<PAGE>   1
                                                                    Exhibit 4.21

                                                                  EXECUTION COPY


                                TECO ENERGY, INC.


                                       and


                              THE BANK OF NEW YORK
                                   As Trustee


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


                          THIRD SUPPLEMENTAL INDENTURE


                          dated as of December 1, 2000


                           Supplementing the Indenture


                           dated as of August 17, 1998


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


                                  $206,200,000


                    8.50% Junior Subordinated Notes Due 2041
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                                TABLE OF CONTENTS


<TABLE>
                                                                                                                  PAGE
<S>                                                                                                               <C>
ARTICLE ONE                DEFINITIONS AND OTHER PROVISIONS OF GENERAL APPLICATION..............................    2

         Section 101.      Definitions..........................................................................    2

         Section 102.      Section References...................................................................    4

ARTICLE TWO                DESIGNATION AND TERMS OF THE NOTES...................................................    4

         Section 201.      Establishment of Series..............................................................    4

         Section 202.      Maturity.............................................................................    4

         Section 203.      Variations in Terms of Notes.........................................................    4

         Section 204.      Amount and Denominations.............................................................    4

         Section 205.      Interest Rates and Interest Payment Dates............................................    6

         Section 206.      Extension of Interest Payment Period.................................................    7

         Section 207.      Notice of Extension..................................................................    8

         Section 208.      Limitation of Amendments and Termination of the Indenture............................    8

         Section 209.      Limitation of Transactions...........................................................    9

         Section 210.      Authentication and Delivery of the Notes.............................................    9

         Section 211.      No Sinking Fund......................................................................   10

         Section 212.      Appointment of Agents and the Depository.............................................   10

         Section 213.      Redemption...........................................................................   10

ARTICLE THREE              REDEMPTION OF THE NOTES..............................................................   10

         Section 301.      Special Event Redemption.............................................................   10

         Section 302.      Optional Redemption by Company.......................................................   11

ARTICLE FOUR               ADDITIONAL COVENANTS OF THE COMPANY..................................................   12

         Section 401.      Payment of Expenses..................................................................   12

         Section 402.      Payment Upon Resignation or Removal..................................................   13

         Section 403.      Covenant to List on Exchange.........................................................   13

ARTICLE FIVE               SUBORDINATION........................................................................   13

         Section 501.      Subordination........................................................................   13

         Section 502.      Default on Senior Indebtedness.......................................................   13

         Section 503.      Liquidation; Dissolution; Bankruptcy.................................................   14

         Section 504.      Subrogation..........................................................................   15
</TABLE>

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                                TABLE OF CONTENTS

                                   (CONTINUED)

<TABLE>
<CAPTION>
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<S>                                                                                                               <C>
         Section 505.      Trustee to Effectuate Subordination..................................................   16

         Section 506.      Notice by the Company................................................................   16

         Section 507.      Rights of the Trustee; Holders of Senior Indebtedness................................   17

         Section 508.      Subordination May Not Be Impaired....................................................   17

ARTICLE SIX                EVENTS OF DEFAULT WITH RESPECT TO THE NOTES..........................................   18

         Section 601.      Definition...........................................................................   18

         Section 602.      Acceleration.........................................................................   18

         Section 603.      Suits................................................................................   19

ARTICLE SEVEN              AMENDMENT TO ORIGINAL INDENTURE......................................................   19

         Section 701.      Amendment to Section 801 of Original Indenture.......................................   19

         Section 702.      Effectiveness of Amendment...........................................................   20

ARTICLE EIGHT              MISCELLANEOUS........................................................................   20

         Section 801.      Effect On Original Indenture.........................................................   20

         Section 802.      Counterparts.........................................................................   20

         Section 803.      Recitals.............................................................................   20

         Section 804.      Governing Law........................................................................   20
</TABLE>

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         This Third Supplemental Indenture, dated as of the first day of
December, 2000 between TECO Energy, Inc., a corporation duly organized and
existing under the laws of the State of Florida (hereinafter called the
"Company") and having its principal office at TECO Plaza, 702 North Franklin
Street, Tampa, Florida 33602, and The Bank of New York, (hereinafter called the
"Trustee") and having its principal corporate trust office at 101 Barclay
Street, 8th Floor West, New York, New York 10286.

                                   WITNESSETH:

         WHEREAS, the Company and the Trustee entered into an Indenture, dated
as of August 17, 1998, as heretofore amended (as so amended, the "Original
Indenture"), pursuant to which one or more series of debt of the Company (the
"Securities") may be issued from time to time; and

         WHEREAS, Section 201 of the Original Indenture permits the terms of any
series of Securities to be established in an indenture supplemental to the
Original Indenture; and

         WHEREAS, Section 901(7) of the Original Indenture provides that a
supplemental indenture may be entered into by the Company and the Trustee
without the consent of any Holders of the Securities to establish the form and
terms of the Securities of any series; and

         WHEREAS, the Company has requested the Trustee to join with it in the
execution and delivery of this Third Supplemental Indenture in order to
supplement and amend the Original Indenture by, among other things, establishing
the form and terms of one series of Securities to be known as the Company's
"8.50% Junior Subordinated Notes Due 2041" (the "Notes") and amending and adding
certain provisions thereof for the benefit of the Holders of the Notes; and

         WHEREAS, TECO Capital Trust I, a Delaware statutory business trust (the
"Trust"), intends to offer to the public $200,000,000 aggregate liquidation
amount of its 8.50% Trust Preferred Securities (the "Trust Preferred
Securities"), representing preferred undivided beneficial interests in the
assets of the Trust, and proposes to invest the proceeds from such offering in a
like aggregate principal amount of the preferred securities (the "Company
Preferred Securities") of TECO Funding Company I, LLC, a Delaware limited
liability company (the "LLC"), and the LLC will invest the proceeds of the
Company Preferred Securities, together with the proceeds of its common
securities, in $206,200,000 aggregate principal amount of the Notes; and

         WHEREAS, the Company and the Trustee desire to enter into this Third
Supplemental Indenture for the purposes set forth in Sections 201 and 901 of the
Original Indenture as referred to above; and

         WHEREAS, the Company has furnished the Trustee with a Board Resolution
authorizing the execution of this Third Supplemental Indenture; and

         WHEREAS, all things necessary to make this Third Supplemental Indenture
a valid agreement of the Company and the Trustee and a valid supplement to the
Original Indenture have been done,
<PAGE>   5
         NOW, THEREFORE, THIS THIRD SUPPLEMENTAL INDENTURE WITNESSETH:

         For and in consideration of the premises and the purchase of the Notes
to be issued hereunder by holders thereof, the Company and the Trustee mutually
covenant and agree, for the equal and proportionate benefit of the respective
holders from time to time of the Notes, as follows:

                                  ARTICLE ONE
             DEFINITIONS AND OTHER PROVISIONS OF GENERAL APPLICATION

         SECTION 101. DEFINITIONS

         All capitalized terms that are used herein and not otherwise defined
herein shall have the meanings assigned to them in the Original Indenture.

         "90-Day Period" shall have the meaning set forth in Section 301.

         "Additional Interest" shall have the meaning set forth in Section
205(c).

         "Business Day" shall mean a day on which banks are open for business in
New York and Delaware.

         "Change in 1940 Act Law" shall have the meaning set forth in Section
301.

         "Clearing Agency" means an organization registered as a "clearing
agency" pursuant to Section 17A of the Securities Exchange Act of 1934, as
amended. The Depository Trust Company will be the initial Clearing Agency.

         "Company Agreement" means the Amended and Restated Limited Liability
Company Agreement dated as of December 1, 2000, between the Company and the
Trust, as the same may be amended from time to time.

