Table 3.

Cas9 variants with their origin and specifications.

Cas9 nuclease variants	Origin	PAM sites (5′ to 3′)	Specifications	Functions	Reference
Native Cas9 (SpCas9)	Streptococcus pyrogenes	NGG	100 nt long gRNA	Introduce double stranded breaks; create blunt ends	Mojica et al., 2005
Cas9 nickase (Cas9n)	Engineered from S. pyrogenes	NGG	Mutation in native Cas9 (RuvC or HNH D10, aspartate to alanine substitution)	Generate single stranded break; efficient HDR repair mechanism	Cong et al., 2013; Fauser et al., 2014
dCas9	Engineered from S. pyrogenes	NGG	Mutated Cas9	RNA guided transcription regulation (CRISPRi, CRISPRa); delivers GFP enabling visualization of genetic element dynamics	Hilton et al., 2015
Dimeric RNA-guided FokI nucleases (RFNs)	Engineered from S. pyrogenes	NGG	Fusion of dCas9 protein and FokI nuclease domain	High genome editing frequency and reduced off-target mutations	Tsai et al., 2014; Bortesi and Fischer, 2015
NmCas9	Neisseria meningitidis	NNNNGATT	Longer crRNA component (24 nt)	Reduced off-target effects	Hou et al., 2013
StCas9	Streptococcus thermophilus	NNAGAAW	On target cleavage activities	Reduced off-target effects	Horvath et al., 2008;
SaCas9	Staphylococcus aureus	NNGRRT or NNGRR(N)	On target cleavage activities	Reduced off-target effects	Esvelt et al., 2013
Cas9-DD (Destabilized Cas9)	Engineered from S. pyrogenes	NGG	Conjugation of destabilized domain to Cas9	Temporal, spatial and locus-specific control of gene expression; Increased NHEJ- mediated gene insertion efficiency	Geisinger et al., 2016; Senturk et al., 2015
Cpf1	Prevoltella and Francisella1	NTT	Contain a RuvC-like endonuclease domain, lack HNH endonuclease domain; 42 nt long gRNA	Require one RNA (crRNA); Produce staggered cut ends; easier to deliver in low capacity vectors ex. AAV	Zetsche et al., 2015a