Case Analysis : Crispr Cas Immunity

941 Words Aug 4th, 2015 4 Pages
III. Overview of CRISPR-Cas immunity

Recent advances in molecular techniques and bioinformatics analysis has allowed for the isolation and the sequencing of a large number of prokaryotic genomes which has led to the discovery of many unknown genes.
First discovered in 1987, the CRISPR-Cas system is a prokaryotic adaptive immunity defense system that confers resistance against invading nucleic acids, either viral or plasmid. In other words, if an intracellular parasite (such as a phage or a plasmid) invades the bacterial or achaeal host cell, the host cell is capable of storing short fragments of the foreign nucleic acid originating from the parasite within its own genome (Wiedenheft et al. 2012). The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and the CRISPR associated (Cas) genes are found in approximately 40% of bacterial genomes and in nearly 90% of sequenced archaeal genomes (Zhang and al. 2014). CRISPR immunity involves the three following phases: acquisition, expression and interference. During the acquisition stage, new spacer sequences are incorporated into the CRISPR locus. During the expression stage, the CRISPR array is transcribed into a premature crRNA (pre-crRNA) and then matures into the CRISPR RNA (crRNA). In the last stage, the foreign DNA is destroyed using the processed crRNA in some form of effector complex containing Cas proteins (Weidenheft et al., 2012) (Figure 3).

1. Architecture of the CRISPR-Cas

The CRISPR-Cas locus…
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