Document:

<PAGE>   1
                                                                     EXHIBIT 4.3

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          BOOK-ENTRY-ONLY COLLATERALIZED MORTGAGE OBLIGATIONS (CMOS) -
             WITHOUT OWNER OPTION TO REDEEM/PASS-THROUGH SECURITIES/
                           AND ASSET-BACKED SECURITIES
--------------------------------------------------------------------------------

                           Letter of Representations*
                      [to be Completed by Issuer and Agent]

                   Discover Card Master Trust I, Series 2001-2
                   -------------------------------------------
                                [Name of Issuer]

                         U.S. Bank National Association
                         ------------------------------
                                 [Name of Agent]

                                                                January 16, 2001
                                                                ----------------
                                                                          [Date]

Attention:  General Counsel's Office
The Depository Trust Company
55 Water Street 49th Floor
New York, NY 10041-0099

         Re:     Floating Rate Class A Credit Card Pass-Through Certificates and
                 Floating Rate Class B Credit Card Pass-Through Certificates,
                 Discover Card Master Trust 1, Series 2001-2
                 ---------------------------------------------------------------
                             [Issue description ("The Securities")]

Ladies and Gentlemen:

         This letter sets forth our understanding with respect to certain
matters relating to the Securities. Agent shall act as trustee, paying agent,
fiscal agent, or other such agent of Issuer with respect to the Securities. The
Securities have been issued pursuant to a trust indenture, trust agreement,
pooling and servicing agreement or other such document authorizing the issuance
of the Securities dated October 1, 1993 (the "Document"). Morgan Stanley & Co.
Incorporated; Banc of America Securities LLC, Barclays Capital Inc.; Dresdner
Kleinwort Benson North

----------

*        This Letter of Representations includes the Addendum attached hereto,
         which modifies and supercedes this Letter of Representations to the
         extent set forth therein.

<PAGE>   2

America LLC ["Underwriter/Placement Agent"] is distributing the Securities
through The Depository Trust Company ("DTC").

                  To induce DTC to accept the Securities as eligible for deposit
at DTC, and to act in accordance with its Rules with respect to the Securities,
Issuer and Agent make the following representations to DTC:

                  1. Prior to closing on the Securities on January 16, 2001
there shall be deposited with DTC one or more Security certificates registered
in the name of DTC's nominee, Cede & Co., for each stated maturity of the
Securities in the face amounts set forth on Schedule A hereto, the total of
which represents 100% of the principal amount of such Securities. If however,
the aggregate principal amount of any maturity exceeds $400 million, one
certificate shall be issued with respect to each $400 million of principal
amount and an additional certificate shall be issued with respect to any
remaining principal amount. Each Security certificate shall bear the following
legend:

                           Unless this certificate is presented by an authorized
         representative of The Depository Trust Company, a New York corporation
         ("DTC"), to Issuer or its agent for registration of transfer, exchange,
         or payment, and any certificate issued is registered in the name of
         Cede & Co. or in such other name as is requested by an authorized
         representative of DTC (and any payment is made to Cede & Co. or to such
         other entity as is requested by an authorized representative of DTC),
         ANY TRANSFER, PLEDGE, OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR
         TO ANY PERSON IS WRONGFUL inasmuch as the registered owner hereof, Cede
         & Co., has an interest herein.

Issuer represents:

                  The Security certificate(s) shall remain in Agent's custody as
a "Balance Certificate" subject to the provisions of the Balance Certificate
Agreement between Agent and DTC currently in effect.

                  On each day on which Agent is open for business and on which
it receives an instruction originated by a DTC participant ("Participant")
through DTC's Deposit/Withdrawal at Custodian ("DWAC") system to increase the
Participant's account by a specified number of Securities (a "Deposit
Instruction"), Agent shall, no later than 6:30 p.m. (Eastern Time) that day,
either approve or cancel the Deposit Instruction through the DWAC system.

                  On each day on which Agent is open for business and on which
it receives an instruction originated by Participant through the DWAC system to
decrease the Participant's account by a specified number of Securities (a
"Withdrawal Instruction"), Agent shall, no later than 6:30 pm. (Eastern Time)
that day, either approve or cancel the Withdrawal Instruction through the DWAC
system.

