<PAGE>

                                                                     Exhibit 4.1


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





                         MORRISON KNUDSEN CORPORATION
                                    Issuer

                       11% Senior Notes Due July 1, 2010


                             ____________________

                                   INDENTURE

                           Dated as of July 1, 2000

                             _____________________

                    UNITED STATES TRUST COMPANY OF NEW YORK
                                    Trustee






================================================================================
<PAGE>

                             CROSS-REFERENCE TABLE

TIA                                                      Indenture
Section                                                  Section
-------                                                  ---------

310(a)(1)       ......................................      7.10
   (a)(2)       ......................................      7.10
   (a)(3)       ......................................      N.A.
   (a)(4)       ......................................      N.A.
   (b)          ......................................      7.08; 7.10
   (c)          ......................................      N.A.
311(a)          ......................................      7.11
   (b)          ......................................      7.11
   (c)          ......................................      N.A.
312(a)          ......................................      2.05
   (b)          ......................................      11.03
   (c)          ......................................      11.03
313(a)          ......................................      7.06
   (b)(1)       ......................................      N.A.
   (b)(2)       ......................................      7.06
   (c)          ......................................      11.02
   (d)          ......................................      7.06
314(a)          ......................................      4.02;
                                                            4.14; 11.02
   (b)          ......................................      N.A.
   (c)(1)       ......................................      11.04
   (c)(2)       ......................................      11.04
   (c)(3)       ......................................      N.A.
   (d)          ......................................      N.A.
   (e)          ......................................      11.05
   (f)          ......................................      4.14
315(a)          ......................................      7.01
   (b)          ......................................      7.05; 11.02
   (c)          ......................................      7.01
   (d)          ......................................      7.01
   (e)          ......................................      6.11
316(a)(last sentence).................................      11.06
   (a)(1)(A)    ......................................      6.05
   (a)(1)(B)    ......................................      6.04
   (a)(2)       ......................................      N.A.
   (b)          ......................................      6.07
317(a)(1)       ......................................      6.08
   (a)(2)       ......................................      6.09
   (b)          ......................................      2.04
318(a)          ......................................      11.01


                 N.A. means Not Applicable.

________________________
Note:  This Cross-Reference Table shall not, for any purpose, be deemed to be
part of the Indenture.
<PAGE>

                               TABLE OF CONTENTS


<TABLE>
<CAPTION>
                                                                            Page
                                                                            ----
                                   ARTICLE I

                  Definitions and Incorporation by Reference
                  ------------------------------------------
<S>                                                                         <C>
SECTION 1.01.    Definitions                                                 1
SECTION 1.02.    Other Definitions.......................................   33
SECTION 1.03.    Incorporation by Reference of Trust
                 Indenture Act...........................................   34
SECTION 1.04.    Rules of Construction...................................   34

                                  ARTICLE II

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

SECTION 2.01.    Form and Dating.........................................   35
SECTION 2.02.    Execution and Authentication............................   35
SECTION 2.03.    Registrar and Paying Agent..............................   36
SECTION 2.04.    Paying Agent To Hold Money in Trust.....................   37
SECTION 2.05.    Securityholder Lists....................................   37
SECTION 2.06.    Transfer and Exchange...................................   37
SECTION 2.07.    Replacement Securities..................................   38
SECTION 2.08.    Outstanding Securities..................................   38
SECTION 2.09.    Temporary Securities....................................   39
SECTION 2.10.    Cancellation............................................   39
SECTION 2.11.    Defaulted Interest......................................   39
SECTION 2.12.    CUSIP Numbers...........................................   39
SECTION 2.13.    Issuance of Additional Securities.......................   40

                                  ARTICLE III

                                  Redemption
                                  ----------

SECTION 3.01.    Notices to Trustee......................................   40
SECTION 3.02.    Selection of Securities To Be Redeemed..................   41
SECTION 3.03.    Notice of Redemption....................................   41
SECTION 3.04.    Effect of Notice of Redemption..........................   42
SECTION 3.05.    Deposit of Redemption Price.............................   42
SECTION 3.06.    Securities Redeemed in Part.............................   42

                                  ARTICLE IV

                                   Covenants
                                   ---------

SECTION 4.01.    Payment of Securities...................................   42
</TABLE>
<PAGE>

                                                                               2

<TABLE>
<S>                                                                         <C>
SECTION 4.02.    SEC Reports............................................... 43
SECTION 4.03.    Limitation on Indebtedness................................ 43
SECTION 4.04.    Limitation on Restricted Payments......................... 46
SECTION 4.05.    Conduct of Business....................................... 50
SECTION 4.06.    Limitation on Restrictions on Distributions from
                    Restricted Subsidiaries................................ 50
SECTION 4.07.    Limitation on Sales of Assets and Subsidiary Stock........ 51
SECTION 4.08.    Limitation on Affiliate Transactions...................... 56
SECTION 4.09.    Limitation on the Sale or Issuance of Capital Stock of
                    Restricted Subsidiaries................................ 57
SECTION 4.10.    Change of Control......................................... 58
SECTION 4.11.    Limitation on Liens....................................... 60
SECTION 4.12.    Limitation on Sale/Leaseback Transactions................. 60
SECTION 4.13.    Future Guarantors......................................... 61
SECTION 4.14.    Compliance Certificate.................................... 61
SECTION 4.15.    Further Instruments and Acts.............................. 61
SECTION 4.16.    Suspension of Certain Covenants........................... 61

                                 ARTICLE V

                             Successor Company
                             -----------------

SECTION 5.01.    When Company May Merge or Transfer Assets................. 62

                                  ARTICLE VI

                             Defaults and Remedies
                             ---------------------

SECTION 6.01.    Events of Default......................................... 64
SECTION 6.02.    Acceleration.............................................. 66
SECTION 6.03.    Other Remedies............................................ 67
SECTION 6.04.    Waiver of Past Defaults................................... 67
SECTION 6.05.    Control by Majority....................................... 67
SECTION 6.06.    Limitation on Suits....................................... 68
SECTION 6.07.    Rights of Holders To Receive Payment...................... 68
SECTION 6.08.    Collection Suit by Trustee................................ 68
SECTION 6.09.    Trustee May File Proofs of Claim.......................... 69
SECTION 6.10.    Priorities................................................ 69
SECTION 6.11.    Undertaking for Costs..................................... 69
SECTION 6.12.    Waiver of Stay or Extension Laws.......................... 70
</TABLE>
<PAGE>

                                                                               3


                                  ARTICLE VII

                                    Trustee
                                    -------
<TABLE>
<S>                                                                         <C>
SECTION 7.01.    Duties of Trustee......................................    70
SECTION 7.02.    Rights of Trustee......................................    71
SECTION 7.03.    Individual Rights of Trustee...........................    72
SECTION 7.04.    Trustee's Disclaimer...................................    72
SECTION 7.05.    Notice of Defaults.....................................    72
SECTION 7.06.    Reports by Trustee to Holders..........................    73
SECTION 7.07.    Compensation and Indemnity.............................    73
SECTION 7.08.    Replacement of Trustee.................................    74
SECTION 7.09.    Successor Trustee by Merger............................    75
SECTION 7.10.    Eligibility; Disqualification..........................    75
SECTION 7.11.    Preferential Collection of Claims
                   Against Company......................................    75

                                ARTICLE VIII

                      Discharge of Indenture; Defeasance
                      ----------------------------------

SECTION 8.01.   Discharge of Liability on Securities;
                Defeasance..............................................    76
SECTION 8.02.   Conditions to Defeasance................................    77
SECTION 8.03.   Application of Trust Money..............................    78
SECTION 8.04.   Repayment to Company....................................    78
SECTION 8.05.   Indemnity for Government Obligations....................    79
SECTION 8.06.   Reinstatement...........................................    79

                                  ARTICLE IX

                                  Amendments
                                  ----------

SECTION 9.01.    Without Consent of Holders.............................    79
SECTION 9.03.    Compliance with Trust Indenture Act....................    81
SECTION 9.04.    Revocation and Effect of Consents and
                   Waivers..............................................    81
SECTION 9.05.    Notation on or Exchange of Securities..................    82
SECTION 9.06.    Trustee To Sign Amendments.............................    82
SECTION 9.07.    Payment for Consent....................................    82

                                  ARTICLE X

                             Subsidiary Guaranties
                             ---------------------

SECTION 10.01.   Guaranties.............................................    83
SECTION 10.02.   Limitation on Liability................................    85
SECTION 10.03.   Successors and Assigns.................................    85
SECTION 10.04.   No Waiver..............................................    85
SECTION 10.05.   Modification...........................................    85
</TABLE>
<PAGE>

                                                                               4
<TABLE>
<S>                                                                         <C>
SECTION 10.06.    Release of Subsidiary Guarantor........................   86

                                 ARTICLE XI

                                Miscellaneous
                                -------------

SECTION 11.01.    Trust Indenture Act Controls...........................   86
SECTION 11.02.    Notices................................................   87
SECTION 11.03.    Communication by Holders with Other Holders............   87
SECTION 11.04.    Certificate and Opinion as to Conditions Precedent.....   87
SECTION 11.05.    Statements Required in Certificate or Opinion..........   88
SECTION 11.06.    When Securities Disregarded............................   88
SECTION 11.07.    Rules by Trustee, Paying Agent and Registrar...........   89
SECTION 11.08.    Legal Holidays.........................................   89
SECTION 11.09.    Governing Law..........................................   89
SECTION 11.10.    No Recourse Against Others.............................   89
SECTION 11.11.    Successors.............................................   89
SECTION 11.12.    Multiple Originals.....................................   89
SECTION 11.13.    Table of Contents; Headings............................   89
</TABLE>

Rule 144A/Regulation S Appendix

Exhibit  1 -  Form of Initial Security

Exhibit  A -  Form of Exchange Security or Private Exchange
              Security

Schedule A -  Subsidiary Guarantors
<PAGE>

               among MORRISON INDENTURE dated KNUDSEN CORPORATION, a as of July
               1, 2000, Delaware corporation (the "Company"), THE SUBSIDIARY
               GUARANTORS LISTED ON SCHEDULE A HERETO and UNITED STATES TRUST
               COMPANY OF NEW YORK, a New York banking corporation (the
               "Trustee").

          Each party agrees as follows for the benefit of the other parties and
for the equal and ratable benefit of the Holders of the Company's Initial
Securities, Exchange Securities and Private Exchange Securities (collectively,
the "Securities"):

                                   ARTICLE I

                  Definitions and Incorporation by Reference
                  ------------------------------------------

          SECTION 1.01. Definitions.
                        ------------

          "Additional Assets" means:

          (1)  any property, plant or equipment used in a Related Business;

          (2)  the Capital Stock of a Person that becomes a Restricted
               Subsidiary as a result of the acquisition of such Capital Stock
               by the Company or another Restricted Subsidiary; or

          (3)  Capital Stock constituting a minority interest in any Person that
               at such time is a Restricted Subsidiary;

provided, however, that any such Restricted Subsidiary described in clause (2)
--------  -------
or (3) above is primarily engaged in a Related Business.

          "Additional Securities" means, subject to the Company's compliance
with Section 4.03, 11% Senior Notes Due July 1, 2010 issued from time to time
after the Issue Date under the terms of this Indenture (other than pursuant to
Section 2.06, 2.07, 2.09 or 3.06 of this Indenture and other than Exchange
Securities or Private Exchange Securities issued pursuant to an exchange offer
for other Securities outstanding under this Indenture).
<PAGE>

                                                                               2

          "Affiliate" of any specified Person means:

          (1)  any other Person, directly or indirectly, controlling or
               controlled by; or

          (2)  under direct or indirect common control with such specified
               Person.

For the purposes of this definition, "control" when used with respect to any
Person means the power to direct the management and policies of such Person,
directly or indirectly, whether through the ownership of voting securities, by
contract or otherwise; and the terms "controlling" and "controlled" have
meanings correlative to the foregoing.  For purposes of Sections 4.04, 4.07 and
4.08 only, "Affiliate" shall also mean any beneficial owner of Capital Stock
representing 5% or more of the total voting power of the Voting Stock (on a
fully diluted basis) of the Company or of rights or warrants to purchase such
Capital Stock (whether or not currently exercisable) and any Person who would be
an Affiliate of any such beneficial owner pursuant to the first sentence hereof.

          "Asset Disposition" means any sale, lease, transfer or other
disposition (or series of related sales, leases, transfers or dispositions) by
the Company or any Restricted Subsidiary, including any disposition by means of
a merger, consolidation or similar transaction (each referred to for the
purposes of this definition as a "disposition"), of:

          (1)  any shares of Capital Stock of a Restricted Subsidiary (other
               than directors' qualifying shares or shares required by
               applicable law to be held by a Person other than the Company or a
               Restricted Subsidiary);

          (2)  all or substantially all the assets of any division or line of
               business of the Company or any Restricted Subsidiary; or

          (3)  any other assets of the Company or any Restricted Subsidiary
               outside of the ordinary course of business of the Company or such
               Restricted Subsidiary

(other than, in the case of clauses (1), (2) and (3) above,

               (A)  a disposition by a Restricted Subsidiary to the Company or
                    by the Company or a
<PAGE>

                                                                               3

                    Restricted Subsidiary to a Wholly Owned Subsidiary;

               (B)  for purposes of Section 4.07 only, a disposition that
                    constitutes a Restricted Payment permitted by Section 4.04
                    or a Permitted Investment;

               (C)  the sale or other disposition of obsolete or worn-out
                    property in the ordinary course of business;

               (D)  the sale or other disposition in the ordinary course of
                    business of equipment that is no longer necessary for the
                    construction or operations and maintenance project for which
                    it was acquired; provided, however, that it is unprofitable,
                                     --------  -------
                    impracticable or undesirable to employ such equipment on
                    another project; and

               (E)  a disposition of assets with a fair market value of less
                    than $500,000).

          "Attributable Debt" in respect of a Sale/Leaseback Transaction means,
as at the time of determination, the present value (discounted at the interest
rate borne by the Securities, compounded annually) of the total obligations of
the lessee for rental payments during the remaining term of the lease included
in such Sale/Leaseback Transaction (including any period for which such lease
has been extended).

          "Average Life" means, as of the date of determination, with respect to
any Indebtedness, the quotient obtained by dividing:

          (1)  the sum of the products of the numbers of years from the date of
               determination to the dates of each successive scheduled principal
               payment of or redemption or similar payment with respect to such
               Indebtedness multiplied by the amount of such payment by

          (2)  the sum of all such payments.

          "Board of Directors" means the Board of Directors of the Company or
any committee thereof duly authorized to act on behalf of such Board.
<PAGE>

                                                                               4

          "Business Day" means each day which is not a Legal Holiday.

          "Capital Lease Obligation" means an obligation that is required to be
classified and accounted for as a capital lease for financial reporting purposes
in accordance with GAAP, and the amount of Indebtedness represented by such
obligation shall be the capitalized amount of such obligation determined in
accordance with GAAP; and the Stated Maturity thereof shall be the date of the
last payment of rent or any other amount due under such lease prior to the first
date upon which such lease may be terminated by the lessee without payment of a
penalty.

          "Capital Stock" of any Person means any and all shares, interests,
rights to purchase, warrants, options, participations or other equivalents of or
interests in (however designated) equity of such Person, including any Preferred
Stock, but excluding any debt securities convertible into such equity.

          "Change of Control" means the occurrence of any of the following
events:

          (1) any "person" (as that term is used in Sections 13(d) and 14(d) of
     the Exchange Act), other than one or more Permitted Holders, is or becomes
     the "beneficial owner" (as defined in Rules 13d-3 and 13d-5 under the
     Exchange Act, except that for purposes of this clause (1) such person shall
     be deemed to have "beneficial ownership" of all shares that any such person
     has the right to acquire prior to the Stated Maturity of the Securities,
     whether such right is exercisable immediately or only after the passage of
     time), directly or indirectly, of more than 35% of the total voting power
     of the Voting Stock of the Company; provided, however, that the Permitted
                                         --------  -------
     Holders beneficially own (as defined in Rules 13d-3 and 13d-5 under the
     Exchange Act), directly or indirectly, in the aggregate a lesser percentage
     of the total voting power of the Voting Stock of the Company than such
     other person and do not have the right or ability by voting power, contract
     or otherwise to elect or designate for election a majority of the Board of
     Directors (for the purposes of this clause (1), such other person shall be
     deemed to beneficially own any Voting Stock of a person (the "specified
     person") held by any other person (the "parent entity"), if such other
     person is the beneficial owner (as defined above in this clause (1)),
     directly or indirectly, of more than 35% of the voting
<PAGE>

                                                                               5

     power of the Voting Stock of such parent entity and the Permitted Holders
     beneficially own (as defined in this proviso), directly or indirectly, in
     the aggregate a lesser percentage of the voting power of the Voting Stock
     of such parent entity and do not have the right or ability by voting power,
     contract or otherwise to elect or designate for election a majority of the
     board of directors of such parent entity);

          (2) individuals who on the Issue Date constituted the Board of
     Directors (together with any new directors whose election by such Board of
     Directors or whose nomination for election by the shareholders of the
     Company was approved by a vote of a majority of the directors of the
     Company then still in office who were either directors on the Issue Date or
     whose election or nomination for election was previously so approved,
     including those who become directors in a merger approved by the Board of
     Directors) cease for any reason to constitute a majority of the Board of
     Directors then in office;

          (3) the adoption of a plan relating to the liquidation or dissolution
     of the Company; or

          (4) the merger or consolidation of the Company with or into another
     Person or the merger of another Person with or into the Company, or the
     sale of all or substantially all the assets of the Company (determined on a
     consolidated basis) to another Person (other than, in all such cases, a
     Person that is controlled by the Permitted Holders), other than a
     transaction following which (A) in the case of a merger or consolidation
     transaction, securities that represented 100% of the Voting Stock of the
     Company immediately prior to such transaction (or other securities into
     which such securities are converted as part of such merger or consolidation
     transaction) constitute a majority of the voting power of the Voting Stock
     of the surviving Person in such merger or consolidation transaction, and
     (B) in the case of a sale of assets transaction, the transferee Person
     becomes the obligor in respect of the Securities and a Subsidiary of the
     Company.

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

          "Company" means the party named as such in this Indenture until a
successor replaces it and, thereafter, means the successor and, for purposes of
any provision
<PAGE>

                                                                               6

contained herein and required by the TIA, each other obligor on the indenture
securities.

          "Comparable Treasury Issue" means the United States Treasury security
selected by an "Independent Investment Banker" as having a maturity comparable
to the remaining term of the Securities that would be utilized, at the time of
selection and in accordance with customary financial practice, in pricing new
issues of corporate debt securities of comparable maturity to the remaining term
of the Securities.  "Independent Investment Banker" means one of the Reference
Treasury Dealers appointed by the Trustee after consultation with the Company.

          "Comparable Treasury Price" means, with respect to any redemption
date,

          (i)  the average of four Reference Treasury Dealer Quotations for the
     redemption date, after excluding the highest and lowest of those Reference
     Treasury Dealer Quotations, or

          (ii) if the Trustee obtains fewer than four Reference Treasury Dealer
     Quotations, the average of all quotations obtained.

          "Consolidated Coverage Ratio" as of any date of determination means
the ratio of (x) the aggregate amount of EBITDA for the period of the most
recent four consecutive fiscal quarters ending at least 45 days prior to the
date of such determination to (y) Consolidated Interest Expense for such four
fiscal quarters; provided, however, that:
                 --------  -------

          (1) if the Company or any Restricted Subsidiary has Incurred any
     Indebtedness since the beginning of such period that remains outstanding or
     if the transaction giving rise to the need to calculate the Consolidated
     Coverage Ratio is an Incurrence of Indebtedness, or both, EBITDA and
     Consolidated Interest Expense for such period shall be calculated after
     giving effect on a pro forma basis to such Indebtedness as if such
     Indebtedness had been Incurred on the first day of such period;

          (2) if the Company or any Restricted Subsidiary has repaid,
     repurchased, defeased or otherwise discharged any Indebtedness since the
     beginning of such period or if any Indebtedness is to be repaid,
     repurchased, defeased or otherwise discharged (in each case other than
     Indebtedness Incurred under any
<PAGE>

                                                                               7

revolving credit facility unless such Indebtedness has been permanently repaid
and has not been replaced) on the date of the transaction giving rise to the
need to calculate the Consolidated Coverage Ratio, EBITDA and Consolidated
Interest Expense for such period shall be calculated on a pro forma basis as if
such discharge had occurred on the first day of such period and as if the
Company or such Restricted Subsidiary has not earned the interest income
actually earned during such period in respect of cash or Temporary Cash
Investments used to repay, repurchase, defease or otherwise discharge such
Indebtedness;

     (3) if since the beginning of such period the Company or any Restricted
Subsidiary shall have made any Asset Disposition, the EBITDA for such period
shall be reduced by an amount equal to the EBITDA (if positive) directly
attributable to the assets which are the subject of such Asset Disposition for
such period, or increased by an amount equal to the EBITDA (if negative)
directly attributable thereto for such period and Consolidated Interest Expense
for such period shall be reduced by an amount equal to the Consolidated Interest
Expense directly attributable to any Indebtedness of the Company or any
Restricted Subsidiary repaid, repurchased, defeased or otherwise discharged with
respect to the Company and its continuing Restricted Subsidiaries in connection
with such Asset Disposition for such period (or, if the Capital Stock of any
Restricted Subsidiary is sold, the Consolidated Interest Expense for such period
directly attributable to the Indebtedness of such Restricted Subsidiary to the
extent the Company and its continuing Restricted Subsidiaries are no longer
liable for such Indebtedness after such sale);

     (4) if since the beginning of such period the Company or any Restricted
Subsidiary (by merger or otherwise) shall have made an Investment in any
Restricted Subsidiary (or any person which becomes a Restricted Subsidiary) or
an acquisition of assets, including any acquisition of assets occurring in
connection with a transaction requiring a calculation to be made hereunder,
which constitutes all or substantially all of an operating unit of a business,
EBITDA and Consolidated Interest Expense for such period shall be calculated
after giving pro forma effect thereto (including the Incurrence of any
Indebtedness) as if such Investment or acquisition occurred on the first day of
such period; and
<PAGE>

                                                                               8

          (5) if since the beginning of such period any Person (that
     subsequently became a Restricted Subsidiary or was merged with or into the
     Company or any Restricted Subsidiary since the beginning of such period)
     shall have made any Asset Disposition, any Investment or acquisition of
     assets that would have required an adjustment pursuant to clause (3) or (4)
     above if made by the Company or a Restricted Subsidiary during such period,
     EBITDA and Consolidated Interest Expense for such period shall be
     calculated after giving pro forma effect thereto as if such Asset
     Disposition, Investment or acquisition occurred on the first day of such
     period.

For purposes of this definition, whenever pro forma effect is to be given to an
                                          --- -----
acquisition of assets, the amount of income or earnings relating thereto and the
amount of Consolidated Interest Expense associated with any Indebtedness
Incurred in connection therewith, the pro forma calculations (A) shall be
determined in good faith by a responsible financial or accounting Officer of the
Company and (B) shall include for such period the reduction or increase in costs
that were directly attributable to any acquisition of assets and calculated on a
basis that is consistent with Regulation S-X under the Securities Act in effect
and applied as of the Issue Date.  If any Indebtedness bears a floating rate of
interest and is being given pro forma effect, the interest on such Indebtedness
shall be calculated as if the rate in effect on the date of determination had
been the applicable rate for the entire period (taking into account any Interest
Rate Agreement applicable to such Indebtedness if such Interest Rate Agreement
has a remaining term in excess of 12 months).

          "Consolidated Interest Expense" means, for any period, the total
consolidated interest expense of the Company and its consolidated subsidiaries
(excluding its Unrestricted Subsidiaries other than WGSG), plus, to the extent
not included in such total consolidated interest expense and to the extent
incurred (including by Permitted Joint Ventures in an amount proportional to the
Company's interests therein), without duplication:

          (1) interest expense attributable to capital leases and the interest
     expense attributable to leases constituting part of a Sale/Leaseback
     Transaction;

          (2) amortization of debt discount and debt issuance cost;
<PAGE>

                                                                               9

          (3) capitalized interest;

          (4) non-cash interest expenses;

          (5) commissions, discounts and other fees and charges owed with
     respect to letters of credit and bankers' acceptance financing;

          (6) net payments pursuant to Hedging Obligations;

          (7) Preferred Stock dividends in respect of all Preferred Stock held
     by Persons other than the Company or a Wholly Owned Subsidiary (other than
     dividends payable solely in Capital Stock (other than Disqualified Stock)
     of the Company or the issuer of such Preferred Stock);

          (8) interest incurred in connection with Investments in discontinued
     operations;

          (9) interest accruing on any Indebtedness of any other Person to the
     extent such Indebtedness is Guaranteed by (or secured by the assets of) the
     Company or any Restricted Subsidiary; and

          (10) the cash contributions to any employee stock ownership plan or
     similar trust to the extent such contributions are used by such plan or
     trust to pay interest or fees to any Person (other than the Company) in
     connection with Indebtedness Incurred by such plan or trust.

          Notwithstanding the foregoing, the amount of interest expense and
other items of WGSG that would be included above shall be included in the
computation of Consolidated Interest Expense only to the extent (and in the same
proportion) of the Company's interest in WGSG.

          "Consolidated Net Income" means, for any period, the consolidated net
income of the Company and its consolidated subsidiaries; provided, however, that
                                                         --------  -------
there shall not be included in such Consolidated Net Income:

          (1) any net income of any Person (other than the Company) if such
     Person is not a Restricted Subsidiary, is not a Permitted Joint Venture or
     is not WGSG, except that:

               (A) subject to the exclusion contained in clause (4) below, the
          Company's equity in the net
<PAGE>

                                                                              10

          income of any such Person for such period shall be included in such
          Consolidated Net Income up to the aggregate amount of cash actually
          distributed by such Person during such period to the Company or a
          Restricted Subsidiary as a dividend or other distribution (subject, in
          the case of a dividend or other distribution paid to a Restricted
          Subsidiary, to the limitations contained in clause (3) below); and

               (B) the Company's equity in a net loss of any such Person for
          such period shall be included in determining such Consolidated Net
          Income;

          (2) any net income (or loss) of any Person acquired by the Company or
     a Subsidiary in a pooling of interests transaction for any period prior to
     the date of such acquisition;

          (3) any net income of any Restricted Subsidiary if such Restricted
     Subsidiary is subject to restrictions, directly or indirectly, on the
     payment of dividends or the making of distributions by such Restricted
     Subsidiary, directly or indirectly, to the Company, except that:

               (A) subject to the exclusion contained in clause (4) below, the
          Company's equity in the net income of any such Restricted Subsidiary
          for such period shall be included in such Consolidated Net Income up
          to the aggregate amount of cash actually distributed by such
          Restricted Subsidiary during such period to the Company or another
          Restricted Subsidiary as a dividend or other distribution (subject, in
          the case of a dividend or other distribution paid to another
          Restricted Subsidiary, to the limitation contained in this clause);
          and

               (B) the Company's equity in a net loss of any such Restricted
          Subsidiary for such period shall be included in determining such
          Consolidated Net Income;

          (4) any gain or loss realized upon the sale or other disposition of
     any assets of the Company, its consolidated Subsidiaries or any other
     Person (including pursuant to any sale-and-leaseback arrangement) which is
     not sold or otherwise disposed of in the ordinary course of business and
     any gain or loss
<PAGE>

                                                                              11

     realized upon the sale or other disposition of any Capital Stock of any
     Person;

          (5) extraordinary gains or losses;

          (6) nonrecurring charges taken by the Company in connection with its
     acquisition of certain assets of and its assumption of certain liabilities
     of Raytheon Engineers & Constructors International, Inc., but not exceeding
     $25.0 million of such charges in the aggregate; and

          (7) the cumulative effect of a change in accounting principles.

Notwithstanding the foregoing, for the purpose of Section 4.04 only, there shall
be excluded from Consolidated Net Income any repurchases, repayments or
redemptions of Investments, proceeds realized on the sale of Investments or
return of capital to the Company or a Restricted Subsidiary to the extent such
repurchases, repayments, redemptions, proceeds or returns increase the amount of
Restricted Payments permitted under such Section pursuant to Section
4.04(a)(3)(D).

          "Consolidated Net Worth" means the total of the amounts shown on the
balance sheet of the Company and its consolidated subsidiaries, as of the end of
the most recent fiscal quarter of the Company ending at least 45 days prior to
the taking of any action for the purpose of which the determination is being
made, as the sum of:

          (1) the par or stated value of all outstanding Capital Stock of the
     Company plus

          (2) paid-in capital or capital surplus relating to such Capital Stock
     plus

          (3) any retained earnings or earned surplus less (A) any accumulated
deficit and (B) any amounts attributable to Disqualified Stock.

