Role of DNA · RNA Hybrids in Eukaryotes Purification of Two Ribonucleases H from Yeast Cells

Two ribonucleases H, which specifically degrade RNA in RNA‐DNA hybrid structures, have been extensively purified from extracts of Saccharomyces corevisiae. Ribonuclease H1 can be obtained in high yield by a rapid purification procedure mainly involving ammonium sulfate fractionation and phosphocellulose chromatography. The enzyme preparation was shown to be homogeneous by acrylamide gel electrophoresis with sodium dodecylsulfate. Ribonuclease H2 was also obtained in an essentially homogeneous form by phosphocellulose and Amberlite chromatography. About 60 mg of ribonuclease H1 and 2 mg of ribonuclease H2 were obtained from 100 g of wet cells. Using T7 DNA · RNA, hybrids, the specific activity of ribonuclease H2 was approximately 10‐fold higher than that of ribonuclease H1.