<PAGE>   3

                  Agent agrees that its approval of a Deposit or Withdrawal
Instruction shall be deemed to be the receipt by DTC of a new reissued or
reregistered certificated Security on registration of transfer to the name of
Cede & Co. for the quantity of Securities evidenced by the Balance Certificate
after the Deposit or Withdrawal Instruction is effected.

                  2. Issuer: (a) understands that DTC has no Obligation to, and
will not, communicate to its Participants or to any person having an interest in
the Securities any information contained in the Security certificate(s); and (b)
acknowledges that neither DTC's Participants nor any person having an interest
in the Securities shall be deemed to have notice of the provisions of the
Security certificates by virtue of submission of such certificate(s) to DTC.

                  3. In the event of any solicitation of consents from or voting
by holders of the Securities, Issuer or Agent shall establish a record date for
such purposes (with no provision for revocation of consents or votes by
subsequent holders) and shall send notice of such record date to DTC no fewer
than 15 calendar days in advance of such record date. Notices to DTC pursuant to
this Paragraph by telecopy shall be directed to DTC's Reorganization Department,
Proxy Unit at (212) 855-5181 or (212) 855-5182. If the party sending the notice
does not receive a telecopy receipt from DTC confirming that the notice has been
received, such party shall telephone (212) 855-5202. Notices to DTC pursuant to
this Paragraph, by mail or by any other means, shall be sent to:

                                    Supervisor, Proxy Unit
                                    Reorganization Department
                                    The Depository Trust Company
                                    55 Water Street 50th Floor
                                    New York, NY 10041-0099

                  4. In the event of a full or partial redemption, Issuer or
Agent shall send a notice to DTC specifying: (a) the amount of the redemption or
refunding; (b) in the case of a refunding, the maturity date(s) established
under the refunding; and (c) the date such notice is to be distributed to
Security holders (the "Publication Date"). Such notice shall be sent to DTC by a
secure means (e.g. legible telecopy, registered or certified mail, overnight
delivery) in a timely manner designed to assure that such notice is in DTC's
possession no later than the close of business on the business day before or, if
possible, two business days before the Publication Date. Issuer or Agent shall
forward such notice either in a separate secure transmission for each CUSIP
number or in a secure transmission for multiple CUSIP numbers (if applicable)
which includes a manifest or list of each CUSIP number submitted in that
transmission. (The party sending such notice shall have a method to verify
subsequently the use of such means and the timeliness of such notice). The
Publication Date shall be no fewer than 30 days nor more than 60 days prior to
the redemption date or, in the case of an advance refunding, the date that the
proceeds are deposited in escrow. Notices to DTC pursuant to this Paragraph by
telecopy shall be directed to DTC's Call Notification Department at (516)
227-4164 or (516) 227-4190. If the party sending the notice does not receive a
telecopy receipt from DTC confirming that the notice has been received,

<PAGE>   4

such party shall telephone (516) 227-4070. Notices to DTC pursuant to this
Paragraph, by mail or by any other means, shall be sent to:

                               Manager, Call Notification Department
                               The Depository Trust Company
                               711 Stewart Avenue
                               Garden City, NY  11530-4719

                  5. In the event of an invitation to tender the Securities
(including mandatory tenders, exchanges, and capital changes), notice by Issuer
or Agent to Security holders shall be sent to DTC specifying the terms of the
tender and the Publication Date of such notice. Such notice shall be sent to DTC
by a secure means (e.g. legible telecopy, registered or certified mail,
overnight delivery) in a timely manner designed to assure that such notice is in
DTC's possession no later than the close of business on the business day before
or, if possible, two business days before the Publication Date. Issuer or Agent
shall forward such notice either in a separate secure transmission for each
CUSIP number or in a secure transmission for multiple CUSIP numbers (if
applicable) which includes a manifest or list of each CUSIP number submitted in
that transmission. (The party sending such notice shall have a method to verify
subsequently the use and timeliness of such notice.) Notices to DTC pursuant to
this Paragraph and notices of other corporate actions by telecopy shall be
directed to DTC's Reorganization Department at (212) 855-5488. If the party
sending the notice does not receive a telecopy receipt from DTC confirming that
the notice has been received, such party shall telephone (212) 855-5290. Notices
to DTC pursuant to this Paragraph, by mail or by any other means, shall be sent
to:

