Document:

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                                                                     EXHIBIT 4.4

                   FORM OF SERIES 2000C CONVERTIBLE DEBENTURE
                            KIEWIT MATERIALS COMPANY
                             A DELAWARE CORPORATION

Registered Debenture No.                                $
8.25% Convertible Debenture                                Due: October 31, 2010

     KIEWIT MATERIALS COMPANY, a corporation organized and existing under the
laws of the State of Delaware, and having its principal place of business in the
City of Omaha, Nebraska (hereinafter called the "Corporation"), for the value
received, hereby promises to pay to                or registered assigns
(hereinafter called the "Debentureholder") on October 31, 2010, the principal
sum of                ($          ) Dollars.

     This debenture is one of the 2000C series of registered convertible
debentures of the Corporation, due October 31, 2010 unless previously redeemed
or converted, limited to the aggregate principal amount of                and
No/100 ($          ) Dollars, all issued or to be issued pursuant to an
indenture, dated as of September 14, 2000 (the "Indenture"), executed and
delivered by the Corporation and UMB Bank, N.A. as Trustee, (hereinafter
referred to as "Trustee"). This debenture is subject to the terms of the
Indenture, and all indentures supplemental thereto, and reference is hereby made
to the Indenture and any such supplemental indenture for a description of the
rights, limitations, obligations and immunities of the Corporation, the holders
of the debentures and the Trustee. Capitalized terms used and not defined herein
have the meanings ascribed to those terms in the Indenture.

          (1) TYPE OF PAYMENT:  Payment of interest and principal shall be in
     any coin or currency of the United States of America which at the time of
     payment shall be legal tender for the payment of public or private debts.

          (2) INTEREST:  Except as hereinafter provided, the Corporation
     promises to pay to the registered holder hereof or his registered assigns,
     interest on the principal sum of this debenture at the rate of eight and
     twenty five hundredths (8.25%) per annum until the Corporation's obligation
     with respect to the payment of the principal amount shall have been
     discharged. Interest shall accrue upon this debenture from the most recent
     date to which interest has been paid, or if no interest has been paid, from
     the date of original issuance. In the event of conversion as provided in
     paragraph (7)(a) hereof, interest shall cease accruing on the principal
     amount of this debenture on June 30, 2004. In the event of conversion as
     provided in paragraph (7)(b) hereof, interest shall cease accruing on the
     principal amount of this debenture on the Conversion Date. Interest on this
     debenture shall be paid annually on each November 1st, commencing November
     1, 2000 to the registered owner as recorded on the Security Register
     maintained by the Corporation as of the preceding October 15.

          (3) PLACE OF PAYMENT:  The principal and interest on this debenture
     shall be payable at the office of the Corporation in Omaha, Nebraska.

          (4) DEFAULT:  This debenture shall be deemed to be in default whenever
     the principal sum and/or interest becomes payable and remains unpaid for a
     period of sixty (60) days.

          (5) REDEMPTION:  This debenture is subject to redemption at any time
     prior to the date of maturity at its principal amount plus all accrued and
     unpaid interest to the date of redemption, provided, however, that the
     entire series is redeemed. This debenture may not be redeemed during the
     thirty-one (31) day conversion period provided for in paragraph (7)(a)
     hereof. Redemption shall be preceded by notice thereof, mailed to the
     registered holder by first class mail no later than thirty (30) days
     preceding the date of redemption. The registered holder may convert this
     debenture into Common Stock during that thirty (30) day period preceding
     the date set for redemption as provided for in paragraph 7(b) hereof.
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          (6) TRANSFER:  The debenture may be transferred by the registered
     holder at the principal office of the Corporation in Omaha, Nebraska on
     registry books kept for such purpose at the office of the Trustee, upon
     surrender and cancellation of this debenture, and the payment of applicable
     charges as recorded on the Security Register and the delivery of a form of
     assignment with medallion signature guarantee or other guarantee,
     acceptable to the Trustee. The Corporation and the Trustee may treat the
     registered holder of this debenture, as recorded on the Security Register,
     as the absolute owner for all purposes.