          "Credit Agreement" means the Credit Agreement to be entered into by
and among, the Company, certain of its Subsidiaries, the lenders referred to
therein, Credit Suisse First Boston, as Administrative Agent, Bank of Montreal,
as Syndication Agent, and Bank of America, N.A. and U.S. Bank National
Association, as Documentation Agents, together with the related documents
thereto (including the term loans and revolving loans thereunder, any guarantees
and security
<PAGE>

                                                                              12

documents), as amended, extended, renewed, restated, supplemented or otherwise
modified (in whole or in part, and without limitation as to amount, terms,
conditions, covenants and other provisions) from time to time, and any agreement
(and related document) governing Indebtedness incurred to Refinance, in whole or
in part, the borrowings and commitments then outstanding or permitted to be
outstanding under such Credit Agreement or a successor Credit Agreement, whether
by the same or any other lender or group of lenders.

          "Currency Agreement" means in respect of a Person any foreign exchange
contract, currency swap agreement or other similar agreement designed to protect
such Person against fluctuations in currency values.

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

          "Disqualified Stock" means, with respect to any Person, any Capital
Stock which by its terms (or by the terms of any security into which it is
convertible or for which it is exchangeable at the option of the holder) or upon
the happening of any event:

          (1) matures or is mandatorily redeemable pursuant to a sinking fund
     obligation or otherwise;

          (2) is convertible or exchangeable at the option of the holder for
     Indebtedness or Disqualified Stock; or

          (3) is mandatorily redeemable or must be purchased upon the occurrence
     of certain events or otherwise, in whole or in part;

in each case on or prior to the first anniversary of the Stated Maturity of the
Securities; provided, however, that any Capital Stock that would not constitute
            --------  -------
Disqualified Stock but for provisions thereof giving holders thereof the right
to require such Person to purchase or redeem such Capital Stock upon the
occurrence of an "asset sale" or "change of control" occurring prior to the
first anniversary of the Stated Maturity of the Securities shall not constitute
Disqualified Stock if:

          (1) the "asset sale" or "change of control" provisions applicable to
     such Capital Stock are not more favorable to the holders of such Capital
     Stock
<PAGE>

                                                                              13

     than the terms applicable to the Securities in Sections 4.07 and 4.10; and

          (2) any such requirement only becomes operative after compliance with
     such terms applicable to the Securities, including the purchase of any
     Securities tendered pursuant thereto.

          "EBITDA" for any period means the sum of Consolidated Net Income, plus
the following to the extent deducted or not included in calculating such
Consolidated Net Income:

          (1) all income tax expense;

          (2) Consolidated Interest Expense;

          (3) depreciation and amortization expense (excluding amortization
     expense attributable to a prepaid operating activity item that was paid in
     cash in a prior period); and

          (4) all other non-cash charges (excluding any such non-cash charge to
     the extent that it represents an accrual of or reserve for cash
     expenditures in any future period);

in each case for such period.  Notwithstanding the foregoing, the provision for
taxes based on the income or profits of, and the depreciation and amortization
and non-cash charges of, a Restricted Subsidiary, a Permitted Joint Venture or
WGSG shall be added to Consolidated Net Income to compute EBITDA only to the
extent (and in the same proportion) that the net income of such Person was
included in calculating Consolidated Net Income and, in the case of a Restricted
Subsidiary, only if a corresponding amount would be permitted at the date of
determination to be dividended to the Company by such Restricted Subsidiary
without prior approval (that has not been obtained), pursuant to the terms of
its charter and all agreements, instruments, judgments, decrees, orders,
statutes, rules and governmental regulations applicable to such Restricted
Subsidiary or its stockholders.  For purposes of determining the Consolidated
Coverage Ratio, EBITDA will be deemed to be equal to $70.0 million for each of
the fiscal quarters ended August 27, 1999, December 3, 1999, March 3, 2000 and
June 2, 2000.

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

                                                                              14

          "Facilities" means the Term Loan Facilities and the Revolving Credit
Facilities.

          "Foreign Subsidiary" means any Restricted Subsidiary organized in a
jurisdiction outside the United States.

          "GAAP" means generally accepted accounting principles in the United
States of America as in effect as of the Issue Date, including those set forth
in:

          (1) the opinions and pronouncements of the Accounting Principles Board
     of the American Institute of Certified Public Accountants;

          (2) statements and pronouncements of the Financial Accounting
     Standards Board;

          (3) such other statements by such other entity as approved by a
     significant segment of the accounting profession; and

          (4) the rules and regulations of the SEC governing the inclusion of
     financial statements (including pro forma financial statements) in periodic
                                     ---------
     reports required to be filed pursuant to Section 13 of the Exchange Act,
     including opinions and pronouncements in staff accounting bulletins and
     similar written statements from the accounting staff of the SEC.

          "Guarantee" means any obligation, contingent or otherwise, of any
Person directly or indirectly guaranteeing any Indebtedness of any Person and
any obligation, direct or indirect, contingent or otherwise, of such Person:

          (1) to purchase or pay (or advance or supply funds for the purchase or
     payment of) such Indebtedness of such Person (whether arising by virtue of
     partnership arrangements, or by agreements to keep-well, to purchase
     assets, goods, securities or services, to take-or-pay or to maintain
     financial statement conditions or otherwise); or

          (2) entered into for the purpose of assuring in any other manner the
     obligee of such Indebtedness of the payment thereof or to protect such
     obligee against loss in respect thereof (in whole or in part);

provided, however, that the term "Guarantee" shall not include endorsements for
--------  -------
collection or deposit in the
<PAGE>

                                                                              15

ordinary course of business. The term "Guarantee" used as a verb has a
corresponding meaning. The term "Guarantor" shall mean any Person Guaranteeing
any obligation.

          "Guaranty Agreement" means a supplemental indenture, in a form
satisfactory to the Trustee, pursuant to which a Subsidiary Guarantor guarantees
the Company's obligations with respect to the Securities on the terms provided
for in this Indenture.

          "Hedging Obligations" of any Person means the monetary obligations of
such Person pursuant to any Hedging Agreement.

          "Hedging Agreement" means any interest rate protection agreement,
foreign currency exchange agreement, commodity price protection agreement or
other interest or currency exchange rate or commodity price hedging arrangement.

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

          "Incur" means issue, assume, Guarantee, incur or otherwise become
liable for; provided, however, that (i) any Indebtedness or Capital Stock of a
            --------  -------
Person existing at the time such Person becomes a Restricted Subsidiary (whether
by merger, consolidation, acquisition or otherwise) shall be deemed to be
Incurred by such Person at the time it becomes a Restricted Subsidiary and (ii)
a change in GAAP that results in an obligation of such Person that exists at
such time becoming, without any expenditure of cash by such Person, Indebtedness
will not be deemed an Incurrence of such Indebtedness.  The term "Incurrence"
when used as a noun shall have a correlative meaning.  The accretion of
principal of a non-interest bearing or other discount security shall not be
deemed the Incurrence of Indebtedness.

          "Indebtedness" means, with respect to any Person on any date of
determination (without duplication):

          (1) the principal in respect of (A) indebtedness of such Person for
     money borrowed and (B) indebtedness evidenced by notes, debentures, bonds
     or other similar instruments for the payment of which such Person is
     responsible or liable, including, in each case, any premium on such
     indebtedness to the extent such premium has become due and payable;
<PAGE>

                                                                              16

          (2) all Capital Lease Obligations of such Person and all Attributable
Debt in respect of Sale/Leaseback Transactions entered into by such Person;

          (3) all obligations of such Person issued or assumed as the deferred
purchase price of property, all conditional sale obligations of such Person and
all obligations of such Person under any title retention agreement (but
excluding trade accounts payable arising in the ordinary course of business);

          (4) all obligations of such Person for the reimbursement of any
obligor on any letter of credit, banker's acceptance or similar credit
transaction (other than obligations with respect to letters of credit securing
obligations (other than obligations described in clauses (1) through (3) above)
entered into in the ordinary course of business of such Person to the extent
such letters of credit are not drawn upon or, if and to the extent drawn upon,
such drawing is reimbursed no later than the tenth Business Day following
payment on the letter of credit);

          (5) the amount of all obligations of such Person with respect to the
redemption, repayment or other repurchase of any Disqualified Stock of such
Person or, with respect to any Preferred Stock of any Subsidiary of such Person,
the principal amount of such Preferred Stock to be determined in accordance with
this Indenture (but excluding, in each case, any accrued dividends);

          (6) all obligations of the type referred to in clauses (1) through (5)
of other Persons and all dividends of other Persons for the payment of which, in
either case, such Person is responsible or liable, directly or indirectly, as
obligor, guarantor or otherwise, including by means of any Guarantee;

          (7) all obligations of the type referred to in clauses (1) through (6)
of other Persons secured by any Lien on any property or asset of such Person
(whether or not such obligation is assumed by such Person), the amount of such
obligation being deemed to be the lesser of the value of such property or assets
and the amount of the obligation so secured; and

          (8) to the extent not otherwise included in this definition, Hedging
Obligations of such Person.
<PAGE>

                                                                              17

The amount of Indebtedness of any Person at any date shall be the outstanding
balance at such date of all unconditional obligations as described above and the
maximum liability, upon the occurrence of the contingency giving rise to the
obligation, of any contingent obligations at such date. Notwithstanding the
foregoing, Indebtedness shall not include any endorsements for collection or
deposits in the ordinary course of business.

          "Indenture" means this Indenture as amended or supplemented from time
to time.

          "Interest Rate Agreement" means in respect of a Person any interest
rate swap agreement, interest rate cap agreement or other financial agreement or
arrangement designed to protect such Person against fluctuations in interest
rates.

          "Investment" in any Person means any direct or indirect advance, loan
(other than advances to customers in the ordinary course of business that are
recorded as accounts receivable on the balance sheet of the lender) or other
extensions of credit (including by way of Guarantee or similar arrangement) or
capital contribution to (by means of any transfer of cash or other property to
others or any payment for property or services for the account or use of
others), or any purchase or acquisition of Capital Stock, Indebtedness or other
similar instruments issued by such Person.  Except as otherwise provided for
herein, the amount of an Investment shall be its fair value at the time the
Investment is made and without giving effect to subsequent changes in value.

          For purposes of the definition of "Unrestricted Subsidiary", the
definition of "Restricted Payment" and Section 4.04:

          (1) "Investment" shall include the portion (proportionate to the
     Company's equity interest in such Subsidiary) of the fair market value of
     the net assets of any Subsidiary of the Company at the time that such
     Subsidiary is designated an Unrestricted Subsidiary; provided, however,
                                                          --------  -------
     that upon a redesignation of such Subsidiary as a Restricted Subsidiary,
     the Company shall be deemed to continue to have a permanent "Investment" in
     an Unrestricted Subsidiary equal to an amount (if positive) equal to (A)
     the Company's "Investment" in such Subsidiary at the time of such
     redesignation less (B) the portion (proportionate to the Company's equity
     interest in such Subsidiary) of
<PAGE>

                                                                              18

     the fair market value of the net assets of such Subsidiary at the time of
     such redesignation; and

          (2) any property transferred to or from an Unrestricted Subsidiary
     shall be valued at its fair market value at the time of such transfer, in
     each case as determined in good faith by the Board of Directors.

          "Investment Grade Rating" means a rating equal to or higher than Baa3
(or the equivalent) by Moody's Investors Service, Inc. and BBB-(or the
equivalent) by Standard &Poor's Ratings Group, Inc., or an equivalent rating by
any other Rating Agency.

          "Issue Date" means July 7, 2000.

          "Lien" means any mortgage, pledge, security interest, encumbrance,
lien or charge of any kind (including any conditional sale or other title
retention agreement or lease in the nature thereof).

          "MK-Ohio" means:

          (1) Morrison Knudsen Corporation, an Ohio corporation, and its
     successors and assigns;

          (2) any Affiliate of the Company which owns a substantial portion of
     the assets (determined by their fair value) of Morrison Knudsen
     Corporation, an Ohio corporation, as it existed on the Issue Date; or

          (3) any other Person which owns a majority of the assets (determined
     by their fair value) of Morrison Knudsen Corporation, an Ohio corporation,
     as it existed on the Issue Date.

          "Net Available Cash" from an Asset Disposition means cash payments
received therefrom (including any cash payments received by way of deferred
payment of principal pursuant to a note or installment receivable or otherwise
and proceeds from the sale or other disposition of any securities received as
consideration, but only as and when received, but excluding any other
consideration received in the form of assumption by the acquiring Person of
Indebtedness or other obligations relating to such properties or assets or
received in any other noncash form), in each case net of:

          (1) all legal, advisory, title and recording tax expenses,
     underwriting, brokerage or other customary
<PAGE>

                                                                              19

     selling commissions and other fees and expenses incurred, and all federal,
     state, provincial, foreign and local taxes required to be accrued as a
     liability under GAAP, as a consequence of such Asset Disposition;

          (2) all payments made on any Indebtedness which is secured by any
     assets subject to such Asset Disposition, in accordance with the terms of
     any Lien upon or other security agreement of any kind with respect to such
     assets, or which must by its terms, or in order to obtain a necessary
     consent to such Asset Disposition, or by applicable law, be repaid out of
     the proceeds from such Asset Disposition;

          (3) all distributions and other payments required to be made to
     minority interest holders in Restricted Subsidiaries as a result of such
     Asset Disposition;

          (4) payments of unassumed liabilities relating to the assets sold (not
     constituting Indebtedness) made at the time of, or within 30 days after,
     the date of the applicable Asset Disposition; and

          (5) the deduction of appropriate amounts provided by the seller as a
     reserve, in accordance with GAAP, against any liabilities associated with
     the property or other assets disposed in such Asset Disposition and
     retained by the Company or any Restricted Subsidiary after such Asset
     Disposition including pension and other post-employment benefit
     liabilities, liabilities related to environmental matters and liabilities
     under any indemnification obligations associated with such Asset
     Disposition.

          "Net Cash Proceeds", with respect to any issuance or sale of Capital
Stock, means the cash proceeds of such issuance or sale net of attorneys' fees,
accountants' fees, underwriters' or placement agents' fees, discounts or
commissions and brokerage, consultant and other fees actually incurred in
connection with such issuance or sale and net of taxes paid or payable as a
result thereof.

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

          "Officers' Certificate" means a certificate signed by two Officers.
<PAGE>

                                                                              20

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

          "Permitted Asset Swap" means an Asset Disposition by the Company or a
Restricted Subsidiary to the extent the Company or such Restricted Subsidiary
receives consideration therefor in the form of (1) productive assets to be used
by the Company or such Restricted Subsidiary in a Related Business and in the
ordinary course of its business or (2) all the Capital Stock of a Person if such
Person is engaged exclusively in a Related Business.

          "Permitted Holders" means Dennis R. Washington (or in the event of his
incompetence or death, his estate, heirs, executor, administrator, committee or
other personal representative (collectively, "heirs")) or any Person controlled,
directly or indirectly, by Dennis R. Washington or his heirs.

          "Permitted Investment" means an Investment by the Company or any
Restricted Subsidiary in:

          (1) the Company, a Restricted Subsidiary or a Person that will, upon
     the making of such Investment, become a Restricted Subsidiary; provided,
                                                                    --------
     however, that the primary business of such Restricted Subsidiary is a
     -------
     Related Business;

          (2) another Person if as a result of such

     Investment such other Person is merged or consolidated with or into, or
     transfers or conveys all or substantially all its assets to, the Company or
     a Restricted Subsidiary; provided, however, that such Person's primary
                              --------  -------
     business is a Related Business;

          (3) cash and Temporary Cash Investments;

          (4) receivables owing to the Company or any Restricted Subsidiary if
     created or acquired in the ordinary course of business and payable or
     dischargeable in accordance with customary trade terms; provided, however,
                                                             --------  -------
     that such trade terms may include such concessionary trade terms as the
     Company or any such Restricted Subsidiary deems reasonable under the
     circumstances;

          (5) payroll, travel and similar advances to cover matters that are
     expected at the time of such advances
<PAGE>

                                                                              21

     ultimately to be treated as expenses for accounting purposes and that are
     made in the ordinary course of business;

          (6) loans or advances to employees made in the ordinary course of
     business in accordance with the past practices of the Company or such
     Restricted Subsidiary as permitted pursuant to Section 4.08;

          (7) stock, obligations or securities received in settlement of debts
     created in the ordinary course of business and owing to the Company or any
     Restricted Subsidiary or in satisfaction of judgments;

          (8) any Person to the extent such Investment represents the non-cash
     portion of the consideration received for an Asset Disposition as permitted
     pursuant to Section 4.07;

          (9) any Permitted Joint Venture or WGSG; provided, however, that such
                                                   --------  -------
     Investment is made in the ordinary course of business and is consistent
     with the past practices of the Company and its Subsidiaries; and

         (10) so long as no Default shall have occurred and be continuing (or
     result therefrom), any Person; provided, however, that the aggregate amount
                                    --------  -------
     of all Investments made after the Issue Date pursuant to this clause (10)
     and then outstanding does not exceed $20.0 million.

          "Permitted Joint Venture" means any joint venture (which may be in the
form of a limited liability company, partnership, corporation or other entity)
in which the Company or any of its Restricted Subsidiaries is a joint venturor;
provided, however, that (a) the other equity investors in such joint venture
--------  -------
participate in Investments in such joint venture on substantially the same basis
as the Company or such Restricted Subsidiary, and (b) the existence and
activities of such joint venture are limited to the duration and scope of
projects for which such joint venture was established to provide engineering,
construction or operations and maintenance services or services in other Related
Business, as the case may be.

          "Permitted Liens" means, with respect to any Person:

          (1) pledges or deposits by such Person under worker's compensation
     laws, unemployment insurance laws
<PAGE>

                                                                              22

     or similar legislation, or good faith deposits in connection with bids,
     tenders, contracts (other than for the payment of Indebtedness) or leases
     to which such Person is a party, or deposits to secure public or statutory
     obligations of such Person or deposits of cash or government bonds to
     secure surety or appeal bonds to which such Person is a party, or deposits
     as security for contested taxes or import duties or for the payment of
     rent, in each case Incurred in the ordinary course of business;

          (2) Liens imposed by law, such as carriers', warehousemen's and
     mechanics' Liens, in each case for sums not yet due or being contested in
     good faith by appropriate proceedings or other Liens arising out of
     judgments or awards against such Person with respect to which such Person
     shall then be proceeding with an appeal or other proceedings for review and
     Liens arising solely by virtue of any statutory or common law provision
     relating to banker's Liens, rights of set-off or similar rights and
     remedies as to deposit accounts or other funds maintained with a creditor
     depository institution; provided, however, that (A) such deposit account is
                             --------  -------
     not a dedicated cash collateral account and is not subject to restrictions
     against access by the Company in excess of those set forth by regulations
     promulgated by the Federal Reserve Board and (B) such deposit account is
     not intended by the Company or any Restricted Subsidiary to provide
     collateral to the depository institution;

          (3) Liens for property taxes not yet subject to penalties for non-
     payment or which are being contested in good faith by appropriate
     proceedings;

          (4) Liens in favor of issuers of surety bonds or letters of credit
     issued pursuant to the request of and for the account of such Person in the
     ordinary course of its business; provided, however, that such letters of
                                      --------  -------
     credit do not constitute Indebtedness;

          (5) survey exceptions, encumbrances, easements or reservations of, or
     rights of others for, licenses, rights-of-way, sewers, electric lines,
     telegraph and telephone lines and other similar purposes, or zoning or
     other restrictions as to the use of real property or Liens incidental to
     the conduct of the business of such Person or to the ownership of its
     properties which were not Incurred in connection with Indebtedness and
     which do not in the aggregate materially adversely affect the
<PAGE>

                                                                              23

     value of said properties or materially impair their use in the operation of
     the business of such Person;

          (6)  Liens securing Indebtedness Incurred to finance the construction,
     purchase or lease of, or repairs, improvements or additions to, property,
     plant or equipment of such Person; provided, however, that the Lien may not
                                        --------  -------
     extend to any other property owned by the Company or any of its Restricted
     Subsidiaries at the time the Lien is Incurred (other than assets and
     property affixed or appurtenant thereto), and the Indebtedness (other than
     any interest thereon) secured by the Lien may not be Incurred more than 180
     days after the later of the acquisition, completion of construction,
     repair, improvement, addition or commencement of full operation of the
     property subject to the Lien;

          (7)  Liens to secure Indebtedness permitted under Section 4.03(b)(1)
     and (b)(2);

          (8)  Liens existing on the Issue Date;

          (9)  Liens on property or shares of Capital Stock of another Person at
     the time such other Person becomes a Subsidiary of such Person; provided,
                                                                     --------
     however, that the Liens may not extend to any other property owned by such
     -------
     Person or any of its Restricted Subsidiaries (other than assets and
     property affixed or appurtenant thereto);

          (10) Liens on property at the time such Person or any of its
     Subsidiaries acquires the property, including any acquisition by means of a
     merger or consolidation with or into such Person or a Subsidiary of such
     Person; provided, however, that the Liens may not extend to any other
             --------  -------
     property owned by such Person or any of its Restricted Subsidiaries (other
     than assets and property affixed or appurtenant thereto);

          (11) Liens securing Indebtedness or other obligations of a Subsidiary
     of such Person owing to such Person or a wholly owned Subsidiary of such
     Person;

          (12) Liens securing Hedging Obligations so long as such Hedging
     Obligations relate to Indebtedness that is, and is permitted to be under
     this Indenture, secured by a Lien on the same property securing such
     Hedging Obligations; and
<PAGE>

                                                                              24

          (13) Liens to secure any Refinancing (or successive Refinancings) as a
     whole, or in part, of any Indebtedness secured by any Lien referred to in
     the foregoing clause (6), (8), (9) or (10); provided, however, that:
                                                 --------  -------
               (A) such new Lien shall be limited to all or part of the same
          property and assets that secured or, under the written agreements
          pursuant to which the original Lien arose, could secure the original
          Lien (plus improvements and accessions to, such property or proceeds
          or distributions thereof); and

               (B) the Indebtedness secured by such Lien at such time is not
          increased to any amount greater than the sum of (x) the outstanding
          principal amount or, if greater, committed amount of the Indebtedness
          described under clauses (6), (8), (9) or (10) at the time the original
          Lien became a Permitted Lien and (y) an amount necessary to pay any
          fees and expenses, including premiums, related to such refinancing,
          refunding, extension, renewal or replacement.

Notwithstanding the foregoing, "Permitted Liens" will not include any Lien
described in clause (6), (9) or (10) above to the extent such Lien applies to
any Additional Assets acquired directly or indirectly from Net Available Cash
pursuant to Section 4.07.  For purposes of this definition, the
term"Indebtedness" shall be deemed to include interest on such Indebtedness.

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

          "Preferred Stock", as applied to the Capital Stock of any Person,
means Capital Stock of any class or classes (however designated) which is
preferred as to the payment of dividends or distributions, or as to the
distribution of assets upon any voluntary or involuntary liquidation or
dissolution of such Person, over shares of Capital Stock of any other class of
such Person.

          "principal" of a Security means the principal of the Security plus the
premium, if any, payable on the
<PAGE>

                                                                              25

Security which is due or overdue or is to become due at the relevant time.

          "pro forma" means, with respect to any calculation made or required to
be made pursuant to the terms hereof, a calculation performed in accordance with
Regulation S-X promulgated under the Securities Act, as interpreted in good
faith by the chief financial officer of the Company after consultation with the
independent certified public accountants of the Company.

          "Rating Agency" means Standard & Poor's Ratings Group, Inc. and
Moody's Investors Service, Inc. or, if Standard & Poor's Ratings Group, Inc. or
Moody's Investors Service, Inc. or both shall not make a rating on the
Securities publicly available, a nationally recognized statistical rating agency
or agencies, as the case may be, selected by the Company (as certified by a
resolution of the Board of Directors) which shall be substituted for Standard &
Poor's Ratings Group, Inc. or Moody's Investors Service, Inc. or both, as the
case may be.

          "Reference Treasury Dealer" means each of Credit Suisse First Boston
Corporation, BMO Nesbitt Burns Corp., and two other primary U.S. government
securities dealers in New York City (each, a "Primary Treasury Dealer")
appointed by the Trustee in consultation with the Company.  If any Reference
Treasury Dealer ceases to be a Primary Treasury Dealer, the Company will
substitute another Primary Treasury Dealer for that dealer.

          "Reference Treasury Dealer Quotations" means, with respect to each
Reference Treasury Dealer and any redemption date, the average, as determined by
the Trustee, of the bid and asked prices for the Comparable Treasury Issue
(expressed in each case as a percentage of its principal amount) quoted in
writing to the Trustee by that Reference Treasury Dealer at 5:00 p.m. on the
third Business Day preceding the redemption date.

          "Refinance" means, in respect of any Indebtedness, to refinance,
extend, renew, refund, repay, prepay, redeem, defease or retire, or to issue
other Indebtedness in exchange or replacement for, such indebtedness.
"Refinanced" and "Refinancing" shall have correlative meanings.

          "Refinancing Indebtedness" means Indebtedness that Refinances any
Indebtedness of the Company or any Restricted Subsidiary existing on the Issue
Date or Incurred in
<PAGE>

                                                                              26

compliance with this Indenture, including Indebtedness that Refinances
Refinancing Indebtedness; provided, however, that:
                          --------  -------

          (1) such Refinancing Indebtedness has a Stated Maturity no earlier
     than the Stated Maturity of the Indebtedness being Refinanced;

          (2) such Refinancing Indebtedness has an Average Life at the time such
     Refinancing Indebtedness is Incurred that is equal to or greater than the
     Average Life of the Indebtedness being Refinanced; and

          (3) such Refinancing Indebtedness has an aggregate principal amount
     (or if Incurred with original issue discount, an aggregate issue price)
     that is equal to or less than the aggregate principal amount (or if
     Incurred with original issue discount, the aggregate accreted value) then
     outstanding or committed (plus fees and expenses, including any premium and
     defeasance costs) under the Indebtedness being Refinanced;

provided further, however, that Refinancing Indebtedness shall not include (A)
-------- -------  -------
Indebtedness of a Subsidiary that Refinances Indebtedness of the Company or (B)
Indebtedness of the Company or a Restricted Subsidiary that Refinances
Indebtedness of an Unrestricted Subsidiary.

          "Related Business" means any business in which the Company (including
its Restricted Subsidiaries that were Subsidiaries of the Company at such time)
was engaged on the Issue Date and any business related, ancillary or
complementary to any such business.

          "Restricted Payment" with respect to any Person means:

          (1) the declaration or payment of any dividends or any other
     distributions of any sort in respect of its Capital Stock (including any
     payment in connection with any merger or consolidation involving such
     Person) or similar payment to the direct or indirect holders of its Capital
     Stock (other than dividends or distributions payable solely in its Capital
     Stock (other than Disqualified Stock) and dividends or distributions
     payable solely to the Company or a Restricted Subsidiary, and other than
     pro rata dividends or other distributions made by a Subsidiary that is not
     a Wholly Owned Subsidiary to minority stockholders (or owners of an
     equivalent interest in
<PAGE>

                                                                              27

     the case of a Subsidiary that is an entity other than a corporation));

          (2) the purchase, redemption or other acquisition or retirement for
     value of any Capital Stock of the Company held by any Person or of any
     Capital Stock of a Restricted Subsidiary held by any Affiliate of the
     Company (other than a Restricted Subsidiary), including the exercise of any
     option to exchange any Capital Stock (other than into Capital Stock of the
     Company that is not Disqualified Stock);

          (3) the purchase, repurchase, redemption, defeasance or other
     acquisition or retirement for value, prior to scheduled maturity, scheduled
     repayment or scheduled sinking fund payment of any Subordinated Obligations
     of such Person (other than the purchase, repurchase or other acquisition of
     Subordinated Obligations purchased in anticipation of satisfying a sinking
     fund obligation, principal installment or final maturity, in each case due
     within one year of the date of such purchase, repurchase or other
     acquisition); or

          (4) the making of any Investment (other than a Permitted Investment)
     in any Person.

          "Restricted Subsidiary" means any Subsidiary of the Company that is
not an Unrestricted Subsidiary.

          "Revolving Credit Facilities" means the 5-year revolving credit
facility contained in the Credit Agreement and any other facility or financing
arrangement that Refinances, in whole or in part, any such revolving credit
facilities.

