title: Properties of the main endonuclease specific for apurinic sites of Escherichia coli (endonuclease VI). Mechanism of apurinic site excision from DNA.
abstract: The main endonuclease for apurinic sites of Escherichia coli (endonuclease VI) has no action on normal strands, either in double-stranded or single-stranded DNA, or on alkylated sites. The enzyme has an optimum pH at 8.5, is inhibited by EDTA and needs Mg2+ for its activity; it has a half-life of 7 min at 40 degrees C. A purified preparation of endonuclease VI, free of endonuclease II activity, contained exonuclease III; the two activities (endonuclease VI and exonuclease III) copurified and were inactivated with the same half-lives at 40 degrees C. Endonuclease VI cuts the DNA strands on the 5' side of the apurinic sites giving a 3'-OH and a 5'-phosphate, and exonuclease III, working afterwards, leaves the apurinic site in the DNA molecule; this apurinic site can subsequently be removed by DNA polymerase I. The details of the excision of apurinic sites in vitro from DNA by endonuclease VI/exonuclease III, DNA polymerase I and ligase, are described; it is suggested that exonuclease III works as an antiligase to facilitate the DNA repair.
mesh_terms: D001080:Apurinic Acid; D004256:DNA Polymerase I / Q000378:metabolism; D004260:DNA Repair; D003851:Deoxyribonucleases / Q000378:metabolism*; D004720:Endonucleases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D005092:Exonucleases / Q000378:metabolism; D007700:Kinetics; D013379:Substrate Specificity
chemical_list: D001080:Apurinic Acid; D004256:DNA Polymerase I; D003851:Deoxyribonucleases; D004720:Endonucleases; D005092:Exonucleases