Facilitates phage DNA recombination through the double-strand break repair (DSBR) and single-strand annealing pathways. Also important for the late, rolling-circle mode of lambda DNA replication. Exonucleolytic cleavage in the 5'- to 3'-direction to yield nucleoside 5'-phosphates. Trimer of three subunits that form a toroid, with a tapered channel passing through the middle.