The FokI catalytic domain must dimerize in order to cleave the DNA at the targeted site, and requires there to be two adjacent zinc finger nuclease, which independently bind to a specific codon at the correct orientation and spacing.
The FokI catalytic domain's main goal is to cleave at the targeted site, but must dimerize in order to cleave the DNA. Therefore, there needs to be two adjacent zinc finger nuclease, which independently bind to a specific codon at the correct orientation and spacing.