 The dimer interface is formed by the parallel helices α4 and α5 and two loops P1 and P2 of the cleavage domain.When the nuclease is unbound to DNA, the endonuclease domain is sequestered by the DNA-binding domain and is released through a conformational change in the DNA-binding domain upon binding to its recognition site.Cleavage only occurs upon dimerization, when the recognition domain is bound to its cognate site and in the presence of magnesium ions.