<PAGE>   1
                                                                     Exhibit 4.3





                       MELLON FUNDING CORPORATION, Issuer



                                       AND



                     MELLON FINANCIAL CORPORATION, Guarantor



                                       TO



                        THE CHASE MANHATTAN BANK, Trustee









                          SECOND SUPPLEMENTAL INDENTURE









                           Dated as of          , 2000
                                       --------







================================================================================
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         Second supplemental indenture, dated as of         , 2000 among Mellon
Funding Corporation (formerly Mellon Financial Company), a corporation duly
organized and existing under the laws of the Commonwealth of Pennsylvania having
its principal office at One Mellon Center, 500 Grant Street, Pittsburgh,
Pennsylvania 15258 (herein called the "Company"), Mellon Financial Corporation
(formerly Mellon Bank Corporation), a corporation duly organized and existing
under the laws of the Commonwealth of Pennsylvania having its principal office
at One Mellon Center, 500 Grant Street, Pittsburgh, Pennsylvania 15258 (herein
called the "Guarantor"), and The Chase Manhattan Bank, a New York banking
association duly organized and existing under the laws of the state of New York
having its principal executive office at 1 Chase Manhattan Plaza, New York, New
York 10081, as Trustee (herein called the "Trustee").

                                    RECITALS

         The Company and the Guarantor have heretofore executed and delivered to
the Trustee a certain indenture, dated as of May 2, 1988 (herein called the
"Indenture"), and the First Supplemental Indenture, dated as of November 29,
1990 (herein called the "First Supplemental Indenture"), pursuant to which one
or more series of unsecured debentures, notes or other evidences of indebtedness
of the Company guaranteed by the Guarantor (herein called the "Securities") may
be issued from time to time by the Company. All capitalized terms used in this
Second Supplemental Indenture which are defined in the Indenture or the First
Supplemental Indenture shall have the meanings assigned to them in the Indenture
or the First Supplemental Indenture, as applicable.

         The Company and the Guarantor desire and have requested the Trustee to
join with them in the execution and delivery of this Second Supplemental
Indenture for the purpose of amending the Indenture in certain respects with
respect to the Securities of any series created on or after the date hereof and
in order to permit the Company to elect that the Securities of any such series,
in whole or in any specified part, shall be defeasible.

         Section 1001(8) of the Indenture provides that a Supplemental Indenture
may be entered into by the Company, the Guarantor and the Trustee without the
consent of any Holders to make provisions with respect to matters arising under
the Indenture which do not adversely affect the interests of the Holders of
Securities of any series in any material respect.

         The Company has furnished the Trustee with (i) an Opinion of Counsel
stating that the execution of the Second Supplemental Indenture is authorized or
permitted by the Indenture, (ii) an Officer's Certificate and an Opinion of
Counsel each stating that all conditions precedent provided for in the Indenture
with respect to this Second Supplemental Indenture have been complied with, and
(iii) a copy of the resolutions of its Board of Directors certified by its
Secretary pursuant to which this Second Supplemental Indenture has been
authorized.

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         All things necessary to make this Second Supplemental Indenture a valid
agreement of the Company, the Guarantor and the Trustee and a valid amendment of
and supplement to the Indenture have been done.

         NOW THEREFORE THIS SECOND SUPPLEMENTAL INDENTURE WITNESSETH:

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

                                   ARTICLE ONE

                           AMENDMENTS TO THE INDENTURE

         SECTION 1.1. Section 101 of the Indenture is amended to include therein
the following provisions:

                  (a)    After the definition of corporation:

                         "'Covenant Defeasance' has the meaning specified in
                  Section 1403."

                  (b)    After the definition of Defaulted Interest:

                         "'Defeasance' has the meaning specified in Section
                  1402."

                  (c)    After the definition of Trust Indenture Act:

                         "U.S. Government Obligation" has the meaning
                  specified in Section 1404."

                  (d)    The definition of Outstanding is amended by adding the
                  following immediately after subpart in (iii):

                         "(iv) Securities as to which Defeasance has been
                  effected pursuant to Section 1402;"

                  SECTION 1.2.  Section 301 of the Indenture is amended by:

                  (a)    Section 301(17) is renumbered Section 301(18).