          "Sale/Leaseback Transaction" means an arrangement relating to property
owned by the Company or a Restricted Subsidiary on the Issue Date or thereafter
acquired by the Company or a Restricted Subsidiary whereby the Company or a
Restricted Subsidiary transfers such property to a Person and the Company or a
Restricted Subsidiary leases it from such Person.

          "SEC" means the Securities and Exchange Commission.

          "Securities" means the Securities issued under this Indenture.
<PAGE>

                                                                              28

          "Senior Indebtedness" means, with respect to any Person on any date of
determination:

          (1) Indebtedness of such Person, whether outstanding on the Issue Date
     or thereafter Incurred; and

          (2) accrued and unpaid interest (including interest accruing on or
     after the filing of any petition in bankruptcy or for reorganization
     relating to such Person to the extent post-filing interest is allowed in
     such proceeding) in respect of (A) indebtedness of such Person for money
     borrowed and (B) indebtedness evidenced by notes, debentures, bonds or
     other similar instruments for the payment of which such Person is
     responsible or liable

unless, in the case of clauses (1) and (2), in the instrument creating or
evidencing the same or pursuant to which the same is outstanding, it is provided
that such obligations are subordinate in right of payment to the Securities or
the Subsidiary Guaranty of that Person, as the case may be; provided, however,
                                                            --------  -------
that Senior Indebtedness shall not include:

          (1) any obligation of such Person to any Subsidiary;

          (2) any liability for Federal, state, local or other taxes owed or
     owing by such Person;

          (3) any accounts payable or other liability to trade creditors arising
     in the ordinary course of business (including guarantees thereof or
     instruments evidencing such liabilities);

          (4) any Indebtedness of such Person (and any accrued and unpaid
     interest in respect thereof) which is subordinate or junior in any respect
     to any other Indebtedness or other obligation of such Person; or

          (5) that portion of any Indebtedness which at the time of Incurrence
     is Incurred in violation of this Indenture.

          "Significant Subsidiary" means any Restricted Subsidiary that would be
a "Significant Subsidiary" of the Company within the meaning of Rule 1-02 under
Regulation S-X promulgated by the SEC.
<PAGE>

                                                                              29

          "Stated Maturity" means, with respect to any security, the date
specified in such security as the fixed date on which the final payment of
principal of such security is due and payable, including pursuant to any
mandatory redemption provision (but excluding any provision providing for the
repurchase of such security at the option of the holder thereof upon the
happening of any contingency unless such contingency has occurred).

          "Subordinated Obligation" means with respect to a Person, any
Indebtedness of such Person (whether outstanding on the Issue Date or thereafter
Incurred) which is subordinate or junior in right of payment to the Securities
or a Subsidiary Guaranty of such Person, as the case may be, pursuant to a
written agreement to that effect.

          "Subsidiary" means, with respect to any Person, any corporation,
association, partnership or other business entity of which more than 50% of the
total voting power of shares of Voting Stock is at the time owned or controlled,
directly or indirectly, by:

          (1) such Person;

          (2) such Person and one or more Subsidiaries of such Person; or

          (3) one or more Subsidiaries of such Person;

provided, however, that a Permitted Joint Venture shall be deemed not to be a
--------  -------
Subsidiary of the Company or of any Restricted Subsidiary.

          "Subsidiary Guarantor" means each Subsidiary of the Company that
executes this Indenture as a guarantor and each other Subsidiary of the Company
that thereafter enters into a Subsidiary Guaranty pursuant to the terms of this
Indenture.

          "Subsidiary Guaranty" means a Guarantee by a Subsidiary Guarantor of
the Company's obligations with respect to the Securities.

          "Temporary Cash Investments" means any of the following:

          (1) any investment in direct obligations of the United States of
     America or any agency thereof or obligations guaranteed by the United
     States of America or any agency thereof;
<PAGE>

                                                                              30

          (2) investments in time deposit accounts, certificates of deposit and
     money market deposits maturing within 180 days of the date of acquisition
     thereof issued by a bank or trust company which is organized under the laws
     of the United States of America, any state thereof or any foreign country
     recognized by the United States of America, and which bank or trust company
     has capital, surplus and undivided profits aggregating in excess of $50.0
     million (or the foreign currency equivalent thereof) and has outstanding
     debt which is rated "A" (or such similar equivalent rating) or higher by at
     least one nationally recognized statistical rating organization (as defined
     in Rule 436 under the Securities Act) or any money-market fund sponsored by
     a registered broker dealer or mutual fund distributor;

          (3) repurchase obligations with a term of not more than 30 days for
     underlying securities of the types described in clause (1) above entered
     into with a bank meeting the qualifications described in clause (2) above;

          (4) investments in commercial paper, maturing not more than 90 days
     after the date of acquisition, issued by a corporation (other than an
     Affiliate of the Company) organized and in existence under the laws of the
     United States of America or any foreign country recognized by the United
     States of America with a rating at the time as of which any investment
     therein is made of "P-1" (or higher) according to Moody's Investors
     Service, Inc. or "A-1" (or higher) according to Standard and Poor's Ratings
     Group; and

          (5) investments in securities with maturities of six months or less
     from the date of acquisition issued or fully guaranteed by any state,
     commonwealth or territory of the United States of America, or by any
     political subdivision or taxing authority thereof, and rated at least "A"
     by Standard & Poor's Ratings Group or "A" by Moody's Investors Service,
     Inc.

          "Term Loan Facilities" means the term loan facilities contained in the
Credit Agreement and any other facility or financing arrangement that Refinances
in whole or in part any such term loan facilities.

          "TIA" means the Trust Indenture Act of 1939 (15 U.S.C. (S)(S) 77aaa-
                                                          ------
77bbbb) as in effect on the date of this Indenture.
<PAGE>

                                                                              31

          "Treasury Rate" means, with respect to any redemption date,

          (i)  the yield, under the heading which represents the average for the
     immediately preceding week, appearing in the most recently published
     statistical release designated "H.15(519)" or any successor publication
     which is published weekly by the Board of Governors of the Federal Reserve
     System and which establishes yields on actively traded United States
     Treasury securities adjusted to constant maturity under the caption
     "Treasury Constant Maturities", for the maturity corresponding to the
     Comparable Treasury Issue (if no maturity is within three months before or
     after the maturity date of the Securities, yields for the two published
     maturities most closely corresponding to the Comparable Treasury Issue will
     be determined and the Treasury Rate shall be interpolated or extrapolated
     from those yields on a straight line basis, rounding to the nearest month)
     or

          (ii) if the release referred to in (i) (or any successor release) is
     not published during the week preceding the calculation date or does not
     contain the yields referred to above, the rate per annum equal to the
     semiannual equivalent yield to maturity of the Comparable Treasury Issue,
     calculated using a price for the Comparable Treasury Issue (expressed as a
     percentage of its principal amount) equal to the Comparable Treasury Price
     for that redemption date.

          The Treasury Rate will be calculated on the third Business Day
preceding the redemption date.

          "Trustee" means the party named as such in this Indenture until a
successor replaces it and, thereafter, means the successor.

          "Trust Officer" means the Chairman of the Board, the President or any
other officer or assistant officer of the Trustee assigned by the Trustee to
administer its corporate trust matters.

          "Uniform Commercial Code" means the New York Uniform Commercial Code
as in effect from time to time.

          "Unrestricted Subsidiary" means:

          (1) WGSG;
<PAGE>

                                                                              32
          (2) Industrial Constructors Corp., a Montana corporation.

          (3) any Subsidiary of the Company that at the time of determination
     shall be designated an Unrestricted Subsidiary by the Board of Directors in
     the manner provided below; and

          (4) any Subsidiary of an Unrestricted Subsidiary.

The Board of Directors may designate any Subsidiary of the Company (including
any newly acquired or newly formed Subsidiary) to be an Unrestricted Subsidiary
unless such Subsidiary or any of its Subsidiaries owns any Capital Stock or
Indebtedness of, or holds any Lien on any property of, the Company or any other
Subsidiary of the Company that is not a Subsidiary of the Subsidiary to be so
designated; provided, however, that either (A) the Subsidiary to be so
            --------  -------
designated has total assets of $1,000 or less or (B) if such Subsidiary has
assets greater than $1,000, such designation would be permitted under Section
4.04 and the definition of "Investment".

          The Board of Directors may designate any Unrestricted Subsidiary to be
a Restricted Subsidiary; provided, however, that immediately after giving effect
                         --------  -------
to such designation (A) the Company could Incur $1.00 of additional Indebtedness
under Section 4.03(a) and (B) no Default shall have occurred and be continuing.
Any such designation by the Board of Directors shall be evidenced to the Trustee
by promptly filing with the Trustee a copy of the resolution of the Board of
Directors giving effect to such designation and an Officers' Certificate
certifying that such designation complied with the foregoing provisions.

          "U.S. Government Obligations" means direct obligations (or
certificates representing an ownership interest in such obligations) of the
United States of America (including any agency or instrumentality thereof) for
the payment of which the full faith and credit of the United States of America
is pledged and which are not callable at the issuer's option.

          "Voting Stock" of a Person means all classes of Capital Stock or other
interests (including partnership interests) of such Person then outstanding and
normally entitled (without regard to the occurrence of any contingency) to vote
in the election of directors, managers or trustees thereof.
<PAGE>

                                                                              33

          "WGSG" means Westinghouse Government Environmental Services Company,
LLC, a Delaware limited liability company, and Westinghouse Government Services
Company, LLC, a Delaware limited liability company, and their respective
subsidiaries.

          "Wholly Owned Subsidiary" means a Restricted Subsidiary all the
Capital Stock of which (other than directors' qualifying shares) is owned by the
Company or one or more Wholly Owned Subsidiaries.


<TABLE>
<CAPTION>
                       SECTION 1.02.  Other Definitions.
                                      -----------------

                                                              Defined in
                              Term                              Section
                              ----                              -------
<S>                                                           <C>
                     "Affiliate Transaction".................    4.08

                     "Appendix"..............................    2.01

                     "Bankruptcy Law"........................    6.01

                     "Change of Control Offer"...............    4.10(b)

                     "covenant defeasance option"............    8.01(b)

                     "Custodian".............................    6.01

                     "Event of Default"......................    6.01

                     "Exchange Securities"...................  Appendix

                     "Initial Securities"....................  Appendix

                     "legal defeasance options"..............    8.01(b)

                     "Legal Holiday".........................   11.08

                     "Obligations"...........................   10.01

                     "Offer".................................    4.07(b)

                     "Offer Amount"..........................    4.07(c)(2)

                     "Offer Period"..........................    4.07(c)(2)

                     "Paying Agent"..........................    2.03

                     "Private Exchange Securities"...........  Appendix

                     "Purchase Date".........................    4.07(c)(1)

                     "Registrar".............................    2.03
</TABLE>
<PAGE>

                                                                              34

<TABLE>
<S>                                                            <C>
                     "Successor Company".....................    5.01

                     "Transfer Restricted Securities.........  Appendix
</TABLE>

          SECTION 1.03.  Incorporation by Reference of Trust Indenture Act.
                         -------------------------------------------------
This Indenture is subject to the mandatory provisions of the TIA which are
incorporated by reference in and made a part of this Indenture.  The following
TIA terms have the following meanings:

          "Commission" means the SEC;

          "indenture securities" means the Securities;

          "indenture security holder" means a Securityholder;

          "indenture to be qualified" means this Indenture;

          "indenture trustee" or "institutional trustee" means the Trustee; and

          "obligor" on the indenture securities means the Company and any other
obligor on the indenture 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 have the
meanings assigned to them by such definitions.

          SECTION 1.04.  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) "including" means including without limitation;

          (5) words in the singular include the plural and words in the plural
     include the singular;
<PAGE>

                                                                              35

          (6) unsecured Indebtedness shall not be deemed to be subordinate or
     junior to Secured Indebtedness merely by virtue of its nature as unsecured
     Indebtedness;

          (7) the principal amount of any noninterest bearing or other discount
     security at any date shall be the principal amount thereof that would be
     shown on a balance sheet of the issuer dated such date prepared in
     accordance with GAAP;

          (8) the principal amount of any Preferred Stock shall be (i) the
     maximum liquidation value of such Preferred Stock or (ii) the maximum
     mandatory redemption or mandatory repurchase price with respect to such
     Preferred Stock, whichever is greater; and

          (9) all references to the date the Securities were originally issued
     shall refer to the Issue Date.

                                  ARTICLE II

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

          SECTION 2.01.  Form and Dating.  Provisions and definitions relating
                         ---------------
to the Initial Securities, the Private Exchange Securities and the Exchange
Securities are set forth in the Rule 144A/Regulation S Appendix attached hereto
(the "Appendix") which is hereby incorporated in and expressly made part of this
Indenture. The Initial Securities and the Trustee's certificate of
authentication shall be substantially in the form of Exhibit 1 to the Appendix
which is hereby incorporated in and expressly made a part of this Indenture.
The Exchange Securities, the Private Exchange Securities and the Trustee's
certificate of authentication shall be substantially in the form of Exhibit A to
this Indenture, which is hereby incorporated in and expressly made a part of
this Indenture.  The Securities may have notations, legends or endorsements
required by law, stock exchange rule, agreements to which the Company is
subject, if any, or usage (provided that any such notation, legend or
endorsement is in a form acceptable to the Company).  Each Security shall be
dated the date of its authentication.  The terms of the Securities set forth in
the Appendix and Exhibit A are part of the terms of this Indenture.

          SECTION 2.02.  Execution and Authentication.  One Officer shall sign
                         ----------------------------
the Securities for the Company by manual or facsimile signature.
<PAGE>

                                                                              36

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

          A Security shall not be valid until an authorized signatory of the
Trustee manually signs the certificate of authentication on the Security.  The
signature shall be conclusive evidence that the Security has been authenticated
under this Indenture.

          On the Issue Date, the Trustee shall authenticate and deliver $300.0
million of 11% Senior Notes Due July 1, 2010 and, at any time and from time to
time thereafter, the Trustee shall authenticate and deliver Securities for
original issue in an aggregate principal amount specified in such order, in each
case upon a written order of the Company signed by two Officers or by an Officer
and either an Assistant Treasurer or an Assistant Secretary of the Company.
Such order shall specify the amount of the Securities to be authenticated and
the date on which the original issue of Securities is to be authenticated and,
in the case of an issuance of Additional Securities pursuant to Section 2.13
after the Issue Date, shall certify that such issuance is in compliance with
Section 4.03.

          The Trustee may appoint an authenticating agent reasonably acceptable
to the Company to authenticate the Securities.  Unless limited by the terms of
such 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 any Registrar, Paying Agent or agent for service of notices
and demands.

          SECTION 2.03.  Registrar and Paying Agent.  The Company shall maintain
                         --------------------------
an office or agency where Securities may be presented for registration of
transfer or for exchange (the "Registrar") and an office or agency where
Securities may be presented for payment (the "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 Company shall enter into an appropriate agency agreement with any
Registrar, Paying Agent or co-registrar not a party to this Indenture, which
shall incorporate the
<PAGE>

                                                                              37

terms of the TIA. The agreement shall implement the provisions of this Indenture
that relate to such agent. The Company shall notify the Trustee 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 and shall be entitled to appropriate
compensation therefor pursuant to Section 7.07. The Company or any Wholly Owned
Subsidiary incorporated or organized within The United States of America may act
as Paying Agent, Registrar, co-registrar or transfer agent.

          The Company initially appoints the Trustee as Registrar and Paying
Agent in connection with the Securities.

          SECTION 2.04.  Paying Agent To Hold Money in Trust.  Prior to each due
                         -----------------------------------
date of the principal and interest on any Security, the Company shall deposit
with the Paying Agent a sum sufficient to pay such principal and interest when
so becoming due.  The Company shall require each Paying Agent (other than the
Trustee) to agree in writing that the Paying Agent shall hold in trust for the
benefit of Securityholders or the Trustee all money held by the Paying Agent for
the payment of principal of or interest on the Securities and shall notify the
Trustee of any default by the Company in making any such payment.  If the
Company or a Subsidiary acts as Paying Agent, it shall segregate the money held
by it as Paying Agent and hold it as a separate trust fund.  The Company at any
time may require a Paying Agent to pay all money held by it to the Trustee and
to account for any funds disbursed by the Paying Agent.  Upon complying with
this Section, the Paying Agent shall have no further liability for the money
delivered to the Trustee.

          SECTION 2.05.  Securityholder Lists.  The Trustee shall preserve in as
                         --------------------
current a form as is reasonably practicable the most recent list available to it
of the names and addresses of Securityholders.  If the Trustee is not the
Registrar, the Company shall furnish to the Trustee, in writing at least five
Business Days before each interest payment date and at such other times as the
Trustee may request in writing, a list in such form and as of such date as the
Trustee may reasonably require of the names and addresses of Securityholders.

          SECTION 2.06.  Transfer and Exchange.  The Securities shall be issued
                         ---------------------
in registered form and shall be transferable only upon the surrender of a
Security for registration of transfer.  When a Security is presented to the
Registrar or a co-registrar with a request to register a
<PAGE>

                                                                              38

transfer, the Registrar shall register the transfer as requested if the
requirements of this Indenture and Section 8-401(1) of the Uniform Commercial
Code are met. When Securities are presented to the Registrar or a co-registrar
with a request to exchange them for an equal principal amount of Securities of
other denominations, the Registrar shall make the exchange as requested if the
same requirements are met.

          SECTION 2.07.  Replacement Securities.  If a mutilated Security is
                         ----------------------
surrendered to the Registrar or if the Holder of a Security claims that the
Security has been lost, destroyed or wrongfully taken, the Company shall issue
and the Trustee shall authenticate a replacement Security if the requirements of
Section 8-405 of the Uniform Commercial Code are met and the Holder satisfies
any other reasonable requirements of the Trustee.  If required by the Trustee or
the Company, such Holder shall furnish an indemnity bond sufficient in the
judgment of the Company and the Trustee to protect the Company, the Trustee, the
Paying Agent, the Registrar and any co-registrar from any loss which any of them
may suffer if a Security is replaced.  The Company and the Trustee may charge
the Holder for their expenses in replacing a Security.

          Every replacement Security is an additional obligation of the Company.

          SECTION 2.08.  Outstanding Securities.  Securities outstanding at any
                         ----------------------
time are all Securities authenticated by the Trustee except for those canceled
by it, those delivered to it for cancellation and those described in this
Section as not outstanding.  A Security does not cease to be outstanding because
the Company or an Affiliate of the Company holds the Security.

          If a Security is replaced pursuant to Section 2.07, it ceases to be
outstanding unless the Trustee and the Company receive proof satisfactory to
them that the replaced Security is held by a bona fide purchaser.

          If the Paying Agent segregates and holds in trust, in accordance with
this Indenture, on a redemption date or maturity date money sufficient to pay
all principal and interest payable on that date with respect to the Securities
(or portions thereof) to be redeemed or maturing, as the case may be, then on
and after that date such Securities (or portions thereof) cease to be
outstanding and interest on them ceases to accrue.
<PAGE>

                                                                              39

          SECTION 2.09.  Temporary Securities.  Until definitive Securities are
                         --------------------
ready for delivery, 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 considers
appropriate for temporary Securities.  Without unreasonable delay, the Company
shall prepare and the Trustee shall authenticate definitive Securities and
deliver them in exchange for temporary Securities.

          SECTION 2.10.  Cancellation.  The Company at any time may deliver
                         ------------
Securities to the Trustee for cancellation. The Registrar and the Paying Agent
shall forward to the Trustee any Securities surrendered to them for registration
of transfer, exchange or payment.  The Trustee and no one else shall cancel and
destroy (subject to the record retention requirements of the Exchange Act) all
Securities surrendered for registration of transfer, exchange, payment or
cancellation and deliver a certificate of such destruction to the Company unless
the Company directs the Trustee to deliver canceled Securities to the Company.
The Company may not issue new Securities to replace Securities it has redeemed,
paid or delivered to the Trustee for cancellation.

          SECTION 2.11.  Defaulted Interest.  If the Company defaults in a
                         ------------------
payment of interest on the Securities, the Company shall pay defaulted interest
(plus interest on such defaulted interest to the extent lawful) in any lawful
manner.  The Company may pay the defaulted interest to the persons who are
Securityholders on a subsequent special record date.  The Company shall fix or
cause to be fixed any such special record date and payment date to the
reasonable satisfaction of the Trustee and shall promptly mail to each
Securityholder a notice that states the special record date, the payment date
and the amount of defaulted interest to be paid.

          SECTION 2.12.  CUSIP Numbers.  The Company in issuing the Securities
                         -------------
may use "CUSIP" numbers (if then generally in use) and, if so, the Trustee shall
use "CUSIP" numbers in notices of redemption as a convenience to Holders;
provided, however, that any such notice may state that no representation is made
--------  -------
as to the correctness of such numbers either as printed on the Securities or as
contained in any notice of a redemption and that reliance may be placed only on
the other identification numbers printed on the Securities, and any such
redemption shall not be affected by any defect in or omission of such numbers.
<PAGE>

                                                                              40

          SECTION 2.13.  Issuance of Additional Securities. The Company shall be
                         ---------------------------------
entitled, subject to its compliance with Section 4.03, to issue Additional
Securities under this Indenture which shall have identical terms as the Initial
Securities issued on the Issue Date, other than with respect to the date of
issuance and issue price.  The Initial Securities issued on the Issue Date, any
Additional Securities and all Exchange Securities or Private Exchange Securities
issued in exchange therefor shall be treated as a single class for all purposes
under this Indenture.

          With respect to any Additional Securities, the Company shall set forth
in a resolution of the Board of Directors and an Officers' Certificate, a copy
of each which shall be delivered to the Trustee, the following information:

          (1) the aggregate principal amount of such
     Additional Securities to be authenticated and delivered pursuant to this
     Indenture;

          (2) the issue price, the issue date and the CUSIP number of such
     Additional Securities; provided, however, that no Additional Securities may
                            --------  -------
     be issued at a price that would cause such Additional Securities to have
     "original issue discount" within the meaning of Section 1273 of the Code;
     and

          (3) whether such Additional Securities shall be Transfer Restricted
     Securities and issued in the form of Initial Securities as set forth in the
     Appendix to this Indenture or shall be issued in the form of Exchange
     Securities as set forth in Exhibit A.

                                  ARTICLE III

                                  Redemption
                                  ----------
          SECTION 3.01.  Notices to Trustee.  If the Company elects to redeem
                         ------------------
Securities pursuant to paragraph 5 of the Securities, it shall notify the
Trustee in writing of the redemption date, the principal amount of Securities to
be redeemed and the paragraph of the Securities pursuant to which the redemption
will occur.

          The Company shall give each notice to the Trustee provided for in this
Section at least 60 days before the redemption date unless the Trustee consents
to a shorter period.  Such notice shall be accompanied by an Officers'
<PAGE>

                                                                              41

Certificate from the Company to the effect that such redemption will comply with
the conditions herein.

          SECTION 3.02.  Selection of Securities To Be Redeemed.  If fewer than
                         --------------------------------------
all the Securities are to be redeemed, the Trustee shall select the Securities
to be redeemed pro rata or by lot or by a method that complies with applicable
legal and securities exchange requirements, if any, and that the Trustee in its
sole discretion shall deem to be fair and appropriate and in accordance with
methods generally used at the time of selection by fiduciaries in similar
circumstances.  The Trustee shall make the selection from outstanding Securities
not previously called for redemption.  The Trustee may select for redemption
portions of the principal of Securities that have denominations larger than
$1,000.  Securities and portions of them the Trustee selects shall be in
principal amounts of $1,000 or a whole multiple of $1,000.  Provisions of this
Indenture that apply to Securities called for redemption also apply to portions
of Securities called for redemption.  The Trustee shall notify the Company
promptly of the Securities or portions of Securities to be redeemed.

          SECTION 3.03.  Notice of Redemption.  At least 30 days but not more
                         --------------------
than 60 days before a date for redemption of Securities, the Company shall mail
a notice of redemption by first-class mail to each Holder of Securities to be
redeemed at such Holder's registered address.

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

          (1) the redemption date;

          (2) the redemption price;

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

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

          (5) if fewer than all the outstanding Securities are to be redeemed,
     the identification and principal amounts of the particular Securities to be
     redeemed;

          (6) that, unless the Company defaults in making such redemption
     payment, interest on Securities (or portion thereof) called for redemption
     ceases to accrue on and after the redemption date; and
<PAGE>

                                                                              42

          (7)  that no representation is made as to the correctness or accuracy
     of the CUSIP number, if any, listed in such notice or printed on the
     Securities.

          At the Company's request, the Trustee shall give the notice of
redemption in the Company's name and at the Company's expense.  In such event,
the Company shall provide the Trustee with the information required by this
Section.

          SECTION 3.04.  Effect of Notice of Redemption. Once notice of
                         ------------------------------
redemption is mailed, Securities called for redemption become due and payable on
the redemption date and at the redemption price stated in the notice.  Upon
surrender to the Paying Agent, such Securities shall be paid at the redemption
price stated in the notice, plus accrued interest to the redemption date
(subject to the right of Holders of record on the relevant record date to
receive interest due on the related interest payment date).  Failure to give
notice or any defect in the notice to any Holder shall not affect the validity
of the notice to any other Holder.

          SECTION 3.05.  Deposit of Redemption Price.  Prior to the redemption
                         ---------------------------
date, the Company shall deposit with the Paying Agent (or, if the Company or a
Subsidiary is the Paying Agent, shall segregate and hold in trust) money
sufficient to pay the redemption price of and accrued interest on all Securities
to be redeemed on that date other than Securities or portions of Securities
called for redemption which have been delivered by the Company to the Trustee
for cancellation.

          SECTION 3.06.  Securities Redeemed in Part.  Upon surrender of a
                         ---------------------------
Security that is redeemed in part, the Company shall execute and the Trustee
shall authenticate for the Holder (at the Company's expense) a new Security
equal in principal amount to the unredeemed portion of the Security surrendered.

                                  ARTICLE IV

                                  Covenants
                                  ---------

          SECTION 4.01.  Payment of Securities.  The Company shall promptly pay
                         ---------------------
the principal of and interest on the Securities on the dates and in the manner
provided in the Securities and in this Indenture.  Principal and interest shall
be considered paid on the date due if on such date the Trustee or the Paying
Agent holds in accordance with this
<PAGE>

                                                                              43

Indenture money sufficient to pay all principal and interest then due.

          The Company shall pay interest on overdue principal at the rate
specified therefor in the Securities, and it shall pay interest on overdue
installments of interest at the same rate to the extent lawful.

          SECTION 4.02.  SEC Reports.  Notwithstanding that the Company may not
                         -----------
be subject to the reporting requirements of Section 13 or 15(d) of the Exchange
Act, the Company shall file with the SEC and provide the Trustee and
Securityholders with such annual reports and such information, documents and
other reports as are specified in Sections 13 and 15(d) of the Exchange Act and
applicable to a U.S. corporation subject to such Sections, such information,
documents and other reports to be so filed and provided at the times specified
for the filing of such information, documents and reports under such Sections.
In addition, the Company shall furnish to each Holder of Securities and to
prospective investors, upon the request of such Holder, any information required
to be delivered pursuant to Rule 144A(d)(4) under the Securities Act so long as
any Securities are not freely transferable under the Securities Act.  The
Company also shall comply with the other provisions of TIA (S) 314(a).

          SECTION 4.03.  Limitation on Indebtedness.  (a)  The Company shall
                         --------------------------
not, and shall not permit any Restricted Subsidiary to, Incur, directly or
indirectly, any Indebtedness; provided, however, that the Company and the
                              --------  -------
Subsidiary Guarantors shall be entitled to Incur Indebtedness if, on the date of
such Incurrence and after giving effect thereto, no Default has occurred and is
continuing, and the Consolidated Coverage Ratio exceeds 2.25 to 1.0.

