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Ribonuclease H from human KB cells, chick embryos, calf thymus, avian myeloblastosis virus, and Rous associated virus specifically degrades the RNA of DNA.RNA hybrids, producing mono- and oligoribonucleotides terminated in 5'-phosphates. The cellular RNase H is an endonuclease, whereas the viral enzyme appears to be an exonuclease. Viral DNA polymerase and RNase H copurify through all separation steps. Therefore, RNase H activity is an intrinsic part of the viral DNA polymerase. DNA.RNA hybrids are also degraded by nucleases associated with cellular DNA polymerases and by exonuclease III. However, these nucleases differ from RNase H in their ability to degrade both strands of DNA.RNA hybrids.
Keller et al. (Wed,) studied this question.