                  (b)    A new Section 301(17) is added to read in its entirety
                  as follows:

                         "(17) if applicable, that the Securities of the
                  series, in whole or any specified part, shall be defeasible
                  pursuant to Section 1402 or Section 1403 or both such
                  Sections, any provisions to permit a pledge of obligations
                  other than U. S. Government Obligations (or the establishment
                  of other arrangements) to satisfy the



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                  requirements of Section 1404(1) for defeasance of such
                  Securities and, if other than by a Board Resolution, the
                  manner in which any elections by the Company to defease such
                  Securities shall be evidenced;"

         SECTION 1.3. The following Article Fourteen is added immediately
following the last paragraph of Section 1303:

                                "ARTICLE FOURTEEN

                           DEFEASANCE AND COVENANT DEFEASANCE

                           SECTION 1401. COMPANY'S OPTION TO EFFECT DEFEASANCE
                  OR COVENANT DEFEASANCE.

                           The Company may elect, at its option at any time, to
                  have Section 1402 or Section 1403 applied to any Securities or
                  any series of Securities, as the case may be, designated
                  pursuant to Section 301 as being defeasible pursuant to such
                  Section 1402 or 1403, in accordance with any applicable
                  requirements provided pursuant to Section 301 and upon
                  compliance with the conditions set forth below in this
                  Article. Any such election shall be evidenced by a Board
                  Resolution or in another manner specified as contemplated by
                  Section 301 for such Securities.

                           SECTION 1402. DEFEASANCE AND DISCHARGE.

                           Upon the Company's exercise of its option (if any) to
                  have this Section applied to any Securities or any series of
                  Securities, as the case may be, each of the Company and the
                  Guarantor shall be deemed to have been discharged from its
                  respective obligations with respect to such Securities as
                  provided in this Section on and after the date the conditions
                  set forth in Section 1404 are satisfied (hereinafter called
                  "Defeasance"). For this purpose, such Defeasance means that
                  the Company shall be deemed to have paid and discharged the
                  entire indebtedness represented by such Securities and that
                  each of the Company and the Guarantor shall be deemed to have
                  satisfied all its obligations under such Securities and this
                  Indenture insofar as such Securities are concerned (and the
                  Trustee, at the expense of the Company, shall execute proper
                  instruments acknowledging the same), subject to the following
                  which shall survive until otherwise terminated or discharged
                  hereunder: (1) the rights of Holders of such Securities to
                  receive, solely from the trust fund described in Section 1404
                  and as more fully set forth in such Section, payments in
                  respect of the principal of and any premium and interest on
                  such Securities when payments are due, (2) the Company's
                  obligations with respect to such Securities under Sections
                  304, 305, 306, 707, 1102 and 1103, (3) the rights, powers,
                  trusts, duties and immunities of the Trustee hereunder and (4)
                  this Article. Subject to compliance with this Article, the
                  Company may exercise its option (if any) to have this Section
                  applied to any



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                  Securities notwithstanding the prior exercise of its option
                  (if any) to have Section 1403 applied to such Securities.

                           SECTION 1403. COVENANT DEFEASANCE.

                           Upon the Company's exercise of its option (if any) to
                  have this Section applied to any Securities or any series of
                  Securities, as the case may be, (1) each of the Company and
                  the Guarantor shall be released from its respective
                  obligations under Sections 1105 through 1108, inclusive, and
                  any covenants provided pursuant to Section 301(12), 1001(2) or
                  1001(6) for the benefit of the Holders of such Securities and
                  (2) the occurrence of any event specified in Sections 601(4)
                  (with respect to any of Sections 1105 through 1108, inclusive,
                  and any such covenants provided pursuant to Section 301(12),
                  1001(2) or 1001(6)) and 601(7) shall be deemed not to be or
                  result in an Event of Default, in each case with respect to
                  such Securities as provided in this Section on and after the
                  date the conditions set forth in Section 1404 are satisfied
                  (hereinafter called "Covenant Defeasance"). For this purpose,
                  such Covenant Defeasance means that, with respect to such
                  Securities, each of the Company and the Guarantor may omit to
                  comply with and shall have no liability in respect of any
                  term, condition or limitation set forth in any such specified
                  Section (to the extent so specified in the case of Section
                  601(4)), whether directly or indirectly by reason of any
                  reference elsewhere herein to any such Section or by reason of
                  any reference in any such Section to any other provision
                  herein or in any other document, but the remainder of this
                  Indenture and such Securities shall be unaffected thereby.