         "Compounded Interest" shall have the meaning set forth in Section 206.

         "Coupon Rate" shall have the meaning set forth in Section 205(a).

         "Deferred Interest" shall have the meaning set forth in Section 206.

         "Delaware Trustee" shall mean the corporation identified as the
"Delaware Trustee" in the preamble to the Trust Agreement solely in its capacity
as Delaware Trustee of the Trust created and continued thereunder and not in its
individual capacity, or its successor in interest in such capacity, or any
successor trustee appointed as therein provided.

         "Depository" shall have the meaning set forth in Section 212(b).

         "Dissolution Event" means that the LLC and the Trust are to be
dissolved in accordance with the Company Agreement and the Trust Agreement, and
the Notes held by the LLC are to be distributed to the holders of the Trust
Preferred Securities issued by the Trust pro rata in accordance with the Company
Agreement and the Trust Agreement.


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         "Extended Interest Payment Period" shall have the meaning set forth in
Section 206.

         "Global Note" shall have the meaning set forth in Section 204(c)(i)(A).

         "Guarantee" shall mean the Guarantee Agreement executed and delivered
by the Depositor and The Bank of New York, as guarantee trustee,
contemporaneously with the execution and delivery of the Trust Agreement, for
the benefit of the Holders of the Company Preferred Securities, as amended from
time to time.

         "Interest Payment Date" shall have the meaning set forth in Section
205(a).

         "Investment Company Event" shall have the meaning set forth in Section
301.

         "Maturity Date" means the date on which the Notes mature and on which
the principal shall be due and payable together with all accrued and unpaid
interest thereon including Compounded Interest and Additional Interest, if any.

         "Ministerial Action" shall have the meaning set forth in Section 301.

         "Non Book-Entry Preferred Securities" shall have the meaning set forth
in Section 204(c)(i)(B).

         "Optional Redemption Price" shall have the meaning set forth in Section
302(a).

         "Property Trustee" shall mean the commercial bank or trust company
acting solely in its capacity as the "Property Trustee" under the Trust
Agreement, and any successor "Property Trustee" acting in such capacity.

         "Redemption Price" shall have the meaning set forth in Section 301.

         "Senior Indebtedness" shall mean (i) all obligations in respect of (A)
indebtedness of the Company for money borrowed and (B) indebtedness evidenced by
securities, debentures, bonds, notes or other similar instruments issued by the
Company; (ii) all capital lease obligations of the Company; (iii) all
obligations of the Company issued or assumed as the deferred purchase price of
property, all conditional sale obligations of the Company and all obligations of
the Company under any title retention agreement (but excluding trade accounts
payable arising in the ordinary course of business); (iv) all obligations of the
Company for reimbursement on any letter of credit, banker's acceptance, security
purchase facility or similar credit transaction; (v) all obligations of the type
referred to in clauses (i) through (iv) of other Persons for the payment of
which the Company is responsible or liable as obligor, guarantor or otherwise;
and (vi) all obligations of the type referred to in clauses (i) through (v) of
other Persons secured by any lien on any property or asset of the Company
(whether or not such obligation is assumed by the Company), except for any such
indebtedness that is by its terms subordinated to or pari passu with the Notes,
as the case may be. For greater certainty, "Senior Indebtedness" includes all
indebtedness for money borrowed between or among the Company and its Affiliates,
except for such indebtedness that is by its terms subordinated to or pari passu
with the Notes, as the case may be. Such Senior Indebtedness shall continue to
be Senior Indebtedness and be entitled to


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the benefits of Article Five hereof irrespective of any amendment, modification
or waiver of any term of such Senior Indebtedness.

         "Special Event" shall have the meaning set forth in Section 301.

         "Tax Event" shall have the meaning set forth in Section 301.

         "Trust Agreement" shall mean the Amended and Restated Trust Agreement
of TECO Capital Trust I, a Delaware statutory business trust, dated as of
December 1, 2000.

         "Trust Preferred Security Certificate" shall mean a certificate
evidencing ownership of Trust Preferred Securities, substantially in the form
set forth in the Trust Agreement.

         SECTION 102. SECTION REFERENCES

         Each reference to a particular section set forth in this Third
Supplemental Indenture shall, unless the context otherwise requires, refer to
this Third Supplemental Indenture.

                                  ARTICLE TWO
                       DESIGNATION AND TERMS OF THE NOTES

         SECTION 201. ESTABLISHMENT OF SERIES

         There is hereby created a series of Securities to be known and
designated as the "8.50% Junior Subordinated Notes Due 2041" (the "Notes"), to
be in substantially in the form set forth in Exhibit A attached hereto, subject
to changes in the form thereof made by the Company and acceptable to the
Trustee, and which shall be subordinated to all Senior Indebtedness of the
Company. For the purposes of the Original Indenture, the Notes shall constitute
a single series of Securities.

         SECTION 202. MATURITY

         The Maturity Date of the Notes is January 31, 2041.

         SECTION 203. VARIATIONS IN TERMS OF NOTES

         Subject to the terms and conditions set forth in the Original Indenture
and in this Third Supplemental Indenture, the terms of any particular Note may
vary from the terms of any other Note as contemplated by Section 301 of the
Original Indenture, and the terms for a particular Note will be set forth in
such Note as delivered to the Trustee or an Authenticating Agent for
authentication pursuant to Section 303 of the Original Indenture.

         SECTION 204. AMOUNT AND DENOMINATIONS

                  (a) The aggregate principal amount of Notes that may be issued
under this Third Supplemental Indenture is limited to $206,200,000.

                  (b) Except as provided in Section 204(c), the Notes shall be
issued in fully registered certificated form without interest coupons in
denominations of $25 or integral


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multiples of $25. The Place of Payment for the Notes issued in certificated form
where the transfer of such Notes will be registrable and where such Notes will
be exchangeable for Notes bearing identical terms and provisions shall be the
Corporate Trust Office of the Trustee; provided, however, that payment of
interest may be made at the option of the Company by check mailed to the Holder
at such address as shall appear in the Security Register. Notwithstanding the
foregoing, so long as the Holder of any Notes is the LLC or the Property
Trustee, the payment of the principal of and interest (including Compounded
Interest and Additional Interest, if any) on such Notes held by the LLC or the
Property Trustee will be made at such place and to such account as may be
designated to the Company in writing by such Holder by wire transfer of
immediately available funds.

                  (c) Global Note.

                           (i) In connection with a Dissolution Event,

                                    (A) the Notes in certificated form may be
                           presented to the Trustee by the LLC or the Property
                           Trustee in exchange for a global Note in an aggregate
                           principal amount equal to the aggregate principal
                           amount of all outstanding Notes (a "Global Note"), to
                           be registered in the name of the Depository, and
                           delivered by the Trustee to the Depository for
                           crediting to the accounts of its participants
                           pursuant to the instructions of the LLC. The Company
                           upon any such presentation shall execute a Global
                           Note in such aggregate principal amount and deliver
                           the same to the Trustee for authentication and
                           delivery in accordance with the Original Indenture
                           and this Third Supplemental Indenture. Payments on
                           the Notes issued as a Global Note will be made to the
                           Depository; and

                                    (B) if any Trust Preferred Securities are
                           held in non-book-entry certificated form, the Notes
                           in certificated form may be presented to the Trustee
                           by the LLC or the Property Trustee and any Trust
                           Preferred Security Certificate which represents Trust
                           Preferred Securities other than Trust Preferred
                           Securities held by the Clearing Agency or its nominee
                           ("Non Book-Entry Preferred Securities") will be
                           deemed to represent beneficial interests in Notes
                           presented to the Trustee by the LLC or the Property
                           Trustee having an aggregate principal amount equal to
                           the aggregate liquidation amount of the
                           Non-Book-Entry Trust Preferred Securities until such
                           Trust Preferred Security Certificates are presented
                           to the Security Registrar for transfer or reissuance
                           at which time such Trust Preferred Security
                           Certificates will be cancelled and a Note, registered
                           in the name of the holder of the Trust Preferred
                           Security Certificate or the transferee of the holder
                           of such Trust Preferred Security Certificate, as the
                           case may be, with an aggregate principal amount equal
                           to the aggregate liquidation amount of the Trust
                           Preferred Security Certificate cancelled, will be
                           executed by the Company and delivered to the Trustee
                           for authentication and delivery in accordance with
                           the Original Indenture and this Third Supplemental
                           Indenture. On issue of such Notes, Notes with an




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                           equivalent aggregate principal amount that were
                           presented by the LLC to the Trustee will be deemed to
                           have been cancelled.