                               Manager, Reorganization Department
                               Reorganization Window
                               The Depository Trust Company
                               55 Water Street 50TH Floor
                               New York, NY  10041-0099

                  6. It is understood that if the Security holders shall at any
time have the right to tender the Securities to Issuer and require that Issuer
repurchase such holders' Securities pursuant to the document and Cede & Co., as
nominee of DTC, or its registered assigns, as the record owner, is entitled to
tender the Securities, such tenders will be effected by means of DTC's Repayment
Option Procedures. Under the Repayment Option Procedures, DTC shall receive,
during the applicable tender period, instructions from its Participants to
tender Securities for purchase. Issuer and Agent agree that such tender for
purchase may be made by DTC by means of a book-entry credit of such Securities
to the account of Agent, provided that such credit is made on or before the
final day of the applicable tender period. DTC agrees that promptly after the
recording of any such book-entry credit, it will provide to Agent an Agent
Receipt and Confirmation or the equivalent, in accordance with the Repayment
Option Procedures, identifying the Securities and the aggregate principal amount
thereof as to which such tender for purchase has been made.

                  Agent shall send DTC notice regarding such optional tender by
hand or by a secure means (e.g., legible facsimile transmission, registered or
certified mail, overnight delivery) in a timely manner designed to assure that
such notice is in DTC's possession no later than the close of business two
business days before the Publication Date. The Publication Date shall be no
fewer than 15 days prior to the expiration date of the applicable tender period.
Such notice shall

<PAGE>   5

state whether any partial redemption of the Securities is scheduled to occur
during the applicable optional tender period. Notices to DTC pursuant to this
Paragraph by telecopy shall be directed to DTC's Put Bond Unit at (212)
855-5235. If the party sending the notice does not receive a telecopy receipt
from DTC confirming that the notice has been received, such party shall
telephone (212) 855-5230. Notices to DTC pursuant to this Paragraph, by mail or
by any other means, shall be sent to:

                                Supervisor, Put Bond Unit
                                Reorganization Window
                                The Depository Trust Company
                                55 Water Street 50TH Floor
                                New York, NY  10041-0099

                  7. All notices and payment advices sent to DTC shall contain
the CUSIP number of the Securities.

                  8. Issuer or Agent shall send DTC written notice with respect
to the dollar amount per $1,000 original face value (or other minimum authorized
denomination if less than $1,000 face value) payable on each payment date
allocated as to the interest and principal portions thereof preferably five, but
no fewer than two, business days prior to such payment date. Such notices, which
shall also contain the current pool factor, any special adjustments to
principal/interest rates (e.g., adjustments due to deferred interest or
shortfall), and Agent contact's name and telephone number, shall be sent by
telecopy to DTC's Dividend Department at (212) 855-4555, and receipt of such
notices shall be confirmed by telephoning (212) 855-4550. Notices to DTC,
pursuant to this Paragraph, by mail or by any other means, shall be sent to:

                                Manager, Announcements
                                Dividend Department
                                The Depository Trust Company
                                55 Water Street 25TH Floor
                                New York, NY  10041-0099

                  9. Issuer represents: The interest accrual period is payment
date to payment date.

                  10. Issuer or Agent shall provide a written notice of interest
payment information, including the stated coupon rate information, to DTC as
soon as the information is available. Issuer or Agent shall provide such notice
directly to DTC electronically, as previously arranged by Issuer or Agent and
DTC. If electronic transmission has not been arranged, absent any other
arrangements between Issuer or Agent and DTC, such information shall be sent by
telecopy to DTC's Dividend Department at (212) 855-4555 or (212) 855-4556. If
the party sending the notice does not receive a telecopy receipt from DTC
confirming that the notice has been received, such party shall telephone (212)
855-4550. Notices to DTC pursuant to this Paragraph, by mail or by any other
means, shall be sent to DTC's Dividend Department as indicated in Paragraph 8.

