Studies on in vitro DNA synthesis: purification of dna C gene product containing dna D activity from Escherichia coli

The conversion of varphiX174 single-stranded DNA to duplex DNA by extracts of E. coli requires products of the E. coli DNA replication genes. By use of this complementation system, the dna C gene product has been purified from wild-type E. coli as well as from a dna C temperature-sensitive mutant. The latter preparations are temperature sensitive when compared to the wild-type gene product. The dna C and dna D gene products copurify, have similar characteristics, are both temperature sensitive in preparations from dna C temperature-sensitive cells, and are both undetectable in preparations from dna D temperature-sensitive cells.

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.