Partial purification of a double-stranded RNA specific ribonuclease (RNAse D) from Krebs II ascites cells

In a search for eucaryotic enzymes which might process the heterogenous nuclear RNA (HnRNA) from animal cells into messenger RNA, a ribonuclease called RNAse D analogous to E. coli RNAse III in its ability to cleave specifically synthetic or viral double-stranded polyribonucleotides has been detected and extensively purified from the cytosol of Krebs II mouse ascites cells. The purification procedure involved cellular fractionation followed by DEAE and CM-cellulose chromatography and resulted in an RNAse D preparation contaminated with trace amounts of single-strand specific RNAse (equivalent to less than 0.3 ng per ml) as assayed against poly(rC). Significant levels of RNAse H activity against poly(rA) - poly(dT) were still present in these preparations.