Purchase, sale or borrowing transactions occurring in the usual course of business between affiliated persons of registered investment companies shall be exempt from section 17(a) of the Act provided (a) the transactions involve notes, drafts, time payment contracts, bills of exchange, acceptance or other property of a commercial character rather than of an investment character; (b) the buyer or lender is a bank; and (c) the seller or borrower is a bank or is engaged principally in the business of installment financing.