Table 1.

Identified CRISPR-Cas systems in procaryotes, their required elements, as well as the types of molecules each one targets.

Class	Type	Pre-crRNA Processing	Effector Protein(s)	Target Cleavage	Target
I	I	Cas6	Cascade complex (Cas8, Cas7, Cas5, Cas6, Cas11 and Cas3)	Cas3	dsDNA
	III	Cas6	Cas7, Cas5, Cas10	Cas10	dsDNA/ssRNA
	IV	Cas6	Cas7, Cas5, Csf1	-	dsDNA
II	II	RNA III/Cas9	Cas9	Cas9	dsDNA
	V	Cas12	Cas12	Cas12	dsDNA/ssDNA/ssRNA
	VI	Cas13	Cas13	Cas13	ssRNA