<PAGE>   6

                  11. Interest payments and principal payments that are part of
periodic principal-and-interest payments shall be received by Cede & Co., as
nominee of DTC, or its registered assigns, in same-day funds no later than 2:30
p.m. (Eastern Time) on each payment date. Issuer shall remit by 1:00 p.m.
(Eastern Time) on the payment date all such interest payments due Agent, or at
such earlier time as may be required by Agent to guarantee that DTC shall
receive payment in same-day funds no later than 2:30 p.m. (Eastern Time) on the
payment date. Absent any other arrangements between Issuer or Agent and DTC,
such funds shall be wired to the Dividend Deposit Account number that will be
stamped on the signature page hereof at the time DTC executes this Letter of
Representations.

                  12. Issuer or Agent shall provide DTC's Dividend Department,
no later than 12:00 noon (Eastern Time) on the payment date, automated
notification of CUSIP-level detail. If the circumstances prevent the funds paid
to DTC from equaling the dollar amount associated with the detail payments by
12:00 noon (Eastern Time), Issuer or Agent must provide CUSIP-level
reconciliation to DTC no later than 2:30 p.m. (Eastern Time). Reconciliation
must be provided by either automated means or written format. Such
reconciliation notice, if sent by telecopy, shall be directed to DTC Dividend
Department at (212) 855-4633 and receipt of such reconciliation notice shall be
confirmed by telephoning (212) 855-4430.

                  13. Maturity and redemption payments allocated with respect to
each CUSIP number shall be received by Cede & Co., as nominee of DTC, or its
registered assigns, in same-day funds no later than 2:30 p.m. (Eastern Time) on
the payment date. Issuer shall remit by 1:00 p.m. (Eastern Time) on the payment
date all such maturity and redemption payments due Agent, or at such earlier
time as required by Agent to guarantee that DTC shall receive payment in
same-day funds no later than 2:30 p.m. (Eastern Time) on the payment date.
Absent any other arrangements between Issuer or Agent and DTC, such funds shall
be wired to the Redemption Deposit Account number that will be stamped on the
signature page hereof at the time DTC executes this Letter of Representations.

                  14. Principal payments (plus accrued interest, if any) as the
result of optional tenders for purchase effected by means of DTC's Repayment
Option Procedures shall be received by Cede & Co., as nominee of DTC, or its
registered assigns, in same-day funds no later than 2:30 p.m. (Eastern Time) on
the payment date. Issuer shall remit by 1:00 p.m. (Eastern Time) on the payment
date all such reorganization payments due Agent, or at such earlier time as
required by Agent to guarantee that DTC shall receive payment in same-day funds
no later than 2:30 p.m. (Eastern Time) on the payment date. Absent any other
arrangements between Issuer or Agent and DTC, such funds shall be wired to the
Reorganization Deposit Account number that will be stamped on the signature page
hereof at the time DTC executes this Letter of Representations.

                  15. Agent shall send DTC all periodic certificate holders
remittance reports with respect to the Securities. If sent by facsimile
transmission, such reports shall be sent to (212) 855-4777. If the party sending
the report does not receive a telecopy receipt from DTC confirming that the
notice has been received, such party shall telephone (212) 855-4590.

                  16. DTC may direct Issuer or Agent to use any other number or
address as the number or address to which notices or payments of interest or
principal may be sent.

<PAGE>   7

                  17. In the event of a redemption, acceleration, or any other
similar transaction (e.g., tender made and accepted in response to Issuer's or
Agent's invitation) necessitating a reduction in the aggregate principal amount
of Securities outstanding or an advance refunding of part of the Securities
outstanding, DTC, in its discretion: (a) may request Issuer or Agent to issue
and authenticate a new Security certificate; or (b) may make an appropriate
notation on the Security certificate indicating the date and amount of such
reduction in principal except in the case of final maturity, in which case the
certificate will be presented to Issuer or Agent prior to payment, if required.

                  18. In the event that Issuer determines that beneficial owners
of Securities shall be able to obtain certificated Securities, Issuer or Agent
shall notify DTC of the availability of certificates. In such event, Issuer or
Agent shall issue, transfer, and exchange certificates in appropriate amounts,
as required by DTC and others.

