are referred to the Indenture and said Act for
a statement of them. The Securities are general unsecured obligations of the
Company limited in aggregate principal amount to $150,000,000 ($172,500,000 if
the Initial Purchasers exercise their over-allotment option in full).

5.   REDEMPTION.

     Subject to the provisions of Paragraph 7 of this Security, the Securities
will not be subject to redemption prior to December 15, 2000. On or after
December 15, 2000 the Securities will be redeemable at the option of the
Company, in whole or in part, at the following Redemption Prices (expressed as a
percentage of principal amount) set forth below with respect to the indicated
Redemption Date.

     If redeemed during the 12-month period beginning December 15:

<TABLE>
<CAPTION>
          Year                                              Redemption Price
          ----                                              ----------------
          <S>                                               <C>
          2000............................................. 102.50 %
          2001 and thereafter.............................. 101.25
</TABLE>

                                  -2-        
<PAGE>
 
 
together, in each case, with accrued interest (including any Additional Amounts
(as defined below) or Additional Interest) to the Redemption Date; provided that
Securities that are Tax Affected Securities are also redeemable, in whole but
not in part, under the circumstances described in Paragraph 7 of this Security,
at a Redemption Price equal to 100% of the principal amount thereof plus
interest accrued to the Redemption Date. Any such redemption will comply with
Article 3 of the Indenture.

     The Securities will not be subject to any sinking fund.

6.   PAYMENT OF ADDITIONAL AMOUNTS.

     The Company will pay to a Non-U.S. Holder of any Security such additional
amounts ("Additional Amounts") as may be necessary in order that every net
payment of the principal of, premium, if any, and interest on this Security
(including payment on redemption or repurchase), after deduction or withholding
for or on account of any present or future tax, assessment or governmental
charge imposed upon or as a result of such payment by the United States or any
political subdivision or taxing authority thereof or therein (each, a "Taxing
Jurisdiction"), will not be less than the amount provided for in this Security
to be then due and payable; provided, however, that the foregoing obligation to
pay Additional Amounts will not apply to:

          (a) any tax, assessment or other governmental charge which would not
     have been so imposed but for (i) the existence of any present or former
     connection between such Non-U.S. Holder (or between a fiduciary, settlor,
     beneficiary, member, shareholder of or possessor of a power over such Non-
     U.S. Holder, if such Non-U.S. Holder is an estate, a trust, a partnership
     or a corporation) and the Taxing Jurisdiction, including, without
     limitation, such Non-U.S. Holder (or such fiduciary, settlor, beneficiary,
     member, shareholder or possessor) being or having been a citizen,
     domiciliary or resident of the United States or treated as a resident
     thereof, or being or having been engaged in trade or business or present
     therein, or having or having had a permanent establishment therein or (ii)
     such Non-U.S. Holder's present or former status as a personal holding
     company, a foreign personal holding company with respect to the United
     States, a controlled foreign corporation, a passive foreign investment
     company, or a foreign private foundation or foreign tax exempt entity for
     United States federal tax purposes, or a corporation which accumulates
     earnings to avoid United States federal income tax;

          (b) any tax, assessment or other governmental charge which would not
     have been so imposed but for the presentation by the Non-U.S. Holder of
     this Security for payment on a date more than 15 days after the date on
     which such payment became due and payable or the date on which payment
     thereof is duly provided for, whichever occurs later;

          (c) any estate, inheritance, gift, sales, transfer, personal property
     or similar tax, assessment or governmental charge;

                                      -3-
<PAGE>
 

          (d) any tax, assessment or other governmental charge which would not
     have been imposed but for the failure to comply with any certification,
     identification or other reporting concerning the nationality, residence,
     identity or connection with the United States of such Non-U.S. Holder (or
     beneficial owner of such Security), if compliance is required or imposed by
     a statute, treaty, regulation or administrative practice of the United
     States or any political subdivision or taxing authority thereof or therein
     as a precondition to exemption from all or part of such tax, assessment or
     other governmental charge;

          (e) any tax, assessment or other governmental charge which is payable
     otherwise than by deduction or withholding from payments of principal of,
     premium, if any, or interest on such Security;

          (f) any tax, assessment or other governmental charge imposed on
     interest received by a Non-U.S. Holder actually or constructively holding
     10% or more of the total combined voting power of all classes of stock of
     the Company entitled to vote;

          (g) any tax, assessment or other governmental charge imposed on a Non-
     U.S. Holder that is a partnership or a fiduciary or other than the sole
     beneficial owner of such payment, but only to the extent that any
     beneficial owner or member of the partnership or beneficiary or settlor
     with respect to the fiduciary would not have been entitled to the payment
     of Additional Amounts had the beneficial owner, member, beneficiary or
     settlor directly been the Holder of this Security; or

          (h) any combination of items (a), (b), (c), (d), (e), (f) and (g).

