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                                                                     EXHIBIT 3.1

                       RESTATED ARTICLES OF INCORPORATION

                                       OF

                           CORNERSTONE PROPERTIES INC.



            Pursuant to the provisions of Section 78.403 of the Nevada Revised
Statutes, the Articles of Incorporation of Cornerstone Properties Inc., as
amended to the date of this certificate, are hereby restated as follows:

                                    ARTICLE 1

                                      NAME

            Effective at 12:01 a.m. on September 18, 1995, the name of the
Corporation is CORNERSTONE PROPERTIES INC.

                                    ARTICLE 2

                               PERIOD OF DURATION

            The period of duration of the Corporation is perpetual.

                                    ARTICLE 3

                                    PURPOSE

            The purpose for which the Corporation is organized is to engage in
the business of making real estate investments (directly or as a partner),
including, without limitation, the acquisition, development, encumbrance and
disposal of real estate or interests in real estate and all activities related
thereto, either on the Corporation's own behalf or on behalf of other persons or
entities, to do all acts and things in furtherance of such purposes and to
engage in any lawful activity.

                                    ARTICLE 4

                             DATA RESPECTING SHARES

            Section 4.01 Authorized Shares. The aggregate number of shares that
the Corporation shall have the authority to issue is One Hundred Fifteen Million
(115,000,000) shares of Capital Stock consisting of Fifteen Million (15,000,000)
shares of Preferred Stock with no par value per share and One Hundred Million
(100,000,000) shares of Common Stock with no par value per share.

            The designations and powers, preferences and rights, and the
qualifications,
<PAGE>   2
limitations or restrictions thereof, of the shares of each class are as follows:

            1. The Preferred Stock is to be issued in one or more series, from
time to time, with each such series to have such designations, preferences and
relative participating, optional or other special rights, and qualifications,
limitations or restrictions thereof, as shall be stated and expressed in the
resolution or resolutions providing for the creation of such series adopted by
the Board of Directors of the Corporation, subject to the limitations prescribed
by law and in accordance with the provisions hereof, the Board of Directors
being hereby expressly vested with authority to adopt any such resolution or
resolutions. The authority of the Board of Directors with respect to each series
shall include, but not be limited to, the determination or fixing of the
following:

            (i) The number of shares to constitute the series and the
      distinctive designation thereof;

            (ii) The dividend rate on the shares of the series, whether
      dividends shall be cumulative, and, if so, from what date or dates;

            (iii) Whether or not the shares of the series shall be redeemable
      and, if redeemable, the terms and provisions upon which the shares of the
      series may be redeemed and the premium, if any, and any dividends accrued
      thereon which the shares of the series shall be entitled to receive upon
      redemption thereof;

            (iv) Whether or not the shares of the series shall be subject to the
      operation of a retirement or sinking fund to be applied to the purchase or
      redemption of such shares for retirement and, if such retirement or
      sinking fund be established, the annual amount thereof and the terms and
      provisions relative to the operation thereof;

            (v) Whether or not the shares of the series shall be convertible
      into shares of any class or classes, with or without par value, or of any
      other series of the same class, and, if convertible, the terms of
      conversion, the conversion price or prices or the rate at which such
      conversion may be made and the method, if any, of adjusting the same;

            (vi) The rights of the shares of the series in the event of
      voluntary or involuntary liquidation, dissolution or winding up of the
      Corporation;

            (vii) The restrictions, if any, on the payment of dividends upon,
      and the making of distributions to, any class of stock ranking junior to
      the shares of the series, and the restrictions, if any, on the purchase or
      redemption of the shares of any such junior class;

            (viii) Whether the series shall have voting rights, in addition to
      the voting rights provided by law, and, if so, the terms of such voting
      rights; and

            (ix) Any other relative rights, preferences and limitations of that
      series.

            2. Holders of Preferred Stock shall be entitled to receive, when and
as declared by the Board of Directors, out of funds legally available for the
payment of dividends, dividends at the rates fixed by the Board of Directors for
the respective series, before any dividends shall be declared and paid, or set
apart for payment, on the Common

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Stock with respect to the same dividend period.

            3. Any shares of any series of Preferred Stock which shall at any
time have been redeemed or purchased or otherwise retired pursuant to law by the
Corporation, upon compliance with the applicable provisions of law, and any such
shares surrendered to the Corporation for conversion or exchange into or for
other shares of the Corporation, shall have the status of authorized and
unissued shares of Preferred Stock.

