at par of special obligations directly to the Fund. Such special obligations shall bear interest at a rate equal to the average rate of interest, computed as to the end of the calendar month next preceding the date of such issue, borne by all marketable interest-bearing obligations of the United States then forming a part of the public debt, except that if such average rate is not a multiple of one-eighth of 1 per centum, the rate of interest of such special obligations shall be the multiple of one-eighth of 1 per centum next lower than such average rate. All requests of the Institute to the Secretary of the Treasury provided for in this section shall be binding upon the Secretary. (d) Authority To sell obligations At the request of the Institute, the Secretary of the Treasury shall redeem any obligation issued directly to the Fund. Obligations issued to the Fund under subsection (c)(2) shall be redeemed at par plus accrued interest. Any other obligations issued directly to the Fund shall be redeemed at the market price. (e) Proceeds from certain transactions credited to Fund In addition to the appropriations received pursuant to this Act, the interest on, and the proceeds from the sale or redemption of, any obligations held in the Fund pursuant to this Act, shall be credited to and form a part of the Fund. (f) Fund reserves Five to ten percent of the original amount appropriated to the Fund must remain in the Fund at all times. (g) Expenditures The Secretary of the Treasury is authorized to pay to the Institute from the interests and earnings of the Fund, and moneys credited to the Fund pursuant to this section, such sums as the Board determines are necessary and appropriate to enable the Institute to carry out the provisions of this Act. 7. Administrative provisions (a) Executive Director The Board shall appoint an Executive Director who shall be the chief executive officer and principal executive of the Institute and who shall supervise the affairs of, assist the directions of, and carry out the functions of