Table 1.

Overview of CRISPR-Cas classification and subtype defining characteristics [4–8].

	Class I			Class II
	Type I	Type III	Type IV	Type II	Type V	Type VI
Integration module	Cas1/2 [3]	Cas1/2	Unknown	Cas1/2	Cas1/2	Cas1/2
Effector module	4 – 7 Cas protein Cascade			Cas9 [10]	Cas12a (cpf1)/Cas12b/Cas12c/[17]	Cas13a/Cas13b/Cas13c [20]
Molecule substrate	DNA					RNA
Organism	bacteria and archaea		archaea	bacteria	bacteria and archaea	bacteria
Nuclease domain	HDa fused to Cas3	HD fused to Cas10	unknown	RuvC and HNH	RuvC and Nuc	HEPN domains (2)
tracrRNA	no	No	no	yes	cpf1-no	no
Cleavage motif	subtype dependant (7)	subtype dependant (2)	subtype dependant (2)	CG rich NGG (blunt ends)	AT rich (staggered ends)	non-G PFS (ssRNA)

^aHistidine-aspartate domain