 The non-specific cleavage domain from the type IIs restriction endonuclease FokI is typically used as the cleavage domain in ZFNs.This cleavage domain must dimerize in order to cleave DNA 
and thus a pair of ZFNs are required to target non-palindromic DNA sites.Standard ZFNs fuse the cleavage domain to the C-terminus of each zinc finger domain.