                           (ii) Unless and until it is exchanged for the Notes
                  in registered form, a Global Note may be transferred, in whole
                  but not in part, only to another nominee of the Depository, or
                  to a successor Depository selected or approved by the Company
                  or to a nominee of such successor Depository.

                           (iii) If at any time the Depository notifies the
                  Company that it is unwilling or unable to continue as
                  Depository or if at any time the Depository for such series
                  shall no longer be registered or in good standing under the
                  Securities Exchange Act of 1934, as amended, or other
                  applicable statute or regulation, and a successor Depository
                  for such series is not appointed by the Company within 90 days
                  after the Company receives such notice or becomes aware of
                  such condition, as the case may be, the Company will execute,
                  and, subject to Article Eleven of the Original Indenture, the
                  Trustee, upon written notice from the Company, will
                  authenticate and deliver the Notes in definitive registered
                  form without coupons, in authorized denominations, and in an
                  aggregate principal amount equal to the principal amount of
                  the Global Note in exchange for such Global Note. In addition,
                  the Company may at any time determine that the Notes shall no
                  longer be represented by the Global Note. In such event the
                  Company will execute, and subject to Section 303 of the
                  Original Indenture, the Trustee, upon receipt of an Officers'
                  Certificate evidencing such determination by the Company, will
                  authenticate and deliver the Notes in definitive registered
                  form without coupons, in authorized denominations, and in an
                  aggregate principal amount equal to the principal amount of
                  the Global Note in exchange for such Global Note. Upon the
                  exchange of the Global Note for such Notes in definitive
                  registered form without coupons, in authorized denominations,
                  the Global Note shall be cancelled by the Trustee. Such Notes
                  in definitive registered form issued in exchange for the
                  Global Note shall be registered in such names and in such
                  authorized denominations as the Depository, pursuant to
                  instructions from its direct or indirect participants or
                  otherwise, shall instruct the Trustee. The Trustee shall
                  deliver such Notes to the Depository for delivery to the
                  Persons in whose names such Notes are so registered.

         SECTION 205. INTEREST RATES AND INTEREST PAYMENT DATES

                  (a) Each Note will bear interest at the rate of 8.50% per
annum (the "Coupon Rate") from the original date of issuance until the principal
thereof becomes due and payable, and on any overdue principal and (to the extent
that payment of such interest is enforceable under applicable law) on any
overdue installment of interest at the Coupon Rate, compounded quarterly,
payable (subject to the provisions of Section 206) quarterly in arrears on
January 31, April 30, July 31 and October 31 of each year (each, an "Interest
Payment Date"), commencing on January 31, 2001, to the Person in whose name such
Note or any predecessor Note is registered at the close of business on the
Regular Record Date for such interest installment, which, with respect to (i)
Notes of which the LLC or the Property Trustee is the Holder and the Company
Preferred Securities or the Trust Preferred Securities are in book-entry only
form or


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(ii) a Global Note, shall be the close of business on the Business Day next
preceding that Interest Payment Date. Notwithstanding the foregoing sentence, if
(x) the Notes are held by the LLC or the Property Trustee , the Company
Preferred Securities are not held in book-entry form and the Trust Preferred
Securities are no longer in book-entry only form or (y) the Notes are not
represented by a Global Note, the Company may select a Regular Record Date for
such interest installment which shall be fifteen (15) days before an Interest
Payment Date.

                  (b) The amount of interest payable for any period will be
computed on the basis of a 360-day year of twelve 30-day months. Except for the
effect of any adjustment in the Interest Payment Date as provided in the
following sentence, the amount of interest payable for any period shorter than a
full quarterly period for which interest is computed, will be computed on the
basis of the actual number of days elapsed in such a 90-day period. In the event
that any date on which interest is payable on the Notes is not a Business Day,
then payment of interest payable on such date will be made on the next
succeeding day which is a Business Day (and without any interest or other
payment in respect of any such delay), except that, if such Business Day is in
the next succeeding calendar year, such payment shall be made on the immediately
preceding Business Day, in each case with the same force and effect as if made
on such date.

                  (c) If, at any time while the LLC or the Property Trustee is
the Holder of any Notes, the LLC, the Trust or the Property Trustee is required
to pay any taxes, duties, assessments or governmental charges of whatever nature
(other than withholding taxes) imposed by the United States, or any other taxing
authority, then, in any case, the Company will pay as additional interest
("Additional Interest") on the Notes held by the LLC or the Property Trustee,
such additional amounts as shall be required so that the net amounts received
and retained by the LLC or the Trust and the Property Trustee after the payment
of such taxes, duties, assessments or other governmental charges will be equal
to the amounts the LLC or the Trust and the Property Trustee would have received
had no such taxes, duties, assessments or other government charges been imposed.

         SECTION 206. EXTENSION OF INTEREST PAYMENT PERIOD

         The Company shall have the right, at any time and from time to time
during the term of the Notes, so long as no Event of Default with respect to the
Notes has occurred and is continuing, to defer payments of interest by extending
the interest payment period of such Notes for a period not exceeding 20
consecutive quarters (the "Extended Interest Payment Period"), during which
Extended Interest Payment Period no interest shall be due and payable; provided
that no Extended Interest Payment Period may extend beyond the Maturity Date. To
the extent permitted by applicable law, interest, the payment of which has been
deferred because of the extension of the interest payment period pursuant to
this Section 206, will bear interest thereon at the Coupon Rate compounded
quarterly for each quarter of the Extended Interest Payment Period ("Compounded
Interest"). At the end of the Extended Interest Payment Period, the Company
shall pay all interest accrued and unpaid on the Notes, including any Additional
Interest and Compounded Interest (together, "Deferred Interest") that shall be
payable to the Holders of the Notes in whose names the Notes are registered in
the Security Register on the first record date after the end of the Extended
Interest Payment Period. Before the termination of any Extended Interest Payment
Period, the Company may further extend such period, provided that such period
together with all such further extensions thereof shall not exceed 20
consecutive


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<PAGE>   11
quarters or extend beyond the Maturity Date. Upon the termination of any
Extended Interest Payment Period and upon the payment of all Deferred Interest
then due, the Company may commence a new Extended Interest Payment Period,
subject to the foregoing requirements. No interest shall be due and payable
during an Extended Interest Payment Period, except (i) at the end thereof and
(ii) upon a redemption of the Notes during an Extended Interest Payment Period,
but the Company may prepay at any time all or any portion of the interest
accrued during an Extended Interest Payment Period.