        (7) CONVERSION

          (a) This debenture is convertible into the $0.01 par value common
     stock ("Common Stock") of the Corporation on the following basis: during
     the period commencing on October 1, 2004 and ending on October 31, 2004,
     the registered holder may convert the entire principal amount of this
     debenture, plus a cash payment equal to the product of
     multiplied by the Average Closing Market Price on the Conversion Date, into
                    (               ) shares of Common Stock, subject to
     adjustment upon the occurrence of certain events as provided in the
     Indenture.

          (b) If any of the following events occur prior to October 1, 2004,
     this debenture is convertible into Common Stock: (i) for thirty (30) days
     following the occurrence of the registered holder's death; (ii) for thirty
     (30) days following a Change of Control; and (iii) for thirty (30) days
     prior to redemption of the registered holder's debentures, as provided for
     in paragraph (5) hereof. During any such period, the registered holder or
     the registered holder's representative or estate, as the case may be, may
     convert the entire principal amount of the debenture plus a cash payment
     equal to the product of                multiplied by the Average Closing
     Market Price on the Conversion Date, into                (               )
     shares of Common Stock, subject to adjustment upon the occurrence of
     certain events as provided in the Indenture.

          (c) During the period commencing on November 1, 2004 and ending on
     October 31, 2010, the date of maturity, the debenture is not convertible,
     in whole or in part.

          (d) The conversion privilege shall be deemed exercised by submission
     of this debenture with a written request for conversion plus the required
     cash payment during the applicable conversion period at the principal
     office of the Corporation. The Corporation shall thereafter, within a sixty
     (60) day period, issue certificates registered in the name of the
     registered holder representing the shares of Common Stock into which this
     debenture has been converted.

          (8) SUBORDINATION:  In the payment of their claims, all creditors of
     the Corporation shall rank equally with the holders of convertible
     debentures. All claims of the debentureholders against earnings or assets
     are hereby made superior to those of stockholders, and the Corporation
     agrees that as long as any of its convertible debentures are outstanding,
     it will not pay any dividends on its stock until all liability for unpaid
     interest on its debentures has been paid. In the event of dissolution or
     liquidation of the Corporation, the holders of all debentures shall be
     entitled to be paid in full, both principal and interest, before any assets
     of the Corporation are distributed to any stockholder.

          (9) LIMITATION OF LIABILITY:  No recourse shall be had for the
     payment of the principal or interest of this debenture, against any
     incorporator, stockholder, officer, or director, past, present, or future,
     of the Corporation, all such liability being expressly waived by the owner
     of this debenture.

          (10) VALIDATION:  This debenture shall not be valid or become
     obligatory for any purpose until the certificate of authentication thereon
     shall have been signed by the Trustee.

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     IN WITNESS WHEREOF, Kiewit Materials Company has caused this debenture to
become signed and its corporate seal to be hereunto affixed by its officers duly
authorized thereunto, all as of the      day of          , 2000.

<TABLE>
<S>                                                         <C>
ATTEST:                                                                      KIEWIT MATERIALS COMPANY

-----------------------------------------------------
                                                            By --------------------------------------------------
Assistant Secretary
                                                                                     President
</TABLE>

TRUSTEE'S CERTIFICATE OF AUTHENTICATION:  This is one of the debentures
described in the Indenture, dated as of September 14, 2000, by and between
Kiewit Materials Company and UMB Bank, N.A., as Trustee.

<TABLE>
<S>                                                         <C>
Dated -----------------------------------------------       By --------------------------------------------------
                                                                                Authorized Officer
</TABLE>

This Debenture and the transfer thereof are subject to restrictions which are
stated in an Agreement between the Debentureholder(s) whose name(s) appear(s)
hereon and KIEWIT MATERIALS COMPANY, dated September 14, 2000.

