RecBCD (EC3.1.11.5, Exonuclease V, Escherichia coli exonuclease V, E. coli exonuclease V, gene recBC endoenzyme, RecBC deoxyribonuclease, gene recBC DNase, gene recBCD enzymes) is an enzyme of the E. coli bacterium that initiates recombinational repair from potentially lethal double strand breaks in DNA which may result from ionizing radiation, replication errors, endonucleases, oxidative damage, and a host of other factors. The RecBCD enzyme is both a helicase that unwinds, or separates the strands of DNA, and a nuclease that makes single-stranded nicks in DNA.