          (b)  Notwithstanding the foregoing Section 4.03(a), so long as no
Default has occurred and is continuing, the Company and the Restricted
Subsidiaries shall be entitled to Incur any or all of the following
Indebtedness:

          (1)  Indebtedness Incurred by the Company pursuant to any Revolving
     Credit Facilities; provided, however, that, immediately after giving effect
                        --------  -------
     to any such Incurrence, the aggregate principal amount of all Indebtedness
     Incurred under this clause (1) and then outstanding does not exceed the
     greater of (A) $500.0 million less the sum of all principal
<PAGE>

                                                                              44

     payments with respect to such Indebtedness pursuant to Section
     4.07(a)(3)(A), and (B) the sum of 50% of the book value of the inventory of
     the Company and its Restricted Subsidiaries and 80% of the book value of
     the accounts receivable (whether categorized as billed or unbilled) of the
     Company and its Restricted Subsidiaries;

          (2)  Indebtedness Incurred by the Company pursuant to any Term Loan
     Facilities; provided, however, that, after giving effect to any such
                 --------  -------
     Incurrence, the aggregate principal amount of all Indebtedness Incurred
     under this clause (2) and then outstanding does not exceed $500.0 million
     less the aggregate sum of all principal payments actually made from time to
     time after the Issue Date with respect to such Indebtedness (other than
     principal payments made from any permitted Refinancings thereof);

          (3)  Indebtedness owed to and held by the Company or a Wholly Owned
     Subsidiary; provided, however, that (A) any subsequent issuance or transfer
                 --------  -------
     of any Capital Stock which results in any such Wholly Owned Subsidiary
     ceasing to be a Wholly Owned Subsidiary or any subsequent transfer of such
     Indebtedness (other than to the Company or a Wholly Owned Subsidiary) shall
     be deemed, in each case, to constitute the Incurrence of such Indebtedness
     by the obligor thereon and (B) if the Company is the obligor on such
     Indebtedness, such Indebtedness is expressly subordinated to the prior
     payment in full in cash of all obligations with respect to the Securities;

          (4)  the Initial Securities issued on the Issue Date and the Exchange
     Securities issued in exchange therefor;

          (5)  Indebtedness outstanding on the Issue Date (other than
     Indebtedness described in clause (1), (2), (3) or (4) of this Section
     4.03(b));

          (6)  Indebtedness of a Restricted Subsidiary Incurred and outstanding
     on or prior to the date on which such Subsidiary was acquired by the
     Company (other than Indebtedness Incurred in connection with, or to provide
     all or any portion of the funds or credit support utilized to consummate,
     the transaction or series of related transactions pursuant to which such
     Subsidiary became a Subsidiary or was acquired by the Company); provided,
                                                                     --------
     however, that on the date of such
     -------
<PAGE>

                                                                              45

     acquisition and after giving pro forma effect thereto, the Company would
     have been able to Incur at least $1.00 of additional Indebtedness pursuant
     to Section 4.03(a);

          (7)  Indebtedness Incurred by the Company or any of its Restricted
     Subsidiaries consisting of advances received in the ordinary course of
     business for cash management purposes from any domestic or foreign
     Unrestricted Subsidiary or joint venture that is engaged primarily in a
     Related Business;

          (8)  Refinancing Indebtedness in respect of Indebtedness Incurred
     pursuant to Section 4.03(a) or pursuant to clause (4), (5) or (6) of this
     Section 4.03(b) or this clause (8); provided, however, that to the extent
                                         --------  -------
     such Refinancing Indebtedness directly or indirectly Refinances
     Indebtedness of a Restricted Subsidiary Incurred pursuant to clause (6),
     such Refinancing Indebtedness shall be Incurred only by the Company or such
     Restricted Subsidiary;

          (9)  any obligations of the Company or any of its Restricted
     Subsidiaries under Hedging Agreements entered into in the ordinary course
     of business to hedge or mitigate risks to which the Company or any of its
     Restricted Subsidiaries is exposed in the conduct of its business or the
     management of its liabilities and not for speculative purposes;

          (10) obligations in respect of standby letters of credit or
     performance, bid and surety bonds and completion guarantees provided by the
     Company or any Restricted Subsidiary in the ordinary course of business or
     pursuant to self-insurance obligations and not in connection with the
     borrowing of money or the obtaining of advances or credit;

          (11) Indebtedness consisting of the Subsidiary Guaranty of a
     Subsidiary Guarantor and any Guarantee by a Subsidiary Guarantor of
     Indebtedness Incurred pursuant to Section 4.03(a), pursuant to clause (1),
     (2), (3), (4), (5) or (13) of this Section 4.03(b) or pursuant to clause
     (8) of this Section 4.03(b) to the extent the Refinancing Indebtedness
     Incurred thereby directly or indirectly refinances Indebtedness Incurred
     pursuant to Section 4.03 (a) or pursuant to clauses (4) or (5) of this
     Section 4.03(b);
<PAGE>

                                                                              46

         (12)  Indebtedness Incurred by Foreign Subsidiaries in the ordinary
     course of business for working capital purposes; and

         (13)  Indebtedness of the Company or any Subsidiary Guarantor in an
     aggregate principal amount which, when taken together with all other
     Indebtedness of the Company outstanding on the date of such Incurrence
     (other than Indebtedness permitted by clauses (1) through (12) of this
     Section 4.03(b) or Section 4.03(a)) does not exceed $50.0 million.

          (c)  Notwithstanding the foregoing, neither the Company nor any
Subsidiary Guarantor shall Incur any Indebtedness pursuant to Section 4.03(b) if
the proceeds thereof are used, directly or indirectly, to Refinance any
Subordinated Obligations of the Company or any Subsidiary Guarantor unless such
Indebtedness shall be subordinated to the Securities or the applicable
Subsidiary Guaranty to at least the same extent as such Subordinated
Obligations.

          (d)  For purposes of determining compliance with this Section 4.03,
(1) in the event that an item of Indebtedness meets the criteria of more than
one of the types of Indebtedness described above, the Company, in its sole
discretion, shall classify such item of Indebtedness at the time of Incurrence
and only be required to include the amount and type of such Indebtedness in one
of the above clauses, (2) the Company shall be entitled to divide and classify
an item of Indebtedness in more than one of the types of Indebtedness described
above and (3) the Company shall be entitled after Incurrence of any Indebtedness
pursuant to Section 4.03(b) to reclassify such Indebtedness to any other type of
Indebtedness permitted pursuant to Section 4.03(b); provided, however, that such
                                                    --------  -------
Indebtedness at the time of reclassification could have been Incurred and could
have been classified as such other type of Indebtedness pursuant to Section
4.03(b).

          SECTION 4.04.  Limitation on Restricted Payments. (a)  The Company
                         ---------------------------------
shall not, and shall not permit any Restricted Subsidiary, directly or
indirectly, to make a Restricted Payment if at the time the Company or such
Restricted Subsidiary makes such Restricted Payment:

          (1)  a Default shall have occurred and be continuing (or would result
     therefrom);
<PAGE>

                                                                              47

          (2)  the Company is not entitled to Incur an additional $1.00 of
     Indebtedness pursuant to Section 4.03(a); or

          (3)  the aggregate amount of such Restricted Payment and all other
     Restricted Payments since the Issue Date would exceed the sum of (without
     duplication):

               (A) 50% of the Consolidated Net Income accrued during the period
          (treated as one accounting period) from the beginning of the fiscal
          quarter immediately following the fiscal quarter during which the
          Issue Date occurs to the end of the most recent fiscal quarter ending
          at least 45 days prior to the date of such Restricted Payment (or, in
          case such Consolidated Net Income shall be a deficit, minus 100% of
          such deficit); plus
                         ----

               (B) 100% of the aggregate Net Cash Proceeds received by the
          Company from the issuance or sale of its Capital Stock (other than
          Disqualified Stock) subsequent to the Issue Date (other than an
          issuance or sale to a Subsidiary of the Company and other than an
          issuance or sale to an employee stock ownership plan or to a trust
          established by the Company or any of its Subsidiaries for the benefit
          of their employees) and 100% of any capital cash contribution received
          by the Company from its stockholders subsequent to the Issue Date;
          plus
          ----

               (C) the amount by which Indebtedness of the Company is reduced on
          the Company's balance sheet upon the conversion or exchange (other
          than by a Subsidiary of the Company) subsequent to the Issue Date of
          any Indebtedness of the Company convertible or exchangeable for
          Capital Stock (other than Disqualified Stock) of the Company (less the
          amount of any cash, or the fair value of any other property,
          distributed by the Company upon such conversion or exchange); plus
                                                                        ----

               (D) an amount equal to the sum of (x) the net reduction in the
          Investments (other than Permitted Investments) made by the Company or
          any Restricted Subsidiary in any Person resulting from repurchases,
          repayments or redemptions of such Investments by such Person, proceeds
          realized on
<PAGE>

                                                                              48

          the sale of such Investments or proceeds representing the return of
          capital (excluding dividends and similar distributions), in each case
          received by the Company or any Restricted Subsidiary, and (y) to the
          extent such Person is an Unrestricted Subsidiary, the portion
          (proportionate to the Company's equity interest in such Subsidiary) of
          the fair market value of the net assets of such Unrestricted
          Subsidiary at the time such Unrestricted Subsidiary is designated a
          Restricted Subsidiary; provided, however, that the foregoing sum shall
                                 --------  -------
          not exceed, in the case of any such Person, the amount of Investments
          (excluding Permitted Investments) previously made (and treated as a
          Restricted Payment) by the Company or any Restricted Subsidiary in
          such Person.

          (b)  The provisions of Section 4.04(a) shall not prohibit:

          (1) any Restricted Payment (other than a Restricted Payment described
     in clause (1) or clause (4) of the definition of "Restricted Payment") made
     out of the Net Cash Proceeds of the substantially concurrent sale of, or
     made by exchange for, Capital Stock of the Company (other than Disqualified
     Stock and other than Capital Stock issued or sold to a Subsidiary of the
     Company or an employee stock ownership plan or to a trust established by
     the Company or any of its Subsidiaries for the benefit of their employees)
     or a substantially concurrent capital cash contribution received by the
     Company from its stockholders; provided, however, that (A) such Restricted
                                    --------  -------
     Payment shall be excluded in the calculation of the amount of Restricted
     Payments and (B) the Net Cash Proceeds from such sale or such capital cash
     contribution (to the extent so used for such Restricted Payment) shall be
     excluded from the calculation of amounts under Section 4.04(a)(3)(B);

          (2) any purchase, repurchase, redemption, defeasance or other
     acquisition or retirement for value of Subordinated Obligations made by
     exchange for, or out of the proceeds of the substantially concurrent sale
     of, Indebtedness which is permitted to be Incurred pursuant to Section
     4.03; provided, however, that such purchase, repurchase, redemption,
           --------  -------
     defeasance or other acquisition or retirement for value shall be excluded
     in the calculation of the amount of Restricted Payments;
<PAGE>

                                                                              49

          (3) dividends paid within 60 days after the date of declaration
     thereof if at such date of declaration such dividend would have complied
     with this Section 4.04; provided, however, that at the time of payment of
                             --------  -------
     such dividend, no other Default shall have occurred and be continuing (or
     result therefrom); provided further, however, that such dividend shall be
                        ----------------  -------
     included in the calculation of the amount of Restricted Payments;

          (4) so long as no Default has occurred and is continuing, the
     repurchase or other acquisition of shares of Capital Stock of the Company
     or any of its Subsidiaries from employees, former employees, directors or
     former directors of the Company or any of its Subsidiaries (or permitted
     transferees of such employees, former employees, directors or former
     directors), pursuant to the terms of the agreements (including employment
     agreements) or plans (or amendments thereto) approved by the Board of
     Directors under which such individuals purchase or sell or are granted the
     option to purchase or sell, shares of such Capital Stock; provided,
                                                               --------
     however, that the aggregate amount of such repurchases and other
     -------
     acquisitions shall not exceed $3.0 million in any calendar year (with any
     unused amounts in any calendar year being available to be carried over to
     succeeding calendar years); provided further, however, that such
                                 ----------------  -------
     repurchases and other acquisitions shall be excluded in the calculation of
     the amount of Restricted Payments;

          (5) upon the occurrence of a Change of Control and within 60 days
     after the completion of the offer to repurchase the Securities pursuant to
     Section 4.10 (including the purchase of the Securities tendered), any
     purchase or redemption of Subordinated Obligations or any Capital Stock
     required pursuant to the terms thereof as a result of such Change of
     Control at a purchase or redemption price not to exceed 101% of the
     outstanding principal amount thereof, plus accrued and unpaid interest or
     dividends (if any); provided, however, that (A) at the time of such
                         --------  -------
     purchase or redemption no Default shall have occurred and be continuing (or
     would result therefrom) and (B) such purchase or redemption shall be
     included in the calculation of the amount of Restricted Payments; or

          (6) so long as no Default has occurred and is continuing, other
     Restricted Payments; provided, however, that the aggregate amount of such
                          --------  -------
     Restricted
<PAGE>

                                                                              50

     Payments shall not exceed $20.0 million; provided further, however, that
                                              ----------------  -------
     such Restricted Payments shall be excluded in the calculation of the amount
     of Restricted Payments.

          SECTION 4.05.  Conduct of Business.  The Company and its Restricted
                         -------------------
Subsidiaries shall not engage in any business which is not a Related Business,
except to such extent as would not be material to the Company and its Restricted
Subsidiaries taken as a whole.  The Company shall not permit WGSG (1) to engage
in any business that is not directly related to the business conducted by WGSG
on the Issue Date and consistent with past practices or (2) to Incur and have
outstanding any Indebtedness to any Person other than a shareholder in excess of
the amount of such Indebtedness it could Incur and have outstanding as of the
Issue Date pursuant to the Economic Rights Agreement dated as of March 19, 1999,
the Amended and Restated Limited Liability Company Agreement of Westinghouse
Government Services Company, LLC, dated as of March 19, 1999, and the Amended
and Restated Limited Liability Company Agreement of Westinghouse Government
Environmental Services Company, LLC, dated as of March 19, 1999.  If the Company
has any interest in WGSG, the Company shall not permit its ownership interest in
WGSG to be less than 60%.

          SECTION 4.06.  Limitation on Restrictions on Distributions from
                         ------------------------------------------------
Restricted Subsidiaries. The Company shall not, and shall not permit any
-----------------------
Restricted Subsidiary to, create or otherwise cause or permit to exist or become
effective any consensual encumbrance or restriction on the ability of any
Restricted Subsidiary to (a) pay dividends or make any other distributions on
its Capital Stock to the Company or a Restricted Subsidiary or pay any
Indebtedness owed to the Company, (b) make any loans or advances to the Company
or (c) transfer any of its property or assets to the Company, except:

          (1) any encumbrance or restriction pursuant to an agreement in effect
     at or entered into on the Issue Date;

          (2) any encumbrance or restriction with respect to a Restricted
     Subsidiary pursuant to an agreement relating to any Indebtedness Incurred
     by such Restricted Subsidiary on or prior to the date on which such
     Restricted Subsidiary was acquired by the Company (other than Indebtedness
     Incurred as consideration in, or to provide all or any portion of the funds
     or credit support utilized to consummate, the transaction or
<PAGE>

                                                                              51

     series of related transactions pursuant to which such Restricted Subsidiary
     became a Restricted Subsidiary or was acquired by the Company) and
     outstanding on such date;

          (3) any encumbrance or restriction pursuant to an agreement effecting
     a Refinancing of Indebtedness Incurred pursuant to an agreement referred to
     in Section 4.06(1) or (2) or this clause (3) or contained in any amendment
     to an agreement referred to in Section 4.06(1) or (2) or this clause (3);
     provided, however, that the encumbrances and restrictions with respect to
     --------  -------
     such Restricted Subsidiary contained in any such refinancing agreement or
     amendment are no less favorable to the Securityholders than encumbrances
     and restrictions with respect to such Restricted Subsidiary contained in
     such predecessor agreements;

          (4) any such encumbrance or restriction consisting of customary non
     assignment provisions in leases governing leasehold interests to the extent
     such provisions restrict the transfer of the lease or the property leased
     thereunder;

          (5) in the case of clause (c) above, restrictions contained in
     security agreements or mortgages securing Indebtedness of a Restricted
     Subsidiary to the extent such restrictions restrict the transfer of the
     property subject to such security agreements or mortgages;

          (6) any restriction with respect to a Restricted Subsidiary imposed
     pursuant to an agreement entered into for the sale or disposition of all or
     substantially all the Capital Stock or assets of such Restricted Subsidiary
     pending the closing of such sale or disposition;

          (7) any encumbrance or restriction existing under or by reason of
     applicable law; and

          (8) in the case of clause (c) above, any restriction with respect to
     the distribution of cash or other deposits imposed on a Restricted
     Subsidiary under a contract entered into in the ordinary course of
     business.

          SECTION 4.07.  Limitation on Sales of Assets and Subsidiary Stock.
                         --------------------------------------------------
(a)  The Company shall not, and shall not permit any Restricted Subsidiary to,
directly or indirectly, consummate any Asset Disposition unless:
<PAGE>

                                                                              52

          (1) the Company or such Restricted Subsidiary receives consideration
     at the time of such Asset Disposition at least equal to the fair market
     value (including as to the value of all non-cash consideration), as
     determined in good faith by the Board of Directors, of the shares and
     assets subject to such Asset Disposition;

          (2) except to the extent such Asset Disposition constitutes a
     Permitted Asset Swap, at least 75% of the consideration thereof received by
     the Company or such Restricted Subsidiary is in the form of cash or cash
     equivalents; and

          (3) an amount equal to 100% of the Net Available Cash from such Asset
     Disposition is applied by the Company (or such Restricted Subsidiary, as
     the case may be)

               (A) first, to the extent the Company elects (or is required by
                   -----
          the terms of any Indebtedness), to prepay, repay, redeem, defease or
          purchase Senior Indebtedness of the Company or Indebtedness (other
          than any Disqualified Stock) of a Restricted Subsidiary (in each case
          other than Indebtedness owed to the Company or an Affiliate of the
          Company) within one year from the later of the date of such Asset
          Disposition or the receipt of such Net Available Cash;

               (B) second, to the extent of the balance of such Net Available
                   ------
          Cash after application in accordance with clause (A), to the extent
          the Company elects, to acquire Additional Assets within one year from
          the later of the date of such Asset Disposition or the receipt of such
          Net Available Cash; and

               (C) third, to the extent of the balance of such Net Available
                   -----
          Cash after application in accordance with clauses (A) and (B), to make
          an offer to the holders of the Securities (and to holders of other
          Senior Indebtedness of the Company designated by the Company) to
          purchase Securities (and such other Senior Indebtedness of the
          Company) pursuant to and subject to the conditions of Section 4.07(b);

               provided, however, that in connection with any prepayment,
               --------  -------
               repayment or purchase of
<PAGE>

                                                                              53

               Indebtedness pursuant to clause (A) or (C) above, the Company or
               such Restricted Subsidiary shall permanently retire such
               Indebtedness and shall cause the related loan commitment (if any)
               to be permanently reduced in an amount equal to the principal
               amount so prepaid, repaid or purchased.

          Notwithstanding the foregoing provisions of this Section 4.07, the
Company and the Restricted Subsidiaries shall not be required to apply any Net
Available Cash in accordance with this Section 4.07(a) except to the extent that
the aggregate Net Available Cash from all Asset Dispositions which are not
applied in accordance with this Section 4.07(a) exceeds $25.0 million.  Pending
application of Net Available Cash pursuant to this Section 4.07(a), such Net
Available Cash shall be invested in Temporary Cash Investments or applied to
temporarily reduce revolving credit indebtedness.

          For the purposes of this Section 4.07(a), the following are deemed to
be cash or cash equivalents:

          (1) the assumption of Indebtedness of the Company or any Restricted
     Subsidiary and the release of the Company or such Restricted Subsidiary
     from all liability on such Indebtedness in connection with such Asset
     Disposition; and

          (2) securities received by the Company or any Restricted Subsidiary
     from the transferee that are promptly converted by the Company or such
     Restricted Subsidiary into cash.

          (b)  In the event of an Asset Disposition that requires the purchase
of Securities (and other Senior Indebtedness of the Company) pursuant to Section
4.07(a)(3)(C), the Company shall purchase Securities tendered pursuant to an
offer by the Company for the Securities (and such other Senior Indebtedness of
the Company) (the "Offer") at a purchase price of 100% of their principal amount
(or, in the event such other Senior Indebtedness of the Company was issued with
significant original issue discount, 100% of the accreted value thereof),
without premium, plus accrued but unpaid interest (or, in respect of such other
Senior Indebtedness of the Company, such lesser price, if any, as may be
provided for by the terms of such Senior Indebtedness of the Company) in
accordance with the procedures set forth in Section 4.07(c). The Company shall
not be required to make such an Offer to
<PAGE>

                                                                              54

purchase Securities (and other Senior Indebtedness of the Company) pursuant to
this Section 4.07 if the Net Available Cash available therefor is less than
$25.0 million (which lesser amount shall be carried forward for purposes of
determining whether such an Offer is required with respect to the Net Available
Cash from any subsequent Asset Disposition).

          (c) (1)  Promptly, and in any event within 10 days after the Company
     becomes obligated to make an Offer, the Company shall deliver to the
     Trustee and send, by first-class mail to each Holder, a written notice
     stating that the Holder may elect to have his Securities purchased by the
     Company either in whole or in part (subject to prorating as described in
     Section 4.07(b) in the event the Offer is oversubscribed) in integral
     multiples of $1,000 of principal amount, at the applicable purchase price.
     The notice shall specify a purchase date not less than 30 days or more than
     60 days after the date of such notice (the "Purchase Date") and shall
     contain such information concerning the business of the Company which the
     Company in good faith believes will enable such Holders to make an informed
     decision (which at a minimum will include (A) the most recently filed
     Annual Report on Form 10-K (including audited consolidated financial
     statements) of the Company, the most recent subsequently filed Quarterly
     Report on Form 10-Q and any Current Report on Form 8-K of the Company filed
     subsequent to such Quarterly Report, other than Current Reports describing
     Asset Dispositions otherwise described in the offering materials (or
     corresponding successor reports), (B) a description of material
     developments in the Company's business subsequent to the date of the latest
     of such Reports, and (C) if material, appropriate pro forma financial
     information) and all instructions and materials necessary to tender
     Securities pursuant to the Offer, together with the information contained
     in clause (3).

          (2)  Not later than the date upon which written notice of an Offer is
     delivered to the Trustee as provided below, the Company shall deliver to
     the Trustee an Officers' Certificate as to (A) the amount of the Offer (the
     "Offer Amount"), including information as to any other Senior Indebtedness
     included in the Offer, (B) the allocation of the Net Available Cash from
     the Asset Dispositions pursuant to which such Offer is being made and (C)
     the compliance of such allocation with the provisions of
<PAGE>

                                                                              55

     Section 4.07(a) and (b). On such date, the Company shall also irrevocably
     deposit with the Trustee or with a Paying Agent (or, if the Company is
     acting as its own Paying Agent, segregate and hold in trust) in Temporary
     Cash Investments, maturing on the last day prior to the Purchase Date or on
     the Purchase Date if funds are immediately available by open of business,
     an amount equal to the Offer Amount to be held for payment in accordance
     with the provisions of this Section. If the Offer includes other Senior
     Indebtedness, the deposit described in the preceding sentence may be made
     with any other paying agent pursuant to arrangements satisfactory to the
     Trustee. Upon the expiration of the period for which the Offer remains open
     (the "Offer Period"), the Company shall deliver to the Trustee for
     cancellation the Securities or portions thereof which have been properly
     tendered to and are to be accepted by the Company. The Trustee shall, on
     the Purchase Date, mail or deliver payment (or cause the delivery of
     payment) to each tendering Holder in the amount of the purchase price. In
     the event that the aggregate purchase price of the Securities delivered by
     the Company to the Trustee is less than the Offer Amount applicable to the
     Securities, the Trustee shall deliver the excess to the Company immediately
     after the expiration of the Offer Period for application in accordance with
     this Section 4.07. If the aggregate purchase price of the securities
     tendered exceeds the Net Available Cash allotted to their purchase, the
     Company shall select the securities to be purchased on a pro rata basis but
     in round denominations, which in the case of the Securities will be
     denominations of $1,000 principal amount or multiples thereof.

          (3) Holders electing to have a Security purchased shall be required to
     surrender the Security, with an appropriate form duly completed, to the
     Company at the address specified in the notice at least three Business Days
     prior to the Purchase Date. Holders shall be entitled to withdraw their
     election if the Trustee or the Company receives not later than one Business
     Day prior to the Purchase Date, a telex, facsimile transmission or letter
     setting forth the name of the Holder, the principal amount of the Security
     which was delivered for purchase by the Holder and a statement that such
     Holder is withdrawing his election to have such Security purchased. Holders
     whose Securities are purchased only in part shall be issued new Securities
     equal in principal amount to the unpurchased portion of the Securities
     surrendered.
<PAGE>

                                                                              56

          (4)  At the time the Company delivers Securities to the Trustee which
     are to be accepted for purchase, the Company shall also deliver an
     Officers' Certificate stating that such Securities are to be accepted by
     the Company pursuant to and in accordance with the terms of this Section.
     A Security shall be deemed to have been accepted for purchase at the time
     the Trustee, directly or through an agent, mails or delivers payment
     therefor to the surrendering Holder.

          (d)  The Company shall comply, to the extent applicable, with the
requirements of Section 14(e) of the Exchange Act and any other securities laws
or regulations in connection with the repurchase of Securities pursuant to this
Section.  To the extent that the provisions of any securities laws or
regulations conflict with provisions of this Section, the Company shall comply
with the applicable securities laws and regulations and shall not be deemed to
have breached its obligations under this Section by virtue of its compliance
with such securities laws or regulations.

          SECTION 4.08. Limitation on Affiliate Transactions. (a) The Company
                        ------------------------------------
shall not, and shall not permit any Restricted Subsidiary to, enter into or
permit to exist any transaction (including the purchase, sale, lease or exchange
of any property, employee compensation arrangements or the rendering of any
service) with, or for the benefit of, any Affiliate of the Company (an
"Affiliate Transaction") unless:

          (1) the terms of the Affiliate Transaction are no less favorable to
     the Company or such Restricted Subsidiary than those that could be obtained
     at the time of the Affiliate Transaction in arm's-length dealings with a
     Person who is not an Affiliate;

          (2) if such Affiliate Transaction involves an amount in excess of
     $10.0 million, the terms of the Affiliate Transaction are set forth in
     writing and a majority of the non-employee directors of the Company
     disinterested with respect to such Affiliate Transactions have determined
     in good faith that the criteria set forth in clause (1) are satisfied and
     have approved the relevant Affiliate Transaction as evidenced by a Board
     Resolution; and

          (3) if such Affiliate Transaction involves an amount in excess of
     $25.0 million, the Board of Directors shall also have received a written
     opinion from a nationally recognized investment banking,
<PAGE>

                                                                              57

     appraisal or accounting firm that is not an Affiliate of the Company to the
     effect that such Affiliate Transaction is on terms that are not less
     favorable than those that could have been obtained in a similar transaction
     at such time from a Person that is not an Affiliate of the Company.

          (b)  The provisions of Section 4.08(a) shall not prohibit:

          (1) any Investment (other than a Permitted Investment) or other
     Restricted Payment, in each case permitted to be made pursuant to Section
     4.04;

          (2) any issuance of securities, or other payments, awards or grants in
     cash, securities or otherwise pursuant to, or the funding of, employment or
     indemnification arrangements, stock options and stock ownership plans
     approved by the Board of Directors;

          (3) loans or advances to employees in the ordinary course of business
     in accordance with the past practices of the Company or its Restricted
     Subsidiaries, but in any event not to exceed $4.0 million in the aggregate
     outstanding at any one time;

          (4) the payment of reasonable fees to, or the entry into customary
     indemnification agreements with, directors of the Company and its
     Restricted Subsidiaries who are not employees of the Company or its
     Restricted Subsidiaries;

          (5) any transaction with a Restricted Subsidiary or joint venture or
     similar entity which would constitute an Affiliate Transaction solely
     because the Company or a Restricted Subsidiary owns an equity interest in
     or otherwise controls such Restricted Subsidiary, joint venture or similar
     entity; and

          (6) the issuance or sale of any Capital Stock (other than Disqualified
     Stock) of the Company.

          SECTION 4.09.  Limitation on the Sale or Issuance of Capital Stock of
                         ------------------------------------------------------
Restricted Subsidiaries. The Company
-----------------------

          (1) shall not, and shall not permit any Restricted Subsidiary to,
     sell, lease, transfer or otherwise dispose of any Capital Stock of any
     Restricted
<PAGE>

                                                                              58

     Subsidiary to any Person (other than the Company or a Wholly Owned
     Subsidiary), and

          (2) shall not permit any Restricted Subsidiary to issue any of its
     Capital Stock (other than, if necessary, shares of its Capital Stock
     constituting directors' or other legally required qualifying shares) to any
     Person (other than to the Company or a Wholly Owned Subsidiary),

unless

          (A) immediately after giving effect to such issuance, sale or other
     disposition, neither the Company nor any of its Subsidiaries own any
     Capital Stock of such Restricted Subsidiary; or

          (B) immediately after giving effect to such issuance, sale or other
     disposition, such Restricted Subsidiary would no longer constitute a
     Restricted Subsidiary and any Investment in such Person remaining after
     giving effect thereto would have been permitted to be made under Section
     4.04 if made on the date of such issuance, sale or other disposition.

