Practice question

Zinc finger nucleases and transcription activator-like effector nucleases are chimeric nucleases sharing cleavage module. Both fuse sequence specific DNA binding domain to non-specific FokI endonuclease catalytic domain from Flavobacterium okeanokoites. FokI must dimerize to cut DNA, so two ZFN or TALEN monomers bind opposite strands with spacer. DNA binding domains differ: zinc fingers versus TALE repeats, but nuclease domain identical. CRISPR instead uses Cas9 nuclease. Conservation of FokI domain explains similar requirements for FokI dimerization and spacing rules in both platforms.