Fig. 1.

Bacterial CRISPR-Cas9 systems behave as an adaptive immune response against invading bacteriophages. Following infection (Phase 1), Cas1 and Cas2 mediate incorporation of short sequences of the viral genome as spacers within the bacterial CRISPR locus. At re-exposure (Phase 2), the CRISPR locus gets expressed as pre-crRNA, along with tracrRNA. The pre-crRNA is processed to yield guide RNAs (gRNAs) which bind the ribonucleoprotein Cas9 and target this complex to complementary sequences of the infiltrating bacteriophage genome, prompting its Cas9-mediated cleavage. Reprinted from “CRISPR-Cas9 Adaptive Immune System of Streptococcus pyogenes Against Bacteriophages”, by BioRender.com (2021). Retrieved from https://app.biorender.com/biorender-templates