<sod>The '''CRISPR/Cas system''' is a prokaryotic [[immune system]] that confers resistance to foreign genetic elements such as those present within [[plasmids]] and [[phage]]s,<ref>{{cite journal | vauthors = Redman M, King A, Watson C, King D | title = What is CRISPR/Cas9? | journal = Archives of Disease in Childhood. Education and Practice Edition | date = April 2016 | pmid = 27059283 | doi = 10.1136/archdischild-2016-310459 | volume=101 | pages=213–215}}</ref><ref name="pmid17379808">{{cite journal | vauthors = Barrangou R, Fremaux C, Deveau H, Richards M, Boyaval P, Moineau S, Romero DA, Horvath P | title = CRISPR provides acquired resistance against viruses in prokaryotes | journal = Science | volume = 315 | issue = 5819 | pages = 1709–12 | date = March 2007 | pmid = 17379808 | pmc =  | doi = 10.1126/science.1138140 | bibcode = 2007Sci...315.1709B }} {{Registration required}}</ref><ref name="pmid19095942">{{cite journal | vauthors = Marraffini LA, Sontheimer EJ | title = CRISPR interference limits horizontal gene transfer in staphylococci by targeting DNA | journal = Science | volume = 322 | issue = 5909 | pages = 1843–5 | date = December 2008 | pmid = 19095942 | pmc = 2695655 | doi = 10.1126/science.1165771 | bibcode = 2008Sci...322.1843M }}{{Open access}}</ref> and provides a form of [[acquired immunity]]. '''CRISPR''' associated proteins ('''Cas''') use the CRISPR spacers to recognize and cut these exogenous genetic elements in a manner analogous to [[RNA interference]] in [[eukaryote|eukaryotic]] organisms.<ref name="pmid20125085" /> CRISPRs are found in approximately 40% of sequenced [[bacterial]] genomes and 90% of sequenced [[archaea]].<ref name="pmid17521438">{{cite journal | vauthors = Grissa I, Vergnaud G, Pourcel C | title = The CRISPRdb database and tools to display CRISPRs and to generate dictionaries of spacers and repeats | journal = BMC Bioinformatics | volume = 8 | pages = 172 | year = 2007 | pmid = 17521438 | pmc = 1892036 | doi = 10.1186/1471-2105-8-172 }}{{Open access}}</ref><ref group="note">71/79 Archaea, 463/1008 Bacteria [http://crispr.u-psud.fr/crispr/CRISPRdatabase.php CRISPRdb], Date: 19.6.2010 {{wayback|url=http://crispr.u-psud.fr/crispr/CRISPRdatabase.php |date=20150516061838 }}</ref><eod>
<sod>The '''CRISPR/Cas system''' is a prokaryotic [[immune system]] that confers resistance to foreign genetic elements such as those present within [[plasmids]] and [[phage]]s,<ref>{{cite journal | vauthors = Redman M, King A, Watson C, King D | title = What is CRISPR/Cas9? | journal = Archives of Disease in Childhood. Education and Practice Edition | date = April 2016 | pmid = 27059283 | doi = 10.1136/archdischild-2016-310459 | volume=101 | pages=213–215}}</ref><ref name="pmid17379808">{{cite journal | vauthors = Barrangou R, Fremaux C, Deveau H, Richards M, Boyaval P, Moineau S, Romero DA, Horvath P | title = CRISPR provides acquired resistance against viruses in prokaryotes | journal = Science | volume = 315 | issue = 5819 | pages = 1709–12 | date = March 2007 | pmid = 17379808 | pmc =  | doi = 10.1126/science.1138140 | bibcode = 2007Sci...315.1709B }} {{Registration required}}</ref><ref name="pmid19095942">{{cite journal | vauthors = Marraffini LA, Sontheimer EJ | title = CRISPR interference limits horizontal gene transfer in staphylococci by targeting DNA | journal = Science | volume = 322 | issue = 5909 | pages = 1843–5 | date = December 2008 | pmid = 19095942 | pmc = 2695655 | doi = 10.1126/science.1165771 | bibcode = 2008Sci...322.1843M }}{{Open access}}</ref> and provides a form of [[acquired immunity]]. CRISPR associated proteins ('''Cas''') use the CRISPR spacers to recognize and cut these exogenous genetic elements in a manner analogous to [[RNA interference]] in [[eukaryote|eukaryotic]] organisms.<ref name="pmid20125085" /> CRISPRs are found in approximately 40% of sequenced [[bacterial]] genomes and 90% of sequenced [[archaea]].<ref name="pmid17521438">{{cite journal | vauthors = Grissa I, Vergnaud G, Pourcel C | title = The CRISPRdb database and tools to display CRISPRs and to generate dictionaries of spacers and repeats | journal = BMC Bioinformatics | volume = 8 | pages = 172 | year = 2007 | pmid = 17521438 | pmc = 1892036 | doi = 10.1186/1471-2105-8-172 }}{{Open access}}</ref><ref group="note">71/79 Archaea, 463/1008 Bacteria [http://crispr.u-psud.fr/crispr/CRISPRdatabase.php CRISPRdb], Date: 19.6.2010 {{wayback|url=http://crispr.u-psud.fr/crispr/CRISPRdatabase.php |date=20150516061838 }}</ref><eod>