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. Author manuscript; available in PMC: 2022 May 16.
Published in final edited form as: Trends Genet. 2021 Sep 22;37(12):1053–1055. doi: 10.1016/j.tig.2021.09.002

Figure 1. The PAM requirement of CRISPR-Cas enzymes.

Figure 1.

(A) The PAM permits CRISPR-Cas systems to distinguish self from non-self-DNA. (B) Schematic of the SpCas9-gRNA-target DNA complex, with the PAM highlighted in blue. (C) For genome editing applications, PAM availability dictates the genetic locations that Cas enzymes can target. (D) Protein engineering approaches have been utilized to relax or nearly remove the PAM requirement of Cas enzymes, improving PAM density and enabling more accurate single-base targeting of the genome.

Abbreviations: PAM, protospacer adjacent motif; gRNA, guide RNA.