Ribosomal Nuclease with Activity Towards Double-Stranded RNA

Abstract

Ribonucleolytic activity has been suggested to be associated with plant ribosomes, but its role has not been elucidated (Hsiao 1968, Farkas 1982). According to Wilson (1982) nucleolytic ribosomal enzymes represent only a small fraction of the total nucleolytic activity of plant tissues. In our earlier investigations ribonucleolytic activity has been observed in nuclei, plastids, mitochondria, postribosomal supernatant and cytoplasmic ribosomes of rye embryos and 24-h seedlings. Specific ribonucleolytic activity was highest in the ribosome fraction from dry rye embryos (Siwecka et al., 1971). We have further demonstrated that deoxyribonucleolytic activity is also associated with rye embryo ribosomes. Both these activities are strongly associated with ribosomes and their subunits but a part of activity may be released by washing with 0.5 M ammonium chloride or 4 M urea (Siwecka et al., 1979). The NH₄Cl ribosomal wash seems to contain an enzyme hydrolyzing double-stranded RNA, namely, double-stranded viral RNA from Penicillium chrysbgenum and the double-stranded poly(A)*poly(U) complex (Siwecka et al., 1982). So far there have been no reports on isolation from higher plants of enzymes hydrolyzing double-stranded RNA.