                  19. DTC may discontinue providing its services as securities
depository with respect to the Securities at any time be giving reasonable
notice to Issuer or Agent (at which time DTC will confirm with Issuer or Agent
the aggregate principal amount of Securities outstanding). Under such
circumstances, at DTC's request Issuer and Agent shall cooperate fully with DTC
by taking appropriate action to make available one or more separate certificates
evidencing Securities to any Participant having Securities credited to its DTC
accounts.

                  20. Nothing herein shall be deemed to require Agent to advance
funds on behalf of Issuer.

                  21. This Letter of Representations may be executed in any
number of counterparts, each of which when so executed shall be deemed to be an
original, but all such counterparts together shall constitute but one and the
same instrument.

                  22. This Letter of Representations shall be governed by, and
construed in accordance with, the laws of the State of New York, without giving
effect to principles of conflicts of law.

                  23. The sender of each notice delivered to DTC pursuant to
this Letter of Representations is responsible for confirming that such notice
was properly received by DTC.

                  24. Issuer recognizes that DTC does not in any way undertake
to, and shall not have any responsibility to, monitor or ascertain the
compliance of any transactions in the Securities with the following, as amended
from time to time: (a) any exemptions from registration under the Securities Act
of 1933; (b) the Investment Company Act of 1940; (c) the Employee Retirement
Income Security Act of 1974; (d) the Internal Revenue Code of 1986; (e) any
rules of any self-regulatory organizations (as defined under the Securities
Exchange Act of 1934); or (f) any other local, state, or federal laws or
regulations thereunder.

                  25. Issuer hereby authorizes DTC to provide to Agent listings
of Participants' holdings, known as Securities Position Listings ("SPLs") with
respect to the Securities from time to time at the request of the Agent. DTC
charges a fee for such SPLs. This authorization, unless

<PAGE>   8

revoked by Issuer, shall continue with respect to the Securities while any
Securities are on deposit at DTC, until and unless Agent shall no longer be
acting. In such event, Issuer shall provide DTC with similar evidence,
satisfactory to DTC, of the authorization of any successor thereto so to act.
Requests for SPLs shall be sent by telecopy to the Proxy Unit of DTC's
Reorganization Department at (212) 855-5181 or (212) 855-5182. Receipt of such
requests shall be confirmed by telephoning (212) 855-5202. Requests for SPLs,
sent by mail or by any other means, shall be directed to the address indicated
in Paragraph 3.

                  26. Issuer and Agent shall comply with the applicable
requirements stated in DTC's Operational Arrangements, as they may be amended
from time to time. DTC's Operational Arrangements are posted on DTC's website at
"www.DTC.org."

                  27. The following riders(s), attached hereto, are hereby
incorporated into this Letter of Representations:

                  (1) Addendum;

                  (2) Schedule A

                  (3) Schedule B

                  (4) Rider

<PAGE>   9
NOTES:

A. IF THERE IS AN AGENT (AS DEFINED IN THIS
LETTER OF REPRESENTATIONS), AGENT AS WELL AS
ISSUER MUST SIGN THIS LETTER. IF THERE IS NO
AGENT, IN SIGNING THIS LETTER ISSUER ITSELF
UNDERTAKES TO PERFORM ALL OF THE OBLIGATIONS
SET FORTH HEREIN.

B. SCHEDULE B CONTAINS STATEMENTS THAT DTC
BELIEVES ACCURATELY DESCRIBE DTC, THE METHOD
OF EFFECTING BOOK-ENTRY TRANSFERS OF
SECURITIES DISTRIBUTED THROUGH DTC, AND
CERTAIN RELATED MATTERS.

                                Very truly yours,

                                DISCOVER CARD MASTER TRUST I, by DISCOVER BANK
                                ------------------------------------------------
                                                  [Issuer]

                                By:           /s/ Michael F. Rickert
                                   ---------------------------------------------
                                          [Authorized Officer's Signature]

                                         U.S. BANK NATIONAL ASSOCIATION
                                ------------------------------------------------
                                                    [Agent]

                                By:           /s/ Patricia M. Child
                                   ---------------------------------------------
                                          [Authorized Officer's Signature]

Received and Accepted:
THE DEPOSITORY TRUST COMPANY

By:   /s/ Richard B. Nesson
   ----------------------------------

Funds should be wired to:
The Chase Manhattan Bank
ABA #021 000 021
For credit to a/c Cede & Co.
c/o The Depository Trust Company

[Select Appropriate Account.]

