Exonuclease V, a RecBCD complex from E. coli has several different enzyme activities, including an ATP-dependent single-stranded DNA endonuclease activity, ss- and ds- DNA exonuclease activity. The hydrolysis in each case is bi-directional (from both the 3' and 5' ends) and processive, producing oligonucleotides. All Exonuclease V activities have divalent cation requirements. Mg2+ is required for the exonuclease activity, while Ca2+ inhibits the exonuclease activity and allows double-stranded DNA unwinding (helicase activity) without hydrolysis.