          SECTION 4.10.  Change of Control.  (a)  Upon the occurrence of a
                         -----------------
Change of Control, each Holder shall have the right to require that the Company
purchase such Holder's Securities at a purchase price in cash equal to 101% of
the principal amount thereof plus accrued and unpaid interest, if any, to the
date of purchase (subject to the right of holders of record on the relevant
record date to receive interest on the relevant interest payment date), in
accordance with the terms contemplated in Section 4.10(b).

          (b)  Within 30 days following any Change of Control, the Company shall
mail a notice to each Holder with a copy to the Trustee (the "Change of Control
Offer") stating:

          (1) that a Change of Control has occurred and that such Holder has the
     right to require the Company to purchase such Holder's Securities at a
     purchase price in cash equal to 101% of the principal amount thereof on the
     date of purchase, plus accrued and unpaid interest, if any, to the date of
     purchase (subject to the right of Holders of record on the relevant record
     date to receive interest on the relevant interest payment date);
<PAGE>

                                                                              59

          (2) the circumstances and relevant facts regarding such Change of
     Control (including information with respect to pro forma historical income,
     cash flow and capitalization, each after giving effect to such Change of
     Control);

          (3) the purchase date (which shall be no earlier than 30 days or later
     than 60 days from the date such notice is mailed); and

          (4) the instructions, as determined by the Company, consistent with
     this Section, that a Holder must follow in order to have its Securities
     purchased.

          (c)  Holders electing to have a Security purchased will be required to
surrender the Security, with an appropriate form duly completed, to the Company
at the address specified in the notice at least three Business Days prior to the
purchase date.  Holders will be entitled to withdraw their election if the
Trustee or the Company receives not later than one Business Day prior to the
purchase date, a telegram, telex, facsimile transmission or letter setting forth
the name of the Holder, the principal amount of the Security which was delivered
for purchase by the Holder and a statement that such Holder is withdrawing his
election to have such Security purchased.

          (d)  On the purchase date, all Securities purchased by the Company
under this Section shall be delivered by the Company to the Trustee for
cancellation, and the Company shall pay the purchase price plus accrued and
unpaid interest, if any, to the Holders entitled thereto.

          (e)  Notwithstanding the foregoing provisions of this Section, the
Company shall not be required to make a Change of Control Offer upon a Change of
Control if a third party makes the Change of Control Offer in the manner, at the
times and otherwise in compliance with the requirements set forth in Section
applicable to a Change of Control Offer made by the Company and purchases all
Securities validly tendered and not withdrawn under such Change of Control
Offer.

          (f)  The Company shall comply, to the extent applicable, with the
requirements of Section 14(e) of the Exchange Act and any other securities laws
or regulations in connection with the repurchase of Securities pursuant to this
Section.  To the extent that the provisions of any securities laws or
regulations conflict with provisions of this Section, the Company shall comply
with the applicable
<PAGE>

                                                                              60

securities laws and regulations and shall not be deemed to have breached its
obligations under this Section by virtue of its compliance with such securities
laws or regulations.

          SECTION 4.11.  Limitation on Liens.  The Company shall not, and shall
                         -------------------
not permit any Restricted Subsidiary to, directly or indirectly, Incur or permit
to exist any Lien (the "Initial Lien") of any nature whatsoever on any of its
                        ------------
properties (including Capital Stock of a Restricted Subsidiary), whether owned
at the Issue Date or thereafter acquired, other than Permitted Liens, without
effectively providing that the Securities shall be secured equally and ratably
with (or prior to) the obligations so secured for so long as such obligations
are so secured.

          Any Lien created for the benefit of the Holders of the Securities
pursuant to the preceding sentence shall provide by its terms that such Lien
shall be automatically and unconditionally released and discharged upon the
release and discharge of the Initial Lien.

          SECTION 4.12.  Limitation on Sale/Leaseback Transactions.  The Company
                         -----------------------------------------
shall not, and shall not permit any Restricted Subsidiary to, enter into any
Sale/Leaseback Transaction with respect to any property unless:

          (1) the Company or such Restricted Subsidiary would be entitled to (A)
     Incur Indebtedness in an amount equal to the Attributable Debt with respect
     to such Sale/Leaseback Transaction pursuant to Section 4.03 and (B) create
     a Lien on such property securing such Attributable Debt without equally and
     ratably securing the Securities pursuant to Section 4.11;

          (2) the net proceeds received by the Company or any Restricted
     Subsidiary in connection with such Sale/ Leaseback Transaction are at least
     equal to the fair value (as determined by the Board of Directors) of such
     property; and

          (3) the Company applies the proceeds of such transaction in compliance
     with Section 4.07.

Notwithstanding clauses 1(B), 2 and 3 of this Section 4.12, the Company and the
Restricted Subsidiaries may enter into Sale/Leaseback Transactions with respect
to construction and similar equipment.
<PAGE>

                                                                              61

          SECTION 4.13.  Future Guarantors.  The Company shall cause each
                         -----------------
Restricted Subsidiary that Guarantees any Indebtedness of the Company or any
other Restricted Subsidiary to at the same time execute and deliver to the
Trustee a Guaranty Agreement pursuant to which such Restricted Subsidiary will
Guarantee payment of the Securities on the same terms and conditions as those
set forth in Article X of this Indenture.

          SECTION 4.14.  Compliance Certificate.  The Company shall deliver to
                         ----------------------
the Trustee within 120 days after the end of each fiscal year of the Company an
Officers' Certificate stating that in the course of the performance by the
signers of their duties as Officers of the Company they would normally have
knowledge of any Default and whether or not the signers know of any Default that
occurred during such period.  If they do, the certificate shall describe the
Default, its status and what action the Company is taking or proposes to take
with respect thereto.  The Company also shall comply with TIA (S) 314(a)(4).

          SECTION 4.15.  Further Instruments and Acts.  Upon request of the
                         ----------------------------
Trustee, the Company shall execute and deliver such further instruments and do
such further acts as may be reasonably necessary or proper to carry out more
effectively the purpose of this Indenture.

          SECTION 4.16.  Suspension of Certain Covenants. During any period of
                         -------------------------------
time that (a) the Securities have an Investment Grade Rating from both Rating
Agencies and (b) no Default has occurred and is continuing under this Indenture,
the Company and the Restricted Subsidiaries will not be subject to the
provisions in Sections 4.03, 4.04, 4.07 and 4.08 (collectively, the "Suspended
Covenants").  In the event that the Company and the Restricted Subsidiaries are
not subject to the Suspended Covenants for any period of time as a result of the
preceding sentence and, subsequently, one or both of the Rating Agencies
withdraws its rating or downgrades the rating assigned to the Securities below
an Investment Grade Rating, or a Default occurs and is continuing, then the
Company and the Restricted Subsidiaries will thereafter again be subject to the
Suspended Covenants, and compliance with the Suspended Covenants with respect to
Restricted Payments made after the time of such withdrawal, downgrade or Default
will be calculated in accordance with the terms of Section 4.04 as though such
covenant had been in effect since the Issue Date.
<PAGE>

                                                                              62

                                   ARTICLE V

                               Successor Company
                               -----------------

          SECTION 5.01.  When Company May Merge or Transfer Assets.  (a)  The
                         -----------------------------------------
Company shall not consolidate with or merge with or into, or convey, transfer or
lease, in one transaction or a series of transactions, directly or indirectly,
all or substantially all its assets to, any Person, unless:

          (1) the resulting, surviving or transferee Person (the "Successor
                                                                  ---------
     Company") shall be a Person organized and existing under the laws of the
     -------
     United States of America, any State thereof or the District of Columbia and
     the Successor Company (if not the Company) shall expressly assume, by an
     indenture supplemental hereto, executed and delivered to the Trustee, in
     form satisfactory to the Trustee, all the obligations of the Company under
     the Securities and this Indenture;

          (2) immediately after giving pro forma effect to such transaction (and
     treating any Indebtedness which becomes an obligation of the Successor
     Company or any Subsidiary as a result of such transaction as having been
     Incurred by such Successor Company or such Subsidiary at the time of such
     transaction), no Default shall have occurred and be continuing;

          (3) immediately after giving pro forma effect to such transaction, the
     Successor Company would be able to Incur an additional $1.00 of
     Indebtedness pursuant to Section 4.03(a);

          (4) immediately after giving pro forma effect to such transaction, the
     Successor Company shall have Consolidated Net Worth in an amount that is
     not less than the Consolidated Net Worth of the Company immediately prior
     to such transaction;

          (5) the Company shall have delivered to the Trustee an Officers'
     Certificate and an Opinion of Counsel, each stating that such
     consolidation, merger or transfer and such supplemental indenture (if any)
     comply with this Indenture; and

          (6) the Company shall have delivered to the Trustee an Opinion of
     Counsel to the effect that the Holders will not recognize income, gain or
     loss for Federal income tax purposes as a result of such
<PAGE>

                                                                              63

     transaction and will be subject to Federal income tax on the same amounts,
     in the same manner and at the same times as would have been the case if
     such transaction had not occurred;

provided, however, that clauses (3) and (4) will not be applicable to (A) a
--------  -------
Restricted Subsidiary consolidating with, merging into or transferring all or
part of its properties and assets to the Company or (B) the Company merging with
an Affiliate of the Company solely for the purpose and with the sole effect of
reincorporating the Company in another jurisdiction.

          The Successor Company shall be the successor to the Company and shall
succeed to, and be substituted for, and may exercise every right and power of,
the Company under this Indenture, but the predecessor Company in the case of a
conveyance, transfer or lease shall not be released from this obligation to pay
the principal of and interest on the Securities.

          (b)  The Company shall not permit any Subsidiary Guarantor to
consolidate with or merge with or into, or convey, transfer or lease, in one
transaction or a series of transactions, all or substantially all of its assets
to any Person unless:

          (1) except in the case of a Subsidiary Guarantor (other than MK-Ohio)
     that has been disposed of its entirety to another Person (other than to the
     Company or an Affiliate of the Company), whether through a merger,
     consolidation or sale of Capital Stock or assets, if in connection
     therewith the Company provides an Officers' Certificate to the Trustee to
     the effect that the Company will comply with its obligations under Section
     4.07 in respect of such disposition, the resulting, surviving or transferee
     Person (if not such Subsidiary) shall be a Person organized and existing
     under the laws of the jurisdiction under which such Subsidiary was
     organized or under the laws of the United States of America, or any State
     thereof or the District of Columbia, and such Person shall expressly
     assume, by a Guaranty Agreement, in a form satisfactory to the Trustee, all
     the obligations of such Subsidiary, if any, under its Subsidiary Guaranty;

          (2) immediately after giving effect to such transaction or
     transactions on a pro forma basis (and treating any Indebtedness which
     becomes an obligation of the resulting, surviving or transferee Person as a
<PAGE>

                                                                              64

     result of such transaction as having been issued by such Person at the time
     of such transaction), no Default shall have occurred and be continuing; and

          (3) the Company delivers to the Trustee an Officers' Certificate and
     an Opinion of Counsel, each stating that such consolidation, merger or
     transfer and such Guaranty Agreement, if any, complies with this Indenture.

                                  ARTICLE VI

                             Defaults and Remedies
                             ---------------------

          SECTION 6.01.  Events of Default.  An "Event of Default" occurs if:
                         -----------------

          (1) the Company defaults in any payment of interest on any Security
     when the same becomes due and payable, and such default continues for a
     period of 30 days;

          (2) the Company (i) defaults in the payment of the principal of any
     Security when the same becomes due and payable at its Stated Maturity, upon
     optional redemption, upon declaration or otherwise, or (ii) fails to
     purchase Securities when required pursuant to this Indenture or the
     Securities;

          (3) the Company fails to comply with Section 5.01;

          (4) the Company fails to comply with Section 4.02, 4.03, 4.04, 4.05,
     4.06, 4.07, 4.08, 4.09, 4.10, 4.11, 4.12 or 4.13 (other than a failure to
     purchase Securities when required under Section 4.07 or 4.10) and such
     failure continues for 30 days after the notice specified below;

          (5) the Company or a Subsidiary Guarantor fails to comply with any of
     its agreements in the Securities or this Indenture (other than those
     referred to in clause (1), (2), (3) or (4) above) and such failure
     continues for 60 days after the notice specified below;

          (6) Indebtedness of the Company or any Significant Subsidiary is not
     paid within any applicable grace period after final maturity or is
     accelerated by the holders thereof because of a default and the total
     amount of such Indebtedness unpaid or accelerated
<PAGE>

                                                                              65

     exceeds $25.0 million, or its foreign currency equivalent at the time;

          (7) the Company or any Significant Subsidiary pursuant to or within
     the meaning of any Bankruptcy Law:

               (A) commences a voluntary case;

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

               (C) consents to the appointment of a Custodian of it or for any
          substantial part of its property; or

               (D) makes a general assignment for the benefit of its creditors;

or takes any comparable action under any foreign laws relating to insolvency;

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

               (A) is for relief against the Company or any Significant
          Subsidiary in an involuntary case;

               (B) appoints a Custodian of the Company or any Significant
          Subsidiary or for any substantial part of its property; or

               (C) orders the winding up or liquidation of the Company or any
          Significant Subsidiary;

     or any similar relief is granted under any foreign laws and the order or
     decree remains unstayed and in effect for 60 days;

          (9) any judgment or decree for the payment of money in excess of $25.0
     million or its foreign currency equivalent at the time is entered against
     the Company or any Significant Subsidiary, remains undischarged, unstayed
     or unsatisfied for a period of 60 days following the entry of such judgment
     or decree and is not discharged, waived or the execution thereof stayed
     within 10 days after the notice specified below; or
<PAGE>

                                                                              66

          (10) a Subsidiary Guaranty ceases to be in full force and effect
     (other than in accordance with the terms of such Subsidiary Guaranty) or a
     Subsidiary Guarantor denies or disaffirms its obligations under its
     Subsidiary Guaranty.

          The foregoing will constitute Events of Default whatever the reason
for any such Event of Default and whether it is voluntary or involuntary or is
effected by operation of law or pursuant to any judgment, decree or order of any
court or any order, rule or regulation of any administrative or governmental
body.

          The term "Bankruptcy Law" means Title 11, United States Code, or any
                                                    ------------------
similar Federal or state law for the relief of debtors.  The term "Custodian"
means any receiver, trustee, assignee, liquidator, custodian or similar official
under any Bankruptcy Law.

          A Default under clauses (4), (5) or (9) is not an Event of Default
until the Trustee or the holders of at least 25% in principal amount of the
outstanding Securities notify the Company of the Default and the Company does
not cure such Default within the time specified after receipt of such notice.
Such notice must specify the Default, demand that it be remedied and state that
such notice is a "Notice of Default".

          The Company shall deliver to the Trustee, within 30 days after the
occurrence thereof, written notice in the form of an Officers' Certificate of
any Event of Default under clause (6) or (10) and any event which with the
giving of notice or the lapse of time would become an Event of Default under
clause (4), (5) or (9), its status and what action the Company is taking or
proposes to take with respect thereto.

          SECTION 6.02.  Acceleration.  If an Event of Default (other than an
                         ------------
Event of Default specified in Section 6.01(7) or (8) with respect to the
Company) occurs and is continuing, the Trustee by notice to the Company, or the
Holders of at least 25% in principal amount of the Securities by notice to the
Company and the Trustee, may declare the principal of and accrued but unpaid
interest on all the Securities to be due and payable.  Upon such a declaration,
such principal and interest shall be due and payable immediately.  If an Event
of Default specified in Section 6.01(7) or (8) with respect to the Company
occurs, the principal of and interest on all the Securities shall ipso facto
                                                                  ---- -----
become and be immediately due and payable without
<PAGE>

                                                                              67

any declaration or other act on the part of the Trustee or any Securityholders.
The Holders of a majority in principal amount of the Securities by notice to the
Trustee may rescind an acceleration and its consequences if the rescission would
not conflict with any judgment or decree and if all existing Events of Default
have been cured or waived except nonpayment of principal or interest that has
become due solely because of acceleration. No such rescission shall affect any
subsequent Default or impair any right consequent thereto.

          SECTION 6.03.  Other Remedies.  If an Event of Default occurs and is
                         --------------
continuing, the Trustee may pursue any available remedy to collect the payment
of principal of or interest on the Securities or to enforce the performance of
any provision of the Securities or this Indenture.

          The Trustee may maintain a proceeding even if it does not possess any
of the Securities or does not produce any of them in the proceeding.  A delay or
omission by the Trustee or any Securityholder in exercising any right or remedy
accruing upon an Event of Default shall not impair the right or remedy or
constitute a waiver of or acquiescence in the Event of Default.  No remedy is
exclusive of any other remedy.  All available remedies are cumulative.

          SECTION 6.04.  Waiver of Past Defaults.  The Holders of a majority in
                         -----------------------
principal amount of the Securities by notice to the Trustee may waive an
existing Default and its consequences except (i) a Default in the payment of the
principal of or interest on a Security (ii) a Default arising from the failure
to redeem or purchase any Security when required pursuant to this Indenture or
(iii) a Default in respect of a provision that under Section 9.02 cannot be
amended without the consent of each Securityholder affected. When a Default is
waived, it is deemed cured, but no such waiver shall extend to any subsequent or
other Default or impair any consequent right.

          SECTION 6.05.  Control by Majority.  The Holders of a majority in
                         -------------------
principal amount of the Securities may direct the time, method and place of
conducting any proceeding for any remedy available to the Trustee or of
exercising any trust or power conferred on the Trustee.  However, the Trustee
may refuse to follow any direction that conflicts with law or this Indenture or,
subject to Section 7.01, that the Trustee determines is unduly prejudicial to
the rights of other Securityholders or would involve the Trustee in personal
liability; provided, however, that the Trustee may take any other action deemed
           --------  -------
proper by the Trustee that is
<PAGE>

                                                                              68

not inconsistent with such direction. Prior to taking any action hereunder, the
Trustee shall be entitled to indemnification satisfactory to it in its sole
discretion against all losses and expenses caused by taking or not taking such
action.

          SECTION 6.06.  Limitation on Suits.  Except to enforce the right to
                         -------------------
receive payment of principal, premium (if any) or interest when due, no
Securityholder may pursue any remedy with respect to this Indenture or the
Securities unless:

          (1) the Holder gives to the Trustee written notice stating that an
     Event of Default is continuing;

          (2) the Holders of at least 25% in principal amount of the Securities
     make a written request to the Trustee to pursue the remedy;

          (3) such Holder or Holders offer to the Trustee reasonable security or
     indemnity against any loss, liability or expense;

          (4) the Trustee does not comply with the request within 60 days after
     receipt of the request and the offer of security or indemnity; and

          (5) the Holders of a majority in principal amount of the Securities do
     not give the Trustee a direction inconsistent with the request during such
     60-day period.

          A Securityholder may not use this Indenture to prejudice the rights of
another Securityholder or to obtain a preference or priority over another
Securityholder.

          SECTION 6.07.  Rights of Holders To Receive Payment.  Notwithstanding
                         ------------------------------------
any other provision of this Indenture, the right of any Holder to receive
payment of principal of and interest on the Securities held by such Holder, on
or after the respective due dates expressed in the Securities, or to bring suit
for the enforcement of any such payment on or after such respective dates, shall
not be impaired or affected without the consent of such Holder.

          SECTION 6.08.  Collection Suit by Trustee.  If an Event of Default
                         --------------------------
specified in Section 6.01(1) or (2) occurs and is continuing, the Trustee may
recover judgment in its own name and as trustee of an express trust against the
Company for the whole amount then due and owing (together
<PAGE>

                                                                              69

with interest on any unpaid interest to the extent lawful) and the amounts
provided for in Section 7.07.

          SECTION 6.09.  Trustee May File Proofs of Claim. The Trustee may file
                         ---------------------------------
such proofs of claim and other papers or documents as may be necessary or
advisable in order to have the claims of the Trustee and the Securityholders
allowed in any judicial proceedings relative to the Company, its creditors or
its property and, unless prohibited by law or applicable regulations, may vote
on behalf of the Holders in any election of a trustee in bankruptcy or other
Person performing similar functions, and any Custodian in any such judicial
proceeding is hereby authorized by each Holder to make 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 its counsel, and any other amounts due the Trustee under Section
7.07.

          SECTION 6.10.  Priorities.  If the Trustee collects any money or
                         -----------
property pursuant to this Article VI, it shall pay out the money or property in
the following order:

          FIRST:  to the Trustee for amounts due under Section 7.07;

          SECOND: to Securityholders for amounts due and unpaid on the
     Securities for principal and interest, ratably, without preference or
     priority of any kind, according to the amounts due and payable on the
     Securities for principal and interest, respectively; and

          THIRD:  to the Company.

          The Trustee may fix a record date and payment date for any payment to
Securityholders pursuant to this Section. At least 15 days before such record
date, the Company shall mail to each Securityholder and the Trustee a notice
that states the record date, the payment date and amount to be paid.

          SECTION 6.11.  Undertaking for Costs.  In any suit for the enforcement
                         ----------------------
of any right or remedy under this Indenture or in any suit against the Trustee
for any action taken or omitted by it as Trustee, a court in its discretion may
require the filing by any party litigant in the suit of an undertaking to pay
the costs of the suit, and the court in its discretion may assess reasonable
costs, including rea-
<PAGE>

                                                                              70

sonable attorneys' fees, against any party litigant in the suit, having due
regard to the merits and good faith of the claims or defenses made by the party
litigant. This Section does not apply to a suit by the Trustee, a suit by a
Holder pursuant to Section 6.07 or a suit by Holders of more than 10% in
principal amount of the Securities.

          SECTION 6.12.  Waiver of Stay or Extension Laws. The Company (to the
                         ---------------------------------
extent it may lawfully do so) shall not at any time insist upon, or plead, or in
any manner whatsoever claim or take the benefit or advantage of, any stay or
extension law wherever enacted, now or at any time hereafter in force, which may
affect the covenants or the performance of this Indenture; and the Company (to
the extent that it may lawfully do so) hereby expressly waives all benefit or
advantage of any such law, and shall not hinder, delay or impede the execution
of any power herein granted to the Trustee, but shall suffer and permit the
execution of every such power as though no such law had been enacted.


                                  ARTICLE VII

                                    Trustee
                                    -------

          SECTION 7.01.  Duties of Trustee.  (a)  If an Event of Default has
                         ------------------
occurred and is continuing, the Trustee shall exercise the rights and powers
vested in it by this Indenture and use the same degree of care and skill in
their exercise as a prudent person would exercise or use under the circumstances
in the conduct of such person's own affairs.

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

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

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

                                                                              71

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

          (1) this paragraph does not limit the effect of paragraph (b) of this
     Section;

          (2) 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; and

          (3) 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 6.05.

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

          (e)  The Trustee shall not be liable for interest on any money
received by it except as the Trustee may agree in writing with the Company.

          (f)  Money held in trust by the Trustee need not be segregated from
other funds except to the extent required by law.

          (g)  No provision of this Indenture shall require the Trustee to
expend or risk its own funds or otherwise incur financial liability in the
performance of any of its duties hereunder or in the exercise of any of its
rights or powers, if it shall have reasonable grounds to believe that repayment
of such funds or adequate indemnity against such risk or liability is not
reasonably assured to it.

          (h)  Every provision of this Indenture relating to the conduct or
affecting the liability of or affording protection to the Trustee shall be
subject to the provisions of this Section and to the provisions of the TIA.

          SECTION 7.02.  Rights of Trustee.  (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.

          (b)  Before the Trustee acts or refrains from acting, it may require
an Officers' Certificate or an Opin-
<PAGE>

                                                                              72

ion of Counsel. The Trustee shall not be liable for any action it takes or omits
to take in good faith in reliance on the Officers' Certificate or Opinion of
Counsel.

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

          (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; provided, however, that the Trustee's conduct does not constitute wilful
        --------  -------
misconduct or negligence.

          (e)  The Trustee may consult with counsel, and the advice or opinion
of counsel with respect to legal matters relating to this Indenture and the
Securities shall be full and complete authorization and protection from
liability in respect to any action taken, omitted or suffered by it hereunder in
good faith and in accordance with the advice or opinion of such counsel.

          SECTION 7.03.  Individual Rights of Trustee.  The Trustee in its
                         -----------------------------
individual or any other capacity may become the owner or pledgee of Securities
and may otherwise deal with the Company or its Affiliates with the same rights
it would have if it were not Trustee. Any Paying Agent, Registrar, co-registrar
or co-paying agent may do the same with like rights. However, the Trustee must
comply with Sections 7.10 and 7.11.

          SECTION 7.04.  Trustee's Disclaimer. The Trustee shall not be
                         ---------------------
responsible for and makes no representation as to the validity or adequacy of
this Indenture or the Securities, it shall not be accountable for the Company's
use of the proceeds from the Securities, and it shall not be responsible for any
statement of the Company in this Indenture or in any document issued in
connection with the sale of the Securities or in the Securities other than the
Trustee's certificate of authentication.

          SECTION 7.05.  Notice of Defaults. If a Default occurs and is
                         -------------------
continuing and if it is known to the Trustee, the Trustee shall mail to each
Securityholder notice of the Default within 90 days after it occurs.  Except in
the case of a Default in payment of principal of or interest on any Security
(including payments pursuant to the mandatory redemption provisions of such
Security, if any), the Trustee may withhold the notice if and so long as a
committee of its
<PAGE>

                                                                              73

Trust Officers in good faith determines that withholding the notice is in the
interests of Securityholders.

          SECTION 7.06.  Reports by Trustee to Holders. As promptly as
                         ------------------------------
practicable after each July 1 beginning with the July 1 following the date of
this Indenture, and in any event prior to September 1 in each year, the Trustee
shall mail to each Securityholder a brief report dated as of July 1 that
complies with TIA (S) 313(a). The Trustee also shall comply with TIA (S) 313(b).

          A copy of each report at the time of its mailing to Securityholders
shall be filed with the SEC and each stock exchange (if any) on which the
Securities are listed. The Company agrees to notify promptly the Trustee
whenever the Securities become listed on any stock exchange and of any delisting
thereof.

          SECTION 7.07.  Compensation and Indemnity. The Company shall pay to
                         ---------------------------
the Trustee from time to time reasonable compensation for its services. The
Trustee's compensation shall not be limited by any law on compensation of a
trustee of an express trust. The Company shall reimburse the Trustee upon
request for all reasonable out-of-pocket expenses incurred or made by it,
including costs of collection, in addition to the compensation for its services.
Such expenses shall include the reasonable compensation and expenses,
disbursements and advances of the Trustee's agents, counsel, accountants and
experts. The Company shall indemnify the Trustee against any and all loss,
liability or expense (including attorneys' fees) incurred by it in connection
with the administration of this trust and the performance of its duties
hereunder. The Trustee shall notify the Company promptly of any claim for which
it may seek indemnity. Failure by the Trustee to so notify the Company shall not
relieve the Company of its obligations hereunder. The Company shall defend the
claim and the Trustee may have separate counsel and the Company shall pay the
fees and expenses of such counsel. The Company need not reimburse any expense or
indemnify against any loss, liability or expense incurred by the Trustee through
the Trustee's own wilful misconduct, negligence or bad faith.

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

                                                                              74

          The Company's payment obligations pursuant to this Section shall
survive the discharge of this Indenture. When the Trustee incurs expenses after
the occurrence of a Default specified in Section 6.01(7) or (8) with respect to
the Company, the expenses are intended to constitute expenses of administration
under the Bankruptcy Law.

          SECTION 7.08.  Replacement of Trustee. The Trustee may resign at any
                         -----------------------
time by so notifying the Company. The Holders of a majority in principal amount
of the Securities may remove the Trustee by so notifying the Trustee and may
appoint a successor Trustee. The Company shall remove the Trustee if:

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

          (2) the Trustee is adjudged bankrupt or insolvent;

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

          (4) the Trustee otherwise becomes incapable of acting.

          If the Trustee resigns, is removed by the Company or by the Holders of
a majority in principal amount of the Securities and such Holders do not
reasonably promptly appoint a successor Trustee, or if a vacancy exists in the
office of Trustee for any reason (the Trustee in such event being referred to
herein as the retiring Trustee), the Company shall promptly appoint a successor
Trustee.

          A successor Trustee shall deliver a written acceptance of its
appointment to the retiring Trustee and to the Company. Thereupon 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. The successor Trustee shall mail a notice of its
succession to Securityholders. The retiring Trustee shall promptly transfer all
property held by it as Trustee to the successor Trustee, subject to the lien
provided for in Section 7.07.