         SECTION 207. NOTICE OF EXTENSION

                  (a) If the Property Trustee is the sole holder of the Company
Preferred Securities or the Notes at the time the Company selects an Extended
Interest Payment Period, the Company shall give written notice to the Property
Trustee and the Trustee of its selection of such Extended Interest Payment
Period one Business Day before the earlier of (i) the next succeeding date on
which Distributions on the Company Preferred Securities issued by the LLC are
payable, or (ii) the date the Company is required to give notice of the record
date, or the date such Distributions are payable, to the New York Stock Exchange
or other applicable self-regulatory organization or to holders of the Trust
Preferred Securities issued by the Trust, but in any event at least one Business
Day before such record date.

                  (b) If the Property Trustee is not the only holder of the
Company Preferred Securities or the Notes at the time the Company selects an
Extended Interest Payment Period, the Company shall give the holders of the
Company Preferred Securities or the Notes, as the case may be, and the Trustee
written notice of its selection of such Extended Interest Payment Period at
least ten Business Days before the earlier of (i) the next succeeding Interest
Payment Date, or (ii) the date the Company is required to give notice of the
record or payment date of such interest payment to the New York Stock Exchange
or other applicable self regulatory organization or to Holders of the Notes.

                  (c) The quarter in which any notice is given pursuant to
paragraphs (a) or (b) of this Section 207 shall be counted as one of the 20
quarters permitted in the maximum Extended Interest Payment Period permitted
under Section 206.

         SECTION 208. LIMITATION OF AMENDMENTS AND TERMINATION OF THE INDENTURE

         Unless and until the principal (and premium, if any) of the Notes and
all accrued and unpaid interest thereon have been paid in full, (a) without the
prior consent of the holders of not less than a majority in aggregate
liquidation amount of the Trust Preferred Securities then outstanding (unless
the consent of the holders of a greater aggregate liquidation amount is required
by the Original Indenture), (i) the Company will not enter into any amendment to
the Original Indenture, as supplemented hereby, that would adversely affect the
holders of any of the Trust Preferred Securities; (ii) no termination of the
Original Indenture, as supplemented hereby, shall occur; and (b) without the
consent of each holder of Trust Preferred Securities then outstanding, no
amendment to Section 603 hereof may be made.

         If at any time while the Notes are held by the LLC no Trust Preferred
Securities of the Trust remain outstanding, unless and until the principal (and
premium, if any) of the Notes and


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<PAGE>   12
all accrued and unpaid interest thereon have been paid in full, (a) without the
prior consent of the holders of not less than a majority in aggregate
liquidation amount of the Company Preferred Securities then outstanding (unless
the consent of the holders of a greater aggregate liquidation amount is required
by the Original Indenture), (i) the Company will not enter into any amendment to
the Indenture that would adversely affect the holders of any of the Company
Preferred Securities, (ii) no termination of the Indenture shall occur; and (b)
without the consent of each holder of Company Preferred Securities then
outstanding, no amendment to Section 603 hereof may be made.

         SECTION 209. LIMITATION OF TRANSACTIONS

         If (i) the Company shall exercise its right to defer payment of
interest as provided in Section 206, (ii) the Company shall have actual
knowledge that an event has occurred that with the giving of notice or the lapse
of time, or both, would constitute an Event of Default with respect to the Notes
and the Company has not taken reasonable steps to cure the event, or (iii) the
Company shall be in default with respect to its payment obligations under the
Guarantee, then (a) the Company shall not declare or pay any dividend on, make
any distributions with respect to, or redeem, purchase, acquire or make a
liquidation payment with respect to, any of its capital stock (other than (i) as
a result of a reclassification of its capital stock or the exchange or
conversion of one class or series of its capital stock for another class or
series of its capital stock, (ii) any payment of a rights dividend in connection
with the implementation of a shareholder rights plan, or the issuance of stock
under any such plan in the future, or the redemption or repurchase of any such
rights pursuant thereto, (iii) purchases of its common stock related to the
issuance of such stock under any of the Company's benefit plans for its
directors, officers or employees, (iv) obligations under any dividend
reinvestment plan or stock purchase plan of the Company, (v) the purchase of
fractional interests in shares of its capital stock pursuant to the conversion
or exchange provisions of such capital stock or security being converted or
exchanged or (vi) dividends or distributions in its common stock) or make any
guarantee payment with respect thereto, (b) the Company shall not make any
payment of interest, principal or premium, if any, on or repay, repurchase or
redeem any debt securities issued by the Company which rank pari passu with or
junior to the Notes and (c) the Company shall not make any guarantee payments
with respect to any of the payment obligations referred to in subparagraph (b)
of this Section 209 (other than pursuant to the Guarantee and any similar
guarantee issued by the Company on behalf of holders of preferred securities
issued by an issuer holding Securities issued under the Indenture).

         SECTION 210. AUTHENTICATION AND DELIVERY OF THE NOTES

         Notes in the aggregate principal amount of $206,200,000 may, upon
execution of this Third Supplemental Indenture, be executed by the Company and
delivered to the Trustee for authentication, and the Trustee shall thereupon
authenticate and deliver said Notes to or upon the written order of the Company,
signed by its Chairman of the Board, its President, any Vice President, its
Treasurer or any Assistant Treasurer, without any further action by the Company.
As provided in and pursuant to Section 303 of the Original Indenture, each time
that the Company delivers Notes to the Trustee or Authenticating Agent for
authentication, the Company shall deliver a Company Order in the form of Exhibit
B to this Third Supplemental Indenture for


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the authentication and delivery of such Notes and the Trustee or such
Authenticating Agent shall authenticate and deliver such Notes.

         SECTION 211. NO SINKING FUND

         The Notes shall not be entitled to the benefit of any sinking fund or
analogous provision.

         SECTION 212. APPOINTMENT OF AGENTS AND THE DEPOSITORY

                  (a) The Company hereby appoints, or confirms the appointment
of, The Bank of New York as the initial Trustee, Securities Registrar and Paying
Agent with respect to the Notes, subject to the provisions of the Original
Indenture with respect to resignation, removal and succession, and subject,
further, to the right of the Company to appoint additional agents (including
Paying Agents).

                  (b) The Depository Trust Company (or its nominee) shall act as
the initial Depository (the "Depository") for any Global Note which may be
issued pursuant to this Third Supplemental Indenture.

         SECTION 213. REDEMPTION

         The Notes are not subject to redemption at the option of the Holder and
are subject to redemption solely at the option of the Company or otherwise as
provided in Article Three hereof.

                                 ARTICLE THREE
                             REDEMPTION OF THE NOTES

         SECTION 301. SPECIAL EVENT REDEMPTION

         If a Special Event (as defined below) has occurred and is continuing
then, notwithstanding Section 302(a) but subject to Section 302(b), the Company
shall have the right upon not less than 35 days nor more than 60 days notice to
the Holders of the Notes to redeem the Notes, in whole but not in part, for cash
within 90 days following the occurrence of such Special Event (the "90-Day
Period") at a redemption price equal to 100% of the principal amount to be
redeemed plus any accrued and unpaid interest thereon, including Compounded
Interest and Additional Interest, if any, to the date of such redemption (the
"Redemption Price"); provided, however, that in the case of an occurrence of a
Tax Event, if at the time there is available to the Company the opportunity to
eliminate, within the 90-Day Period, the Tax Event by taking some ministerial
action ("Ministerial Action"), such as filing a form or making an election, or
pursuing some other similar reasonable measure which has no adverse effect on
the Company, the LLC or the holders of the Company Preferred Securities, the
Trust or the Holders of the Trust Preferred Securities issued by the Trust, the
Company shall pursue such Ministerial Action in lieu of redemption, and,
provided, further, that the Company shall have no right to redeem the Notes
while it is pursuing any Ministerial Action pursuant to its obligations under
the Trust Agreement. The Redemption Price shall be paid on the date of such
redemption, provided that the Company shall deposit with the Trustee an amount
sufficient to pay the Redemption Price by 10:00 a.m., New York time, on the date
such Redemption Price is to be paid.

