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                                                                   EXHIBIT 10.43



                                 AMENDMENT NO. 1

                                       TO

                 AMENDED AND RESTATED MASTER OPERATING AGREEMENT


         THIS AMENDMENT NO. 1 (this "Amendment"), dated as of September 15, 2000
(the "Effective Date"), is made and entered into by and between UBS AG, a
corporation organized under the laws of Switzerland ("UBS AG"), and Perot
Systems Corporation, a Delaware corporation ("PSC"). As used in this Amendment,
"party" means either UBS AG or PSC, as appropriate, and "parties" means UBS AG
and PSC, collectively.

                                    RECITALS

         A. Swiss Bank Corporation (a predecessor of UBS AG) and PSC entered
into an Amended and Restated Master Operating Agreement, dated as of January 1,
1997 (the "Master Operating Agreement").

         B. The parties desire to amend the Master Operating Agreement as set
forth below.

         C. Concurrently with the execution of this Amendment, the parties are
entering into Amendment No. 1 to Second Amended and Restated Agreement For EPI
Operational Management Services (the "SBC Warburg EPI Amendment").

         In consideration of the foregoing and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto agree as follows:

                                   AMENDMENTS
1.       DEFINITIONS.

         (a)      A definition of "Network" is hereby added to Section 1.1 of
                  the Master Operating Agreement to read in its entirety as
                  follows:

                  "Network" means all hardware, software, cabling,
                  telecommunications facilities and transport services that are
                  used to connect, transmit, architect, manage, monitor and
                  support all data, voice and video services in connection with
                  the business and operations of the SBC Entities.

                  The term "Network" shall not include the following: (A) file,
                  application, database, mail, fax, Chat, Unix/NT platforms and
                  web servers; and (B) workstations, terminals, printers, fax
                  machines or other end-user devices attached to LANs.

         (b)      A definition of "Network Services" is hereby added to Section
                  1.1 of the Master Operating Agreement to read in its entirety
                  as follows:

                  "Network Services" means all services relating to the
                  Operational Management of the Network of any SBC Entity,
                  including without limitation all management, administration,
                  operations, maintenance, support, design, engineering,
                  planning, provisioning, procurement, staging, configuration,
                  installation, implementation, training and related services,
                  and specifically including without limitation:




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                  (i)      IP Services - LAN technologies including routing and
                           switching, etc., MAN/WAN technologies including
                           multiplexors, DSUs/CSUs, encryptors, etc;

                  (ii)     Transport Services including ATM, frame relay, DSL,
                           Internet, ISDN, leased lines, wireless, etc., and
                           remote access technologies including VPNs,
                           authentication, encryption, etc;

                  (iii)    Voice Services - Voice technologies including PBXs,
                           key systems, telephones, audio-conferencing, trader
                           turrets, telco services such as PSTN, cellular, and
                           trader circuits, voice mail systems, voice response
                           units, automatic call distribution systems, CTI, IVR
                           systems, etc;

                  (iv)     Video Services - Video technologies including
                           multi-point boardroom video, desktop video,
                           video/audio streaming and real time CATV
                           distribution; and

                  (v)      Internet, Intranet and Extranet
                           communications/security infrastructure including
                           firewalls, intrusion detection systems,
                           authentication systems, encryption systems,
                           application proxy servers, network cache servers,
                           Internet service providers, etc.

                  The term "Network Services" shall not include the following
                  services relating to the Network:

                  (i)      Level 1 Help Desk/Call Centers that interface with
                           the end use/customer on all Network Services
                           problems;

                  (ii)     NT and Unix procurement, staging, configuration,
                           installation, implementation and support; and

                  (iii)    Design, architecture, maintenance and support of the
                           Chat infrastructure, meta-directory infrastructure
                           and web server infrastructure.

         (c)      The term "EPI" at Section 1.1(g) of the Master Operating
                  Agreement is hereby amended to read in its entirety as
                  follows:

                  "EPI" means all existing and future information technology
                  services provided by or on behalf of any SBC Entity that are
                  related to the Operational Management of that SBC Entity's
                  mainframe and other computers (including personal computers),
                  including peripheral equipment. The term "EPI" shall not
                  include any information technology services related to the
                  Operational Management of the Network.

         (d)      The term "Services" is hereby amended to read in its entirety
                  as follows:

                  "Services" means, with respect to each EPI Agreement, the
                  services required for the Operational Management of the EPI of
                  the applicable SBC Entity and which are described as such in
                  that EPI Agreement, together with any additional services that
                  are to be provided by PSC under that EPI Agreement.


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2.       REMOVAL OF NETWORK SERVICES.

         From and after the Transition Date (as defined in the SBC Warburg EPI
         Amendment), Network Services shall no longer be included as part of the
         Services that are the subject of the Master Operating Agreement, except
         inasmuch as services related to the Network and Network Services are
         necessary for PSC to fulfill its obligation to complete the transition
         of Network Services to the Designated UBS Entity (as defined in the SBC
         Warburg EPI Amendment) pursuant to the SBC Warburg EPI Amendment (which
         may include, among other things, the continued provision of certain
         Network Services pursuant to Section 2.2(g) of the SBC Warburg EPI
         Amendment). This Amendment shall not affect any rights or obligations
         of the parties under the Master Operating Agreement in connection with
         any Network Services provided by Perot Systems prior to the completion
         of the transition of Network Services pursuant to the SBC Warburg EPI
         Amendment.

3.       MISCELLANEOUS.

         (a)      Any capitalized terms not defined herein shall have the
                  meaning given them in the Master Operating Agreement.

         (b)      The section headings used in this Amendment are for reference
                  and convenience only and shall not enter into the
                  interpretation of this Amendment.

         (c)      The terms and conditions set forth in this Amendment shall be
                  deemed a part of the Master Operating Agreement for all
                  purposes. In the event of a conflict or inconsistency between
                  the terms and conditions set forth in this Amendment and those
                  set forth in the Master Operating Agreement, the terms and
                  conditions of this Amendment shall prevail.

         (d)      Except as provided in this Amendment, the Master Operating
                  Agreement shall remain unchanged and in full force and effect.

         (e)      This Amendment may be executed in several counterparts, all of
                  which taken together constitute one single agreement between
                  the parties hereto.



         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
signed and sealed by their duly authorized representatives all as of the day and
year first above written.



UBS AG                                      PEROT SYSTEMS CORPORATION



By:  /s/ Patrick O'Donnell                  By:  /s/ James A. Champy
   -------------------------------             ---------------------------------
Title:  Managing Director                   Title:  Vice President

By: /s/ Robert B. Mills
   -------------------------------
Title:  Managing Director and CFO



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