ATP-dependent helicase/nuclease subunit A

UniProtKB accession:  P23478

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UniProtKB description:  An essential component of the DNA double-stranded break repair machinery, the heterodimer acts both as a highly processive, ATP-dependent DNA helicase and an ATP-dependent, dual-direction single-stranded exonuclease. Recognizes the B.subtilis Chi site (5'-AGCGG-3') which transforms the enzyme from a helicase which degrades both DNA strands to one with only 5' -> 3' exonuclease activity. This generates a double-stranded DNA with a protruding 3'-terminated single-stranded tail suitable for the initiation of homologous recombination (Chi fragment). The AddA nuclease domain in particular is required for Chi fragment generation; this subunit has 3' -> 5' nuclease and a helicase motor with 3' -> 5' helicase activity (PubMed:17570399, PubMed:21071401). The 3'-5' helicase activity of isolated AddA acts on 3'-tailed substrate and requires AddB to bind to blunt-ended DNA (PubMed:21071401). RecA thread formation during DNA double-strand break repair requires RecJ or AddAB (PubMed:16385024).