            4. Whenever, at any time, dividends on the then outstanding
Preferred Stock as may be required with respect to any series outstanding shall
have been paid or declared and set apart for payment on the then outstanding
Preferred Stock, and after complying with respect to any retirement or sinking
fund or funds for any series of Preferred Stock, the Board of Directors may,
subject to the provisions of the resolution or resolutions creating any series
of Preferred Stock with respect to the payment of dividends on any series of
Preferred Stock, declare and pay dividends on the Common Stock, and the
Preferred Stock shall not be entitled to share therein.

            5. The holders of Common Stock shall have the right to vote on all
questions to the exclusion of the Preferred Stock except as by law expressly
provided or as otherwise provided in the resolution or resolutions creating any
series of Preferred Stock. At all meetings of the stockholders of the
Corporation the holders of shares of Common Stock shall be entitled to one vote
for each share of Common Stock held by them, respectively.

            Section 4.02 Assessment of Shares. The Capital Stock of the
Corporation, after the amount of subscription price has been paid, shall not be
subject to pay the debts of the Corporation, and no Capital Stock issued as
fully paid up shall ever be assessable or assessed.

            Section 4.03 Denial of Preemptive Rights. No shareholder of the
Corporation shall have any preemptive or other right, by reason of his status as
a shareholder, to acquire any unissued shares, treasury shares, or securities
convertible into shares of the Capital Stock of the Corporation. This denial of
preemptive rights shall, and is intended to, negate any rights which would
otherwise be given to shareholders pursuant to NRS 78.265 or any successor
statute.

            Section 4.04 Treasury Shares. Capital Stock issued and thereafter
acquired by the Corporation shall not carry voting or dividend rights and shall
not be counted as outstanding shares for any purpose.

                                    ARTICLE 5

                   PRINCIPAL OFFICE AND INITIAL RESIDENT AGENT

            Section 5.01 Principal Office. The address of the principal office
of the Corporation is One East First Street, Reno, Washoe County, Nevada 89501.

            Section 5.02 Initial Resident Agent. The name of the initial
resident agent of the Corporation, a corporate resident of the State of Nevada,
whose business address is at the above address, is THE CORPORATION TRUST COMPANY
OF NEVADA.

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                                    ARTICLE 6

                            DATA RESPECTING DIRECTORS

            Section 6.01 Style of Governing Board. The members of the governing
board of the Corporation shall be styled Directors.

            Section 6.02 Initial Board of Directors. The initial Board of
Directors shall consist of four (4) members, who need not be residents of the
State of Nevada or shareholders of the Corporation.

            Section 6.03 Names and Addresses. The names and post office
addresses of the persons who are to serve as Directors until the next annual
meeting of the shareholders, or until their successors shall have been elected
and qualified, are as follows:

<TABLE>
<CAPTION>
          Name                         Post Office Address
          ----                         -------------------
<S>                                    <C>
      Dr. Rolf-E. Breuer               Deutsche Bank AG
                                       Taunusanlage 12
                                       60325 Frankfurt am Main

      Blake Eagle                      M.I.T. Center for Real Estate
                                       Building W31 - 310
                                       Cambridge, MA 02139


      Dr. Karl-Ludwig Hermann          93 Doubling Road
                                       Greenwich, CT 06830

      Gerhard A. Koning                Commerzbank AG
                                       Neue Mainzer Strasse 32 -36
                                       D-60261 Frankfurt am Main

      Hans C. Mautner                  Corporate Property Investors, Inc.
                                       3 Dag Hammarskjold Plaza
                                       305 East 47th Street
                                       New York, NY 10017

      John S. Moody                    Cornerstone Properties Inc.
                                       31 West 52nd Street, Suite 1600
                                       New York, NY 10019

      Gerald Rauenhorst                Opus Corporation
                                       800 Opus Center
                                       9900 Bren Road East
                                       Minneapolis, MN 55440

      Dr. Walter Schorr                Bankhaus Gebrueder Bethmann
                                       Bethmannstrasse 7 - 9
                                       60311 Frankfurt am Main
</TABLE>

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<TABLE>
<CAPTION>
<S>                                    <C>
      Michael J.G. Topham              Hines
                                       #1 Hans Street
                                       London SW1 XOJD
                                       England

      Berthold T. Wetteskind           Deutsche Immobilien Anlagegesellschaft mbH
                                       Bockenheimer Landstrasse 42
                                       60323 Frankfurt am Main
</TABLE>

            Section 6.04 Vacancies. All vacancies, including without limitation
those caused by an increase in the number of Directors, may be filled by a
majority of the remaining Directors, even though less than a quorum.

