RecBCD

Exodeoxyribonuclease V (EC 3.1.11.5, 'RecBCD, 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 E. coli 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. It catalyses exonucleolytic cleavage (in the presence of ATP) in either 5′- to 3′- or 3′- to 5′-direction to yield 5′-phosphooligonucleotides.

==Structure== The enzyme complex is composed of three different subunits called RecB, RecC, and RecD and hence the complex is named RecBCD (Figure 1). Before the discovery of the recD gene, the enzyme was known as “RecBC.” Each subunit is encoded by a separate gene: