EXHIBIT 99.4
                       ASSIGNMENT AND ASSUMPTION AGREEMENT
                     (Re: Contract of Sale of CGC Unit One)

                  KNOW THAT, SKYLINE HOLDINGS LLC, a Delaware limited liability
company having an office c/o Boston Properties Limited Partnership, 599
Lexington Avenue, New York, New York 10022 (the "ASSIGNOR") for One ($1.00)
Dollar and other good and valuable consideration paid to it by BP/CGCENTER I
LLC, a Delaware limited liability company having an office c/o Boston Properties
Limited Partnership, 599 Lexington Avenue, New York, New York 10022 ("ASSIGNEE")
hereby assigns unto the Assignee all of its right, title and interest, as
purchaser, in, to and under that certain Agreement, dated as of February 6,
2001, between Dai-Ichi Life Investment Properties, Inc. ("SELLER"), as seller,
and Assignor, as purchaser (the "CONTRACT"), including all of Assignor's right,
title and interest in and to the deposit made pursuant to the Contract, with
respect to premises known as Unit One of Citigroup Center, New York, New York.

                  The Assignee accepts from Assignor all of Assignor's right,
title and interest, as purchaser, in, to and under the Contract and hereby
assumes the performance of all of the terms, covenants and conditions of the
Contract to be performed by the purchaser thereunder.

                  Assignor and Assignee agree to indemnify, hold harmless and
defend (with counsel reasonably satisfactory to Seller) Seller Indemnified
Parties (defined below) from and against all claims, demands, causes of action,
liabilities, loss, cost, damage and expense (including, without limitation,
reasonable attorneys' fees and disbursements), in connection with or arising
from the failure of Assignor and/or Assignee to pay New York City Real Property
Transfer Taxes and New York State Real Estate Transfer Taxes, if applicable, due
in connection with this assignment or any transfer of membership interests in
Assignor or Assignee.

                  SELLER INDEMNIFIED PARTIES means Seller, Citibank, N.A., any
disclosed or undisclosed officer, director, employee, trustee, shareholder,
partner, principal, parent, subsidiary or other direct or indirect affiliate of
Seller or Citibank, N.A., or any officer, director, employee, trustee,
shareholder, partner or principal of any such shareholder, partner, principal,
parent, subsidiary or other direct or indirect affiliate or any advisor or
consultant of any of the foregoing.

                  This Assignment and Assumption Agreement may be signed in
counterparts, each of which shall be deemed an original and all of which, when
taken together, shall constitute one and the same instrument.


                  IN WITNESS WHEREOF, the Assignor and Assignee have duly
executed this Assignment by their respective duly authorized representatives as
of the 25th day of April, 2001.

                                                 SKYLINE HOLDINGS LLC, a
                                                 Delaware limited liability
                                                 company

                                                 By: /s/ ROBERT E. SELSAM
                                                     ---------------------------
                                                     Robert E. Selsam
                                                     Authorized Signatory

                                                 BP/CGCENTER I LLC, a Delaware
                                                 limited liability company

                                                 By: /s/ ROBERT E. SELSAM
                                                     ---------------------------
                                                     Robert E. Selsam
                                                     Vice President

AGREED TO AND ACCEPTED BY:

DAI-ICHI LIFE INVESTMENT PROPERTIES, INC.

By: /s/ HITOSHI YAMAUCHI
    ------------------------
Name:  Hitoshi Yamauchi
Title: Senior Vice President

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