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. 2020 Jul 25;1(5):100102. doi: 10.1016/j.xplc.2020.100102

Figure 1.

Figure 1

CRISPR-Cas Systems Used for Genome Editing in Plants.

(A) The CRISPR-SpCas9 system comprised of the endonuclease SpCas9, harboring RuvC and HNH catalytic domains, and the sgRNA that guides the complex to an endogenous target sequence upstream of a G-rich PAM (5′-NGG-3′), leading to blunt and/or staggered DNA breaks.

(B) The CRISPR-Cas12a system involves the endonuclease Cas12a that is guided to the target locus, downstream of a T-rich PAM (5′-TTTN-3′), by a short crRNA, leading to a staggered DNA cleavage by a single RuvC domain after conformational changes: (1) and (2).

(C) The CRISPR-Cas12b system relies on a Cas12b endonuclease, harboring a single RuvC catalytic domain that mediates staggered DNA cleavage—(1) and (2)—and an sgRNA that targets the complex to a specific site downstream of a T-rich PAM (5′-VTTV-3′). The schemes are not at scale and are for illustrative purposes only.