Fig. 1
From: Bio-informatic analysis of CRISPR protospacer adjacent motifs (PAMs) in T4 genome
A schematic illustration of the components and mechanism of CRISPR-Cas9. 1. CRISPR-Cas9 is a fusion between Cas9 nuclease and single guiding RNA (sg RNA). Spacer sequences in sg RNA are phage DNA sequences that were integrated into bacterial DNA from previous exposures. 2. A latter phage attack causes the injection of its DNA genome inside the bacterial cell. 3. CRISPR-Cas9 complex recognizes the target cleaving site in phage genome by the help of the protospacer-adjacent motif (PAM) sequence, at this step CRISPR-Cas9 binds the phage DNA sequences that are complementary to sg RNA which are located the upstream genomic sequence of PAM. 4. Cas9 cuts the double strands upstream of the PAM to induce DNA double-strand breaks. Different PAM sequences are used by several types of CRISPR systems and the PAM sequence NGG was used for illustration. Created with BioRender.com