Table 1.

Comparison of different programmable nucleases

Variable	ZFN	TALEN	CRISPR
DNA-binding moiety	Protein	Protein	RNA
Target site size, bp	18–36	30–40	22
Nuclease	FokI	FokI	Cas
Cytotoxicity	Variable to high	Low	Low
Design availability	More complex	Complex	Simple
Ease of multiplexing	Low	Low	High

ZFN, zinc f inger nuclease; TALEN, transcription activator-like effector nuclease; CRISPR, clustered regularly interspaced short palindromic repeats.