An essential component of the DNA double-stranded break repair machinery, the heterodimer acts as both an 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 helicase activity. RecA thread formation during DNA double-strand break repair requires RecJ or AddAB. ATP + H2O = ADP + H(+) + phosphate At low magnesium concentrations there is no nuclease activity, but helicase activity is unaffected. Heterodimer of AddA and AddB. This enzyme is a functional homolog of the E.coli RecBCD enzyme; unlike the RecBCD enzyme it degrades both duplex strands symmetrically. Belongs to the helicase family. AddA subfamily.