                                        3<PAGE>   1
                                                                Exhibit 10.22(a)

                             FIRST AMENDMENT TO THE
            AMENDED AND RESTATED LIMITED LIABILITY COMPANY AGREEMENT
                                       FOR
                   CHARTER COMMUNICATIONS HOLDING COMPANY, LLC
                      A DELAWARE LIMITED LIABILITY COMPANY

         This First Amendment to the Amended and Restated Limited Liability
Company Agreement for Charter Communications Holding Company, LLC, a Delaware
limited liability company ("COMPANY"), is adopted effective as of September 13,
2000 ("EFFECTIVE DATE") by Charter Communications, Inc., a Delaware corporation
("PUBLICCO"), with reference to the following facts:

         A. The Company is being operated pursuant to that certain Amended and
Restated Limited Liability Company Agreement entered into and made effective as
of February 14, 2000, by and among Charter Investment, Inc, Vulcan Cable III
Inc., PublicCo, and certain other parties (the "LLC AGREEMENT"). Unless
otherwise defined, capitalized terms used herein have the meanings assigned to
them in the LLC Agreement.

         B. Pursuant to that certain Merger Agreement and Plan of Reorganization
dated as of August 11, 2000, among PublicCo, Interactive Broadcaster Services
Corporation, and Craig T. Moncreiff, the certificate of incorporation of
PublicCo is being amended as of the Effective Date. PublicCo desires to make
certain conforming changes to the LLC Agreement.

         C. Section 10.11 of the LLC Agreement provides that an amendment to the
LLC Agreement to incorporate the changes made by this First Amendment shall be
effective as an amendment upon the approval of Members holding more than fifty
percent (50%) of the Class B Common Units. On the Effective Date, PublicCo owns
all outstanding Class B Common Units and desires to approve the amendments to
the LLC Agreement made by this First Amendment.

         NOW, THEREFORE, the LLC Agreement is hereby amended as follows:

         1.       Section 2.5 of the LLC Agreement is amended and restated in
its entirety to read as follows:

                  2.5 Purpose of Company. The Company may carry on any lawful
         business, purpose, or activity that may be carried on by a limited
         liability company under applicable law; (i) provided, however, that,
         until all outstanding shares of Class B Common Stock have been
         converted into shares of Class A Common Stock in accordance with Clause
         (b)(viii) of Article Fourth of PublicCo's certificate of incorporation
         as constituted as of the Class B Common Measuring Date, without the
         Approval of the Class A Common Members, the Company shall not engage
         directly or indirectly, including without limitation through any
         Subsidiary, in any business other than (A) the Cable Transmission
         Business (as defined below), (B) as a member or shareholder of, and
         subscriber to, the portal joint venture with Broadband Partners and (C)
         as an owner and operator of the business of Interactive Broadcaster
         Services Corporation, a California corporation, which shall include
         solely the ownership of its
<PAGE>   2
         assets and continuation of its business substantially as owned and
         conducted as of September 13, 2000; (ii) provided further, that to the
         extent that, as of the Class B Common Measuring Date, the Company was
         directly or indirectly engaged in or had agreed to acquire directly or
         indirectly any business other than the Cable Transmission Business or
         as a member of, and subscriber to, the portal joint venture with
         Broadband Partners (any such other business, an "INCIDENTAL BUSINESS,"
         and collectively, "INCIDENTAL BUSINESSES"), so long as (a) such
         Incidental Businesses so engaged in by the Company on the Class B
         Common Measuring Date in the aggregate on such date accounted for less
         than ten percent (10%) of the consolidated revenues of the total
         business engaged in by the Company or (b) such Incidental Businesses
         which on the Class B Common Measuring Date the Company had agreed to
         acquire in the aggregate on such date accounted for less than ten
         percent (10%) of the consolidated revenues of the total businesses to
         be acquired, as applicable, the Company may, directly or indirectly,
         including through any Subsidiary, continue to conduct any such
         Incidental Business and the foregoing limitation on the business and
         purpose of the Company shall not require that any such Incidental
         Business be divested by the Company, but the Company shall not,
         directly or indirectly, expand any such Incidental Business by means of
         any acquisition or any commitment of the Company or its Subsidiaries'
         resources or financial support. "CABLE TRANSMISSION BUSINESS" means the
         transmission of video, audio (including telephony) and data over cable
         television systems owned, operated or managed by the Company or its
         Subsidiaries; provided, that the businesses of RCN Corporation and its
         Subsidiaries shall not be deemed to be a Cable Transmission Business.

