Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) contribute to a bacterial system for defence against infection from phages, similar to acquired immunity in eukaryotes. Key components of CRISPR have been adapted for use as a tool for genome engineering in a variety of organisms.
The editing system consists of two components: CRISPR-associated endonuclease 9 (Cas9) and a guide RNA (gRNA). Cas9 protein creates a double strand DNA break at a site in the genome that is defined by the sequence of a gRNA molecule that is bound to the Cas9 protein.
The location at which the Cas9 protein cuts the DNA is defined by the unique sequence of the RNA that is bound to it. The gRNA consists of two sections, a scaffold region required for the RNA to bind to Cas9 and a 20 nucleotide targeting-sequence, which directs Cas9 to the desired cut position in the genome.