     Notwithstanding the foregoing, the Company shall not be obligated to pay
Additional Amounts in respect of payments becoming due on the Securities more
than 15 days after the Redemption Date with respect to any redemption of the
Securities described in Paragraph 7 of this Security to the extent that the
Company's obligation to pay such Additional Amounts arises from the Tax Law
Change that resulted in such redemption.

     Except as specifically provided herein and in the Indenture, the Company
shall not be required to make any payment with respect to any tax, assessment or
other governmental charge imposed by any government or any political subdivision
or taxing authority thereof or therein. Whenever in this Security there is a
reference, in any context, to the payment of the principal of, premium, if any,
or interest on, or in respect of, any Security such mention shall be deemed to
include mention of the payment of Additional Amounts payable as described in the
preceding paragraph to the extent that, in such context, Additional Amounts are,
were or would be payable in respect of such Security, and express mention of the
payment of Additional Amounts (if applicable) in any provisions of this Security
shall not be construed as excluding Additional Amounts in those provisions of
this Security where such express mention is not made.

                                      -4-
<PAGE>
 

7.   REDEMPTION FOR TAX REASONS.

     If the Company determines that, principally as a result of a Tax Law
Change, the Company is or would become obligated on the next succeeding Interest
Payment Date to pay Additional Amounts to the Holder of any Security, as
described in Paragraph 6 of this Security, and such obligation cannot be avoided
by the Company taking reasonable measures available to it, then the Company may,
at its option, redeem the Tax Affected Securities in whole, but not in part, at
any time, on giving not less than 20 days' notice to the Holders prior to the
Redemption Date, at a Redemption Price equal to 100% of the principal amount
plus interest accrued to, but excluding, the Redemption Date and any Additional
Amounts then payable; provided, that no such notice of redemption shall be given
earlier than 90 days prior to the earliest date on which the Company would be
obligated to pay any such Additional Amounts were a payment in respect of the
Tax Affected Securities then made. Prior to the publication of any notice of
redemption pursuant to this paragraph, the Company shall deliver to the Trustee
(a) an Officers' Certificate stating that the Company is entitled to effect such
redemption and setting forth a statement of facts showing that the conditions
precedent to the right of the Company so to redeem have occurred and (b) an
Opinion of Counsel of recognized standing selected by the Company and reasonably
acceptable to the Trustee to the effect that the circumstances referred to above
in this paragraph exist. The Trustee shall accept such opinion as sufficient
evidence of the satisfaction of the conditions precedent described above, in
which event it shall be conclusive and binding on the Holders. The Company's
right to redeem the Tax Affected Securities shall continue as long as the
Company is obligated to pay such Additional Amounts, notwithstanding that the
Company shall have made payments of Additional Amounts specified in Paragraph 6.

8.   NOTICE OF REDEMPTION.

     In the event of a redemption pursuant to Paragraph 7 of this Security,
notice of Redemption will be sent by first class mail, at least 30 days and not
more than 60 days prior to the Redemption Date to the Holder of each Security to
be redeemed at such Holder's last address as then shown upon the registry books
of the Registrar. Securities may be redeemed in part in integral multiples of
$1,000 only.

     Except as set forth in the Indenture, from and after any Redemption Date,
if monies for the redemption of the Securities called for redemption shall have
been deposited with the Paying Agent on such Redemption Date and payment of the
Securities called for redemption is not prohibited under Article 11 of the
Indenture, the Securities called for redemption will cease to bear interest and
the only right of the Holders of such Securities will be to receive payment of
the Redemption Price, plus any accrued and unpaid interest (including any
Additional Amounts or Additional Interest) to the Redemption Date.

9.   DENOMINATIONS; TRANSFER; EXCHANGE.

                                      -5-
<PAGE>
 

     The Securities are in registered form, without coupons, in denominations of
$1,000 and integral multiplies of $1,000. A Holder may register the transfer of,
or exchange Securities in accordance with, the Indenture. The Registrar may
require a Holder, among other things, to furnish appropriate endorsements and
transfer documents and to pay any taxes and fees required by law or permitted by
the Indenture. The Registrar need not register the transfer of or exchange any
Securities selected for redemption.

10.  PERSONS DEEMED OWNERS.

     The registered Holder of a Security may be treated as the owner of it for
all purposes.

11.  UNCLAIMED MONEY.

     If money for the payment of principal or interest remains unclaimed for two
years, the Trustee and the Paying Agent(s) will pay the money back to the
Company at its written request. After that, all liability of the Trustee and
such Paying Agent(s) with respect to such money shall cease.

