Table 1.

Differences between type I, II, III, and V CRISPR/Cas systems

Classification	Type I	Type II	Type III	Type V
Signature protein	Cas3 (or Cas3′)	Cas9 (1368 amino acids)	Csm (III-A) or Cmr (III-B)	Cas12a (1200–1300 amino acids)
Effector	Cascade	crRNA and tracrRNA (sgRNA)	Cascade	crRNA
PAM sequence	3-nt	G-rich sequence, 5′-NGG-3′	Without PAM	5′-YTN-3′(FnCas12a), 5′-TTTN-3′(AsCas12a, LbCas12a)
Cleavage product	SSBs	DSB (flat end)	SSBs at every 6-nt	DSB (Sticky end with 5 nucleotides protruding)