CRISPR loci appear to be mobile elements with a wide host range. This entry represents proteins found only in CRISPR-containing species, near other CRISPR-associated proteins (cas). The species range so far for these proteins is pathogenic bacteria only. Clusters of short DNA repeats with nonhomologous spacers, which are found at regular intervals in the genomes of phylogenetically distinct prokaryotic species, comprise a family with recognisable features. This family is known as CRISPR (short for Clustered, Regularly Interspaced Short Palindromic Repeats).