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                                    ARTICLE 7

                          DATA RESPECTING INCORPORATORS

            The names and post office addresses of the incorporators of the
Corporation are as follows:

<TABLE>
<CAPTION>
          Name                                  Post Office Address
          ----                                  -------------------
<S>                                             <C>
      August E. Shouse                          First City National Bank Bldg.
                                                Houston, Texas  77002

      Glendon E. Johnson, Jr.                   First City National Bank Bldg.
                                                Houston, Texas  77002

      Robert J. Bachman                         First City National Bank Bldg.
                                                Houston, Texas  77002
</TABLE>

                                    ARTICLE 8

                            PROTECTION OF REIT STATUS

            Section 8.01 So long as the Corporation has two or more stockholders
and subject to the terms and provisions of this Article,

            (a) Shares of stock of the Corporation shall not be transferred to
      any Person (as defined in Section 8.03, below) if such transfer would
      cause such Person to be the Owner (as defined in Section 8.03, below) of
      more than 6% of the value of the outstanding shares of capital stock (the
      "Limit") of the Corporation, and any intended transferee of such shares
      shall acquire no rights in such shares.

            (b) No Person shall at any time be or become the Owner of shares in
      excess of the Limit. If, notwithstanding the provisions of (a) above, at
      any time a Person shall be or become an Owner of shares of the Corporation
      in excess of the Limit, those shares of the Corporation most recently
      acquired by such Person which are in excess of the Limit, including for
      this purpose shares deemed Owned through attribution, shall constitute
      "Excess Shares." Excess Shares shall have the following characteristics:

                  (1) The Owner of Excess Shares shall be deemed to have
            transferred those shares to the Corporation as trustee (the
            "Trustee') for the benefit of such Person to whom such Owner shall
            later transfer such shares provided that such shares shall not be
            Excess Shares in the hands of such Person;

                  (2) An interest in the trust holding such Excess Shares shall
            be freely transferable by the Owner thereof at a price not in excess
            of the price paid by such Owner for the Excess Shares;

                  (3) Holders of Excess Shares shall not be entitled to exercise
            any voting rights with respect to such Excess Shares;

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                  (4) Excess Shares shall not be deemed to be outstanding for
            the purpose of determining a quorum at the annual meeting or any
            special meeting of stockholders;

                  (5) Any dividends or other distributions with respect to
            Excess Shares which would have been payable in respect of shares of
            the Corporation had they not constituted "Excess Shares" shall be
            accumulated by the Trustee and deposited in a savings account in a
            New York bank (which may be the Corporation's dividend disbursing
            agent) for the benefit of, and be payable to, the holder or holders
            of such shares of the Corporation at such time as such Excess Shares
            shall cease to be Excess Shares; and

                  (6) Excess Shares shall be deemed to have been offered for
            sale to the Corporation or its designee at their fair market value
            for a period of ninety (90) days from the date of (i) the transfer
            of stock which made the shares Excess Shares if the Corporation has
            actual knowledge that such transfer creates Excess Shares as of the
            date of transfer or (ii) if such transfer is not actually known to
            the Corporation, the determination by the Board of Directors in good
            faith by resolution duly adopted that a transfer creating Excess
            Shares has taken place. Fair market value shall be determined as of
            the date of (i) or (ii) above, as appropriate, and shall be the
            closing price on the Frankfurt, Luxembourg or Dusseldorf stock
            exchanges; but if the shares are not listed on the Frankfurt,
            Luxembourg or Dusseldorf stock exchanges or on any national stock
            exchange in the United States, then the bid price in the
            over-the-counter market; but if the shares are not traded in the
            over-the-counter market, then the price as determined in good faith
            by the Board of Directors.

            (c) If, notwithstanding the provisions of (a) above, any Person
      shall knowingly own shares in excess of the Limit and the Corporation
      would have qualified as a real estate investment trust ("REIT"), or would
      not have been a personal holding company but for the fact that more than
      50% of the value of its shares are held by five or fewer individuals in
      the last half of the taxable year in violation of the requirements of the
      Internal Revenue Code (the "Code"), then that Person, and all legal
      entities which constitute that Person, shall be jointly and severally
      liable for and shall pay to the Corporation and each shareholder of the
      Corporation other than such Person, on demand, such amounts as will, after
      taking account of all taxes imposed with respect to the receipt or accrual
      of such amount and all costs incurred by the Corporation and each such
      shareholder of the Corporation as a result of the Corporation losing its
      REIT qualification or being deemed a personal holding company, put the
      Corporation and each such shareholder of the Corporation in the same
      financial position as it would have been in had it not lost such REIT
      qualification or become a personal holding company (the "Indemnity"). If
      more than one Person shall hold Excess Shares which cause loss of REIT
      qualification, then all such Persons, together with all legal entities
      which constitute any of them, shall be jointly and severally liable, with
      right of contribution, for the Indemnity. However, the foregoing sentences
      shall not require that the Corporation proceed against any one or several
      of such Persons or the legal entities which constitute them. Should the
      loss of REIT qualification occur as described above, then the Corporation
      may seek to have its qualification restored for the next taxable year, but
      shall not be required to do so. If the Corporation either decides not to
      attempt to requalify for the succeeding year, or is refused such