12.  AMENDMENT; SUPPLEMENT; WAIVER.

     Subject to certain exceptions, the Indenture or the Securities may be
amended or supplemented, and any existing Default or Event of Default or
compliance with any provision may be waived, with the written consent of the
Holders of a majority in aggregate principal amount of the Securities then
outstanding. Without notice to or consent of any Holder, the parties thereto may
amend or supplement the Indenture or the Securities to, among other things, cure
any ambiguity, defect or inconsistency, or make any other change that does not
adversely affect the rights of any Holder of a Security.

13.  CONVERSION RIGHTS.

     Subject to the provisions of the Indenture, the Holders have the right to
convert the principal amount of the Securities into fully paid and nonassessable
shares of Common Stock of the Company at the initial Conversion Price per share
of Common Stock of $36.0525, or at the adjusted Conversion Price per share then
in effect, if adjustment has been made as provided in the Indenture, upon
surrender of the Securities to the Company, together with a fully executed
notice in substantially the form attached hereto and, if required by the
Indenture, an amount equal to accrued interest payable on such Securities.

14.  RANKING.

     Payment of principal, premium, if any, and interest (including any
Additional Amounts or Additional Interest) on the Securities is subordinated, in
the manner and to the extent set forth in the Indenture, to the prior payment in
full of all Senior Indebtedness.

                                      -6-
<PAGE>
 

15.  REPURCHASE AT OPTION OF HOLDER UPON A CHANGE OF CONTROL.

     If there is a Change of Control, the Company shall be required to offer to
purchase on the Repurchase Date all outstanding Securities at a purchase price
equal to 100% of the principal amount thereof, plus accrued and unpaid interest
(including any Additional Amounts or Additional Interest), if any, to the
Repurchase Date. Holders of Securities will receive a Repurchase Offer from the
Company prior to any related Repurchase Date and may elect to have such
Securities purchased by completing the form entitled "Option of Holder to Elect
Purchase" appearing below.

16.  SUCCESSORS.

     When a successor assumes all the obligations of its predecessor under the
Securities and the Indenture, the predecessor will be released from those
obligations.

17.  DEFAULTS AND REMEDIES.

     If an Event of Default occurs and is continuing (other than an Event of
Default relating to certain events of bankruptcy, insolvency or reorganization),
then in every such case, unless the principal of all of the securities shall
have already become due and payable, either the Trustee or the Holders of 25% in
aggregate principal amount of Securities then outstanding may declare all the
Securities to be due and payable immediately in the manner and with the effect
provided in the Indenture. Holders of Securities may not enforce the Indenture
or the Securities except as provided in the Indenture. The Trustee may require
indemnity satisfactory to it before it enforces the Indenture or the Securities.
Subject to certain limitations, Holders of a majority in aggregate principal
amount of the Securities then outstanding may direct the Trustee in its exercise
of any trust or power. The Trustee may withhold from Holders of Securities
notice of any continuing Default or Event of Default (except a Default in
payment of principal or interest), if it determines that withholding notice is
in their interest.

18.  REGISTRATION RIGHTS AGREEMENT.

     The Holder of this Security and the Common Stock issuable upon conversion
thereof is entitled to the benefits of a Registration Rights Agreement (subject
to the provisions thereof), dated as of December 15, 1997, between the Company
and the Initial Purchasers.

19.  RULE 144A INFORMATION.

     Subject to certain limitations in the Indenture, at any time when the
Company is not subject to Section 13 or 15(d) of the United States Securities
Exchange Act of 1934, as amended, upon the request of a Holder of a Restricted
Security or the holder of Common Stock issued upon conversion thereof, the
Company will promptly furnish or cause to be furnished Rule 144A Information (as
defined in the Indenture) to such Holder of Restricted Securities or such holder
of Common Stock issued upon conversion of Restricted Securities, or to a
prospective purchaser of any such security designated by any such Holder or
holder, as the case may be, to the extent required to permit

                                      -7-
<PAGE>
 

compliance by such Holder or holder with Rule 144A under the Securities Act in
connection with the resale of any such security.

20.  TRUSTEE DEALINGS WITH COMPANY.

     The Trustee under the Indenture, in its individual or any other capacity,
may make loans to, accept deposits from, and perform services for the Company or
its Affiliates, and may otherwise deal with the Company or its Affiliates as if
it were not the Trustee.

21.  NO RECOURSE AGAINST OTHERS.

     No stockholder, director, officer or employee, as such, past, present or
future, of the Company or any successor corporation shall have any personal
liability in respect of the obligations of the Company under the Securities or
the Indenture by reason of his, her or its status as such stockholder, director,
officer or employee. Each Holder of a Security by accepting a Security waives
and releases all such liability. This waiver and release are part of the
consideration for the issuance of the Securities.

