Structure and mechanism of CRISPR–cas in microbes

Unique spacer (a) sequences W 91% Repeat sequences cas operon M CRISPR trachNA Transcription (b) AMA/W Precursor chNA l Processing via cas-encoded RNase AR /\R “M dsDNA cleavage occurs trachNA—chNA-Cas complex at site of base pairing of chNA and target DNA. Invading phage (C) New spacer or plasmid DNA / filol I I Ii’lg-B—l—l-E- Integrationk \/\ \AV\ V\ \Cas-mediated processing? Recognition of foreign DNA Invading phage or plasmid DNA (d) Target r: , A _’ Targeting of DNA Upstream Target Downstream "°"'5e'f DNA CR'SPR _’ Protection DNA Repeat Spacer Repeat of self DNA