                                       10
<PAGE>   14
         A "Special Event" shall mean either a Tax Event or an Investment
Company Event. "Tax Event" shall mean that the LLC or the Trust shall have
received an opinion of counsel (which may be regular counsel to the Company or
an Affiliate, but not an employee thereof) experienced in such matters to the
effect that, as a result of (a) any amendment to, or change (including any
announced prospective change) in, the laws (or any regulations thereunder) of
the United States or any political subdivision or taxing authority thereof or
therein affecting taxation, or (b) any official administrative written decision,
pronouncement or action or judicial decision interpreting or applying such laws
or regulations by any court, governmental agency or regulatory authority, in
each case which amendment or change is enacted, promulgated, issued or announced
or which interpretation or application is issued or announced on or after the
date of original issuance of Notes or the Company Preferred Securities, there is
more than an insubstantial risk that (i) the LLC or the Trust is, or will be
within 90 days of the date of the opinion of counsel, subject to United States
Federal income tax with respect to interest received on the Notes or Company
Preferred Securities, (ii) interest payable by the Company to the LLC on the
Notes is not, or will not be within 90 days of the date of the opinion of
counsel, deductible for United States Federal income tax purposes, or (iii) the
LLC or the Trust is, or will be within 90 days of the date of the opinion of
counsel, subject to more than a de minimis amount of other taxes, duties,
assessments or other governmental charges. "Investment Company Event" shall mean
the LLC or the Trust shall have received an opinion of counsel (which may be
regular counsel to the Company or an Affiliate, but not an employee thereof)
experienced in such matters to the effect that, as a result of the occurrence of
a change in law or regulation or a change in interpretation or application of
law or regulation by any legislative body, court, governmental agency or
regulatory authority (a "Change in 1940 Act Law") there is more than an
insubstantial risk that the LLC or the Trust is or will be considered an
"Investment Company" that is required to be registered under the Investment
Company Act of 1940, as amended, which Change in 1940 Act Law becomes effective
on or after the date of original issuance of the Notes or the Company Preferred
Securities.

         SECTION 302. OPTIONAL REDEMPTION BY COMPANY

                  (a) Subject to the provisions of Section 302(b) and to the
provisions of Article Eleven of the Original Indenture, except as otherwise may
be specified in this Third Supplemental Indenture, the Company shall have the
right to redeem the Notes, in whole or in part, from time to time, on or after
December 20, 2005, upon not less than 35 days nor more than 60 days notice to
the Holder of the Notes at a redemption price equal to 100% of the principal
amount to be redeemed plus any accrued and unpaid interest thereon, including
Compounded Interest and Additional Interest, if any, to the date of such
redemption (the "Optional Redemption Price").

         If the Notes are only partially redeemed pursuant to this Section 302,
the Notes will be redeemed pro rata or by lot or by any other method utilized by
the Trustee; provided, that if at the time of redemption the Notes are
registered as a Global Note, the Depository shall determine, in accordance with
its procedures, the principal amount of such Notes held by each Note Holder to
be redeemed. The Optional Redemption Price shall be paid on the date of such
redemption, provided that the Company shall deposit with the Trustee an amount
sufficient to pay the Optional Redemption Price by 10:00 a.m., New York time, on
the date such Optional Redemption Price is to be paid.


                                       11
<PAGE>   15
                  (b) If a partial redemption of the Notes would result in the
delisting of the Trust Preferred Securities from any national securities
exchange or other organization on which the Trust Preferred Securities are then
listed, the Company shall not be permitted to effect such partial redemption and
may only redeem the Notes in whole.

                                  ARTICLE FOUR
                       ADDITIONAL COVENANTS OF THE COMPANY

         SECTION 401. PAYMENT OF EXPENSES

                  (a) In connection with the offering, sale and issuance of the
Notes to the LLC, the Company Preferred Securities to the Trust and the Trust
Preferred Securities by the Trust, the Company, in its capacity as borrower with
respect to the Notes, shall:

                  (i) pay all costs and expenses relating to the offering, sale
         and issuance of the Notes, including commissions to the underwriters
         payable pursuant to the Underwriting Agreement and compensation of the
         Trustee under the Indenture in accordance with the provisions of
         Section 607 of the Original Indenture;

                  (ii) pay all debts and obligations and all costs and expenses
         of the LLC and the Trust (including, but not limited to, costs and
         expenses relating to the organization of the LLC and the Trust, the
         offering, sale and issuance of the Trust Preferred Securities
         (including commissions to the underwriters in connection therewith),
         the fees and expenses of the Property Trustee and the Delaware Trustee,
         the costs and expenses relating to the operation of the Trust,
         including without limitation, costs and expenses of accountants,
         attorneys, statistical or bookkeeping services, expenses for printing
         and engraving and computing or accounting equipment, paying agent(s),
         registrar(s), transfer agent(s), duplicating, travel and telephone and
         other telecommunications expenses and costs and expenses incurred in
         connection with the acquisition, financing, and disposition of Trust
         assets);

                  (iii) be primarily liable for any indemnification obligations
         arising with respect to the Trust Agreement; and

                  (iv) pay any and all taxes (other than United States
         withholding taxes attributable to the Trust or its assets) imposed by
         the United States or any other taxing authority and all liabilities,
         costs and expenses with respect to such taxes of the LLC or the Trust.

                  (b) The foregoing obligations of the Company are for the
benefit of, and shall be enforceable by, any person to whom such fees, expenses,
debts and obligations are owed (each, a "Creditor"), whether or not such
Creditor has received notice thereof. Any such Creditor may enforce such
obligations of the Company directly against the Company, and the Company
irrevocably waives any right or remedy to require that any such Creditor take
any action against the Trust or any other person before proceeding against the
Company. The


                                       12
<PAGE>   16
Company shall execute such additional agreements as may be necessary to give
full effect to the foregoing.

         SECTION 402. PAYMENT UPON RESIGNATION OR REMOVAL

         Upon termination of this Third Supplemental Indenture or the Original
Indenture or the removal or resignation of the Trustee pursuant to this Section
402, the Company shall pay to the Trustee all amounts accrued to the date of
such termination, removal or resignation. Upon termination of the Trust
Agreement or the removal or resignation of the Delaware Trustee or the Property
Trustee, as the case may be, pursuant to Section 8.10 of the Trust Agreement,
the Company shall pay to the Delaware Trustee or the Property Trustee, as the
case may be, all amounts accrued to the date of such termination, removal or
resignation.

         SECTION 403. COVENANT TO LIST ON EXCHANGE

         If the Notes are to be distributed to the holders of Trust Preferred
Securities or to the holders of the Company Preferred Securities if no Trust
Preferred Securities are outstanding, as described in Section 204(c), the
Company will, if the Notes are not already so listed, use its best efforts to
list such Notes on the New York Stock Exchange, Inc. or on such other exchange
as the Trust Preferred Securities or the Company Preferred Securities, as the
case may be, are then listed.

                                  ARTICLE FIVE
                                  SUBORDINATION

         SECTION 501. SUBORDINATION

         The Company resolves, and each Holder of Notes issued hereunder by such
Holder's acceptance thereof covenants and agrees, that all Notes shall be issued
subject to the provisions of this Article Five, and each Holder of a Note,
whether upon original issue or upon transfer or assignment thereof, accepts and
agrees to be bound by such provisions.

