; (2) the Secretary of the Treasury has a senior claim on all assets and collateral under a BioBond to the extent the guarantee provided by the Secretary is not extinguished; and (3) to the extent that a Biobond is fully repaid without resort to the guarantee, all proceeds from reinvested funds shall be the property of the United States. (f) Rule of construction Nothing in this section may be construed to prohibit underwriters from varying terms and conditions consistent with the rules issued by the Secretary of the Treasury with respect to BioBonds. 5. Fiscal agents (a) In general The Secretary of the Treasury shall contract with institutions to carry out the duties of fiscal agents under this Act, under such criteria as the Secretary determines appropriate. (b) Sound underwriting practices The Secretary of the Treasury shall issue rules to ensure that fiscal agents use sound underwriting practices that protect the interests of— (1) the United States; (2) BioBond investors