                           SECTION 1404. CONDITIONS TO DEFEASANCE OR COVENANT
                  DEFEASANCE.

                           The following shall be the conditions to the
                  application of Section 1402 or Section 1403 to any Securities
                  or any series of Securities, as the case may be:

                                    (1) The Company shall irrevocably have
                           deposited or caused to be deposited with the Trustee
                           (or another trustee which satisfies the requirements
                           contemplated by Section 709 and agrees to comply with
                           the provisions of this Article applicable to it) as
                           trust funds in trust for the purpose of making the
                           following payments, specifically pledged as security
                           for, and dedicated solely to, the benefits of the
                           Holders of such Securities, (A) money in an amount,
                           or (B) U.S. Government Obligations which through the
                           scheduled payment of principal and interest in
                           respect thereof in accordance with their terms will
                           provide, not later than one day before the due date
                           of any payment, money in an amount, or (C) such other
                           obligations or arrangements as may be specified as



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                           contemplated by Section 301 with respect to such
                           Securities, or (D) a combination thereof, in each
                           case sufficient, in the option of a nationally
                           recognized firm of independent public accountants
                           expressed in a written certification thereof
                           delivered to the Trustee, to pay and discharge, and
                           which shall be applied by the Trustee (or any such
                           other qualifying trustee) to pay and discharge, the
                           principal of and any premium and interest on such
                           Securities on the respective Stated Maturities, in
                           accordance with the terms of this Indenture and such
                           Securities. As used herein, "U.S. Government
                           Obligation" means (x) any security which is (i) a
                           direct obligation of the United States of America for
                           the payment of which the full faith and credit of the
                           United States of America is pledged or (ii) an
                           obligation of a Person controlled or supervised by
                           and acting as an agency or instrumentality of the
                           United States of America the payment of which is
                           unconditionally guaranteed as a full faith and credit
                           obligation by the United States of America, which, in
                           either case (i) or (ii), is not callable or
                           redeemable at the option of the issuer thereof, and
                           (y) any depositary receipt issued by a bank (as
                           defined in Section 3(a)(2) of the Securities Act of
                           1933, as amended) as custodian with respect to any
                           U.S. Government Obligation which is specified in
                           Clause (x) above and held by such bank for the
                           account of the holder of such depositary receipt, or
                           with respect to any specific payment of principal of
                           or interest on any U.S. Government Obligation which
                           is so specified and held, PROVIDED that (except as
                           required by law) such custodian is not authorized to
                           make any deduction from the amount payable to the
                           holder of such depository receipt from any amount
                           received by the custodian in respect of the U.S.
                           Government Obligation or the specific payment of
                           principal or interest evidenced by such depositary
                           receipt.

                                    (2) In the event of any election to have
                           Section 1402 apply to any Securities or any series of
                           Securities, as the case may be, the Company shall
                           have delivered to the Trustee an Opinion of Counsel
                           stating that (A) (x) the Company has received from,
                           or there has been published by, the Internal Revenue
                           Service a ruling or (y) since the date of this
                           instrument, there has been a change in the applicable
                           Federal income tax law, in either case (x) or (y) to
                           the effect that, and based thereon such opinion shall
                           confirm that, the Holders of such Securities will not
                           recognize gain or loss for Federal income tax
                           purposes as a result of the deposit, Defeasance and
                           discharge to be effected with respect to such



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                           Securities and will be subject to Federal income tax
                           on the same amount, in the same manner and at the
                           same times as would be the case if such deposit,
                           Defeasance and discharge were not to occur and (B) if
                           Securities of such series are then listed on the New
                           York Stock Exchange, to the effect that the
                           Securities of such series will not be delisted as a
                           result of such election.

                                    (3) In the event of any election to have
                           Section 1403 apply to any Securities or any series of
                           Securities, as the case may be, the Company shall
                           have delivered to the Trustee an Opinion of Counsel
                           to the effect that the Holders of such Securities
                           will not recognize gain or loss for Federal income
                           tax purposes as a result of the deposit and Covenant
                           Defeasance to be effected with respect to such
                           Securities and will be subject to Federal income tax
                           on the same amount, in the same manner and at the
                           same times as would be the case if such deposit and
                           Covenant Defeasance were not to occur.

