CRISPR is an RNA-guided gene-editing platform that makes use of a bacterially derived protein (Cas9) and a synthetic guide RNA to introduce a double strand break at a specific location within the genome. Editing is achieved by transfecting a cell with the Cas9 protein along with a specially designed guide RNA (gRNA) that directs the cut through hybridization with its matching genomic sequence.Use of wild-type Cas9 has been shown to lead to off-target cleavage, but a modified version introduces only single strand nicks to the DNA, which can be exploited to introduce subtle genetic changes while avoiding off-target effects common to double strand breaks.
Although recently-developed programmable editing tools, such as zinc finger nucleases and transcription activator-like effector nucleases, have significantly improved the capacity for precise genome modification, these techniques have limitations. CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 technology represents a significant improvement over these other next-generation genome editing tools, reaching a new level of targeting, efficiency, and ease of use. The CRISPR/Cas9 system allows for site-specific genomic targeting in virtually any organism.
The type II CRISPR/Cas system is a prokaryotic adaptive immune response system that uses non-coding RNAs to guide the Cas9 nuclease to induce site-specific DNA cleavage. This DNA damage is repaired by cellular DNA repair mechanisms, either via the non-homologous end joining DNA repair pathway (NHEJ) or the homology directed repair (HDR) pathway.