Dividend Deposit Account #066-026776
Redemption Deposit Account #066-027306
Reorganization Deposit Account #066-027608

cc:      Underwriter/Placement Agent
         Underwriter's/Placement Agent's Counsel

<PAGE>   10
                                    ADDENDUM

                                       to
                 Letter of Representations dated January 16, 2001
                   Discover Card Master Trust I, Series 2001-2

General:                           For purposes of this Letter of
                                   Representations:

                                   "Securities" shall mean the $1,100,000,000
                                   aggregate principal amount of Floating Rate
                                   Class A Credit Card Pass-Through Certificates
                                   and the $57,895,000 aggregate principal
                                   amount of Floating Rate Class B Credit Card
                                   Pass-Through Certificates issued by Discover
                                   Card Master Trust I, Series 2001-2 and
                                   "Security holders" shall mean the holders of
                                   such certificates;

                                   "Issuer" shall mean Discover Bank (formerly
                                   Greenwood Trust Company) ("Discover") on
                                   behalf of Discover Card Master Trust I,
                                   Series 2001-2; and

                                   "Document" shall mean the Pooling and
                                   Servicing Agreement dated as of October 1,
                                   1993, as amended and as supplemented by the
                                   Series Supplement dated as of January 16,
                                   2001 each by and between Discover as Master
                                   Servicer, Servicer and Seller and the Agent.

Paragraph 8:                       The following is hereby added after the third
                                   sentence of Paragraph 8:

                                            "Issuer or Agent will forward such
                                            notice either in a separate secure
                                            transmission for each CUSIP number
                                            or in a secure transmission for
                                            multiple CUSIP numbers (if
                                            applicable) which includes a
                                            manifest or list of each CUSIP
                                            submitted in that transmission."

Paragraph 16:                      The following is hereby inserted after the
                                   word "Agent" in line 1 of Paragraph 16:

                                            ", and if requested, shall confirm
                                            such direction in writing if
                                            practicable,"

Paragraph 17:                      The following is hereby inserted at the end
                                   of Paragraph 17 before the period:

                                            "provided, however, that this
                                            paragraph shall not apply to any
                                            event that causes a reduction in the
                                            aggregate principal amount of
                                            Securities outstanding that occurs
                                            in accordance with their terms,
                                            including, without limitation, an
                                            Amortization Event (as defined in
                                            the Document)".

<PAGE>   11
                                   SCHEDULE A

                   DISCOVER CARD MASTER TRUST I, SERIES 2001-2

   $1,100,000,000 FLOATING RATE CLASS A CREDIT CARD PASS-THROUGH CERTIFICATES
   AND $57,895,000 FLOATING RATE CLASS B CREDIT CARD PASS-THROUGH CERTIFICATES

<TABLE>
<CAPTION>
     Class A Certificates
         CUSIP Number         Principal Amount             Maturity Date*               Interest Rate
     --------------------     ----------------             --------------               -------------
<S>                           <C>                          <C>                          <C>
         25466K DL 0

     Certificate Number:
     -------------------
              1                 $400,000,000                 July 16, 2008                Floating Rate
              2                 $400,000,000                 July 16, 2008                Floating Rate
              3                 $300,000,000                 July 16, 2008                Floating Rate

     Class B Certificates
         CUSIP Number
     --------------------
         25466K DM 8

     Certificate Number:
     -------------------
              1                 $ 57,895,000                 July 16, 2008                Floating Rate
</TABLE>

----------
* Last Possible Distribution Date

<PAGE>   12

                                                                      SCHEDULE B

                        SAMPLE OFFERING DOCUMENT LANGUAGE
                       DESCRIBING BOOK-ENTRY-ONLY ISSUANCE

     1. The Depository Trust Company ("DTC"), New York, NY, will act as
securities depository for the securities (the "Securities"). The Securities will
be issued as fully-registered securities registered in the name of Cede & Co.
(DTC's partnership nominee) or such other name as may be requested by an
authorized representative of DTC. One fully-registered Security certificate will
be issued for [each issue of] the Securities, [each] in the aggregate principal
amount of such issue, and will be deposited with DTC. [If, however, the
aggregate principal amount of [any] issue exceeds $400 million, one certificate
will be issued with respect to each $400 million of principal amount and an
additional certificate will be issued with respect to any remaining principal
amount of such issue.]