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

                                    (5) No event which is, or after notice or
                           lapse of time or both would become, an Event of
                           Default with respect to such Securities or any other
                           Securities shall have occurred and be continuing at
                           the time of such deposit or, with regard to any such
                           event specified in Sections 601(5) and (6), at any
                           time on or prior to the 90th day after the date of
                           such deposit (it being understood that this condition
                           shall not be deemed satisfied until after such 90th
                           day).

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

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

                                    (8) Such Defeasance or Covenant Defeasance
                           shall not result in the trust arising from such
                           deposit constituting an investment company within the
                           meaning of the Investment Company Act of 1940, as
                           amended, unless such trust shall be registered under
                           such Act or exempt from registration thereunder.



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

                           SECTION 1405. DEPOSITED MONEY AND U.S. GOVERNMENT
                  OBLIGATIONS TO BE HELD IN TRUST; MISCELLANEOUS PROVISIONS.

                           Subject to the provisions of the last paragraph of
                  Section 1103, all money and U.S. Government Obligations
                  (including the proceeds thereof) deposited with the Trustee or
                  other qualifying trustee (solely for purposes of this Section
                  and Section 1406, the Trustee and any such other trustee are
                  referred to collectively as the "Trustee") pursuant to Section
                  1404 in respect of any Securities shall be held in trust and
                  applied by the Trustee, in accordance with the provisions of
                  such Securities and this Indenture, to the payment, either
                  directly or through any such Paying Agent (including the
                  Company acting as its own Paying Agent) as the Trustee may
                  determine, to the Holders of such Securities, of all sums due
                  and to become due thereon in respect of principal and any
                  premium and interest, but money so held in trust need not be
                  segregated from other funds except to the extent required by
                  law.

                           The Company shall pay and indemnify the Trustee
                  against any tax, fee or other charge imposed on or assessed
                  against the U.S. Government Obligations deposited pursuant to
                  Section 1404 or the principal and interest received in respect
                  thereof other than any such tax, fee or other charge which by
                  law is for the account of the Holders of Outstanding
                  Securities.

                           Anything in this Article to the contrary
                  notwithstanding, the Trustee shall deliver or pay to the
                  Company from time to time upon Company Request any money or
                  U.S. Government Obligations held by it as provided in Section
                  1404 with respect to any Securities which, in the opinion of a
                  nationally recognized firm of independent public accountants
                  expressed in a written certification thereof delivered to the
                  Trustee, are in excess of the amount thereof which would then
                  be required to be deposited to effect the Defeasance or
                  Covenant Defeasance, as the case may be, with respect to such
                  Securities.

                           SECTION 1406. REINSTATEMENT.

                           If the Trustee or the Paying Agent is unable to apply
                  any money in accordance with this Article with respect to any
                  Securities by reason of any order or judgment of any court or
                  governmental authority enjoining, restraining or otherwise
                  prohibiting such application, then the obligations under this
                  Indenture and such Securities from



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                  which the Company has been discharged or released pursuant to
                  Section 1402 or 1403 shall be revived and reinstated as though
                  no deposit had occurred pursuant to this Article with respect
                  to such Securities, until such time as the Trustee or Paying
                  Agent is permitted to apply all money held in trust pursuant
                  to Section 1405 with respect to such Securities in accordance
                  with this Article; PROVIDED, HOWEVER, that if the Company
                  makes any payment of principal of or any premium or interest
                  on any such Security following such reinstatement of its
                  obligations, the Company shall be subrogated to the rights (if
                  any) of the Holders of such Securities to receive such payment
                  from the money so held in trust."



                                   ARTICLE II

                                  MISCELLANEOUS

         Section 2.1. All the provisions of this Second Supplemental Indenture
shall be deemed to be incorporated in, and made a part of, the Indenture; and
the Indenture, as supplemented and amended by this Second Supplemental
Indenture, shall be read, taken and construed as one and the same instrument.

         Section 2.2. The provisions and benefit of this Second Supplemental
Indenture shall not be effective with respect to Securities outstanding prior to
the date hereof.

         Section 2.3. This Second Supplemental Indenture may be executed in any
number of counterparts, each of which so executed shall be deemed to be an
original, but all such counterparts shall together constitute but one and the
same instrument.

