Multiple forms of ribonuclease H from rat liver cytosol.

Three forms (termed I, II, and III) of ribonuclease H (RNase H) [EC 3.1.4.34] activity are present in rat liver cytosol. These enzymes degrade RNA specifically in RNA-DNA hybrid structures. They were eluted at 0 M, 0.25 M, and 0.5 M KCl in phosphocellulose chromatography, and were further purified by using blue Sepharose. They are further distinguished from one another by their ionic requirements, optimal pH, molecular weights, sedimentation coefficients, and sensitivity to the -SH reagent, p-chloromercuribenzoate, although I and III have similar characteristics. They liberate a mixture of oligonucleotides with 5'-phosphate and 3'-hydroxyl termini.