REF is a family of P1-like phage RecA-dependent nucleases. It does not appear to act as a positive RecA regulator. It is a new kind of enzyme, a RecA-dependent nuclease [1].

1: Creating directed double-strand breaks with the Ref protein: a novel RecA-dependent nuclease from bacteriophage P1. Gruenig MC, Lu D, Won SJ, Dulberger CL, Manlick AJ, Keck JL, Cox MM; J Biol Chem. 2011;286:8240-8251. PMID:21193392