Table 1.

Classification of CRISPR/Cas system with their protein, target molecule, mechanism of spacer acquisition, processing of Pre-CRISPR, self-vs non-self-discrimination and their effectors with the name of isolated organism with references

Class	Type	Protein	Target	Spacer acquisition strategy	Name of CRISPR/Cas system	Pre-CRISPR processing	Self vs nonself-discrimination	Effectors of CRISPR system	Host organism	References
Class1	I	Cas3	ssDNA	Cas1/Cas2/ Cas4	Cas7, Cas5, Cas8, and Cas3	Cas6	PAM	Cas3, Cascade, and crRNA	E. coli	[23]
	III	Cas10	ssDNA	Cas1/Cas2	Cas7, Cas5, and Cas1	Cas6	CRISPR repeat	Cmr/Csm, crRNA, and Cas10	S. epidermics	[24]
	IV	Csf1	–	NA	Cas7, Cas5, and Csf1	–	–	–	–	[21]
Class2	II	Cas9	dsDNA	Cas1/Cas2/ Cas4	Cas9	RNase III, and tracrRNA	PAM	Cas9, tracrRNA, and crRNA	S. thermophilus and S. pyogenes	[8]
	V	Cpf1	ssDNA and dsDNA	Cas1/Cas2/ Cas4	Cas12	Cpf1	PAM	Cpf1, crRNA and tracrRNA	F. novicida	[25]
	VI	C2c2	ssRNA	Cas1/Cas2	Cas13	–	–	C2c1, and crRNA	–	[26]