DOUBLE-STRANDED RIBONUCLEASE-ACTIVITY IN THE DIGESTIVE JUICE AND MIDGUT OF THE SILKWORM, BOMBYX-MORI

1. Nuclease activity capable of degrading Bombyx CPV double-stranded RNA (CPV-dsRNA) was detected in the midgut homogenate and digestive juice of the silkworm, Bombyx mori by using 3.5% polyacrylamide gel electrophoresis (PAGE). 2. The optimal pH range for the reaction was pH 7-10, under which yeast single-stranded RNA was not digested. The breakdown products in the reaction at pH 7 showed a pattern of three distinct bands besides CPV-dsRNA fragments in the PAGE, which indicates specific cleavage of CPV-dsRNA. 3. The products at pH 9 were heterodispersed, giving a continuous smear indicative of random degradation. 4. The activity was elevated by the addition of Mg2+, Mn2+, Ca2+, Na+, NH4 + or K + to the reaction mixture, but inhibited by EDTA. 5. The 0-40% ammonium sulfate saturated fraction of the 1200 g supernatant of midgut homogenate and digestive juice contained nuclease activity which caused degradation of double-stranded, poly(I) . poly(C) and CPV-dsRNA at pH 9.0.