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

                                                                              75

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

          Notwithstanding the replacement of the Trustee pursuant to this
Section, the Company's obligations under Section 7.07 shall continue for the
benefit of the retiring Trustee.

          SECTION 7.09.  Successor Trustee by Merger. If the Trustee
                         ----------------------------
consolidates with, merges or converts into, or transfers all or substantially
all its corporate trust business or assets to, another corporation or banking
association, the resulting, surviving or transferee corporation without any
further act shall be the successor Trustee.

          In case at the time such successor or successors by merger, conversion
or consolidation to the Trustee shall succeed to the trusts created by this
Indenture any of the Securities shall have been authenticated but not delivered,
any such successor to the Trustee may adopt the certificate of authentication of
any predecessor trustee, and deliver such Securities so authenticated; and in
case at that time any of the Securities shall not have been authenticated, any
successor to the Trustee may authenticate such Securities either in the name of
any predecessor hereunder or in the name of the successor to the Trustee; and in
all such cases such certificates shall have the full force which it is anywhere
in the Securities or in this Indenture provided that the certificate of the
Trustee shall have.

          SECTION 7.10.  Eligibility; Disqualification. The Trustee shall at all
                         ------------------------------
times satisfy the requirements of TIA (S) 310(a). The Trustee shall have a
combined capital and surplus of at least $50.0 million as set forth in its most
recent published annual report of condition. The Trustee shall comply with TIA
(S) 310(b); provided, however, that there shall be excluded from the operation
            --------  -------
of TIA (S) 310(b)(1) any indenture or indentures under which other securities or
certificates of interest or participation in other securities of the Company are
outstanding if the requirements for such exclusion set forth in TIA (S)
310(b)(1) are met.


          SECTION 7.11.  Preferential Collection of Claims Against Company. The
                         --------------------------------------------------
Trustee shall comply with TIA (S) 311(a), excluding any creditor relationship
listed in TIA (S) 311(b). A Trustee who has resigned or been removed shall be
subject to TIA (S) 311(a) to the extent indicated.
<PAGE>

                                                                              76

                                 ARTICLE VIII

                      Discharge of Indenture; Defeasance
                      ----------------------------------

          SECTION 8.01.  Discharge of Liability on Securities; Defeasance. (a)
                         -------------------------------------------------
When (1) the Company delivers to the Trustee all outstanding Securities (other
than Securities replaced pursuant to Section 2.07) for cancellation or (2) all
outstanding Securities have become due and payable, whether at maturity or on a
redemption date as a result of the mailing of a notice of redemption pursuant to
Article III hereof and the Company irrevocably deposits with the Trustee funds
sufficient to pay at maturity or upon redemption all outstanding Securities,
including interest thereon to maturity or such redemption date (other than
Securities replaced pursuant to Section 2.07), and if in either case the Company
pays all other sums payable hereunder by the Company, then this Indenture shall,
subject to Section 8.01(c), cease to be of further effect. The Trustee shall
acknowledge satisfaction and discharge of this Indenture on demand of the
Company accompanied by an Officers' Certificate and an Opinion of Counsel and at
the cost and expense of the Company.

          (b)  Subject to Sections 8.01(c) and 8.02, the Company at any time may
terminate (1) all its obligations under the Securities and this Indenture
("legal defeasance option") or (2) its obligations under Sections 4.02, 4.03,
4.04, 4.05, 4.06, 4.07, 4.08, 4.09, 4.10, 4.11, 4.12 and 4.13 and the operation
of Sections 6.01(4), 6.01(6), 6.01(7), 6.01(8) and 6.01(9) (but, in the case of
Sections 6.01(7) and (8), with respect only to Significant Subsidiaries) and the
limitations contained in Sections 5.01(a)(3) and (4) ("covenant defeasance
option"). The Company may exercise its legal defeasance option notwithstanding
its prior exercise of its covenant defeasance option.

          If the Company exercises its legal defeasance option, payment of the
Securities may not be accelerated because of an Event of Default with respect
thereto. If the Company exercises its covenant defeasance option, payment of the
Securities may not be accelerated because of an Event of Default specified in
Sections 6.01(4), 6.01(6), 6.01(7), 6.01(8) and 6.01(9) (but, in the case of
Sections 6.01(7) and (8), with respect only to Significant Subsidiaries) or
because of the failure of the Company to comply with Section 5.01(a)(3) or (4).
If the Company exercises its legal defeasance option or its covenant defeasance
option,
<PAGE>

                                                                              77

each Subsidiary Guarantor, if any, shall be released from all its obligations
with respect to its Subsidiary Guaranty.

          Upon satisfaction of the conditions set forth herein and upon request
of the Company, the Trustee shall acknowledge in writing the discharge of those
obligations that the Company terminates.

          (c)  Notwithstanding clauses (a) and (b) above, the Company's
obligations in Sections 2.03, 2.04, 2.05, 2.06, 2.07, 2.08, 7.07 and 7.08 and in
this Article VIII shall survive until the Securities have been paid in full.
Thereafter, the Company's obligations in Sections 7.07, 8.04 and 8.05 shall
survive.

          SECTION 8.02.  Conditions to Defeasance. The Company may exercise its
                         -------------------------
legal defeasance option or its covenant defeasance option only if:

          (1) the Company irrevocably deposits in trust with the Trustee money
     or U.S. Government Obligations for the payment of principal of and interest
     on the Securities to maturity or redemption, as the case may be;

          (2) the Company delivers to the Trustee a certificate from a
     nationally recognized firm of independent accountants expressing their
     opinion that the payments of principal and interest when due and without
     reinvestment on the deposited U.S. Government Obligations plus any
     deposited money without investment will provide cash at such times and in
     such amounts as will be sufficient to pay principal and interest when due
     on all the Securities to maturity or redemption, as the case may be;

          (3) 123 days pass after the deposit is made and during the 123-day
     period no Default specified in Sections 6.01(7) or (8) with respect to the
     Company occurs which is continuing at the end of the period;

          (4) the deposit does not constitute a default under any other
     agreement binding on the Company;

          (5) the Company delivers to the Trustee an Opinion of Counsel to the
     effect that the trust resulting from the deposit does not constitute, or is
     qualified as, a regulated investment company under the Investment Company
     Act of 1940;
<PAGE>
                                                                              78

          (6) in the case of the legal defeasance option, the Company shall have
     delivered to the Trustee an Opinion of Counsel stating that (A) the Company
     has received from, or there has been published by, the Internal Revenue
     Service a ruling, or (B) since the date of this Indenture there has been a
     change in the applicable Federal income tax law, in either case to the
     effect that, and based thereon such Opinion of Counsel shall confirm that,
     the Securityholders will not recognize income, gain or loss for Federal
     income tax purposes as a result of such defeasance and will be subject to
     Federal income tax on the same amounts, in the same manner and at the same
     times as would have been the case if such defeasance had not occurred;

          (7) in the case of the covenant defeasance option, the Company shall
     have delivered to the Trustee an Opinion of Counsel to the effect that the
     Security-holders will not recognize income, gain or loss for Federal income
     tax purposes as a result of such covenant defeasance and will be subject to
     Federal income tax on the same amounts, in the same manner and at the same
     times as would have been the case if such covenant defeasance had not
     occurred; and

          (8) the Company delivers to the Trustee an Officers' Certificate and
     an Opinion of Counsel, each stating that all conditions precedent to the
     defeasance and discharge of the Securities as contemplated by this Article
     VIII have been complied with.

          Before or after a deposit, the Company may make arrangements
satisfactory to the Trustee for the redemption of Securities at a future date in
accordance with Article III.

          SECTION 8.03.  Application of Trust Money.  The Trustee shall hold in
                         ---------------------------
trust money or U.S. Government Obligations deposited with it pursuant to this
Article VIII. It shall apply the deposited money and the money from U.S.
Government Obligations through the Paying Agent and in accordance with this
Indenture to the payment of principal of and interest on the Securities.

          SECTION 8.04.  Repayment to Company. The Trustee and the Paying Agent
                         ---------------------
shall promptly turn over to the Company upon request any excess money or
securities held by them at any time.
<PAGE>

                                                                              79

          Subject to any applicable abandoned property law, the Trustee and the
Paying Agent shall pay to the Company upon request any money held by them for
the payment of principal or interest that remains unclaimed for two years, and,
thereafter, Securityholders entitled to the money must look to the Company for
payment as general creditors.

          SECTION 8.05.  Indemnity for Government Obligations. The Company shall
                         -------------------------------------
pay and shall indemnify the Trustee against any tax, fee or other charge imposed
on or assessed against deposited U.S. Government Obligations or the principal
and interest received on such U.S. Government Obligations.

          SECTION 8.06.  Reinstatement. If the Trustee or Paying Agent is unable
                         --------------
to apply any money or U.S. Government Obligations in accordance with this
Article VIII by reason of any legal proceeding or by reason of any order or
judgment of any court or governmental authority enjoining, restraining or
otherwise prohibiting such application, the Company's obligations under this
Indenture and the Securities shall be revived and reinstated as though no
deposit had occurred pursuant to this Article VIII until such time as the
Trustee or Paying Agent is permitted to apply all such money or U.S. Government
Obligations in accordance with this Article VIII; provided, however, that, if
                                                  --------  -------
the Company has made any payment of interest on or principal of any Securities
because of the reinstatement of its obligations, the Company shall be subrogated
to the rights of the Holders of such Securities to receive such payment from the
money or U.S. Government Obligations held by the Trustee or Paying Agent.


                                  ARTICLE IX

                                  Amendments
                                  ----------

          SECTION 9.01.  Without Consent of Holders. The Company, the Subsidiary
                         ---------------------------
Guarantors and the Trustee may amend this Indenture or the Securities without
notice to or consent of any Securityholder:

          (1) to cure any ambiguity, omission, defect or inconsistency;

          (2) to comply with Article V;

          (3) to provide for uncertificated Securities in addition to or in
     place of certificated Securities;
<PAGE>

                                                                              80

     provided, however, that the uncertificated Securities are issued in
     --------  -------
     registered form for purposes of Section 163(f) of the Code or in a manner
     such that the uncertificated Securities are described in Section
     163(f)(2)(B) of the Code;

          (4) to add guarantees with respect to the Securities, including any
     Subsidiary Guaranties, or to secure the Securities;

          (5) to add to the covenants of the Company or a Subsidiary Guarantor
     for the benefit of the Holders or to surrender any right or power herein
     conferred upon the Company or a Subsidiary Guarantor;

          (6) to comply with any requirements of the SEC in connection with
     qualifying, or maintaining the qualification of, this Indenture under the
     TIA; or

          (7) to make any change that does not adversely affect the rights of
     any Securityholder.

          After an amendment under this Section becomes effective, the Company
shall mail to Securityholders a notice briefly describing such amendment. The
failure to give such notice to all Securityholders, or any defect therein, shall
not impair or affect the validity of an amendment under this Section.

          SECTION 9.02.  With Consent of Holders. The Company, the Subsidiary
                         ------------------------
Guarantors and the Trustee may amend this Indenture or the Securities without
notice to any Securityholder but with the written consent of the Holders of a
majority in principal amount of the Securities then outstanding (including
consents obtained in connection with a tender offer or exchange for the
Securities). However, without the consent of each Securityholder affected
thereby, an amendment may not:

          (1) reduce the amount of Securities whose Holders must consent to an
     amendment;

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

          (3) reduce the principal amount of or extend the Stated Maturity of
     any Security;

          (4) reduce the amount payable upon the redemption of any Security or
     change the time at which any
<PAGE>

                                                                              81

     Security may be redeemed in accordance with Article III;

          (5) make any Security payable in money other than that stated in the
     Security;

          (6) make any changes in the ranking or priority of any Security that
     would adversely affect the Securityholders;

          (7) make any change in Section 6.04 or 6.07 or the second sentence of
     this Section; or

          (8) make any change in any Subsidiary Guaranty that would adversely
     affect the Securityholders.

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

          After an amendment under this Section becomes effective, the Company
shall mail to Securityholders a notice briefly describing such amendment. The
failure to give such notice to all Securityholders, or any defect therein, shall
not impair or affect the validity of an amendment under this Section.

          SECTION 9.03.  Compliance with Trust Indenture Act. Every amendment to
                         ------------------------------------
this Indenture or the Securities shall comply with the TIA as then in effect.

          SECTION 9.04.  Revocation and Effect of Consents and Waivers. A
                         ----------------------------------------------
consent to an amendment or a waiver by a Holder of a Security shall bind the
Holder and every subse-quent Holder of that Security or portion of the Security
that evidences the same debt as the consenting Holder's Security, even if
notation of the consent or waiver is not made on the Security. However, any such
Holder or subse-quent Holder may revoke the consent or waiver as to such
Holder's Security or portion of the Security if the Trustee receives the notice
of revocation before the date the amendment or waiver becomes effective. After
an amendment or waiver becomes effective, it shall bind every Security-holder.
An amendment or waiver becomes effective upon the execution of such amendment or
waiver by the Trustee.

          The Company may, but shall not be obligated to, fix a record date for
the purpose of determining the Securityholders entitled to give their consent or
take any

<PAGE>

                                                                              82

     other action described above or required or permitted to be taken pursuant
     to this Indenture. If a record date is fixed, then notwithstanding the
     immediately preceding paragraph, those Persons who were Securityholders at
     such record date (or their duly designated proxies), and only those
     Persons, shall be entitled to give such consent or to revoke any consent
     previously given or to take any such action, whether or not such Persons
     continue to be Holders after such record date. No such consent shall be
     valid or effective for more than 120 days after such record date.

          SECTION 9.05.  Notation on or Exchange of Securities.  If an
                         --------------------------------------
amendment changes the terms of a Security, the Trustee may require the Holder
of the security to deliver it to Security to deliver it to the Trustee. The
Trustee may place an appropriate notation on the Security regarding 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 the Trustee
shall authenticate a new Security that reflects the changed terms. Failure to
make the appropriate notation or to issue a new Security shall not affect the
validity of such amendment.

          SECTION 9.06.  Trustee To Sign Amendments.  The Trustee shall sign any
                         ---------------------------
amendment authorized pursuant to this Article IX if the amendment does not
adversely affect the rights, duties, liabilities or immunities of the Trustee.
If it does, the Trustee may but need not sign it.  In signing such amendment the
Trustee shall be entitled to receive indemnity reasonably satisfactory to it and
to receive, and (subject to Section 7.01) shall be fully protected in relying
upon, an Officers' Certificate and an Opinion of Counsel stating that such
amendment is authorized or permitted by this Indenture.

          SECTION 9.07.  Payment for Consent.  Neither the Company nor any
                         --------------------
Affiliate of the Company shall, directly or indirectly, pay or cause to be paid
any consideration, whether by way of interest, fee or otherwise, to any Holder
for or as an inducement to any consent, waiver or amendment of any of the terms
or provisions of this Indenture or the Securities unless such consideration is
offered to be paid to all Holders that so consent, waive or agree to amend in
the time frame set forth in solicitation documents relating to such consent,
waiver or agreement.
<PAGE>

                                                                              83

                                   ARTICLE X

                             Subsidiary Guaranties
                             ---------------------

          SECTION 10.01.  Guaranties.  Each Subsidiary Guarantor hereby
                          -----------
unconditionally and irrevocably guarantees, jointly and severally, to each
Holder and to the Trustee and its successors and assigns (a) the full and
punctual payment of principal of and interest on the Securities when due,
whether at maturity, by acceleration, by redemption or otherwise, and all other
monetary obligations of the Company under this Indenture and the Securities and
(b) the full and punctual performance within applicable grace periods of all
other obligations of the Company under this Indenture and the Securities (all
the foregoing being hereinafter collectively called the "Obligations").  Each
Subsidiary Guarantor further agrees that the Obligations may be extended or
renewed, in whole or in part, without notice or further assent from such
Subsidiary Guarantor and that such Subsidiary Guarantor will remain bound under
this Article X notwithstanding any extension or renewal of any Obligation.

          Each Subsidiary Guarantor waives presentation to, demand of, payment
from and protest to the Company of any of the Obligations and also waives notice
of protest for nonpayment.  Each Subsidiary Guarantor waives notice of any
default under the Securities or the Obligations.  The obligations of each
Subsidiary Guarantor hereunder shall not be affected by (a) the failure of any
Holder or the Trustee to assert any claim or demand or to enforce any right or
remedy against the Company or any other Person under this Indenture, the
Securities or any other agreement or otherwise; (b) any extension or renewal of
any thereof; (c) any rescission, waiver, amendment or modification of any of the
terms or provisions of this Indenture, the Securities or any other agreement;
(d) the release of any security held by any Holder or the Trustee for the
Obligations or any of them; (e) the failure of any Holder or the Trustee to
exercise any right or remedy against any other guarantor of the Obligations; or
(f) except as set forth in Section 10.06, any change in the ownership of such
Subsidiary Guarantor.

          Each Subsidiary Guarantor further agrees that its Subsidiary Guaranty
herein constitutes a guarantee of payment, performance and compliance when due
(and not a guarantee of collection) and waives any right to require that any
resort be had by any Holder or the Trustee to any security held for payment of
the Obligations.
<PAGE>

                                                                              84

          Except as expressly set forth in Sections 8.01(b), 10.02 and 10.06,
the obligations of each Subsidiary Guarantor hereunder shall not be subject to
any reduction, limitation, impairment or termination for any reason, including
any claim of waiver, release, surrender, alteration or compromise, and shall not
be subject to any defense of setoff, counterclaim, recoupment or termination
whatsoever or by reason of the invalidity, illegality or unenforceability of the
Obligations or otherwise.  Without limiting the generality of the foregoing, the
obligations of each Subsidiary Guarantor herein shall not be discharged or
impaired or otherwise affected by the failure of any Holder or the Trustee to
assert any claim or demand or to enforce any remedy under this Indenture, the
Securities or any other agreement, by any waiver or modification of any thereof,
by any default, failure or delay, wilful or otherwise, in the performance of the
obligations, or by any other act or thing or omission or delay to do any other
act or thing which may or might in any manner or to any extent vary the risk of
such Subsidiary Guarantor or would otherwise operate as a discharge of such
Subsidiary Guarantor as a matter of law or equity.

          Each Subsidiary Guarantor further agrees that its Guarantee herein
shall continue to be effective or be reinstated, as the case may be, if at any
time payment, or any part thereof, of principal of or interest on any Obligation
is rescinded or must otherwise be restored by any Holder or the Trustee upon the
bankruptcy or reorganization of the Company or otherwise.

          In furtherance of the foregoing and not in limitation of any other
right which any Holder or the Trustee has at law or in equity against any
Subsidiary Guarantor by virtue hereof, upon the failure of the Company to pay
the principal of or interest on any Obligation when and as the same shall become
due, whether at maturity, by acceleration, by redemption or otherwise, or to
perform or comply with any other Obligation, each Subsidiary Guarantor hereby
promises to and shall, upon receipt of written demand by the Trustee, forthwith
pay, or cause to be paid, in cash, to the Holders or the Trustee an amount equal
to the sum of (1) the unpaid amount of such Obligations, (2) accrued and unpaid
interest on such Obligations (but only to the extent not prohibited by law) and
(3) all other monetary Obligations of the Company to the Holders and the
Trustee.

          Each Subsidiary Guarantor agrees that, as between it, on the one hand,
and the Holders and the Trustee, on the other hand, (x) the maturity of the
Obligations Guaranteed
<PAGE>

                                                                              85

hereby may be accelerated as provided in Article VI for the purposes of such
Subsidiary Guarantor's Subsidiary Guaranty herein, notwithstanding any stay,
injunction or other prohibition preventing such acceleration in respect of the
Obligations Guaranteed hereby, and (y) in the event of any declaration of
acceleration of such Obligations as provided in Article VI, such Obligations
(whether or not due and payable) shall forthwith become due and payable by such
Subsidiary Guarantor for the purposes of this Section.

          Each Subsidiary Guarantor also agrees to pay any and all costs and
expenses (including reasonable attorneys' fees) incurred by the Trustee or any
Holder in enforcing any rights under this Section.

          SECTION 10.02.  Limitation on Liability.  Any term or provision of
                          ------------------------
this Indenture to the contrary notwithstanding, the maximum aggregate amount of
the Obligations Guaranteed hereunder by any Subsidiary Guarantor shall not
exceed the maximum amount that can be hereby Guaranteed without rendering this
Indenture, as it relates to such Subsidiary Guarantor, voidable under applicable
law relating to fraudulent conveyance or fraudulent transfer or similar laws
affecting the rights of creditors generally.

          SECTION 10.03.  Successors and Assigns.  This Article X shall be
                          -----------------------
binding upon each Subsidiary Guarantor and its successors and assigns and shall
enure to the benefit of the successors and assigns of the Trustee and the
Holders and, in the event of any transfer or assignment of rights by any Holder
or the Trustee, the rights and privileges conferred upon that party in this
Indenture and in the Securities shall automatically extend to and be vested in
such transferee or assignee, all subject to the terms and conditions of this
Indenture.

          SECTION 10.04.  No Waiver.  Neither a failure nor a delay on the part
                          ----------
of either the Trustee or the Holders in exercising any right, power or privilege
under this Article X shall operate as a waiver thereof, nor shall a single or
partial exercise thereof preclude any other or further exercise of any right,
power or privilege.  The rights, remedies and benefits of the Trustee and the
Holders herein expressly specified are cumulative and not exclusive of any other
rights, remedies or benefits which either may have under this Article X at law,
in equity, by statute or otherwise.

          SECTION 10.05.  Modification.  No modification, amendment or waiver of
                          -------------
any provision of this Article X, nor
<PAGE>

                                                                              86

the consent to any departure by any Subsidiary Guarantor therefrom, shall in any
event be effective unless the same shall be in writing and signed by the
Trustee, and then such waiver or consent shall be effective only in the specific
instance and for the purpose for which given. No notice to or demand on any
Subsidiary Guarantor in any case shall entitle such Subsidiary Guarantor to any
other or further notice or demand in the same, similar or other circumstances.

          SECTION 10.06.  Release of Subsidiary Guarantor. Upon the sale or
                          --------------------------------
other disposition (including by way of consolidation or merger) of a Subsidiary
Guarantor or the sale or disposition of all or substantially all the assets of
such Subsidiary Guarantor (in each case other than a sale or disposition
involving MK-Ohio and other than a sale or disposition to the Company or an
Affiliate of the Company), or upon the release of a Subsidiary Guarantor from
all its Guaranties of Indebtedness that would require such Subsidiary Guarantor
to Guarantee the Securities pursuant to Section 4.13, such Subsidiary Guarantor
shall be deemed released from all obligations under this Article X without any
further action required on the part of the Trustee or any Holder.  At the
request and expense of the Company, and upon receipt of an Officers' Certificate
and an Opinion of Counsel (if requested by the Trustee), the Trustee shall
execute and deliver an appropriate instrument evidencing such release.

                                  ARTICLE XI

                                 Miscellaneous
                                 -------------

          SECTION 11.01.  Trust Indenture Act Controls.  If any provision of
                          -----------------------------
this Indenture limits, qualifies or conflicts with another provision which is
required to be included in this Indenture by the TIA, the required provision
shall control.
<PAGE>

                                                                              87

          SECTION 11.02.  Notices.  Any notice or communication shall be in
                          --------
writing and delivered in person or mailed by first-class mail addressed as
follows:

     if to the Company or any Subsidiary Guarantor:

               Morrison Knudsen Corporation
               720 Park Boulevard
               Boise, Idaho 83712

               Attention of General Counsel


     if to the Trustee:

               United States Trust Company of New York
               114 West 47th Street
               New York, New York 10036

               Attention of Corporate Trust Administration

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

          Any notice or communication mailed to a Securityholder shall be
mailed to the Securityholder at the Securityholder's address as it appears on
the registration books of the Registrar and shall be sufficiently given if so
mailed within the time prescribed.

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

          SECTION 11.03.  Communication by Holders with Other Holders.
                          --------------------------------------------
Securityholders may communicate pursuant to TIA (S) 312(b) with other
Securityholders with respect to their rights under this Indenture or the
Securities.  The Company, any Subsidiary Guarantor the Trustee, the Registrar
and anyone else shall have the protection of TIA (S) 312(c).

          SECTION 11.04.  Certificate and Opinion as to Conditions Precedent.
                          ---------------------------------------------------
Upon any request or application by the Company to the Trustee to take or refrain
from taking
<PAGE>

                                                                              88

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 11.05.  Statements Required in Certificate or Opinion.  Each
                          ----------------------------------------------
certificate or opinion with respect to compliance with a covenant or condition
provided for in this Indenture shall include:

          (1)  a statement that the individual 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;

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

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

          SECTION 11.06.  When Securities Disregarded.  In determining whether
                          ----------------------------
the Holders of the required principal amount of Securities have concurred in any
direction, waiver or consent, Securities owned by the Company or by any Person
directly or indirectly controlling or controlled by or under direct or indirect
common control with the Company shall be disregarded and deemed not to be
outstanding, except that, for the purpose of determining whether the Trustee
shall be protected in relying on any such direction, waiver or consent, only
Securities which the Trustee knows are so owned shall be so disregarded.  Also,
subject to the fore-
<PAGE>

                                                                              89

going, only Securities outstanding at the time shall be considered in any such
determination.

          SECTION 11.07.  Rules by Trustee, Paying Agent and Registrar.  The
                          ---------------------------------------------
Trustee may make reasonable rules for action by or a meeting of Securityholders.
The Registrar and the Paying Agent may make reasonable rules for their
functions.

          SECTION 11.08.  Legal Holidays.  A "Legal Holiday" is a Saturday, a
                          ---------------
Sunday or a day on which banking institutions are not required to be open in the
State of New York. If a payment date is a Legal Holiday, payment shall be made
on the next succeeding day that is not a Legal Holiday, and no interest shall
accrue for the intervening period.  If a regular record date is a Legal Holiday,
the record date shall not be affected.

          SECTION 11.09.  Governing Law.  THIS INDENTURE AND THE SECURITIES
                          --------------
SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF
NEW YORK BUT WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW
TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE
REQUIRED THEREBY.

          SECTION 11.10.  No Recourse Against Others.  A director, officer,
                          ---------------------------
employee or stockholder, as such, of the Company or any Subsidiary Guarantor
shall not have any liability for any obligations of the Company under the
Securities or this Indenture or of such Subsidiary Guarantor under its
Subsidiary Guaranty or this Indenture or for any claim based on, in respect of
or by reason of such obligations or their creation.  By accepting a Security,
each Securityholder shall waive and release all such liability.  The waiver and
release shall be part of the consideration for the issue of the Securities.

          SECTION 11.11.  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 11.12.  Multiple Originals.  The parties may sign any number
                          -------------------
of copies of this Indenture.  Each signed copy shall be an original, but all of
them together represent the same agreement.  One signed copy is enough to prove
this Indenture.

          SECTION 11.13.  Table of Contents; Headings.  The table of contents,
                          ----------------------------
cross-reference sheet and headings of the Articles and Sections of this
Indenture have been inserted
<PAGE>

                                                                              90

for convenience of reference only, are not intended to be considered a part
hereof and shall not modify or restrict any of the terms or provisions hereof.
<PAGE>

                                                                              91

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

                                              MORRISON KNUDSEN CORPORATION,

                                                by   /s/ Jonathan M. Robertson
                                                  -----------------------------
                                                 Name:  Jonathan M. Robertson
                                                 Title: Assistant Secretary

                                              EACH SUBSIDIARY GUARANTOR
                                              LISTED ON SCHEDULE A HERETO,

                                                by   /s/ Jonathan M. Robertson
                                                  -----------------------------
                                                 Name:  Jonathan M. Robertson
                                                 Title: Assistant Secretary


                                              UNITED STATES TRUST COMPANY OF
                                              NEW YORK,

                                                by  /s/ Christine C. Collins
                                                  -----------------------------
                                                 Name:  Christine C. Collins
                                                 Title: Assistant Vice President
<PAGE>

                                                 RULE 144A/REGULATION S APPENDIX


                  PROVISIONS RELATING TO INITIAL SECURITIES,
                  ------------------------------------------
                          PRIVATE EXCHANGE SECURITIES
                          ---------------------------
                           AND EXCHANGE SECURITIES
                           -----------------------

     1.  Definitions
         -----------
     1.1  Definitions
          -----------

     For the purposes of this Appendix the following terms shall have the
meanings indicated below:

          "Depository" means The Depository Trust Company, its nominees and
their respective successors.

          "Exchange Securities" means (1) the 11% Senior Notes Due July 1, 2010
issued pursuant to the Indenture in connection with a Registered Exchange Offer
pursuant to a Registration Rights Agreement and (2) Additional Securities, if
any, issued pursuant to a registration statement filed with the SEC under the
Securities Act.