         Section 2.4. If any provision hereof limits, qualifies or conflicts
with another provision hereof which is required to be included in this Second
Supplemental Indenture by and of the provisions of the Trust Indenture Act, such
required provision shall control.

         Section 2.5. All covenants and agreements in this Second Supplemental
Indenture by the Company and the Guarantor shall bind their respective
successors and assigns, whether so expressed or not.

         Section 2.6. In case any provision in this Second Supplemental
Indenture shall be invalid, illegal or unenforceable, the validity, legality and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.

         Section 2.7. Nothing in this Second Supplemental Indenture, express or
implied, shall give to any person, other than the parties hereto and their
successors hereunder and the Holders, any benefit or legal or equitable right,
remedy or claim under this Second Supplemental Indenture.





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         IN WITNESS WHEREOF, the parties hereto have caused this Second
Supplemental Indenture to be duly executed, and their respective corporate seals
to be hereunto affixed and attested, all as of the day and year first above
written.

                                          MELLON FUNDING CORPORATION,
                                                                          Issuer


                                          BY:
                                             ----------------------------------
                                          Name:   Steven G. Elliott
                                          Title:  President and Chief Executive
                                                  Officer
Attest:



------------------------------
Secretary
                                          MELLON FINANCIAL CORPORATION,
                                                                       Guarantor


                                          BY:
                                             -----------------------------------
                                          Name:   Martin G. McGuinn
                                          Title:  Chairman and
                                                  Chief Executive Officer
Attest:



------------------------------
Secretary


                                          THE CHASE MANHATTAN BANK,
                                                                         Trustee


                                          BY:
                                             -----------------------------------
                                          Name:
                                               ---------------------------------
                                          Title:
                                                --------------------------------


Attest:



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





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COMMONWEALTH OF PENNSYLVANIA        )
                                    )                    ss.:
COUNTY OF ALLEGHENY                 )

                  On the day of         , 2000, before me personally came
Steven G. Elliott, to me known, who, being by me duly sworn, did depose and say
that he is President & Chief Executive Officer of Mellon Funding Corporation,
one of the corporations described in and which executed the foregoing
instrument; that he knows the seal of said corporation; that the seal affixed to
said instrument is such corporate seal; that it was so affixed by authority of
the Board of Directors of said corporation, and that he signed his name thereto
by like authority.

                                        ----------------------------------------
                                        Notary Public
                                                            , Notary Public
                                        --------------------
                                        PITTSBURGH, ALLEGHENY COUNTY
                                        MY COMMISSION EXPIRES
                                                             -------------------
                                        Member, Penn. Assoc. of Notaries
[Notarial Seal]



COMMONWEALTH OF PENNSYLVANIA        )
                                    )                    ss.:
COUNTY OF ALLEGHENY                 )

         On the day of       , 2000 before me personally came Martin G. McGuinn,
to me known, who, being by me duly sworn, did depose and say that he is chairman
and Chief Executive Officer of Mellon Financial Corporation, one of the
corporations described in and which executed the foregoing instrument; that he
knows the seal of said corporation; that the seal affixed to said instrument is
such corporate seal; that it was so affixed by authority of the Board of
Directors of said corporation, and that he signed his name thereto by like
authority.

                                        ----------------------------------------
                                        Notary Public
                                                            , Notary Public
                                        --------------------
                                        PITTSBURGH, ALLEGHENY COUNTY
                                        MY COMMISSION EXPIRES
                                                             -------------------
                                        Member, Penn. Assoc. of Notaries
[Notarial Seal]




                                      -11-
<PAGE>   12


STATE OF NEW YORK          )
                           )                              ss.:
COUNTY OF                  )
          -----------

                  On the day of , 2000, before me personally came , to me known,
who, being by me duly sworn, did depose and say that he is THE CHASE MANHATTAN
BANK, one of the corporations described in and which executed the foregoing
instrument; that he knows the seal of said corporation; that the seal affixed to
said instrument is such corporate seal; that it was so affixed by authority of
the Board of Directors of said corporation, and that he signed his name thereto
by like authority.

                                        ----------------------------------------
                                        Notary Public
                                        Notary Public, State of New York
                                        No.
                                           -------------------------------------
                                        COMMISSION EXPIRES
                                                           ---------------------
[Notarial Seal]


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