Mechanism of Action of Ribonuclease H Isolated from Avian Myeloblastosis Virus and Escherichia coli

Purified preparations of RNA-dependent DNA polymerase isolated from avain myeloblastosis virus contain RNase H activity. Labeled ribohomopolymers are degraded in the presence of their complementary deoxyribopolymer, except [ 3 H]poly(U)·poly(dA). The degradation products formed from [ 3 H]poly(A)·poly(dT) were identified as oligonucleotides containing 3′-hydroxyl and 5′-phosphate termini, while AMP was not detected. The nuclease has been characterized as a processive exonuclease that requires ends of poly(A) chains for activity. Exonucleolytic attack occurs in both 5′ to 3′ and 3′ to 5′ directions. RNase H has also been purified from E. coli . This nuclease degrades all homoribopolymers tested in the presence of their complementary deoxyribopolymers to yield oligonucleotides with 5′-phosphate and 3′-hydroxyl termini. E. coli RNase H has been characterized as an endonuclease.