The heterodimer acts as both an ATP-dependent DNA helicase and an ATP-dependent, dual-direction single-stranded exonuclease. Recognizes the L.lactis chi site (5'-GCGCGTG-3'), which stimulates homologous recombination. The AddA nuclease domain is required for chi fragment generation; this subunit has 3'->5' exonuclease activity and probably also performs the helicase function. ATP + H2O = ADP + H(+) + phosphate Heterodimer of AddA and RexB. Cells lacking this gene have an increased sensitivity to UV and about 300-fold reduced chromosomal conjugational transfer. 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.