Figure 1. Each Zinc Finger Nuclease (ZFN) consists of two functional domains: a) A DNA-binding domain comprised of a chain of two-finger modules, each recognizing a unique hexamer (6 bp) sequence of DNA. Two-finger modules are stitched together to form a Zinc Finger Protein, each with specificity of > 12 bp. b) A DNA-cleaving domain comprised of the nuclease domain of FokI. When a pair of ZFNs binds adjacent sites on DNA with the correct orientation and spacing, a highly-specific pair of ‘genomic scissors’ is created.