         2.       The first two paragraphs of Section 5.7 are amended and
restated in their entirety to read as follows:

                  5.7 Competing Activities. Except as provided by any individual
         contract: (i) any Manager or Member (and their respective officers,
         directors, agents, shareholders, members, partners or Affiliates) may
         engage or invest in, independently or with others, any business
         activity of any type or description, including without limitation those
         that might be the same as or similar to the Company's business or the
         business of any Subsidiary and that might be in direct or indirect
         competition with the Company or any Subsidiary; (ii) neither the
         Company or any Subsidiary nor any Member shall have any right in or to
         such other ventures or activities or to the income or proceeds derived
         therefrom; (iii) no Manager or Member (and their respective officers,
         directors, agents, shareholders, members, partners or Affiliates) shall
         be obligated to present any investment opportunity or prospective
         economic advantage to the Company or any Subsidiary, even if the
         opportunity is of the character that, if presented to the Company or
         any Subsidiary, could be taken by the Company or any Subsidiary;
         and (iv) any Manager or Member (and their respective officers,
         directors, agents, shareholders, members, partners or Affiliates) shall
         have the right to hold any investment opportunity or prospective
         economic advantage for such Manager's or Member's (and their respective
         officers', directors', agents', shareholders', members', partners' or
         Affiliates') own account or to recommend such opportunity to Persons
         other than the Company or any Subsidiary;

                                      -2-
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         (i) provided that as a condition to election as Manager and receiving a
         Membership Interest in the Company upon consummation of the IPO,
         PublicCo agrees that until all outstanding shares of Class B Common
         Stock have been converted into shares of Class A Common Stock in
         accordance with Clause (b)(viii) of Article Fourth of PublicCo's
         certificate of incorporation as constituted as of the Class B Common
         Measuring Date, it shall not engage directly or indirectly, including
         without limitation through any Subsidiary, in any business other than
         (A) the Cable Transmission Business, (B) as a member or shareholder of,
         and subscriber to, the portal joint venture with Broadband Partners;
         and (C) as an owner and operator of the business of Interactive
         Broadcaster Services Corporation, a California corporation, which shall
         include solely the ownership of its assets and continuation of its
         business substantially as owned and conducted as of September 13, 2000;
         (ii) provided further, that to the extent that, as of the Class B
         Common Measuring Date, PublicCo was directly or indirectly engaged in,
         or had agreed to acquire directly or indirectly, an Incidental
         Business, so long as (a) such Incidental Businesses so engaged in by
         PublicCo on the Class B Common Measuring Date in the aggregate on such
         date accounted for less than ten percent (10%) of the consolidated
         revenues of the total business engaged in by PublicCo, or (b) such
         Incidental Businesses which on the Class B Common Measuring Date
         PublicCo had agreed to acquire in the aggregate on such date accounted
         for less than ten percent (10%) of the consolidated revenues of the
         total businesses to be acquired, as applicable, PublicCo may, directly
         or indirectly, including through any Subsidiary, continue to conduct
         any such Incidental Business and the foregoing limitation on the
         business and purpose of PublicCo shall not require that any such
         Incidental Business be divested by PublicCo, but PublicCo shall not,
         directly or indirectly, expand any such Incidental Business by means of
         any acquisition or any commitment of PublicCo or its Subsidiaries'
         resources or financial support. PublicCo also agrees that it shall not
         (i) hold any assets, other than (a) working capital cash and cash
         equivalents held for the payment of current obligations and receivables
         from the Company; (b) Common Units; (c) back-to-back obligations and
         mirror equity interests of the Company, consisting of obligations and
         equity securities (other than Common Units, but including convertible
         securities), which are substantially equivalent to liabilities or
         obligations or securities of PublicCo to third parties; (d) assets
         subject to an existing obligation to contribute such assets (or
         successor assets) to the Company in exchange for Units; (e) assets
         acquired as a result of the issuance of (x) common stock of PublicCo
         and/or preferred stock of PublicCo and/or (y) liabilities or
         obligations of PublicCo, subject to an existing obligation to
         contribute such assets (or successor assets) to the Company in exchange
         for Common Units (in respect of the common stock of PublicCo issued)
         and/or for mirror equity securities (other than Common Units, but
         including convertible securities, in respect of the mirror equity
         securities issued) of the Company and/or liabilities or obligations of
         the Company (in respect of the liabilities or obligations incurred),
         which are substantially equivalent to the equity securities and/or
         liabilities and obligations of PublicCo issued to acquire such assets;
         or (f) goodwill or deferred tax assets, or (ii) incur any liabilities
         or obligations for borrowed money, for acquisition of assets or under
         any capital lease, other than (a) in connection with back-to-back
         obligations of the Company to PublicCo consisting of liabilities or
         obligations of the Company which are substantially equivalent to
         liabilities or