         The payment by the Company of the principal of, premium, if any, and
interest on all Notes issued hereunder shall, to the extent and in the manner
hereinafter set forth, be subordinated and subject in right of payment to the
prior payment in full of all Senior Indebtedness, whether outstanding at the
date of this Third Supplemental Indenture or thereafter incurred.

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

         No provision of this Article Five shall prevent the occurrence of any
default or Event of Default with respect to the Notes.

                                       13
<PAGE>   17
         SECTION 502. DEFAULT ON SENIOR INDEBTEDNESS

         In the event and during the continuation of any default by the Company
in the payment of principal, premium, interest or any other amount due on any
Senior Indebtedness, or in the event that the maturity of any Senior
Indebtedness has been accelerated because of a default, then, in either case, no
payment shall be made by the Company to the Holders of the Notes with respect to
the principal (including redemption and sinking fund payments) of, premium, if
any, interest on, or any other amount owing in respect of, the Notes.

         In the event that, notwithstanding the foregoing, any payment shall be
received by the Trustee or any Holder of the Notes when such payment is
prohibited by the preceding paragraph of this Section 502, such payment shall be
held in trust for the benefit of, and shall be paid over or delivered to, the
holders of Senior Indebtedness or their respective representatives, or to the
trustee or trustees under any indenture pursuant to which any of such Senior
Indebtedness may have been issued, as their respective interests may appear, but
only to the extent that the holders of the Senior Indebtedness (or their
representative or representatives or a trustee) notify the Trustee within 90
days of such payment of the amounts then due and owing on the Senior
Indebtedness and only the amounts specified in such notice to the Trustee shall
be paid to the holders of Senior Indebtedness.

         SECTION 503. LIQUIDATION; DISSOLUTION; BANKRUPTCY

         Upon any payment by the Company, or distribution of assets of the
Company of any kind or character, whether in cash, property or securities, to
creditors upon any dissolution or winding-up or liquidation or reorganization of
the Company, whether voluntary or involuntary or in bankruptcy, insolvency,
receivership or other proceedings, all amounts due upon all Senior Indebtedness
shall first be paid in full, or payment thereof provided for in money in
accordance with its terms, before any payment or distribution is made by the
Company to the Holders of the Notes on account of the principal of, premium, if
any, interest on, or any other amount owing in respect of, the Notes; and upon
any such dissolution or winding-up or liquidation or reorganization, any payment
by the Company, or distribution of assets of the Company of any kind or
character, whether in cash, property or securities, to which the Holders of the
Notes or the Trustee would be entitled to receive from the Company, except for
the provisions of this Article Five, shall be paid by the Company or by any
receiver, trustee in bankruptcy, liquidating trustee, agent or other Person
making such payment or distribution, or by the Holders of the Notes or by the
Trustee under this Indenture if received by them or it, directly to the holders
of Senior Indebtedness (pro rata to such holders on the basis of the respective
amounts of Senior Indebtedness held by such holders, as calculated by the
Company) or their representative or representatives, or to the trustee or
trustees under any indenture pursuant to which any instruments evidencing such
Senior Indebtedness may have been issued, as their respective interests may
appear, to the extent necessary to pay such Senior Indebtedness in full, in
money or money's worth, after giving effect to any concurrent payment or
distribution to or for the holders of such Senior Indebtedness, before any
payment or distribution is made to the Holders of Notes or to the Trustee.

         In the event that, notwithstanding the foregoing, any payment or
distribution of assets of the Company of any kind or character, whether in cash,
property or securities, prohibited by the


                                       14
<PAGE>   18
foregoing, shall be received by the Trustee or the Holders of the Notes before
all Senior Indebtedness is paid in full, or provision is made for such payment
in money in accordance with its terms, such payment or distribution shall be
held in trust for the benefit of and shall be paid over or delivered to the
holders of such Senior Indebtedness or their representative or representatives,
or to the trustee or trustees under any indenture pursuant to which any
instruments evidencing such Senior Indebtedness may have been issued, as their
respective interests may appear, as calculated by the Company, for application
to the payment of all Senior Indebtedness remaining unpaid to the extent
necessary to pay such Senior Indebtedness in full in money in accordance with
its terms, after giving effect to any concurrent payment or distribution to or
for the benefit of the holders of such Senior Indebtedness.

         For purposes of this Article Five, the words "cash, property or
securities" shall not be deemed to include shares of stock of the Company as
reorganized or readjusted, or securities of the Company or any other corporation
provided for by a plan of reorganization or readjustment, the payment of which
is subordinated at least to the extent provided in this Article Five with
respect to the Notes to the payment of all Senior Indebtedness that may at the
time be outstanding, provided, however, that (i) such Senior Indebtedness is
assumed by the new corporation, if any, resulting from any such reorganization
or readjustment, and (ii) the rights of the holders of such Senior Indebtedness
are not, without the consent of such holders, altered by such reorganization or
readjustment. The consolidation of the Company with, or the merger of the
Company into, another corporation or the liquidation or dissolution of the
Company following the conveyance or transfer of its property as an entirety, or
substantially as an entirety, to another corporation upon the terms and
conditions provided for in Article Eight of the Original Indenture shall not be
deemed a dissolution, winding-up, liquidation or reorganization for the purposes
of this Section 503 if such other corporation shall, as a part of such
consolidation, merger, conveyance or transfer, comply with the conditions stated
in Article Eight of the Indenture. Nothing in Section 502 hereof or in this
Section 503 shall apply to claims of, or payments to, the Trustee under or
pursuant to Section 607 of the Original Indenture.

         SECTION 504. SUBROGATION

         Subject to the payment in full of all Senior Indebtedness, the rights
of the Holders of the Notes shall be subrogated to the rights of the holders of
such Senior Indebtedness to receive payments or distributions of cash, property
or securities of the Company applicable to such Senior Indebtedness until the
principal of, premium, if any, and interest on, and all other amounts owing in
respect of, the Notes shall be paid in full; and, for the purposes of such
subrogation, no payments or distributions to the holders of such Senior
Indebtedness of any cash, property or securities to which the Holders of the
Notes or the Trustee would be entitled except for the provisions of this Article
Five, and no payment over pursuant to the provisions of this Article Five, to or
for the benefit of the holders of such Senior Indebtedness by Holders of the
Notes or the Trustee, shall, as between the Company, its creditors other than
holders of Senior Indebtedness, and the Holders of the Notes be deemed to be a
payment by the Company to or on account of such Senior Indebtedness. It is
understood that the provisions of this Article Five are and are intended solely
for the purposes of defining the relative rights of the Holders of the Notes, on
the one hand, and the holders of Senior Indebtedness on the other hand.

                                       15
<PAGE>   19
         Nothing contained in this Article Five or elsewhere in this Third
Supplemental Indenture or the Original Indenture or in the Notes is intended to
or shall impair, as between the Company, its creditors other than the holders of
Senior Indebtedness, and the Holders of the Notes, the obligation of the
Company, which is absolute and unconditional, to pay to the Holders of the Notes
the principal of (and premium, if any) and interest on and all other amounts
owing in respect of the Notes as and when the same shall become due and payable
in accordance with their terms, or is intended to or shall affect the relative
rights of the Holders of the Notes and creditors of the Company, other than the
holders of Senior Indebtedness, nor shall anything herein or therein prevent the
Trustee or the Holder of any Note from exercising all remedies otherwise
permitted by applicable law upon default under the Original Indenture, as
amended and supplemented by this Third Supplemental Indenture, subject to the
rights, if any, under this Article Five of the holders of such Senior
Indebtedness in respect of cash, property or securities of the Company received
upon the exercise of any such remedy.

