FIG 4.

Process of CRISPR-Cas acquired immune system. (Top) Adaptation. The invading DNA is recognized by Cas proteins, fragmented and incorporated into the spacer region of CRISPR, and stored in the genome. Expression (bottom). Pre-crRNA is generated by transcription of the CRISPR region and is processed into smaller units of RNA, named crRNA. (Bottom) Interference. By taking advantage of the homology of the spacer sequence present in crRNA, foreign DNA is captured, and a complex with Cas protein having nuclease activity cleaves DNA.