          "Initial Purchasers" means (1) with respect to the Initial Securities
issued on the Issue Date, Credit Suisse First Boston Corporation, BMO Nesbitt
Burns Corp. and U.S. Bancorp Libra, a division of U.S. Bancorp Investments, Inc.
and (2) with respect to each issuance of Additional Securities, the Persons
purchasing such Additional Securities under the related Purchase Agreement.

          "Initial Securities" means (1) $300.0 million aggregate principal
amount of 11% Senior Notes Due July 1, 2010 issued on the Issue Date and (2)
Additional Securities, if any, issued in a transaction exempt from the
registration requirements of the Securities Act.

          "Private Exchange" means the offer by the Company, pursuant to a
Registration Rights Agreement, to the Initial Purchasers to issue and deliver to
each Initial Purchaser, in exchange for the Initial Securities held by the
Initial Purchaser as part of its initial distribution, a like aggregate
principal amount of Private Exchange Securities.

          "Private Exchange Securities" means any 11% Senior Notes Due July 1,
2010 issued in connection with a Private Exchange.

          "Purchase Agreement" means (1) with respect to the Initial Securities
issued on the Issue Date, the Purchase Agreement dated June 28, 2000, among the
Company, the Subsidiary Guarantors and the Initial Purchasers, as amended, and
(2) with respect to each issuance of Additional
<PAGE>

                                                                               2

Securities, the purchase agreement or underwriting agreement among the Company
and the Persons purchasing such Additional Securities.

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

          "Registered Exchange Offer" means the offer by the Company, pursuant
to a Registration Rights Agreement, to certain Holders of Initial Securities, to
issue and deliver to such Holders, in exchange for the Initial Securities, a
like aggregate principal amount of Exchange Securities registered under the
Securities Act.

          "Registration Rights Agreement" means (1) with respect to the Initial
Securities issued on the Issue Date, the Registration Rights Agreement dated
June 28, 2000, among the Company, the Subsidiary Guarantors and the Initial
Purchasers, as amended, and (2) with respect to each issuance of Additional
Securities issued in a transaction exempt from the registration requirements of
the Securities Act, the registration rights agreement, if any, among the Company
and the Persons purchasing such Additional Securities under the related Purchase
Agreement.

          "Securities" means the Initial Securities, the Exchange Securities and
the Private Exchange Securities, treated as a single class.

          "Securities Act" means the Securities Act of 1933.

          "Securities Custodian" means the custodian with respect to a Global
Security (as appointed by the Depository), or any successor Person thereto and
shall initially be the Trustee.

          "Shelf Registration Statement" means the registration statement issued
by the Company in connection with the offer and sale of Initial Securities or
Private Exchange Securities pursuant to a Registration Rights Agreement.

          "Transfer Restricted Securities" means Securities that bear or are
required to bear the legend set forth in Section 2.3(b)hereto.
<PAGE>

                                                                               3

     1.2  Other Definitions
          -----------------

                                                                 Defined in
          Term                                                     Section
          ----                                                     -------

"Agent Members".................................................  2.1(b)
"Global Security"...............................................  2.1(a)
"Regulation S"..................................................  2.1(a)
"Restricted Global Security"....................................  2.1(a)
"Rule 144A".....................................................  2.1(a)

     2.   The Securities.
          ---------------

     2.1  (a)  Form and Dating.  Initial Securities offered and sold to a QIB in
               ----------------
reliance on Rule 144A under the Securities Act ("Rule 144A") or in reliance on
Regulation S under the Securities Act ("Regulation S"), in each case as provided
in a Purchase Agreement, and Private Exchange Securities, as provided in a
Registration Rights Agreement, shall be issued initially in the form of one or
more permanent global Securities in definitive, fully registered form without
interest coupons with the global securities legend and restricted securities
legend set forth in Exhibit 1 hereto (each, a "Restricted Global Security"),
which shall be deposited on behalf of the purchasers of the Initial Securities
represented thereby with the Trustee, as custodian for the Depository (or with
such other custodian as the Depository may direct), and registered in the name
of the Depository or a nominee of the Depository, duly executed by the Company
and authenticated by the Trustee as hereinafter provided.  The aggregate
principal amount of the Global Securities may from time to time be increased or
decreased by adjustments made on the records of the Trustee and the Depository
or its nominee as hereinafter provided.  Exchange Securities shall be issued in
global form (with the global securities legend set forth in Exhibit 1 hereto) or
in certificated form at the option of the Holders thereof from time to time.
Exchange Securities issued in global form and Restricted Global Securities are
sometimes referred to in this Appendix as "Global Securities."

          (b)  Book-Entry Provisions.  This Section 2.1(b) shall apply only to a
               ----------------------
Global Security deposited with or on behalf of the Depository.

          The Company shall execute and the Trustee shall, in accordance with
this Section 2.1(b), authenticate and deliver initially one or more Global
Securities that (a) shall be registered in the name of the Depository for such
Global Security or Global Securities or the nominee of such Depository and (b)
shall be delivered by the Trustee to such
<PAGE>

                                                                               4

Depository or pursuant to such Depository's instructions or held by the Trustee
as custodian for the Depository.

          Members of, or participants in, the Depository ("Agent Members") shall
have no rights under this Indenture with respect to any Global Security held on
their behalf by the Depository or by the Trustee as the custodian of the
Depository or under such Global Security, and the Company, the Trustee and any
agent of the Company or the Trustee shall be entitled to treat the Depository as
the absolute owner of such Global Security for all purposes whatsoever.
Notwithstanding the foregoing, nothing herein shall prevent the Company, the
Trustee or any agent of the Company or the Trustee from giving effect to any
written certification, proxy or other authorization furnished by the Depository
or impair, as between the Depository and its Agent Members, the operation of
customary practices of such Depository governing the exercise of the rights of a
holder of a beneficial interest in any Global Security.

          (c)  Certificated Securities.  Except as provided in this Section 2.1
               ------------------------
or Section 2.3 or 2.4, owners of beneficial interests in Restricted Global
Securities shall not be entitled to receive physical delivery of certificated
Securities.

     2.2  Authentication.  The Trustee shall authenticate and deliver:  (1) on
          ---------------
the Issue Date, an aggregate principal amount of $300.0 million 11% Senior Notes
Due July 1, 2010, (2) any Additional Securities for an original issue in an
aggregate principal amount specified in the written order of the Company
pursuant to Section 2.02 of the Indenture and (3) Exchange Securities or Private
Exchange Securities for issue only in a Registered Exchange Offer or a Private
Exchange, respectively, pursuant to a Registration Rights Agreement, for a like
principal amount of Initial Securities, in each case upon a written order of the
Company signed by two Officers or by an Officer and either an Assistant
Treasurer or an Assistant Secretary of the Company.  Such order shall specify
the amount of the Securities to be authenticated and the date on which the
original issue of Securities is to be authenticated and, in the case of any
issuance of Additional Securities pursuant to Section 2.13 of the Indenture,
shall certify that such issuance is in compliance with Section 4.03 of the
Indenture.

     2.3  Transfer and Exchange.
          ----------------------

          (a)  Transfer and Exchange of Global Securities. (i)  The transfer and
               -------------------------------------------
exchange of Global Securities or beneficial interests therein shall be effected
through the Depository, in accordance with this Indenture (including
<PAGE>

                                                                               5

applicable restrictions on transfer set forth herein, if any) and the procedures
of the Depository therefor. A transferor of a beneficial interest in a Global
Security shall deliver to the Registrar a written order given in accordance with
the Depository's procedures containing information regarding the participant
account of the Depository to be credited with a beneficial interest in the
Global Security. The Registrar shall, in accordance with such instructions
instruct the Depository to credit to the account of the Person specified in such
instructions a beneficial interest in the Global Security and to debit the
account of the Person making the transfer the beneficial interest in the Global
Security being transferred.

         (ii)  Notwithstanding any other provisions of this Appendix (other than
the provisions set forth in Section 2.4), a Global Security may not be
transferred as a whole except by the Depository to a nominee of the Depository
or by a nominee of the Depository to the Depository or another nominee of the
Depository or by the Depository or any such nominee to a successor Depository or
a nominee of such successor Depository.

        (iii)  In the event that a Restricted Global Security is exchanged for
Securities in certificated registered form pursuant to Section 2.4 of this
Appendix, prior to the consummation of a Registered Exchange Offer or the
effectiveness of a Shelf Registration Statement with respect to such Securities,
such Securities may be exchanged only in accordance with such procedures as are
substantially consistent with the provisions of this Section 2.3 (including the
certification requirements set forth on the reverse of the Initial Securities
intended to ensure that such transfers comply with Rule 144A or Regulation S, as
the case may be) and such other procedures as may from time to time be adopted
by the Company.

          (b)  Legend.
               -------

          (i)  Except as permitted by the following paragraphs (ii), (iii) and
     (iv), each Security certificate evidencing the Restricted Global Securities
     (and all Securities issued in exchange therefor or in substitution thereof)
     shall bear a legend in substantially the following form:

          THIS SECURITY (OR ITS PREDECESSOR) WAS ORIGINALLY ISSUED IN A
          TRANSACTION EXEMPT FROM REGISTRATION UNDER THE SECURITIES ACT OF 1933
          (THE "SECURITIES ACT"), AND THIS SECURITY MAY NOT BE OFFERED, SOLD OR
          OTHERWISE TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR AN
          APPLICABLE EXEMPTION THEREFROM.
<PAGE>

                                                                               6


     EACH PURCHASER OF THIS SECURITY IS HEREBY NOTIFIED THAT THE SELLER OF THIS
     SECURITY MAY BE RELYING ON THE EXEMPTION FROM THE PROVISIONS OF SECTION 5
     OF THE SECURITIES ACT PROVIDED BY RULE 144A THEREUNDER.

     THE HOLDER OF THIS SECURITY AGREES FOR THE BENEFIT OF THE COMPANY THAT (A)
     THIS NOTE MAY BE OFFERED, RESOLD, PLEDGED OR OTHERWISE TRANSFERRED, ONLY
     (I) TO THE COMPANY, (II) IN THE UNITED STATES TO A PERSON WHOM THE SELLER
     REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL BUYER (AS DEFINED IN RULE
     144A UNDER THE SECURITIES ACT) IN A TRANSACTION MEETING THE REQUIREMENTS OF
     RULE 144A, (III) OUTSIDE THE UNITED STATES IN AN OFFSHORE TRANSACTION IN
     ACCORDANCE WITH RULE 904 UNDER THE SECURITIES ACT, (IV) PURSUANT TO
     EXEMPTION FROM REGISTRATION UNDER THE SECURITIES ACT PROVIDED BY RULE 144
     THEREUNDER (IF AVAILABLE) OR (V) PURSUANT TO AN EFFECTIVE REGISTRATION
     STATEMENT UNDER THE SECURITIES ACT, IN EACH OF CASES (I) THROUGH (V) IN
     ACCORDANCE WITH ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED
     STATES, AND (B) THE HOLDER WILL, AND EACH SUBSEQUENT HOLDER IS REQUIRED TO,
     NOTIFY ANY PURCHASER OF THIS NOTE FROM IT OF THE RESALE RESTRICTIONS
     REFERRED TO IN (A) ABOVE.

     (ii) Upon any sale or transfer of a Transfer Restricted Security (including
any Transfer Restricted Security represented by a Restricted Global Security)
pursuant to Rule 144 under the Securities Act, the Registrar shall permit the
transferee thereof to exchange such Transfer Restricted Security for a
certificated Security that does not bear the legend set forth above and rescind
any restriction on the transfer of such Transfer Restricted Security, if the
transferor thereof certifies in writing to the Registrar that such sale or
transfer was made in reliance on Rule 144 (such certification to be in the form
set forth on the reverse of the Security).

   (iii) After a transfer of any Initial Securities or Private Exchange
Securities pursuant to and during the period of the effectiveness of a Shelf
Registration Statement with respect to such Initial Securities or Private
Exchange Securities, as the case may be, all requirements pertaining to legends
on such Initial Security or such Private Exchange Security will cease to apply,
the requirements requiring any such Initial Security or such Private Exchange
Security issued to certain Holders be issued in global form will cease to apply,
and a certificated Initial Security or Private
<PAGE>

                                                                               7


     Exchange Security or an Initial Security or Private Exchange Security in
     global form, in each case without restrictive transfer legends, will be
     available to the transferee of the Holder of such Initial Securities or
     Private Exchange Securities upon exchange of such transferring Holder's
     certificated Initial Security or Private Exchange Security or directions to
     transfer such Holder's interest in the Global Security, as applicable.

         (iv)  Upon the consummation of a Registered Exchange Offer with respect
     to the Initial Securities, all requirements pertaining to such Initial
     Securities that Initial Securities issued to certain Holders be issued in
     global form will still apply with respect to Holders of such Initial
     Securities that do not exchange their Initial Securities, and Exchange
     Securities in certificated or global form will be available to Holders that
     exchange such Initial Securities in such Registered Exchange Offer.

          (v)  Upon the consummation of a Private Exchange with respect to the
     Initial Securities, all requirements pertaining to such Initial Securities
     that Initial Securities issued to certain Holders be issued in global form
     will still apply with respect to Holders of such Initial Securities that do
     not exchange their Initial Securities, and Private Exchange Securities in
     global form with the global securities legend and the Restricted Securities
     Legend set forth in Exhibit 1 hereto will be available to Holders that
     exchange such Initial Securities in such Private Exchange.

          (c)  Cancellation or Adjustment of Global Security. At such time as
               ---------------------------------------------
all beneficial interests in a Global Security have either been exchanged for
certificated Securities, redeemed, purchased or canceled, such Global Security
shall be returned to the Depository for cancellation or retained and canceled by
the Trustee. At any time prior to such cancellation, if any beneficial interest
in a Global Security is exchanged for certificated Securities, redeemed,
purchased or canceled, the principal amount of Securities represented by such
Global Security shall be reduced and an adjustment shall be made on the books
and records of the Trustee (if it is then the Securities Custodian for such
Global Security) with respect to such Global Security, by the Trustee or the
Securities Custodian, to reflect such reduction.
<PAGE>

                                                                               8


          (d)  Obligations with Respect to Transfers and Exchanges of
               ------------------------------------------------------
Securities.
----------
          (i)  To permit registrations of transfers and exchanges, the Company
     shall execute and the Trustee shall authenticate certificated 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 tax, assessments, or similar governmental charge payable
     in connection therewith (other than any such transfer taxes, assessments or
     similar governmental charge payable upon exchange or transfer pursuant to
     Sections 3.06, 4.10 and 9.05 of the Indenture).

        (iii)  The Registrar or co-registrar shall not be required to register
     the transfer of or exchange of any Security for a period beginning 15
     Business Days before the mailing of a notice of an offer to repurchase or
     redeem Securities or 15 Business Days before an interest payment date.

         (iv)  Prior to the due presentation for registration of transfer of any
     Security, the Company, the Trustee, the Paying Agent, the Registrar or any
     co-registrar may deem and treat the person in whose name a Security is
     registered as the absolute owner of such Security for the purpose of
     receiving payment of principal of and interest on such Security and for all
     other purposes whatsoever, whether or not such Security is overdue, and
     none of the Company, the Trustee, the Paying Agent, the Registrar or any
     co-registrar shall be affected by notice to the contrary.

          (v)  All Securities issued upon any transfer or exchange pursuant to
     the terms of this Indenture shall evidence the same debt and shall be
     entitled to the same benefits under this Indenture as the Securities
     surrendered upon such transfer or exchange.

          (e)  No Obligation of the Trustee.
               ----------------------------

          (i)  The Trustee shall have no responsibility or obligation to any
     beneficial owner of a Global Security, a member of, or a participant in the
     Depository or other Person with respect to the accuracy of the records of
     the Depository or its nominee or of any participant or member thereof, with
     respect to any ownership interest in the Securities or with respect to the
     delivery to any
<PAGE>

                                                                               9

     participant, member, beneficial owner or other Person (other than the
     Depository) of any notice (including any notice of redemption) or the
     payment of any amount, under or with respect to such Securities. All
     notices and communications to be given to the Holders and all payments to
     be made to Holders under the Securities shall be given or made only to or
     upon the order of the registered Holders (which shall be the Depository or
     its nominee in the case of a Global Security). The rights of beneficial
     owners in any Global Security shall be exercised only through the
     Depository subject to the applicable rules and procedures of the
     Depository. The Trustee may rely and shall be fully protected in relying
     upon information furnished by the Depository with respect to its members,
     participants and any beneficial owners.

          (ii) The Trustee shall have no obligation or duty to monitor,
     determine or inquire as to compliance with any restrictions on transfer
     imposed under this Indenture or under applicable law with respect to any
     transfer of any interest in any Security (including any transfers between
     or among Depository participants, members or beneficial owners in any
     Global Security) other than to require delivery of such certificates and
     other documentation or evidence as are expressly required by, and to do so
     if and when expressly required by, the terms of this Indenture, and to
     examine the same to determine substantial compliance as to form with the
     express requirements hereof.

     2.4  Certificated Securities.
          -----------------------

          (a)  A Restricted Global Security deposited with the Depository or
with the Trustee as custodian for the Depository pursuant to Section 2.1 shall
be transferred to the beneficial owners thereof in the form of certificated
Securities in an aggregate principal amount equal to the principal amount of
such Global Security, in exchange for such Global Security, only if such
transfer complies with Section 2.3 and (i) the Depository notifies the Company
that it is unwilling or unable to continue as Depository for such Restricted
Global Security or if at any time such Depository ceases to be a "clearing
agency" registered under the Exchange Act and a successor depositary is not
appointed by the Company within 90 days of such notice, or (ii) an Event of
Default has occurred and is continuing or (iii) the Company, in its sole
discretion, notifies the Trustee in writing that it elects to cause the issuance
of certificated Securities under this Indenture.

          (b)  Any Restricted Global Security that is transferable to the
beneficial owners thereof pursuant to this
<PAGE>

                                                                              10


Section shall be surrendered by the Depository to the Trustee located at its
principal corporate trust office in the Borough of Manhattan, The City of New
York, to be so transferred, in whole or from time to time in part, without
charge, and the Trustee shall authenticate and deliver, upon such transfer of
each portion of such Restricted Global Security, an equal aggregate principal
amount of certificated Initial Securities of authorized denominations. Any
portion of a Restricted Global Security transferred pursuant to this Section
shall be executed, authenticated and delivered only in denominations of $1,000
principal amount and any integral multiple thereof and registered in such names
as the Depository shall direct. Any certificated Initial Security or Private
Exchange Security delivered in exchange for an interest in the Restricted Global
Security shall, except as otherwise provided by Section 2.3(b), bear the
restricted securities legend set forth in Exhibit 1 hereto.

          (c)  Subject to the provisions of Section 2.4(b), the registered
Holder of a Global Security shall be entitled to grant proxies and otherwise
authorize any Person, including Agent Members and Persons that may hold
interests through Agent Members, to take any action which a Holder is entitled
to take under this Indenture or the Securities.

          (d)  In the event of the occurrence of either of the events specified
in Section 2.4(a), the Company shall promptly make available to the Trustee a
reasonable supply of certificated Securities in definitive, fully registered
form without interest coupons.
<PAGE>

                                                                       EXHIBIT 1
                                                                              to
                                                 RULE 144A/REGULATION S APPENDIX



                      [FORM OF FACE OF INITIAL SECURITY]

                          [Global Securities Legend]

               UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED
REPRESENTATIVE OF THE DEPOSITARY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"),
NEW YORK, NEW YORK, TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER,
EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF
CEDE & CO. OR 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.

               TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS
IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH
SUCCESSOR'S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE
LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE
INDENTURE REFERRED TO ON THE REVERSE HEREOF.

                        [Restricted Securities Legend]

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

               THE HOLDER OF THIS SECURITY AGREES FOR THE BENEFIT OF THE COMPANY
THAT (A) THIS NOTE MAY BE OFFERED, RESOLD, PLEDGED OR OTHERWISE TRANSFERRED,
ONLY (I) TO THE COMPANY, (II) IN THE UNITED STATES TO A PERSON WHOM THE SELLER
REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL BUYER (AS DEFINED IN RULE 144A
UNDER THE SECURITIES ACT) IN A TRANSACTION MEETING THE REQUIREMENTS OF RULE
144A, (III) OUTSIDE THE UNITED STATES IN AN OFFSHORE TRANSACTION IN ACCORDANCE
WITH RULE 904 UNDER THE SECURITIES ACT, (IV) PURSUANT TO AN EXEMPTION FROM
REGISTRATION UNDER THE SECURITIES ACT PROVIDED BY RULE 144 THEREUNDER (IF
AVAILABLE) OR (V) PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE
SECURITIES ACT, IN EACH OF CASES (I) THROUGH (V) IN ACCORDANCE WITH ANY
APPLICABLE SECURITIES LAWS OF ANY STATE OF
<PAGE>

                                                                               2


THE UNITED STATES, AND (B) THE HOLDER WILL, AND EACH SUBSEQUENT HOLDER IS
REQUIRED TO, NOTIFY ANY PURCHASER OF THIS NOTE FROM IT OF THE RESALE
RESTRICTIONS REFERRED TO IN (A) ABOVE.
<PAGE>

                                                                               3

No.____________                                                      $__________
                                                           CUSIP No. 61844A AA 7
                                                           ISIN No. US61844AAA79

                       11% Senior Notes Due July 1, 2010

          MORRISON KNUDSEN CORPORATION, a Delaware corporation, promises to pay
to               , or registered assigns, the principal sum of
Dollars on July 1, 2010.

          Interest Payment Dates:  January 1 and July 1.

          Record Dates:  December 15 and June 15.

          Additional provisions of this Security are set forth on the other side
of this Security.

Dated:  July 7, 2000

                                         MORRISON KNUDSEN CORPORATION,

                                            by
                                               _____________________
                                               Name:
                                               Title:

                                            by

                                               _____________________
                                               Name:
                                               Title:

TRUSTEE'S CERTIFICATE OF
     AUTHENTICATION

UNITED STATES TRUST COMPANY OF NEW YORK,
as Trustee, certifies that this is one
of the Securities referred to in the Indenture.


by
   _____________________________
        Authorized Signatory
<PAGE>

                                                                               4

                  [FORM OF REVERSE SIDE OF INITIAL SECURITY]

                       11% Senior Note Due July 1, 2010

1.   Interest
     --------

          Morrison Knudsen Corporation, a Delaware corporation (such
corporation, and its successors and assigns under the Indenture hereinafter
referred to, being herein called the "Company"), promises to pay interest on the
principal amount of this Security at the rate per annum shown above; provided,
                                                                     --------
however, that if a Registration Default (as defined in the Registration Rights
-------
Agreement) occurs, additional interest will accrue on this Security at a rate of
0.50% per annum (increasing by an additional 0.50% per annum after the 90th
consecutive day after the date on which such Registration Default occurs) from
and including the date on which any such Registration Default shall occur to but
excluding the date on which all Registration Defaults have been cured. The
Company shall provide the Trustee with written notice, not less than two
Business Days prior to any interest payment date, if additional interest has
accrued on the Securities as a result of a Registration Default, together with
notice of the amount of such additional interest. If the Trustee does not
receive timely notice from the Company of the accrual of additional interest,
solely with respect to its rights and duties under Article VII of the Indenture,
the Trustee may conclusively assume that no additional interest has accrued and
is payable by the Company. The Company will pay interest semiannually, including
any additional interest, on January 1 and July 1 of each year, commencing
January 1, 2001. Interest on the Securities will accrue from the most recent
date to which interest has been paid or, if no interest has been paid, from July
7, 2000. Interest will be computed on the basis of a 360-day year of twelve 30-
day months.

2.  Method of Payment
    -----------------

          The Company will pay interest on the Securities (except defaulted
interest) to the Persons who are registered holders of Securities at the close
of business on the December 15 or June 15 next preceding the interest payment
date even if Securities are canceled after the record date and on or before the
interest payment date. Holders must surrender Securities to a Paying Agent to
collect principal payments. The Company will pay principal and interest in
<PAGE>

                                                                               5

money of the United States that at the time of payment is legal tender for
payment of public and private debts. Payments in respect of the Securities
represented by a Global Security (including principal, premium and interest)
will be made by wire transfer of immediately available funds to the accounts
specified by The Depository Trust Company. The Company will make all payments in
respect of a certificated Security (including principal, premium and interest)
by mailing a check to the registered address of each Holder thereof; provided,
                                                                     --------
however, that payments on a certificated Security will be made by wire transfer
-------
to a U.S. dollar account maintained by the payee with a bank in the United
States if such Holder elects payment by wire transfer by giving written notice
to the Trustee or the Paying Agent to such effect designating such account no
later than 30 days immediately preceding the relevant due date for payment (or
such other date as the Trustee may accept in its discretion).

3.  Paying Agent and Registrar
    --------------------------

          Initially, United States Trust Company of New York, a New York banking
corporation (the "Trustee"), will act as Paying Agent and Registrar. The Company
may appoint and change any Paying Agent, Registrar or co-registrar without
notice. The Company or any of its domestically incorporated Wholly Owned
Subsidiaries may act as Paying Agent, Registrar or co-registrar.

4.  Indenture
    ---------
          The Company issued the Securities under an Indenture dated as of July
1, 2000 ("Indenture"), among the Company, the Subsidiary Guarantors and the
Trustee.  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 of 1939
(15 U.S.C. (S)(S) 77aaa-77bbbb) as in effect on the date of the Indenture (the
    ------
"Act"). Terms defined in the Indenture and not defined herein have the meanings
ascribed thereto in the Indenture. The Securities are subject to all such terms,
and Securityholders are referred to the Indenture and the Act for a statement of
those terms.

          The Securities are general unsecured obligations of the Company. The
Company shall be entitled, subject to its compliance with Section 4.03 of the
Indenture, to issue Additional Securities pursuant to Section 2.13 of the
Indenture. The Initial Securities issued on the Issue Date, any Additional
Securities and all Exchange Securities or Private Exchange Securities issued in
exchange therefor will
<PAGE>

                                                                               6


be treated as a single class for all purposes under the Indenture. The
Indenture contains covenants that limit the ability of the Company and certain
of its subsidiaries to incur additional indebtedness; pay dividends or
distributions on, or redeem or repurchase capital stock; make investments; issue
or sell capital stock of certain subsidiaries; engage in transactions with
affiliates; conduct their business in a different manner; create liens on
assets; transfer or sell assets; guarantee indebtedness; restrict dividends or
other payments of certain subsidiaries; consolidate, merge or transfer all or
substantially all of its assets and the assets of its subsidiaries; and engage
in sale/leaseback transactions. These covenants are subject to important
exceptions and qualifications.

5.   Optional Redemption
     -------------------

          Except as set forth below, the Company will not be entitled to redeem
the Securities at any time prior to their Stated Maturity.

          The Securities will be redeemable as a whole at any time or in part
from time to time, at the Company's option, at a redemption price equal to the
greater of

          (i)  100% of the principal amount of the Securities, plus any interest
     accrued but not paid to the date of redemption, or

         (ii)  the sum of the present values of the remaining scheduled payments
     of principal and interest on the Securities from the redemption date to the
     Stated Maturity of the Securities discounted to the redemption date on a
     semiannual basis (assuming a 360-day year consisting of twelve 30-day
     months) at the Treasury Rate plus 50 basis points, plus any interest
     accrued but not paid to the date of redemption.

6.  Notice of Redemption
    --------------------

          Notice of redemption will be mailed at least 30 days but not more than
60 days before the redemption date to each Holder of Securities to be redeemed
at his registered address. Securities in denominations larger than $1,000
principal amount may be redeemed in part but only in whole multiples of $1,000.
If money sufficient to pay the redemption price of and accrued interest on all
Securities (or portions thereof) to be redeemed on the redemption date is
deposited with the Paying Agent on or before the redemption date and certain
<PAGE>

                                                                               7

other conditions are satisfied, on and after such date interest ceases to accrue
on such Securities (or such portions thereof) called for redemption.

7.  Put Provisions
    --------------

          Upon a Change of Control, any Holder of Securities will have the right
to cause the Company to repurchase all or any part of the Securities of such
Holder at a repurchase price equal to 101% of the principal amount of the
Securities to be repurchased plus accrued interest to the date of repurchase
(subject to the right of Holders of record on the relevant record date to
receive interest due on the related interest payment date) as provided in, and
subject to the terms of, the Indenture.

8.  Guaranty
    --------

          The payment by the Company of the principal of, and premium and
interest on, the Securities is fully and unconditionally guaranteed on a joint
and several senior basis by each of the Subsidiary Guarantors.

