The Discovery of CRISPR/Cas System

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CRISPR is a microbial nuclease mechanism involved in defense against invading phages and plasmids. The Loci of CRISPR in bacteria and viral hosts contain a combination of CRISPR-associated (Cas) genes and non-coding RNA elements capable of programming the specificity of the CRISPR-mediated nucleic acid cleavage. CRISPR is based on the protein CRISPR associated protein Cas, which bacteria and archaea wield as a tool to sever predatory bacteriophage's ( and viruses) DNA.
A breakthrough for the basic understanding of CRISPR defense mechanism was achieved by a group of researchers led by Barrangou, who showed that Streptococcus thermophilus can acquire some form of resistance against a bacteriophage by integrating a genome fragment of an infectious virus into its CRISPR locus (Richter et al 2013). CRISPR systems arm bacteria and archaea with a sequence-specific heritable ‘adaptive immune system’ that has a genetic memory of previous genetic invasion. A CRISPR cluster is a genomic DNA element made up of a string of 24-37 bp short repeat sequences that are divided by unique spacer sequences of similar length.
The sequences stem from a virus' genome, elucidating the genetic memory of previous infection. The second part of the CRISPR/Cas machinery is encoded in the Cas genes, and the Cas proteins attain its purpose within the immunity mechanism. The mechanism of CRISPR/Cas interference is of three phases (Appendix I). Firstly, resistance is acquired via the integration of short sequences from spacers (foreign genetic elements) into repetitive genetic elements known as CRISPR arrays. Secondly, transcription and processing of CRISPR arrays into small RNAs (crRNAs) by Cas proteins. Lastly, targeting of the invading phage or plasmid is m...

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...age fragments. The kit uses the Cel-1 nuclease that identifies and cleaves DNA mismatches from hybridization of wt and mutant sequences.
The prospects of CRISPR/Cas systems to function in genetic tools has been studied since its identification as a prokaryotic defense system. Less than a decade after its discovery, the first steps have been made, as sgRNA:Cas9 complexes are used for efficient gene silencing (Qi et al, 2013). The development of RGEN genome editing tools is only an aspect in which CRISPR/Cas defense system shows its prospect for biotechnological application. The establishment of RGEN genome editing tools further model organisms could simplify their future genetic manipulation (Richter et al 2013). For these reasons, the Science journal elected CRISPR gene-editing technique as the 2013 runner-up for the scientific breakthrough of the year.
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