Table 4.

Functional diversity of the experimentally characterized biosensing effectors of class 2 CRISPR–Cas systems

CRISPR/Cas type	Size (aa)	Nuclease domain	PAM (5′)	Stable binding specificity/bp	Substrate preference	Substrate	Cleavage pattern	Reference
Cas9	~ 1300	RuvC, HNH	NGG	9	/	dsDNA	Blunt ends	[65]
Cas12a(Cpf1)	~ 1300	RuvC, Nuc	TTTN	17	/	dsDNA	Staggered ends	[77]
Cas12b(C2c1)	~ 1100	RuvC, Nuc	TTN	17	/	dsDNA	Staggered ends	[78]
Cas13a(C2c2)	~ 1300	2 HEPN domains	Non-G, PFS	20	di-AC, di-AU	ssRNA	/	[79]
Cas13b	~ 1200	2 HEPN domains	5-A, U, G, and 3′-NAN, NNA	14	di-UC, di-GA	ssRNA	/	[52, 80]
Cas13d	~ 900	2 HEPN domains	No PFS preference	18	/	ssRNA	/	[81, 82]
Cas14a1	~ 400	RuvC, Nuc	No PFS preference	/	/	ssDNA	/	[26]

aa amino acid, bp base pair; PAM protospacer-adjacent motif; PFS Protospacer flanking site