What is CRISPR?
Researchers then later realized that this same method can be applied to the identification and editing of any DNA sequence, not just that of viruses, thereby opening up an entire world of genome engineering.
A guide RNA, either as a crRNA:tracrRNA duplex or a sgRNA molecule, programs the Cas9 nuclease to cut at a specific genomic location. As is shown in the image, the programmable target-specific spacer portion of the sgRNA binds to the genomic target through RNA-DNA base pairing and initiates DNA strand cutting (denoted by scissors in the image). The target site in the genome must lie immediately 5′ of a PAM sequence that contains the canonical (5′) NGG (3′) specific for S. pyogenes Cas9.