22.  AUTHENTICATION.

     The Security shall not be valid until the Trustee or authenticating agent
signs the certificate of authentication on the other side of this Security.

23.  ABBREVIATIONS AND DEFINED TERMS.

     Customary abbreviations may be used in the name of a Holder of a Security
or an assignee, such as: TEN COM (= tenants in common), TENENT (= tenants by the
entireties), JT TEN (= joint tenants with right of survivorship and not as
tenants in common), CUST (= Custodian), and U/G/M/A (= Uniform Gifts to Minors
Act).

24.  CUSIP NUMBERS.

     Pursuant to a recommendation promulgated by the Committee on Uniform
Security Identification Procedures, the Company will cause CUSIP numbers to be
printed on the Securities as a convenience to the Holders of the Securities. No
representation is made as to the accuracy of such numbers as printed on the
Securities, and reliance may be placed only on the other identification numbers
printed hereon.

                                      -8-
<PAGE>
 

                              ASSIGNMENT FORM AND
                            CERTIFICATE OF TRANSFER


     To assign this Security fill in the form below:

     (I) or (we) assign and transfer this Security to


--------------------------------------------------------------------------------
       (Insert assignee's social security or tax identification number)


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

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

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

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

     In connection with any transfer of any of the Securities within the period
prior to the expiration of the holding period applicable to the sales thereof
under Rule 144(k) under the Securities Act of 1933, as amended (the "Securities
Act") (or any successor provision), the undersigned confirms that such
Securities are being transferred:

     CHECK ONE BOX BELOW

     [_]  to the Company or a subsidiary thereof; or

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

     [_]  pursuant to and in compliance with Regulation S under the Securities
          Act; or

     [_]  pursuant to Rule 144 of the Securities Act; or

     [_]  pursuant to an effective registration statement; or

     [_]  pursuant to another available exemption under the Securities Act;

and unless the box below is checked, the undersigned confirms that such
Securities are not being transferred to an "affiliate" of the Company as defined
in Rule 144 under the Securities Act (an "Affiliate").

     [_]  the Securities are being transferred to an Affiliate.
<PAGE>
 

                      OPTION OF HOLDER TO ELECT PURCHASE


     If you want to elect to have this Security purchased by the Company
pursuant to Article 10 of the Indenture, check the box: [_]

     If you want to elect to have only part of this Security purchased by the
Company pursuant to Article 10 of the Indenture, state the amount you want to be
purchased: $________



Date:                         Signature:
      --------------------               ---------------------------------------
                                         (Sign exactly as your name appears on
                                         the other side of this Security)

                                     -10-
<PAGE>
 

               SCHEDULE OF EXCHANGES OF DEFINITIVE SECURITIES/2/


     The following exchanges of a part of this Global Security for definitive
Securities have been made:

<TABLE>
<CAPTION>
                                                            Principal
                   Amount of            Amount of           Amount of this      Signature of
                   decrease in          Increase in         Global Security     authorized
                   Principal Amount     Principal           following such      Trustee or
Date of            of this Global       Amount of this      decrease (or        Securities
Exchange           Security             Global Security     increase)           Custodian
---------------    ----------------     ---------------     ---------------     ------------
<S>                <C>                  <C>                 <C>                 <C>
 
 
 






</TABLE>

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

     /2/This schedule should only be added if the Security is issued in global
form.
<PAGE>
 

                                   EXHIBIT B

                           FORM OF CONVERSION NOTICE


To:  PLATINUM technology, inc.

     The undersigned owner of this Security hereby: (i) irrevocably exercises
the option to convert this Security, or the portion hereof below designated,
into shares of Common Stock of PLATINUM technology, inc. in accordance with the
terms of this Indenture referred to in this Security and (ii) directs that such
shares of Common Stock deliverable upon the conversion, together with any check
in payment for fractional shares and any Security(ies) representing any
unconverted principal amount hereof, be issued and delivered to the registered
holder hereof unless a different name has been indicated below. 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 thereto. Any amount required to
be paid by the undersigned on account of interest accompanies this Security.


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

                                       -----------------------------------------
                                                      (Signature)


     Provide information below for registration of shares of Common Stock if to
be issued, and of Securities if to be issued other than in the name of the
registered holder.


----------------------------------
              (Name)


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


----------------------------------
    City, State and Zip Code)
 (Please print name and address)


----------------------------------
(Social Security or other Taxpayer
Identifying Number)


                                       Principal Amount to be converted: (in an
                                       integral multiple of $1000, if less than
                                       all)

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