TABLE 1.

Different classes of the CRISPR/Cas systems and their unique features.

Type	Organism	Component/Protein	Cleavage domain of proteins	Target
Type I	Escherichia coli, Pseudomonas aeruginosa	Cas1, Cas2, Cas3, Cas5, Cas6, Cas7	HD nuclease domain of Cas3	DNA
Type II	Streptococcus thermophilus	Cas1, Cas2, Cas9, Cas4/Csn2	RuvC-like nuclease domain near the N terminus and HNH (McrA-like) nuclease domain in the middle of Cas9	DNA
Type III	Staphylococcus epidermis, Lactococcus lactis, and Pyrococcus furiosus	Cas1, Cas2, Cas10, Cas6	Catalytic triad of Cas6 protein and Csm/Cmr Complex	DNA/RNA