Table 4.

List of Cas proteins with their PAM sequence targets

CRISPR/Cas system	Types of Cas	Organism isolated from	Major application area	PAM sequence	PAM location relative to target base	Cas size (in amino acids)	References
Type II CRISPR/Cas system	SpCas9	Streptococcus pyogenes	Gene editing	NGG	Downstream of the target site	1368 AA	[171]
	xCas9	Modified from SpCas9	Gene editing	NG, GAA and GAT	Downstream of the target site	1368 AA	[107]
	SaCas9	Staphylococcus aureus	Gene editing	NGRRT or NGRRN	Downstream of the target site	1058 AA	[172]
	SaCas9-KKH	Staphylococcus aureus Cas9	Gene editing	NNNRRT	Downstream of the target site	1058 AA	[173]
	StCas9	Streptococcus thermophilus	Gene editing	NNAGAAW	DSBs	1121 AA	[174]
	ScCas9	Streptococcus canis	Gene editing	NNG	Downstream of the target site	1375 AA	[175]
	CjCas9	Campylobacter jejuni	Efficient genome editing	NNNVRYM	Downstream of the target site	984 AA	[176]
Type V CRISPR/Cas system	LbCas12a	Lachnospiraceae bacterium	Gene editing and diagnosis	TTTV	Upstream of the target site	1228 AA	[177]
	enAsCas12a	Streptococcus pyogenes	Gene editing and diagnosis	TTTV	Upstream of the target site	–	[178]
	Cas12f	Selenomonas sputigena	Diagnosis	TTTV	Double strand cleavage	422–603 AA	[154]
Type V CRISPR/Cas system	Cas14b	Extremophile archaea	Gene editing and diagnosis	T-rich PAM sequences, e.g., TTTA for dsDNA cleavage, no PAM sequence requirement for ssDNA	Upstream of the target site	400–700 AA	[141]
Type I CRISPR/Cas system	Cas3	Escherichia coli	Diagnosis	No PAM sequence requirement	Upstream of the target site	1224	[179]

AA amino acids, DSBs double strand break, PAM protospacer adjacent motif, SpCas9 Streptococcus pyogenes Cas9, SaCas9 Staphylococcus aureus Cas9, StCas9 Streptococcus thermophilus, ScCas9 Streptococcus canis Cas9, LbCas12a Lachnospiraceae bacterium Cas12a, CjCas9 Campylobacter jejuni Cas9, CRISPR/Cas clustered regularly interspaced short palindromic repeats/CRISPR-associated protein, T thymine, A adenine, G guanine, V adenine, cytosine, or guanine, N any nucleotide, R purine