The CRISPR system is said to protect or preserve genome integrity in prokaryotic cells by acting as ...

 The CRISPR (clustered regularly interspaced short palindromic repeats) system is based on a region of the genome that contains DNA sequences from previously encountered foreign DNA separated by short palindromic repeats. The CRISPR region is translated into a long RNA molecule and then cleaved at each palindromic repeat to create short RNA molecules (crRNAs) that are complementary to foreign nucleic acids. If the crRNA binds to a piece of nucleic acid, associated proteins called Cas proteins will destroy the foreign nucleic acid and prevent it from recombining with the genome or replicating. The CRISPR system only works if the foreign DNA has homology with the DNA sequences in the CRISPR region of the genome. This means that novel phages or other DNA sequences would not be recognized or destroyed. Another limitation is that the CRISPR system might destroy DNA that contains useful genes or sequences if it were allowed to recombine with the genome. This could slow down evolution and adaptation.

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