 To let the two cleavage domains dimerize and cleave DNA, the two individual ZFNs must bind opposite strands of DNA with their C-termini a certain distance apart.The most commonly used linker sequences between the zinc finger domain and the cleavage domain requires the 5' edge of each binding site to be separated by 5 to 7 bp.Several different protein engineering techniques have been employed to improve both the activity and specificity of the nuclease domain used in ZFNs.