Ribonuclease H from rat liver. II. Partial purification and characterization of cytosol ribonuclease H1.

We have detected in rat liver cytosol three enzymes (termed C-1, C-2, and C-3) which cleaved the RNA moiety of RNA-DNA hybrid. These enzymes were separated from each other by DEAE-Sephadex and Sephadex G-200 chromatography. C-1 and C-2 specifically act on the RNA moiety of RNA-DNA hybrid, while C-3 degrades single-stranded RNA as well as the RNA of the hybrid. The molecular weights of C-1, C-2, and C-3 are about 110,000, 35,000 and 110,000 daltons, respectively, and their activities are absolutely dependent on divalent cations such as Mg2+ and Mn2+. Cleavage by C-1 and C-2 is endonucleolytic, producing mostly oligonucleotides and a small amount of mononucleotides which possess 3'-hydroxyl termini. It seems likely that C-2 is originally present in the nucleus and is released into cytosol because of its loose binding to the nuclear components. As for biochemical properties, C-1 is very similar to the cytosol ribonuclease H initially reported by Roewekamp and Sekeris, and C-2 is very similar to the nuclear ribonuclease H reported by us in the preceding paper.