ATP-dependent helicase/deoxyribonuclease subunit B

UniProtKB accession:  P23477

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UniProtKB description:  The heterodimer acts both as a highly processive, ATP-dependent DNA helicase and as an ATP-dependent single-stranded exonuclease, acting in both directions. 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' to 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 AddB nuclease domain is not required for Chi fragment generation but for recognition of the Chi site; this subunit has 5' -> 3' nuclease activity but no helicase activity (PubMed:17570399, PubMed:21071401, PubMed:22307084). The 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).