The bonds and interest coupons attached thereto shall be delivered to the purchaser thereof only upon payment of par and accrued interest to the date of delivery thereof, together with any premium bid. The proceeds of the sale of said bonds shall be deposited in the State Treasury of this state, in a fund which is hereby created and designated the “1961 Building Bond Fund”, where they shall remain subject to disposition to be provided for by the Legislature of this state, provided that the State Treasurer, when so directed by the Director of the Office of Management and Enterprise Services and the Oklahoma State Regents for Higher Education acting on behalf of the governing boards, according to the funds allocated, as to the amounts available for investment shall invest said designated amounts of the 1961 Building Bond Fund in direct obligations of the United States of America or in certificates of deposits from banks in this state acceptable as depositories by the State Treasurer when such certificates of deposits are secured by acceptable collateral and yield as much as or more than direct obligations of the United States of America. All such investments of said monies must be so made that the same shall mature in time to enable this state to issue warrants for payment of the valid indebtedness incurred for the purpose for which said bonds are issued, when the said indebtedness has been incurred pursuant to legislative authority. The Director of the Office of Management and Enterprise Services and the Oklahoma State Regents for Higher Education shall promptly certify to the State Treasurer the amount of all sums not needed for payment of construction and other legal expenditures payable from the 1961 Building Bond Fund to meet the construction payment schedule, and upon receipt of such certification the State Treasurer shall forthwith make the investment specified in this section. All interest received by the State Treasurer upon the securities referred to in this section shall be deposited in the 1961 Building Bond Fund.