Breakdown of Double-Stranded RNA by Bull Semen Ribonuclease

Abstract

Bull semen ribonuclease, a basic protein with a molecular weight of 25,500, is similar to pancreatic ribonuclease A in regard to its specific activity (per μmole of enzyme) towards single-stranded RNA, cytosine 2′ :3′-phosphate and poly U, to its pH optimum in the action on single-stranded RNA and to its inactivity towards double-stranded DNA. It has been found, however, that this enzyme also degrades double-stranded RNA, prepared from MS2 infected Escherichia coli cells, as well as the synthetic complex formed by poly A and poly U, under conditions where ribonuclease A has no appreciable effect. The pH optimum of the enzymatic activity on the substrates mentioned above appears to be around 7. The final products of the reaction with poly(A) · poly(U) have been shown to be uridine 3′-phosphate and poly A.