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 AddB nuclease domain is not required for chi fragment generation; this subunit has 5' -> 3' nuclease activity. ATP + H2O = ADP + H(+) + phosphate Binds 1 [4Fe-4S] cluster. Heterodimer of AddA and AddB. Belongs to the helicase family. AddB/RexB type 1 subfamily.