     2. DTC is a limited-purpose trust company organized under the New York
Banking Law, a "banking organization" within the meaning of the New York Banking
Law, a member of the Federal Reserve System, a "clearing corporation" within the
meaning of the New York Uniform Commercial Code, and a "clearing agency"
registered pursuant to the provisions of Section 17A of the Securities Exchange
Act of 1934. DTC holds securities that its participants ("Direct Participants")
deposit with DTC. DTC also facilitates the settlement among Direct Participants
of securities transactions, such as transfers and pledges, in deposited
securities through electronic computerized book-entry changes in Direct
Participants' accounts, thereby eliminating the need for physical movement of
securities certificates. Direct Participants include securities brokers and
dealers, banks, trust companies, clearing corporations, and certain other
organizations. DTC is owned by a number of its Direct Participants and by the
New York Stock Exchange, Inc., the American Stock Exchange LLC, an the National
Association of Securities Dealers, Inc. Access to the DTC system is also
available others such as securities brokers and dealers, banks, and trust
companies that clear through or maintain a custodial relationship with a Direct
Participant, either directly or indirectly ("Indirect Participants"). The Rules
applicable to DTC and its Direct and Indirect Participants are on file with the
Securities Exchange Commission.

     3. Purchases of Securities under the DTC system must be made by or through
Direct Participants, which will receive a credit for the Securities on DTC's
records. The ownership interest of each actual purchaser of each Security
("Beneficial Owner") is in turn to be recorded on the Direct and Indirect
Participants' records. Beneficial Owners are expected to receive written
confirmations providing details of the transaction, as well as periodic
statements of their holdings, from the Direct or Indirect Participant through
which the Beneficial Owner entered into the transaction. Transfers of ownership
interests in the Securities are to be accomplished by entries made on the books
of Direct and Indirect Participants acting on behalf of Beneficial Owners.
Beneficial Owners will not receive certificates representing their ownership
interests in Securities, except in the event that use of the book-entry system
for the Securities is discontinued.

     4. To facilitate subsequent transfers, all Securities deposited by Direct
Participants with DTC are registered in the name of DTC's partnership nominee,
Cede & Co. or such other name as may be requested by an authorized
representative of DTC. The deposit of Securities with DTC and their registration
in the name of Cede & Co. or such other nominee do not

<PAGE>   13

effect any change in beneficial ownership. DTC has no knowledge of the actual
Beneficial Owners of the Securities. DTC's records reflect only the identify of
the Direct Participants to whose accounts such Securities are credited, which
may or may not be the Beneficial Owners. The Direct and Indirect Participants
will remain responsible for keeping account of their holdings on behalf of their
customers.

     5. Conveyance of notices and other communications by DTC to Direct
Participants, by Direct Participants to Indirect Participants, and by Direct
Participants and Indirect Participants to Beneficial Owners will be governed by
arrangements among them, subject to any statutory or regulatory requirements as
may be in effect from time to time. [Beneficial Owners of Securities may wish to
take certain steps to augment transmission to them of notices of significant
events with respect to the Securities, such as redemptions, tenders, defaults,
and proposed amendments to the security documents. Beneficial Owners of
Securities may wish to ascertain that the nominee holding the Securities for
their benefit has agreed to obtain and transmit notices of Beneficial Owners, or
in the alternative, Beneficial Owners may wish to provide their names and
addresses to the registrar and request that copies of the notices be provided
directly to them.]

     6. [Redemption notices shall be sent to DTC. If less than all of the
Securities within an issue are being redeemed, DTC's practice to determine by
lot the amount of the interest of each Direct Participant in such issue to be
redeemed.]

     7. Neither DTC nor Cede & Co. (nor such other DTC nominee) will consent or
vote with respect to the Securities. Under its usual procedures, DTC mails an
Omnibus Proxy to Issuer as soon as possible after the record date. The Omnibus
Proxy assigns Cede & Co.'s consenting or voting rights to those Direct
Participants to whose accounts the Securities are credited on the record date
(identified in a listing attached to the Omnibus Proxy).