                                      -3-
<PAGE>   4
         obligations of PublicCo to a third party; (b) liabilities or
         obligations incident to the acquisition of Units in exchange for common
         stock of PublicCo; or (c) liabilities or obligations as contemplated by
         Clauses (i)(d) and (e) immediately above. PublicCo further agrees (x)
         that it shall not issue, transfer from treasury stock or repurchase
         shares of its common stock unless in connection with any such issuance,
         transfer, or repurchase PublicCo takes all requisite action such that,
         after giving effect to all such issuances, transfers or repurchases,
         the number of outstanding shares of common stock will equal on a
         one-for-one basis the number of Common Units owned by PublicCo; (y)
         that it shall not issue, transfer from treasury stock or repurchase
         shares of preferred stock of PublicCo unless in connection with any
         such issuance, transfer or repurchase PublicCo takes all requisite
         action such that, after giving effect to all such issuances, transfers
         or repurchases, PublicCo holds mirror equity interests of the Company
         which are in the aggregate substantially equivalent to the outstanding
         preferred stock of PublicCo; and (z) upon any reclassification of the
         Common Units, whether by combination, division or otherwise, it shall
         take all requisite action so that the number of outstanding shares of
         common stock will equal on a one-for-one basis the number of Common
         Units owned by PublicCo.

                  The Company agrees that, until all outstanding shares of Class
         B Common Stock have been converted into shares of Class A Common Stock
         in accordance with Clause (b)(viii) of Article Fourth of PublicCo's
         certificate of incorporation as constituted as of the Class B Common
         Measuring Date, without the Approval of the Class A Common Members, (i)
         the Company shall not engage directly or indirectly, including without
         limitation through any Subsidiary, in any business other than (A) the
         Cable Transmission Business, (B) as a member or shareholder of and
         subscriber to, the portal joint venture with Broadband Partners, and
         (C) as an owner and operator of the business of Interactive Broadcaster
         Services Corporation, a California corporation, which shall include
         solely the ownership of its assets and continuation of its business
         substantially as owned and conducted as of September 13, 2000; and (ii)
         to the extent that, as of the Class B Common Measuring Date, the
         Company was directly or indirectly engaged in, or had agreed to acquire
         directly or indirectly, an Incidental Business, so long as (a) such
         Incidental Businesses so engaged in by the Company on the Class B
         Common Measuring Date in the aggregate on such date accounted for less
         than ten percent (10%) of the consolidated revenues of the total
         business engaged in by the Company or (b) such Incidental Businesses
         which on the Class B Common Measuring Date the Company had agreed to
         acquire in the aggregate on such date accounted for less than ten
         percent (10%) of the consolidated revenues of the total businesses to
         be acquired, as applicable, the Company may, directly or indirectly,
         including through any Subsidiary, continue to conduct any such
         Incidental Business and the foregoing limitation on the business and
         purpose of the Company shall not require that any such Incidental
         Business be divested by the Company, but the Company shall not,
         directly or indirectly, expand any such Incidental Business by means of
         any acquisition or any commitment of the Company or its Subsidiaries'
         resources or financial support.

                                      -4-
<PAGE>   5
         IN WITNESS WHEREOF, the undersigned has executed this First Amendment,
effective as of the date first written above.

                                          Charter Communications, Inc.

                                          By:    /s/ Curtis S. Shaw
                                             ----------------------------------
                                          Name:  Cutis S. Shaw
                                          Title: Senior Vice President

                                      -5-

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