         Upon any payment or distribution of assets of the Company referred to
in this Article Five, the Trustee, subject to the provisions of Section 603 of
the Original Indenture, and the Holders of the Notes, shall be entitled to rely
upon any order or decree made by any court of competent jurisdiction in which
such dissolution, winding-up, liquidation or reorganization proceedings are
pending, or a certificate of the receiver, trustee in bankruptcy, liquidation
trustee, agent or other Person making such payment or distribution, delivered to
the Trustee or to the Holders of the Notes, for the purposes of ascertaining the
Persons entitled to participate in such distribution, the holders of Senior
Indebtedness and other indebtedness of the Company, the amount thereof or
payable thereon, the amount or amounts paid or distributed thereon and all other
facts pertinent thereto or to this Article Five.

         SECTION 505. TRUSTEE TO EFFECTUATE SUBORDINATION

         Each Holder of a Note by such Holder's acceptance thereof authorizes
and directs the Trustee on such Holder's behalf to take such action as may be
necessary or appropriate to effectuate the subordination provided in this
Article Five and appoints the Trustee as such Holder's attorney-in-fact for any
and all such purposes.

         SECTION 506. NOTICE BY THE COMPANY

         The Company shall give prompt written notice to a Responsible Officer
of the Trustee of any fact known to the Company that would prohibit the making
of any payment of monies to or by the Trustee in respect of the Notes pursuant
to the provisions of this Article Five. Notwithstanding the provisions of this
Article Five or any other provision of the Original Indenture and this Third
Supplemental Indenture, the Trustee shall not be charged with knowledge of the
existence of any facts that would prohibit the making of any payment of monies
to or by the Trustee in respect of the Notes pursuant to the provisions of this
Article Five unless and until a Responsible Officer shall have received written
notice thereof from the Company or a holder or holders of Senior Indebtedness or
from any representative or trustee therefor; and before the receipt of any such
written notice, the Trustee, subject to the provisions of Section 603 of the
Original Indenture, shall be entitled in all respects to assume that no such
facts exist; provided, however, that if the Trustee shall not have received the
notice provided for in this Section 506 at least two Business Days prior to the
date upon which by the terms hereof


                                       16
<PAGE>   20
any money may become payable for any purpose (including, without limitation, the
payment of the principal of (or premium, if any) or interest on any Note) then,
anything herein contained to the contrary notwithstanding, the Trustee shall
have full power and authority to receive such money and to apply the same to the
purposes for which they were received, and shall not be affected by any notice
to the contrary that may be received by it within two Business Days prior to
such date.

         The Trustee, subject to the provisions of Section 603 of the Original
Indenture, shall be entitled to rely on the delivery to it of a written notice
by a Person representing himself to be a holder of Senior Indebtedness (or a
representative or trustee on behalf of such holder) to establish that such
notice has been given by a holder of such Senior Indebtedness or a
representative or trustee on behalf of any such holder or holders. In the event
that the Trustee determines in good faith that further evidence is required with
respect to the right of any Person as a holder of such Senior Indebtedness to
participate in any payment or distribution pursuant to this Article Five, the
Trustee may request such Person to furnish evidence to the reasonable
satisfaction of the Trustee as to the amount of such Senior Indebtedness held by
such Person, the extent to which such Person is entitled to participate in such
payment or distribution and any other facts pertinent to the rights of such
Person under this Article Five, and if such evidence is not furnished, the
Trustee may defer any payment to such Person pending judicial determination as
to the right of such Person to receive such payment.

         SECTION 507. RIGHTS OF THE TRUSTEE; HOLDERS OF SENIOR INDEBTEDNESS

         The Trustee in its individual capacity shall be entitled to all the
rights set forth in this Article Five in respect of any Senior Indebtedness at
any time held by it, to the same extent as any other holder of Senior
Indebtedness, and nothing in the Original Indenture or this Third Supplemental
Indenture shall deprive the Trustee of any of its rights as such holder.

         With respect to the holders of Senior Indebtedness, the Trustee
undertakes to perform or to observe only such of its covenants and obligations
as are specifically set forth in this Article Five, and no implied covenants or
obligations with respect to the holders of such Senior Indebtedness shall be
read into the Original Indenture or this Third Supplemental Indenture against
the Trustee. The Trustee shall not be deemed to owe any fiduciary duty to the
holders of Senior Indebtedness and, subject to the provisions of Section 603 of
the Original Indenture, the Trustee shall not be liable to any holder of Senior
Indebtedness if it shall pay over or deliver to Holders of Notes, the Company or
any other Person money or assets to which any holder of Senior Indebtedness
shall be entitled by virtue of this Article Five or otherwise.

         SECTION 508. SUBORDINATION MAY NOT BE IMPAIRED

         No right of any present or future holder of any Senior Indebtedness to
enforce subordination as herein provided shall at any time in any way be
prejudiced or impaired by any act or failure to act on the part of the Company
or by any act or failure to act, in good faith, by any such holder, or by any
noncompliance by the Company with the terms, provisions and covenants of the
Original Indenture or this Third Supplemental Indenture, regardless of any
knowledge thereof that any such holder may have or otherwise be charged with.

                                       17
<PAGE>   21
         Without in any way limiting the generality of the foregoing paragraph,
the holders of Senior Indebtedness may, at any time and from time to time,
without the consent of or notice to the Trustee or the Holders of the Notes,
without incurring responsibility to the Holders of the Notes and without
impairing or releasing the subordination provided in this Article Five or the
obligations hereunder of the Holders of the Notes to the holders of such Senior
Indebtedness, do any one or more of the following:

                  (i) change the manner, place or terms of payment or extend the
         time of payment of, or renew or alter, such Senior Indebtedness, or
         otherwise amend or supplement in any manner such Senior Indebtedness or
         any instrument evidencing the same or any agreement under which such
         Senior Indebtedness is outstanding;

                  (ii) sell, exchange, release or otherwise deal with any
         property pledged, mortgaged or otherwise securing such Senior
         Indebtedness;

                  (iii) release any Person liable in any manner for the
         collection of such Senior Indebtedness; and

                  (iv) exercise or refrain from exercising any rights against
         the Company and any other Person.

                                  ARTICLE SIX
                   EVENTS OF DEFAULT WITH RESPECT TO THE NOTES

         SECTION 601. DEFINITION

         All of the events specified in clauses (1), (2) and (4) through (6) of
Section 501 of the Original Indenture shall be "Events of Default" with respect
to the Notes.

         SECTION 602. ACCELERATION

         In addition to the provisions regarding acceleration of maturity upon
an Event of Default provided by Section 502 of the Original Indenture, if an
Event of Default occurs and is continuing with respect to the Notes, so long as
any of the Trust Preferred Securities of the Trust remain outstanding, if, upon
such Event of Default, the Trustee or the Holders of not less than 25% in
aggregate principal amount of the Notes fail to declare the principal of all the
Notes to be so immediately due and payable, the holders of 25% in aggregate
liquidation amount of the Trust Preferred Securities then outstanding shall have
the right, by notice to the Trustee, to declare the principal of and accrued
interest on all the Notes to be due and payable immediately.

         So long as any of the Trust Preferred Securities of the Trust remain
outstanding, the holders of a majority in aggregate liquidation amount of the
Trust Preferred Securities then outstanding shall have the sole right (and the
Holders of the Notes may not, notwithstanding the provisions of Section 502 of
the Original Indenture, exercise any such right) to rescind an acceleration and
its consequences with respect to the Notes if the rescission would not conflict
with any judgment or decree and if all existing Events of Default on the Notes
have been cured or waived except nonpayment of principal or interest that has
become due solely because of the acceleration.

