Fig. 2: Validated genome editing tools in the Class 2 CRISPR system and the architecture in the cleavage site. | Experimental & Molecular Medicine

Fig. 2: Validated genome editing tools in the Class 2 CRISPR system and the architecture in the cleavage site.

From: Recent advances in the CRISPR genome editing tool set

Fig. 2

Cas9 represents a type II system and is guided by crRNA and tracrRNA. The RNP form recognizes the compatible PAM sequence and opens the helical structure when sequence similarity between the crRNA and protospacer exists. Various subtypes have been validated in type V, including Cas12a, Cas12b, Cas12e, and Cas14, where each subtype shows a distinct architecture. Only crRNA is required for Cas12a, while the other subtypes require an additional tracrRNA. Cas14 shows both ssDNA and dsDNA cleavage activity. A PAM requirement exists for dsDNA cleavage. The best characterized RNA nuclease Cas13 belongs to Type VI. In recognition of the PFS sequence, the crRNA-Cas13 complex induces ssRNA cleavage activity. Upon target recognition, Cas13 is armored with collateral ssRNA activity

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