     8. Redemption proceeds, distributions, and dividend payments on the
Securities will be made to Cede & Co., or such other nominee as may be requested
by an authorized representative of DTC. DTC's practice is to credit Direct
Participants' accounts, upon DTC's receipt of funds and corresponding detail
information from Issuer or Agent on payable date in accordance with their
respective holdings shown on DTC's records. Payments by Participants to
Beneficial Owners will be governed by standing instructions and customary
practices, as is the case with securities held for the accounts of customers in
bearer funds or registered in "street name," and will be the responsibility of
such Participant and not of DTC, Agent, or Issuer, subject to any statutory or
regulatory requirements as may be in effect from time to time. Payment of
redemption proceeds, distributions, and dividends to Cede & Co. (or such other
nominee as may be requested by an authorized representative of DTC) is the
responsibility of Issuer or Agent, disbursement of such payments to Direct
Participants shall be the responsibility of DTC, and disbursement of such
payments to the Beneficial Owners shall be the responsibility of Direct and
Indirect Participants.

     9. [A Beneficial Owner shall give notice to elect to have its Securities
purchased or tendered, through its Participant, to [Tender/Remarketing] Agent,
and shall effect delivery of such Securities by causing the Direct Participant
to transfer the Participant's interest in the Securities, on DTC's records, to
[Tender/Remarketing] Agent. The requirement for physical delivery of Securities
in connection with an optional tender or a mandatory purchase will be deemed
satisfied when the ownership rights in the Securities are transferred by Direct

<PAGE>   14

Participants on DTC's records and followed by a book-entry credit of tendered
Securities to [Tender/Remarketing] Agent's DTC account.]

     10. DTC may discontinue providing its services as securities depository
with respect to the Securities at any time by giving reasonable notice to Issuer
or Agent. Under such circumstances, in the event that a successor securities
depository is not obtained, Security certificates are required to be printed and
delivered.

     11. Issuer may decide to discontinue use of the system of book-entry
transfers through DTC (or a successor securities depository). In that event,
Security certificates will be printed and delivered.

     12. The information in this section concerning DTC and DTC's book-entry
system has been obtained from sources that Issuer believes to be reliable, but
Issuer takes no responsibility for the accuracy thereof.

<PAGE>   15

                                      RIDER

                  Issuer and Agent acknowledge that DTC is not a party to the
Document and that no obligations or liabilities shall be deemed to accrue to DTC
with regard to the Document.<PAGE>   1
                                                                EXHIBIT 10.21(A)

                                                     November 28, 2000

Bank One
One Bank One Plaza
14th Floor, Mail Code IL1-0088
Chicago, IL 60670-0088

Attention: April Yebd
           Fax #:  312-732-2715

                   Re:  Termination of Credit Agreement dated September 30, 1999

Reference is made to Section 2.08 (c) of the Credit Agreement dated as of
September 30, 1999 (as amended and in effect on the dated hereof, the "Credit
Agreement"), among the undersigned, as Borrower, the Lenders named therein and
The Chase Manhattan Bank, as Administrative Agent. Terms defined in the Credit
Agreement are used herein with the same meanings.

This notice constitutes a reduction and termination of the Commitments under the
Credit Agreement, from $100,000,000.00 USD to $0 USD effective December 1, 2000.
This reduction and termination notice is conditioned upon the closing and
funding of the credit facility on December 1, 2000, among the undersigned, as
Borrower, and Bank One, NA, as Administrative Agent, and the Lenders referenced
therein.

        (A)   Current Commitments /:                             $100,000,000.00
                                 -----------------------------------------------
        (B)   Reduction and Termination, effective 12/01/00:/    $100,000,000.00
                                                             -------------------
        (C)   Total Commitments, effective 12/01/00:/                      $0.00
                                                     ---------------------------

                                      Very truly yours,

                                      Chicago Bridge & Iron Company, N.V.

                                      By:     Chicago Bridge & Iron Company B.V.
                                      Its:    Managing Director

                                      By:     /s/ Gerald M. Glenn
                                              ----------------------------------
                                      Name:   Gerald M. Glenn
                                      Title:  Managing Director

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