Protospacer Adjacent Motif (PAM) site (PAM)

The genomic DNA protospacer adjacent to an NGG PAM (Protospacer Adjacent Motif) is the specific DNA sequence targeted by the CRISPR-Cas9 system, primarily derived from Streptococcus pyogenes. The PAM is a short, essential DNA sequence (typically 5'-NGG-3') that serves as a recognition signal for the Cas9 nuclease, allowing it to bind and subsequently cleave the adjacent 'protospacer' DNA sequence (Sternberg et al., 2014). This motif is a critical component of bacterial adaptive immunity, as it prevents the Cas9 enzyme from attacking the bacteria's own CRISPR locus while allowing it to target invading viral DNA. In therapeutic applications, the PAM sequence dictates where the CRISPR-Cas9 complex can bind within the human genome to perform precise gene editing (Jinek et al., 2012). By designing a guide RNA to match a protospacer sequence next to an NGG PAM, researchers can induce double-strand breaks at specific genomic locations to disrupt or repair genes, as seen in approved therapies like exagamglogene autotemcel for sickle cell disease (Collias & Beisel, 2021). However, the requirement for a specific PAM sequence limits the targetable range of the genome, and the potential for off-target binding at similar sequences remains a significant safety concern in clinical development. Monitoring these interactions through advanced sequencing techniques is vital for ensuring the precision and safety of gene-editing interventions.

Other names

Genomic DNA protospacer adjacent to NGG PAMNGG PAMCas9 recognition siteProtospacer Adjacent MotifCRISPR target site

The CRISPR-Cas9 complex utilizes a guide RNA (gRNA) to identify a complementary DNA sequence (protospacer) that must be immediately followed by a Protospacer Adjacent Motif (PAM), such as 5'-NGG-3'. Upon PAM recognition by the Cas9 protein, the enzyme induces a double-strand break (DSB) in the DNA, which is subsequently repaired by cellular non-homologous end joining (NHEJ) or homology-directed repair (HDR) to achieve gene disruption or correction (Jinek et al., 2012; Sternberg et al., 2014).