Table 2.

Main features of the different genome-editing nucleases

	ZFNs	TALENs	CRISPR/Cas
Phylogenetic origin	artificial restriction enzyme [252, 253]	Xanthomonas bacteria [254]	Streptococcus pyogenes [255]
DNA binding domain	zinc finger protein [253, 256]	TALE protein [16, 257, 258]	guide RNA [259–261]
DNA cleavage	FokI [262]	FokI [257, 258, 262]	Cas9 [259, 260]
DNA recognition range	18–36 bp (3 bp per module) [253]	30–40 bp (1 bp per module) [257, 258, 263]	22 bp (DNA-RNA base pairing) [261]
DNA cut	dsDNA as a dimer [264]	dsDNA as a dimer [265]	dsDNA complex protein-gRNA [259]
Recognition sequence	5'-GNNGNNGNN-3’ [256]	sequence with 5'-T and A-3' [16, 254, 263]	sequence immediately followed by 5'-NGG-3' [259, 266]
Advantages	Small protein size (< 1 Kb), sequence-based module engineering [267]	High specificity, easy selection of target region [268]	Easy to multiplex, simple synthesis of gRNA, easy selection of target region [269]
Disadvantages	Difficult sequence selection and protein engineering,, expensive and time consuming [267]	Large protein size (> 3 Kb), expensive and time-consuming [269, 270]	Large protein size (> 4 Kb) [269]
Safety concerns	off-target effects: genome mutagenesis and GCRs [271]	off-target effects: genome mutagenesis and GCRs [270]	off-target effects: genome mutagenesis and GCRs [271]