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      requalification, the Indemnity shall be applicable to all five taxable
      years, or such longer or shorter period as successor provisions of the
      Code shall require, until the Corporation is again permitted to qualify as
      a REIT. Should the Corporation decide not to seek requalification as a
      REIT at the end of such period, then the Indemnity shall cease as of the
      end of the fifth taxable year following loss of REIT qualification.

            (d) All certificates evidencing ownership of shares of the
      Corporation shall bear a conspicuous legend describing the restrictions
      set forth in this Article.

            Section 8.02 (a) If the Board of Directors shall at any time
determine in good faith, by resolution duly adopted, that a transfer has taken
place in violation of Section 8.01(a) or that a Person intends to acquire or has
acquired Ownership of any shares of the Corporation which, upon acquisition, has
or would become Excess Shares, the Board of Directors may, but shall not be
obligated to, take such action as it deems advisable to prevent or to refuse to
give effect to such transfer or acquisition, including but not limited to
refusing to give effect to such transfer or acquisition on the books of the
Corporation or instituting proceedings to enjoin such transfer or acquisition.

            (b) Each Person who enters into a transfer in violation of Section
8.01(a), or is or becomes the Owner of Excess Shares, is obliged immediately to
give or cause to be given written notice thereof to the Corporation and such
other information as the Corporation may reasonably require of such Person (1)
with respect to identifying all Owners and amount of Ownership of its
outstanding shares held directly or by attribution by such Person, and (2) such
other information as may be necessary to determine the Corporation's status
under the Code.

            Section 8.03 For the purpose of determinations to be made under this
Article,

            (a) A Person shall be considered to "Own," be the "Owner" or have
      "Ownership" of shares if he is treated as owner of such shares for
      purposes of Subchapter M, Part II of the Code, including ownership by
      reason of the application of the ownership provisions of Sections 542 and
      544 of the Code;

            (b) "Person" includes an individual, corporation, partnership,
      estate, trust, association, joint stock company or other entity but does
      not include (i) any corporation, partnership, association, joint stock
      company or other entity of which (A) the principal voting securities are
      regularly traded on a national securities exchange (including the
      Frankfurt, Luxembourg or Dusseldorf stock exchanges) or quoted on an
      inter-broker quotation system and (B) no more than the Applicable
      Percentage of the value of its capital stock is owned beneficially,
      directly or indirectly (including all shares deemed owned under Section
      856(h) of the Code), by any individual; or (ii) any other person whose
      ownership of Excess Shares the Board of Directors shall determine in good
      faith would not jeopardize the Company's REIT status under Section 856 of
      the Code;

            (c) "Applicable Percentage," for any corporation, partnership,
      association, joint stock company or other entity referred to in Section
      8.03(b)(i), shall be 12% for any such entity that owns less than 50% of
      the value of the capital stock of the Company and, for all other such
      entities, shall be 6%; and

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            (d) In the case of an ambiguity in the application of any of the
      provisions of (a), (b) and (c) above, the Board of Directors shall have
      the power to determine for the purposes of this Article on the basis of
      information known to it (i) whether any Person Owns shares, (ii) whether
      any two or more individuals, corporations, partnerships, estates, trusts,
      associations or joint stock companies or other entities constitute a
      Person, and (iii) whether any of the entities of (ii) above constitute a
      group.

            Section 8.04 If any provision of this Article or any application of
any such provision is determined to be invalid by any federal or state court
having jurisdiction over the issues, the validity of the remaining provisions
shall not be affected and other applications of such provision shall be affected
only to the extent necessary to comply with the determination of such court.

            Section 8.05 Nothing contained in this Article shall limit the
authority of the Board of Directors to take such other action as they deem
necessary or advisable to protect the Corporation and the interests of its
stockholders by preservation of the Corporation's status as a REIT under the
Code.

            Section 8.06 Notwithstanding anything contained in this Certificate
of Incorporation to the contrary, the affirmative vote of the holders of at
least 80% of the outstanding shares of common stock of the Corporation then
entitled to vote shall be required to alter, amend, adopt any provision
inconsistent with, or repeal, this Article 8 or any provision hereof.

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