What Is The CRISPR-Cas9 System?

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The CRISPR-Cas9 system is derived from a bacterial adaptive immune system. The acronym stands for clustered, regularly interspaced, short palindromic repeats, which are sequences of DNA that read the same forward as backwards. In between these are sequences of DNA known as protospacers indicative of particular bacteriophages encountered by bacteria. These sequences are then used as a template for RNAs capable of recognizing viral DNA within a cell and as a means to bind the endonuclease CRISPR associated protein 9 (Cas9). These complexes allow the enzyme to be shuttled to the target DNA to perform a cut on one or both strands of the foreign DNA in either of the enzyme’s two active sites. Recently, scientists have repurposed this bacterial defense mechanism as a genome editing utility to cut, shuttle, or bind desired molecules anywhere within DNA as custom RNA harnesses the multi-tool Cas-9 enzyme (Gupta & Musunuru, 2014). Unlike other methods of genome engineering such as zinc-finger nucleases (ZFNs) or transcription activator-like effector nucleases (TALENs) that have massive barriers to entry in education and expense, CRISPR is a cheap, efficient, customizable utility in genome editing, whose accessible adaptability denotes the rapid advances in its application.
ZFNs and TALENs are the preceding genome editing techniques to
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An additional advantage of CRISPR is its ability to target multiple targets at once. In early 2013, heterologous expression of the CRISPR-Cas9 system and all of its parts was demonstrated in mammalian cells. The modified bacterial system was also able to insert genes at various target locations in the mammalian genome by expressing a multiple target spacer array (Cong et al., 2013). The system was expressed in mammalian cells with varying combinations of codon optimized Cas9 (spCas9). spCas9 used a modified version of RNase

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