Purification and properties of double-stranded RNA-degrading nuclease, dsRNase, from the digestive juice of the silkworm, Bombyx mori

A nuclease which degrades double-stranded RNA was purified from the digestive juice of fifth-instar larvae of the silkworm, Bombyx mori, using gel filtration and affinity column chromatography. The enzyme was found to have a molecular weight of 41,000 as estimated by a gel filtration method and detected as a single band with the same molecular weight on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. It degraded double-stranded RNA of cytoplasmic polyhedrosis virus genome, synthetic Poly(I)/Poly(C), Poly(I) and Poly(C). It also digested copolymer Poly(AU), Poly(A) and Poly(U), but showed weak degradation of Poly(A)/Poly(U), Poly(C)/Poly(G), Poly(G) and natural DNA isolated from calf thymus. The pH range wherein the reaction occurred was greater than 7. The purified enzyme did not require Mgsup(2+) to degrade CPV-dsRNA, whereas divalent cations including Mgsup(2+) and Casup(2+) were needed to degrade synthetic Poly(I)/Poly(C). The enzyme activity was suppressed by Cosup(2+), Znsup(2+) and Mnsup(2+).