Table 1.

Key differences between the Cas9 and Cas12a CRISPR proteins

Feature	Cas9	Cas12a (Cpf1)
CRISPR enzyme	Class 2, Type II-B Molecular weight: ~ 164 kDa Endonuclease domains: RuvC and HNH	Class 2, Type V-A Molecular weight: ~ 158 kDa Endonuclease domains: RuvC only
PAM	3′ NGG	5′ TTTV
guideRNA	~ 120 nt, two RNA sequences crRNA and tracrRNA are synthetically fused to form the single guide RNA (sgRNA)	~ 43 nt, only crRNA is required
crRNA maturation	RNase III dependent	RNase III independent, autonomous processing
DSB cleavage site	3 bases upstream of the protospacer sequence PAM site often destroyed during genome editing	18–23 bases downstream of the PAM PAM site may be preserved after genome editing
DSB cleavage mechanism	Blunt end cuts	5-nt staggered end cut distal to the PAM