The recent discovery of the type II prokaryotic CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) system, originally discovered in the bacterium Streptococcus pyogenes, has provided a revolutionary tool for targeted genome engineering with simple elegance.
The system uses CRISPR-associated endonuclease Cas9, that complexes with small RNAs as guides (gRNAs) to cleave DNA in a sequence-specific manner upstream of the protospacer adaptor motif (PAM) in any genomic location. The CRISPR-Cas9 system is comprised of separate guide RNAs known as the crRNA and tracrRNA. These two separate RNAs have been combined into a single RNA to enable site-specific mammalian genome cutting through the design of a short guide RNA.
Full overview of tools for gene editing