A helicase/nuclease that prepares dsDNA breaks (DSB) for recombinational DNA repair. Binds to DSBs and unwinds DNA via a highly rapid and processive ATP-dependent bidirectional helicase activity. Holoenzyme degrades any linearized DNA that is unable to undergo homologous recombination. In the holoenzyme this subunit has ssDNA-dependent ATPase and 5'-3' helicase activity. When added to pre-assembled RecBC greatly stimulates nuclease activity and augments holoenzyme processivity (By similarity). Unlike the case in E.coli, suppresses RecA-dependent homologous recombination, is instead required for single-strand annealing pathway repair of DSB. Exonucleolytic cleavage (in the presence of ATP) in either 5'- to 3'- or 3'- to 5'-direction to yield 5'-phosphooligonucleotides. Heterotrimer of RecB, RecC and RecD. All subunits contribute to DNA-binding. Unlike E.coli, triple recB-recC-recD deletion is no more sensitive to DNA damaging agents (UV light sensitivity, mitomycin C, methyl methanesulphonate or ionizing radiation) than wild-type; has reduced resistance to H(2)O(2) which is exacerbated by further adnA-adnB deletion. Triple mutants have no effect on homologous recombination or on NHEJ of blunt-end, 5'- or 3'-overhang DSBs or on incompatible 3'-chromosomal overhangs. However the triple mutant disrupts all single-strand annealing repair of DSB. Belongs to the RecD family.