Three distinct nuclease activities, degrading double-stranded substrates, were isolated from the ribosomal salt wash fraction of Ehrlich ascites tumor cells. One of them is an absolutely Mn2+-dependent RNase H, capable of degrading the polyribonucleotide strand of a poly(A) · poly(dT) hybrid only. The other two nuclease activities are: a Mg2+-dependent RNase H and a Mn2+-dependent ribonuclease, specific for double-stranded RNA. These two activities were inseparable by DEAE-cellulose and phosphocellulose chromatography and both were completely inhibited by 20 mmN-ethymaleimide. It is possible that one protein molecule is responsible for the two activities, depending on the nature of the metal ion, though the existence of two different enzyme molecules is not excluded. The three activities are most probably of extranucleolar origin. A function for the double-stranded RNA-specific enzyme is suggested in the processes regulating protein synthesis. The role of the RNase H activities isolated from the ribosomal salt wash fraction is unclear.
ASJC Scopus subject areas
- Molecular Biology