Genome editing based on CRISPR/CAS systems: beginning of a new era of genetic manipulation and inheritance

In 2002, Ruud Jansen of Utrecht University found a 21-37 bp interspaced short sequence repeats distinctly spaced among several bacterial species, such as, Salmonella typhimurium (21bp) and Streptococcus pyogenes (37bp). Jansen’s team found that CRISPRs were unique to certain prokaryotes and not viruses and eukaryotes. Moreover, they identified a common sequence, GTT/AAC, at the ends and a long homologous sequence along the upstream without an open reading frame, indicating a conserved ncRNA segment. Their findings were similar to that of Ishino and Mojica, and they have referred the phenomenon as Clustered Regularly Interspaced Short Palindormic Repeats (CRISPR). The biological meaning of CRISPR remained obscure until 2005, when Pourcel, Mojica and Bolotin, independently, concluded that CRISPR were clearly derived from extrachromosomal DNA elements, with most being similar to bacteriophage and plasmids. Outstandingly, species containing CRISPR elements were protected against corresponding foreign invaders and had no residual prophage as evidence of prior infections.4‒6