Distinct ribonuclease H activities in calf thymus.

Three enzymes with ribonuclease H activity are present in calf thymus. They have been separated on the basis of chromatographic behaviour and molecular weight. They are further distinguished from one another by their ionic requirements and sensitivity to the -SH reagent N-ethylmaleimide. Two of these enzymes are classified as ribonuclease H, the third is obtained in a fraction which possesses ribonuclease H activity but also degrades double-stranded RNA and poly(rA). No association between any of the enzymes and cellular DNA polymerases could be demonstrated.