9.  Denominations; Transfer; Exchange
    ---------------------------------

          The Securities are in registered form without coupons in denominations
of $1,000 principal amount and whole multiples of $1,000. A Holder may transfer
or exchange Securities in accordance with the Indenture. The Registrar may
require a Holder, among other things, to furnish appropriate endorsements or
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 (except, in the case of a Security to be
redeemed in part, the portion of the Security not to be redeemed) or any
Securities for a period of 15 days before a selection of Securities to be
redeemed or 15 days before an interest payment date.

10.  Persons Deemed Owners
     ---------------------

          The registered Holder of this Security may be treated as the owner of
it for all purposes.
<PAGE>

                                                                               8

11.  Unclaimed Money
     ---------------

          If money for the payment of principal or interest remains unclaimed
for two years, the Trustee or Paying Agent shall pay the money back to the
Company at its request unless an abandoned property law designates another
Person.  After any such payment, Holders entitled to the money must look only to
the Company and not to the Trustee for payment.

12.  Discharge and Defeasance
     ------------------------

          Subject to certain conditions, the Company at any time shall be
entitled to terminate some or all of its obligations under the Securities and
the Indenture if the Company deposits with the Trustee money or U.S. Government
Obligations for the payment of principal and interest on the Securities to
redemption or maturity, as the case may be.

13.  Amendment, Waiver
     -----------------

          Subject to certain exceptions set forth in the Indenture, (i) the
Indenture and the Securities may be amended with the written consent of the
Holders of at least a majority in principal amount outstanding of the Securities
and (ii) any default or noncompliance with any provision may be waived with the
written consent of the Holders of a majority in principal amount outstanding of
the Securities.  Subject to certain exceptions set forth in the Indenture,
without the consent of any Securityholder, the Company, the Subsidiary
Guarantors and the Trustee shall be entitled to amend the Indenture or the
Securities to cure any ambiguity, omission, defect or inconsistency, or to
comply with Article V of the Indenture, or to provide for uncertificated
Securities in addition to or in place of certificated Securities, or to add
guarantees with respect to the Securities, including Subsidiary Guaranties, or
to secure the Securities, or to add additional covenants or surrender rights and
powers conferred on the Company or the Subsidiary Guarantors, or to comply with
any request of the SEC in connection with qualifying the Indenture under the
Act, or to make any change that does not adversely affect the rights of any
Securityholder.

14.  Defaults and Remedies
     ---------------------

          Under the Indenture, Events of Default include (i) default for 30 days
in payment of interest on the Securities; (ii) default in payment of principal
on the Securities at maturity, upon redemption pursuant to
<PAGE>

                                                                               9

paragraph 5 of the Securities, upon acceleration or otherwise, or failure by the
Company to redeem or purchase Securities when required; (iii) failure by the
Company to comply with other agreements in the Indenture or the Securities, in
certain cases subject to notice and lapse of time; (iv) certain accelerations
(including failure to pay within any grace period after final maturity) of other
Indebtedness of the Company if the amount accelerated (or so unpaid) exceeds
$25.0 million; (v) certain events of bankruptcy or insolvency with respect to
the Company and the Significant Subsidiaries; (vi) certain judgments or decrees
for the payment of money in excess of $25.0 million; and (vii) certain defaults
with respect to Subsidiary Guaranties. If an Event of Default occurs and is
continuing, the Trustee or the Holders of at least 25% in principal amount of
the Securities may declare all the Securities to be due and payable immediately.
Certain events of bankruptcy or insolvency are Events of Default which will
result in the Securities being due and payable immediately upon the occurrence
of such Events of Default.

          Securityholders may not enforce the Indenture or the Securities except
as provided in the Indenture.  The Trustee may refuse to enforce the Indenture
or the Securities unless it receives indemnity or security satisfactory to it.
Subject to certain limitations, Holders of a majority in principal amount of the
Securities may direct the Trustee in its exercise of any trust or power.  The
Trustee may withhold from Securityholders notice of any continuing Default
(except a Default in payment of principal or interest) if it determines that
withholding notice is in the interest of the Holders.

15.  Trustee Dealings with the Company
     ---------------------------------

          Subject to certain limitations imposed by the Act, the Trustee under
the Indenture, in its individual or any other capacity, may become the owner or
pledgee of Securities and may otherwise deal with and collect obligations owed
to it by the Company or its Affiliates and may otherwise deal with the Company
or its Affiliates with the same rights it would have if it were not Trustee.

16.  No Recourse Against Others
     --------------------------

          A director, officer, employee or stockholder, as such, of the Company
or the Trustee shall not have any liability for any obligations of the Company
under the Securities or the Indenture or for any claim based on, in respect of
or by reason of such obligations or their creation.


<PAGE>

                                                                              10

By accepting a Security, each Securityholder waives and releases all such
liability. The waiver and release are part of the consideration for the issue of
the Securities.

17.  Authentication
     --------------

          This Security shall not be valid until an authorized signatory of the
Trustee (or an authenticating agent) manually signs the certificate of
authentication on the other side of this Security.

18.  Abbreviations
     -------------

          Customary abbreviations may be used in the name of a Securityholder or
an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the
entireties), JT TEN (=joint tenants with rights of survivorship and not as
tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors
Act).

19.  CUSIP Numbers
     -------------

          Pursuant to a recommendation promulgated by the Committee on Uniform
Security Identification Procedures the Company has caused CUSIP numbers to be
printed on the Securities and has directed the Trustee to use CUSIP numbers in
notices of redemption as a convenience to Securityholders. No representation is
made as to the accuracy of such numbers either as printed on the Securities or
as contained in any notice of redemption and reliance may be placed only on the
other identification numbers placed thereon.

20.  Holders' Compliance with Registration Rights Agreement
     ------------------------------------------------------

          Each Holder of a Security, by acceptance hereof, acknowledges and
agrees to the provisions of the Registration Rights Agreement, including the
obligations of the Holders with respect to a registration and the
indemnification of the Company to the extent provided therein.

21.  Governing Law
     -------------

          THIS SECURITY SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH,
THE LAWS OF THE STATE OF NEW YORK BUT WITHOUT GIVING EFFECT TO APPLICABLE
PRINCIPLES OF CONFLICTS OF LAW TO
<PAGE>

                                                                              11

THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE
REQUIRED THEREBY.

          The Company will furnish to any Securityholder upon written request
and without charge to the Securityholder a copy of the Indenture which has in it
the text of this Security in larger type.  Requests may be made to:

          Morrison Knudsen Corporation
          720 Park Boulevard
          Boise, Idaho 83712

          Attention:  General Counsel
<PAGE>

                                                                              12

________________________________________________________________________________

                                ASSIGNMENT FORM

To assign this Security, fill in the form below:

I or we assign and transfer this Security to

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

     (Insert assignee's soc. sec. or tax I.D. No.)

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

________________________________________________________________________________

Date: _________________ Your Signature: _____________________

_______________________________________________________________________________
Sign exactly as your name appears on the other side of this Security.

In connection with any transfer of any of the Securities evidenced by this
certificate occurring prior to the expiration of the period referred to in Rule
144(k) under the Securities Act after the later of the date of original issuance
of such Securities and the last date, if any, on which such Securities were
owned by the Company or any Affiliate of the Company, the undersigned confirms
that such Securities are being transferred in accordance with its terms:

CHECK ONE BOX BELOW

     (1) [_]   to the Company; or

     (2) [_]   pursuant to an effective registration statement under the
               Securities Act of 1933; or

     (3) [_]   inside the United States to a "qualified institutional buyer" (as
               defined in Rule 144A under the Securities Act of 1933) that
               purchases for its own account or for the account of a qualified
               institutional buyer to whom notice is given that such transfer is
               being made in reliance on Rule 144A, in each
<PAGE>

                                                                              13

               case pursuant to and in compliance with Rule 144A under the
               Securities Act of 1933; or

     (4) [_]   outside the United States in an offshore transaction within the
               meaning of Regulation S under the Securities Act in compliance
               with Rule 904 under the Securities Act of 1933; or

     (5) [_]   pursuant to the exemption from registration provided by Rule 144
               under the Securities Act of 1933.

     Unless one of the boxes is checked, the Trustee will refuse to register any
     of the Securities evidenced by this certificate in the name of any person
     other than the registered holder thereof; provided, however, that if box
                                               --------  -------
     (4) or (5) is checked, the Trustee shall be entitled to require, prior to
     registering any such transfer of the Securities, such legal opinions,
     certifications and other information as the Company has reasonably
     requested 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 of 1933, such as the exemption provided
     by Rule 144 under such Act.

                                            ________________________
                                                   Signature

Signature Guarantee:

____________________________                  _________________________
Signature must be guaranteed                  Signature

     Signatures must be guaranteed by an "eligible guarantor institution"
meeting the requirements of the Registrar, which requirements include membership
or participation in the Security Transfer Agent Medallion Program ("STAMP") or
such other "signature guarantee program" as may be determined by the Registrar
in addition to, or in substitution for, STAMP, all in accordance with the
Securities Exchange Act of 1934, as amended.

________________________________________________________________________________
             TO BE COMPLETED BY PURCHASER IF (3) ABOVE IS CHECKED.
<PAGE>

                                                                              14

          The undersigned represents and warrants that it is purchasing this
Security for its own account or an account with respect to which it exercises
sole investment discretion and that it and any such account is a "qualified
institutional buyer" within the meaning of Rule 144A under the Securities Act of
1933, and is aware that the sale to it is being made in reliance on Rule 144A
and acknowledges that it has received such information regarding the Company as
the undersigned has requested pursuant to Rule 144A or has determined not to
request such information and that it is aware that the transferor is relying
upon the undersigned's foregoing representations in order to claim the exemption
from registration provided by Rule 144A.

Dated: ________________                  ______________________________
                                         NOTICE:  To be executed by
                                                  an executive officer
<PAGE>

                                                                              15

                     [TO BE ATTACHED TO GLOBAL SECURITIES]

             SCHEDULE OF INCREASES OR DECREASES IN GLOBAL SECURITY

          The following increases or decreases in this Global Security have been
     made:

<TABLE>
<S>                  <C>                    <C>                    <C>                     <C>
Date of              Amount of decrease     Amount of increase     Principal amount        Signature of
Exchange             in principal           in principal           of this Global          authorized officer
--------
                     amount of this         amount of this         Security following      of Trustee or
                     Global Security        Global Security        such decrease or        Securities
                     ------------------     ------------------
                                                                   increase)               Custodian
                                                                   ------------------      ------------------
</TABLE>
<PAGE>

                                                                              16

                      OPTION OF HOLDER TO ELECT PURCHASE

          If you want to elect to have this Security purchased by the Company
pursuant to Section 4.07 or 4.10 of the Indenture, check the box:

                                      [_]

          If you want to elect to have only part of this Security purchased by
the Company pursuant to Section 4.07 or 4.10 of the Indenture, state the amount
in principal amount:  $__________________

Date: _______________  Your Signature: ____________________________
                                       (Sign exactly as your name
                                       appears on the other side of
                                       this Security.)

Signature Guarantee: _______________________________________
                     (Signature must be guaranteed)

     Signatures must be guaranteed by an "eligible guarantor institution"
meeting the requirements of the Registrar, which requirements include membership
or participation in the Security Transfer Agent Medallion Program ("STAMP") or
such other "signature guarantee program" as may be determined by the Registrar
in addition to, or in substitution for, STAMP, all in accordance with the
Securities Exchange Act of 1934, as amended.
<PAGE>

                                                                       EXHIBIT A

                      [FORM OF FACE OF EXCHANGE SECURITY
                         OR PRIVATE EXCHANGE SECURITY]


         */
         _

         **/
-----------


*/If the Security is to be issued in global form add the Global Securities
-
Legend from Exhibit 1 to Appendix A and the attachment from such Exhibit 1
captioned "[TO BE ATTACHED TO GLOBAL SECURITIES] - SCHEDULE OF INCREASES OR
DECREASES IN GLOBAL SECURITY".

**/If the Security is a Private Exchange Security issued in a Private Exchange
--
to an Initial Purchaser holding an unsold portion of its initial allotment, add
the Restricted Securities Legend from Exhibit 1 to Appendix A and replace the
Assignment Form included in this Exhibit A with the Assignment Form included in
such Exhibit 1.
<PAGE>

                                                                               2

No.____________                                                      $ _________

                                                           CUSIP No. 61844A AB 5
                                                           ISIN No. US61844AAB52

                       11% Senior Notes Due July 1, 2010

          MORRISON KNUDSEN CORPORATION, a Delaware corporation, promises to pay
to                   , or registered assigns, the principal sum of
Dollars on July 1, 2010.

          Interest Payment Dates:  January 1 and July 1.

          Record Dates:  December 15 and June 15.

          Additional provisions of this Security are set forth on the other side
of this Security.

Dated:__________________

                              MORRISON KNUDSEN CORPORATION,

                                by
                                   _____________________________
                                   Name:
                                   Title:

                                by
                                    ____________________________
                                    Name:
                                    Title:

TRUSTEE'S CERTIFICATE OF
     AUTHENTICATION

UNITED STATES TRUST COMPANY
OF NEW YORK, as Trustee,
certifies that this is one
of the Securities referred to
in the Indenture.

by
  _____________________________
     Authorized Signatory
<PAGE>

                                                                               3

                  [FORM OF REVERSE SIDE OF EXCHANGE SECURITY
                         OR PRIVATE EXCHANGE SECURITY]

                       11% Senior Note Due July 1, 2010

1.   Interest
     --------

          Morrison Knudsen Corporation, a Delaware corporation (such
corporation, and its successors and assigns under the Indenture hereinafter
referred to, being herein called the "Company"), promises to pay interest on the
principal amount of this Security at the rate per annum shown above; provided,
                                                                     --------
however, that if a Registration Default (as defined in the Registration Rights
-------
Agreement) occurs, additional interest will accrue on this Security at a rate of
0.50% per annum (increasing by an additional 0.50% per annum after the 90th
consecutive day after the date on which such Registration Default occurs) from
and including the date on which any such Registration Default shall occur to but
excluding the date on which all Registration Defaults have been cured. The
Company shall provide the Trustee with written notice, not less than two
Business Days prior to any interest payment date, if additional interest has
accrued on the Securities as a result of a Registration Default, together with
notice of the amount of such additional interest. If the Trustee does not
receive timely notice from the Company of the accrual of additional interest,
solely with respect to its rights and duties under Article VII of the Indenture,
the Trustee may conclusively assume that no additional interest has accrued and
is payable by the Company. The Company will pay interest semiannually, including
any additional interest, on January 1 and July 1 of each year, commencing
January 1, 2001. Interest on the Securities will accrue from the most recent
date to which interest has been paid or, if no interest has been paid, from July
7, 2000. Interest will be computed on the basis of a 360-day year of twelve 30-
day months.

2.   Method of Payment
     -----------------

          The Company will pay interest on the Securities (except defaulted
interest) to the Persons who are registered holders of Securities at the close
of business on the December 15 or January 15 next preceding the interest payment
date even if Securities are canceled after the record date and on or before the
interest payment date.  Holders must surrender Securities to a Paying Agent to
collect principal payments.  The Company will pay principal and interest in
money of the United States that at the time of payment is legal tender for
payment of public and private debts.  Payments in respect of the Securities
represented by a
<PAGE>

                                                                               4

Global Security (including principal, premium and interest) will be made by wire
transfer of immediately available funds to the accounts specified by The
Depository Trust Company.  The Company will make all payments in respect of a
certificated Security (including principal, premium and interest) by mailing a
check to the registered address of each Holder thereof; provided, however, that
                                                        --------  -------
payments on a certificated Security will be made by wire transfer to a U.S.
dollar account maintained by the payee with a bank in the United States if such
Holder elects payment by wire transfer by giving written notice to the Trustee
or the Paying Agent to such effect designating such account no later than 30
days immediately preceding the relevant due date for payment (or such other date
as the Trustee may accept in its discretion).

3.   Paying Agent and Registrar
     --------------------------

          Initially, United States Trust Company of New York, a New York banking
corporation (the "Trustee"), will act as Paying Agent and Registrar.  The
Company may appoint and change any Paying Agent, Registrar or co-registrar
without notice.  The Company or any of its domestically incorporated Wholly
Owned Subsidiaries may act as Paying Agent, Registrar or co-registrar.

4.   Indenture
     ---------

          The Company issued the Securities under an Indenture dated as of July
1, 2000 ("Indenture"), among the Company, the Subsidiary Guarantors and the
Trustee.  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 of 1939
(15 U.S.C. (S)(S) 77aaa-77bbbb) as in effect on the date of the Indenture (the
    -----
"Act").  Terms defined in the Indenture and not defined herein have the meanings
ascribed thereto in the Indenture.  The Securities are subject to all such
terms, and Securityholders are referred to the Indenture and the Act for a
statement of those terms.

          The Securities are general unsecured obligations of the Company. The
Company shall be entitled, subject to its compliance with Section 4.03 of the
Indenture, to issue Additional Securities pursuant to Section 2.13 of the
Indenture. The Initial Securities issued on the Issue Date, any Additional
Securities and all Exchange Securities or Private Exchange Securities issued in
exchange therefor will be treated as a single class for all purposes under the
Indenture. The Indenture contains covenants that limit the ability of the
Company and certain of its subsidiaries to incur additional indebtedness; pay
dividends or distributions on, or redeem or repurchase capital stock; make
investments; issue or sell capital stock of certain subsidiaries;
<PAGE>

                                                                               5

engage in transactions with affiliates; create liens on assets; transfer or sell
assets; guarantee indebtedness; restrict dividends or other payments of certain
subsidiaries; consolidate, merge or transfer all or substantially all of its
assets and the assets of its subsidiaries; and engage in sale/leaseback
transactions. These covenants are subject to important exceptions and
qualifications.

5.   Optional Redemption
     -------------------

               Except as set forth below, the Company will not be entitled to
redeem the Securities at any time prior to their Stated Maturity.

     The Securities will be redeemable as a whole at any time or in part from
time to time, at the Company's option, at a redemption price equal to the
greater of

     (i)  100% of the principal amount of the Securities, plus any interest
          accrued but not paid to the date of redemption, or

     (ii) the sum of the present values of the remaining scheduled payments of
          principal and interest on the Securities from the redemption date to
          the Stated Maturity of the Securities discounted to the redemption
          date on a semiannual basis (assuming a 360-day year consisting of
          twelve 30-day months) at the Treasury Rate plus 50 basis points, plus
          any interest accrued but not paid to the date of redemption.

6.   Notice of Redemption
     --------------------

          Notice of redemption will be mailed at least 30 days but not more than
60 days before the redemption date to each Holder of Securities to be redeemed
at his registered address.  Securities in denominations larger than $1,000
principal amount may be redeemed in part but only in whole multiples of $1,000.
If money sufficient to pay the redemption price of and accrued interest on all
Securities (or portions thereof) to be redeemed on the redemption date is
deposited with the Paying Agent on or before the redemption date and certain
other conditions are satisfied, on and after such date interest ceases to accrue
on such Securities (or such portions thereof) called for redemption.
<PAGE>

                                                                               6

7.   Put Provisions
     --------------

          Upon a Change of Control, any Holder of Securities will have the right
to cause the Company to repurchase all or any part of the Securities of such
Holder at a repurchase price equal to 101% of the principal amount of the
Securities to be repurchased plus accrued interest to the date of repurchase
(subject to the right of Holders of record on the relevant record date to
receive interest due on the related interest payment date) as provided in, and
subject to the terms of, the Indenture.

8.   Guaranty
     --------

          The payment by the Company of the principal of, and premium and
interest on, the Securities is fully and unconditionally guaranteed on a joint
and several senior basis by each of the Subsidiary Guarantors.

9.   Denominations; Transfer; Exchange
     ---------------------------------

          The Securities are in registered form without coupons in denominations
of $1,000 principal amount and whole multiples of $1,000. A Holder may transfer
or exchange Securities in accordance with the Indenture. The Registrar may
require a Holder, among other things, to furnish appropriate endorsements or
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 (except, in the case of a Security to be
redeemed in part, the portion of the Security not to be redeemed) or any
Securities for a period of 15 days before a selection of Securities to be
redeemed or 15 days before an interest payment date.

10.  Persons Deemed Owners
     ---------------------

          The registered Holder of this 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 or Paying Agent shall pay the money back to the
Company at its request unless an abandoned property law designates another
Person. After any such payment, Holders entitled to the money must look only to
the Company and not to the Trustee for payment.
<PAGE>

                                                                               7

12.  Discharge and Defeasance
     ------------------------

          Subject to certain conditions, the Company at any time shall be
entitled to terminate some or all of its obligations under the Securities and
the Indenture if the Company deposits with the Trustee money or U.S. Government
Obligations for the payment of principal and interest on the Securities to
redemption or maturity, as the case may be.

13.  Amendment, Waiver
     -----------------

          Subject to certain exceptions set forth in the Indenture, (i) the
Indenture and the Securities may be amended with the written consent of the
Holders of at least a majority in principal amount outstanding of the Securities
and (ii) any default or noncompliance with any provision may be waived with the
written consent of the Holders of a majority in principal amount outstanding of
the Securities. Subject to certain exceptions set forth in the Indenture,
without the consent of any Securityholder, the Company, the Subsidiary
Guarantors and the Trustee shall be entitled to amend the Indenture or the
Securities to cure any ambiguity, omission, defect or inconsistency, or to
comply with Article V of the Indenture, or to provide for uncertificated
Securities in addition to or in place of certificated Securities, or to add
guarantees with respect to the Securities, including Subsidiary Guaranties, or
to secure the Securities, or to add additional covenants or surrender rights and
powers conferred on the Company or the Subsidiary Guarantors, or to comply with
any request of the SEC in connection with qualifying the Indenture under the
Act, or to make any change that does not adversely affect the rights of any
Securityholder.

14.  Defaults and Remedies
     ---------------------

          Under the Indenture, Events of Default include (i) default for 30 days
in payment of interest on the Securities; (ii) default in payment of principal
on the Securities at maturity, upon redemption pursuant to paragraph 5 of the
Securities, upon acceleration or otherwise, or failure by the Company to redeem
or purchase Securities when required; (iii) failure by the Company to comply
with other agreements in the Indenture or the Securities, in certain cases
subject to notice and lapse of time; (iv) certain accelerations (including
failure to pay within any grace period after final maturity) of other
Indebtedness of the Company if the amount accelerated (or so unpaid) exceeds
$25.0 million; (v) certain events of bankruptcy or insolvency with respect to
the Company and the Significant Subsidiaries; (vi) certain judgments or decrees
for the payment of money in excess of $25.0 million; and (vii) certain defaults
with respect to Subsidiary Guaranties. If
<PAGE>

                                                                               8

an Event of Default occurs and is continuing, the Trustee or the Holders of at
least 25% in principal amount of the Securities may declare all the Securities
to be due and payable immediately. Certain events of bankruptcy or insolvency
are Events of Default which will result in the Securities being due and payable
immediately upon the occurrence of such Events of Default.

          Securityholders may not enforce the Indenture or the Securities except
as provided in the Indenture.  The Trustee may refuse to enforce the Indenture
or the Securities unless it receives indemnity or security satisfactory to it.
Subject to certain limitations, Holders of a majority in principal amount of the
Securities may direct the Trustee in its exercise of any trust or power.  The
Trustee may withhold from Securityholders notice of any continuing Default
(except a Default in payment of principal or interest) if it determines that
withholding notice is in the interest of the Holders.

15.  Trustee Dealings with the Company
     ---------------------------------

          Subject to certain limitations imposed by the Act,  the Trustee under
the Indenture, in its individual or any other capacity, may become the owner or
pledgee of Securities and may otherwise deal with and collect obligations owed
to it by the Company or its Affiliates and may otherwise deal with the Company
or its Affiliates with the same rights it would have if it were not Trustee.

16.  No Recourse Against Others
     --------------------------

          A director, officer, employee or stockholder, as such, of the Company
or the Trustee shall not have any liability for any obligations of the Company
under the Securities or the Indenture or for any claim based on, in respect of
or by reason of such obligations or their creation. By accepting a Security,
each Securityholder waives and releases all such liability. The waiver and
release are part of the consideration for the issue of the Securities.

17.  Authentication
     --------------

          This Security shall not be valid until an authorized signatory of the
Trustee (or an authenticating agent) manually signs the certificate of
authentication on the other side of this Security.
<PAGE>

                                                                               9

18.  Abbreviations
     -------------

          Customary abbreviations may be used in the name of a Securityholder or
an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the
entireties), JT TEN (=joint tenants with rights of survivorship and not as
tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors
Act).

19.  CUSIP Numbers
     -------------

          Pursuant to a recommendation promulgated by the Committee on Uniform
Security Identification Procedures the Company has caused CUSIP numbers to be
printed on the Securities and has directed the Trustee to use CUSIP numbers in
notices of redemption as a convenience to Securityholders. No representation is
made as to the accuracy of such numbers either as printed on the Securities or
as contained in any notice of redemption and reliance may be placed only on the
other identification numbers placed thereon.

[20.  Holders' Compliance with Registration Rights Agreement
      ------------------------------------------------------

          Each Holder of a Security, by acceptance hereof, acknowledges and
agrees to the provisions of the Registration Rights Agreement, including the
obligations of the Holders with respect to a registration and the
indemnification of the Company to the extent provided therein.]/1/

21.  Governing Law
     -------------

          THIS SECURITY SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH,
THE LAWS OF THE STATE OF NEW YORK BUT WITHOUT GIVING EFFECT TO APPLICABLE
PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF
ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

          The Company will furnish to any Securityholder upon written request
and without charge to the Securityholder a copy of the Indenture which has in it
the text of this Security in larger type.  Requests may be made to:

          Morrison Knudsen Corporation
          720 Park Boulevard
          Boise, Idaho 83712

          Attention: General Counsel

______________

     1.   Delete if this Security is not being issued in exchange for an Initial
     Security.
<PAGE>

                                                                              10

____________________________________________________________________

                                ASSIGNMENT FORM

To assign this Security, fill in the form below:

I or we assign and transfer this Security to

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

     (Insert assignee's soc. sec. or tax I.D. No.)

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

____________________________________________________________________

Date: ________________  Your Signature: ____________________________

____________________________________________________________________
Sign exactly as your name appears on the other side of this Security.
<PAGE>

                                                                              11

                      OPTION OF HOLDER TO ELECT PURCHASE

          If you want to elect to have this Security purchased by the Company
pursuant to Section 4.07 or 4.10 of the Indenture, check the box: [_]


          If you want to elect to have only part of this Security purchased by
the Company pursuant to Section 4.07 or 4.10 of the Indenture, state the amount
in principal amount:  $_____________

Date: _______________      Your Signature: _________________________
                                           (Sign exactly as your name
                                           appears on the other side of
                                           this Security.)

Signature Guarantee: _______________________________________
                         (Signature must be guaranteed)

     Signatures must be guaranteed by an "eligible guarantor institution"
meeting the requirements of the Registrar, which requirements include membership
or participation in the Security Transfer Agent Medallion Program ("STAMP") or
such other "signature guarantee program" as may be determined by the Registrar
in addition to, or in substitution for, STAMP, all in accordance with the
Securities Exchange Act of 1934, as amended.
<PAGE>

                                                                      Schedule A

                             Subsidiary Guarantors
                             ---------------------

                                                       Jurisdiction of
Subsidiary                                              Incorporation
----------                                              -------------

Centennial Engineering, Inc.                               Colorado

Morrison Knudsen Corporation                               Ohio

Morrison Knudsen Corporation (Montana)                     Montana

Morrison Knudsen International, Inc.                       Nevada

Morrison Knudsen Leasing Corporation                       Nevada

Morrison Knudsen LLC                                       Nevada

National Projects, Inc.                                    Nevada

Pomeroy Corporation                                        California

Washington Contractors Group, Inc.                         Montana

Raytheon Engineers & Constructors, Inc.                    Delaware

United Mid-East, Inc.                                      Delaware

Energy Overseas International, Inc.                        Delaware

United Engineers International, Inc.                       Pennsylvania

United Engineers Far East, Ltd.                            Delaware

Raytheon Constructors, Inc.                                Delaware

Raytheon-Catalytic, Inc.                                   Delaware

Raytheon Engineers & Constructors Midwest, Inc.            Delaware

Asia Badger, Inc.                                          Delaware

Badger Energy, Inc.                                        Delaware

Raytheon-Ebasco Overseas Ltd.                              Delaware

Raytheon Engineers & Constructors UK Ltd.                  Delaware

Raytheon Demilitarization Company                          Delaware

Raytheon Constructors International, Inc.                  Delaware

Rust Constructors, Inc.                                    Delaware