CRISPR (clustered regularly interspaced short palindromic repeats) elements and cas (CRISPR-associated) genes are widespread in Bacteria and Archaea. The CRISPR/Cas system operates as a defense mechanism against mobile genetic elements (i.e., viruses or plasmids). Csa1 is part of the archaeal subtype I-A system. Cas1 has not yet been enzymatically characterised [1].

1: Characterization of the CRISPR/Cas subtype I-A system of the hyperthermophilic crenarchaeon Thermoproteus tenax. Plagens A, Tjaden B, Hagemann A, Randau L, Hensel R; J Bacteriol. 2012;194:2491-2500. PMID:22408157