Properties of a purified nucleolar ribonuclease from Ehrlich ascites carcinoma cells

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Abstract
A nucleolar ribonuclease specific for single-stranded RNA was isolated and extensively purified from Ehrlich ascites carcinoma cells. The enzyme is optimally active at neutral pH and degrades RNA via a 2'',3''-cyclic intermediate leaving 3''- or 2'',3''-cyclic terminated oligonucleotides. The ribonuclease has an apparent MW of 38,500 as judged by sedimentation equilibrium and is a basic protein having an isoelectric point > 9.0. The enzyme preferentially cleaves poly(C) over poly(U), poly(A) or poly(C) .cntdot. poly(I). Limit digestion products of poly(C) degradation are on the average tri-, tetra- and pentanucleotides. In the partial digestion of yeast 5.8S rRNA, the nucleolar RNase cleaves only CpA phosphodiester bonds. Spermidine, spermine and histone I inhibit the activity of nucleolar ribonuclease. Antibodies directed toward pancreatic RNase do not cross-react with the Ehrlich nucleolar RNase.