Isolation and characterization of the novel polyadenylate- and polyuridylate-degrading acid endoribonuclease V from calf thymus.

A novel endoribonuclease was detected and purified to homogeneity from calf thymus. The homogeneity was checked by analysis in polyacrylamide gels (both in the presence and in the absence of sodium dodecyl sulfate) as well as by isoelectric focusing. This nuclease activity, which is called Endoribonuclease V, cleaves poly(A) and poly(U); other single- or double-stranded synthetic polyribo- as well as polydeoxyribonucleotides are not degraded. Endoribonuclease V cleaves poly(A) to create first oligoribonucleotides and ultimately 3'-AMP; no P-2':3'-Ado degradation products were detected. The enzyme has a pH optimum of 5.8, an isoelectric point of pH 6.3, a molecular weight of 52,300, and requires neither monovalent nor divalent cations. The enzyme activity is not inhibited by N-ethylmaleimide.