14. Bacterial adaptive immunity—Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)

Clustered regularly interspaced short palindromic repeats (CRISPR) are the bacterial loci that encode regulatory RNAs conferring sequence-directed immunity against phages. CRISPR is believed to be one of the most ancient bacterial adaptive mechanisms of protection against phages. This adaptive immunity involves an active process of integration of short fragments of foreign nucleic acids into clusters of CRISPRs, followed by expression of small RNAs from the loci. These RNAs target pathogen genomes for degradation.

Bacteria and Archaea lack bona fide sexual reproduction. Some of the mechanisms that they use instead for adaptation to stress and genome ...

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