Table 1.

Characteristics of representative Cas proteins used in CRISPR-Dx for COVID-19.

	CRISPR-Cas12a	CRISPR-Cas13a	CRISPR-Cas3	CRISPR-Cas9
Class	2	2	1	2
Type	V	VI	I	II
Effector Cas protein complex	Single unit	Single unit	Multi-subunit	Single unit
Size (amino acid)	~1200 (LbCas12a)	~1200 (LwaCas13a)	~900 (EcoCas3)	~1400 (SpCas9)
Nuclease domain	RuvC	2 HEPN domains	HD	RuvC, HNH
PAM/PFS	5′ T-rich PAM	3′ non-G PFS	Variable PAM (recognition by Cascade)	3′ G-rich PAM
Pre-crRNA processing	Yes	Yes	Yes	No
tracrRNA	No	No	No	Yes
On target substrate (activator)	ssDNA, dsDNA	ssRNA	dsDNA	dsDNA (ssDNA and ssRNA with PAMmer)
Collateral cleavage activity	Yes	Yes	Yes	No
Off target substrate	ssDNA	ssRNA	ssDNA	NA