The heterodimer acts as both an ATP-dependent DNA helicase and an ATP-dependent, dual-direction single-stranded exonuclease. Recognizes the chi site generating a DNA molecule suitable for the initiation of homologous recombination. The AddA nuclease domain is required for chi fragment generation; this subunit has the helicase and 3' -> 5' nuclease activities. ATP + H2O = ADP + H(+) + phosphate Heterodimer of AddA and AddB/RexB. Belongs to the helicase family. AddA subfamily.