                                       18
<PAGE>   22
         If at any time while the Notes are held by the LLC no Trust Preferred
Securities of the Trust remain outstanding, in addition to the provisions
regarding acceleration of maturity upon an Event of Default provided by Section
502 of the Original Indenture, if an Event of Default occurs and is continuing
with respect to the Notes, so long as any of the Company Preferred Securities
remain outstanding, if, upon such Event of Default, the Trustee or the Holders
of not less than 25% in aggregate principal amount of the Notes fail to declare
the principal of all the Notes to be so immediately due and payable, the holders
of 25% in aggregate liquidation amount of the Company Preferred Securities then
outstanding shall have the right, by notice to the Trustee, to declare the
principal of and accrued interest on all the Notes to be due and payable
immediately.

         If at any time while the Notes are held by the LLC and no Trust
Preferred Securities of the Trust remain outstanding, so long as any of the
Company Preferred Securities remain outstanding, the holders of a majority in
aggregate liquidation amount of the Company Preferred Securities then
outstanding shall have the sole right (and the Holders of the Notes may not,
notwithstanding the provisions of Section 502 of the Original Indenture,
exercise any such right) to rescind an acceleration and its consequences with
respect to the Notes if the rescission would not conflict with any judgment or
decree and if all existing Events of Default on the Notes have been cured or
waived except nonpayment of principal or interest that has become due solely
because of the acceleration.

         SECTION 603. SUITS

         So long as any of the Trust Preferred Securities of the Trust remain
outstanding, any holder of a Trust Preferred Security shall have the right, upon
the occurrence and continuance of an Event of Default described in Section
501(1) or 501(2) of the Original Indenture with respect to the Notes, to
institute suit directly against the Company to enforce payment to such holder of
the principal of, and premium, if any, and interest on, the Notes having a
principal amount equal to the aggregate liquidation amount of the Trust
Preferred Securities held by such holder.

         If at any time while the Notes are held by the LLC and no Trust
Preferred Securities of the Trust remain outstanding, so long as any of the
Company Preferred Securities remain outstanding, any holder of a Company
Preferred Security shall have the right, upon the occurrence and continuance of
an Event of Default described in Section 501(1) or 501(2) of the Original
Indenture with respect to the Notes, to institute suit directly against the
Company to enforce payment to such holder of the principal of, and premium, if
any, and interest on, the Notes having a principal amount equal to the aggregate
liquidation amount of the Company Preferred Securities held by such holder.

         The provisions of this Section 603 and any other provisions hereof
granting rights to the holders of the Trust Preferred Securities or the Company
Preferred Securities are intended for the benefit of the Trust Preferred
Securities and the Company Preferred Securities as third party beneficiaries.

                                       19
<PAGE>   23
                                 ARTICLE SEVEN
                         AMENDMENT TO ORIGINAL INDENTURE

         SECTION 701. AMENDMENT TO SECTION 801 OF ORIGINAL INDENTURE

         Subparagraph (1) of Section 801 of the Original Indenture is amended,
effective as provided in Section 702 hereof, to read as follows:

                  "(1) the Corporation formed by such consolidation into which
         the Company is merged or the Person which acquires by conveyance or
         transfer the properties and assets of the Company substantially as an
         entirety (a) shall be, if a Corporation, a Corporation organized and
         existing under the laws of (i) the United States of America or any
         State or the District of Columbia or (ii) a foreign jurisdiction and
         which consents to the jurisdiction of the courts of the United States
         of America or of any State, and (b) shall expressly assume, by an
         indenture supplemental hereto, executed and delivered to the Trustee,
         in form satisfactory to the Trustee, the due and punctual payment of
         the principal of (and premium, if any) and interest on all the
         Securities and the performance of every covenant of this Indenture on
         the part of the Company to be performed or observed;"

         SECTION 702. EFFECTIVENESS OF AMENDMENT.

         The amendment to the Original Indenture set forth in Section 701 hereof
shall be effective upon the approval of the Holders of Outstanding Securities
under the Indenture as required by Section 901 of the Original Indenture. For
this purpose, the Holders of the Notes, by their acquisition thereof, shall be
deemed to have approved such amendment.

                                 ARTICLE EIGHT
                                  MISCELLANEOUS

         SECTION 801. EFFECT ON ORIGINAL INDENTURE

         The Third Supplemental Indenture is a supplement to the Original
Indenture. As supplemented by this Third Supplemental Indenture, the Original
Indenture is in all respects ratified, approved and confirmed, and the Original
Indenture and this Third Supplemental Indenture shall together constitute one
and the same instrument.

         SECTION 802. COUNTERPARTS

         This Third 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 by one and the same instrument.

         SECTION 803. RECITALS

         The recitals contained herein shall be taken as the statements of the
Company, and the Trustee assumes no responsibility for their correctness. The
Trustee makes no representations as to the validity or sufficiency of this Third
Supplemental Indenture.

                                       20
<PAGE>   24
         SECTION 804. GOVERNING LAW

         This Third Supplemental Indenture shall be governed by and construed in
accordance with the laws of the jurisdiction that govern the Original Indenture
and its construction.

              [The balance of this page intentionally left blank.]

                                       21
<PAGE>   25
         IN WITNESS WHEREOF, the parties hereto have caused this Third
Supplemental Indenture to be duly executed and their respective corporate seals
to be hereunto affixed and attested, all as of the date and year first written
above.

                                    TECO ENERGY, INC.


                                    By: /s/ Gordon L. Gillette
                                       ----------------------------------------
                                    Name:    Gordon L. Gillette
                                    Title:   Vice President - Finance and Chief
                                             Financial Officer

[Corporate Seal]

                                    THE BANK OF NEW YORK, AS TRUSTEE


                                    By: /s/ James Hall
                                       ----------------------------------------
                                    Name:    James Hall
                                    Title:   Vice President


[Corporate Seal]
<PAGE>   26
State of New York                   )
                                    ) SS.:
County of New York                  )

         On the 7th day of December, 2000 before me personally came Gordon L.
Gillette, to me known, who, being by me duly sworn, did depose and say that he
is Vice President - Finance of TECO ENERGY, INC., 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.

                                     /s/ Don Aoki
                                    ----------------------------------
                                    Notary Public

State of New York                   )
                                    ) SS.:
County of New York                  )

         On the 18th day of December, 2000 before me personally came James Hall
to me known, who, being by me duly sworn, did depose and say that he/she is Vice
President of THE BANK OF NEW YORK, one of the corporations described in and
which executed the foregoing instrument; that he/she 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/she signed his/her names thereto by like authority.

                                     /s/ Jean F. Newman
                                    ----------------------------------
                                    Notary Public
<PAGE>   27
                                                                       EXHIBIT A

                                  FORM OF NOTE
<PAGE>   28
                                                                       EXHIBIT B

                                TECO ENERGY, INC.

                    8.50% JUNIOR SUBORDINATED NOTES DUE 2041

                           SUPPLEMENTAL COMPANY ORDER

         Pursuant to Section 210 of the Third Supplemental Indenture, dated as
of December 1, 2000, to the Indenture, dated as of August 17, 1998, as amended,
you are instructed to prepare and authenticate a Note, of the series identified
above, in the principal amount of $______________. The Note is being delivered
in exchange for issued and outstanding Notes of the series identified above.

         IN WITNESS WHEREOF, I have hereunto set my hand this ___ day of
________, ____.

                                             TECO ENERGY, INC.



                                             By:_______________________________
                                                Name:
                                                Title: