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The basic model of CRISPR evolution is newly incorporated spacers driving phages to mutate their genomes to avoid the bacterial immune response, creating diversity in both the phage and host populations. To resist a phage infection, the sequence of the CRISPR spacer must correspond perfectly to the sequence of the target phage gene.
The CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR associated nucleases) system was originally discovered to be an acquired immune response mechanism used by archaea and bacteria. It has since been adopted for use as a tool in the genetic engineering of higher organisms.
Cas9 (CRISPR associated protein 9, formerly called Cas5, Csn1, or Csx12) is a 160 kilodalton protein which plays a vital role in the immunological defense of certain bacteria against DNA viruses and plasmids, and is heavily utilized in genetic engineering applications.
CRISPR interference (CRISPRi) is a genetic perturbation technique that allows for sequence-specific repression of gene expression in prokaryotic and eukaryotic cells. [1] It was first developed by Stanley Qi and colleagues in the laboratories of Wendell Lim , Adam Arkin, Jonathan Weissman , and Jennifer Doudna . [ 2 ]
Targeted gene knockout using CRISPR/Cas9 requires the use of a delivery system to introduce the sgRNA and Cas9 into the cell. Although a number of different delivery systems are potentially available for CRISPR, [37] [38] genome-wide loss-of-function screens are predominantly carried out using third generation lentiviral vectors.
CRISPR-Cas9 genome editing techniques have many potential applications. The use of the CRISPR-Cas9-gRNA complex for genome editing [10] was the AAAS's choice for Breakthrough of the Year in 2015. [11] Many bioethical concerns have been raised about the prospect of using CRISPR for germline editing, especially in human embryos. [12]
In December 2020, the second edition of PDF 2.0, ISO 32000-2:2020, was published, with clarifications, corrections, and critical updates to normative references [16] (ISO 32000-2 does not include any proprietary technologies as normative references). [17] In April 2023 the PDF Association made ISO 32000-2 available for download free of charge. [15]