All trustees, guardians, administrators, executors and other fiduciaries, whenever a governing instrument or order directs, requires, authorizes or permits investment in direct obligations of the United States of America, may invest in such obligations either directly or in the form of securities of, or other interests in, any open-end or closed-end management type investment company or investment trust registered under the provisions of 15 U.S.C. Section 80(a)-1 et seq., provided that the portfolio of such investment company or investment trust is limited to direct obligations of the United States of America and to repurchase agreements fully collateralized by direct obligations of the United States of America, and that such investment company or investment trust takes delivery of the collateral for any repurchase agreement, either directly or through an authorized custodian. This section shall not be construed to apply to the investment of any public funds; provided, however, that this section shall be construed to apply to the investment of public funds deposited with a bank trustee acting in a fiduciary capacity in connection with the sale and redemption of bonds, notes and other certificates of indebtedness, notwithstanding Section 31-19-5, Mississippi Code of 1972.