Cas6 is a member of the RAMP (repeat-associated mysterious protein) superfamily [1]. It is among the most widely distributed Cas proteins and is found in both bacteria and archaea [2]. Cas6 functions in the generation of CRISPR-derived guide RNAs for invader defense in prokaryotes [3].

1: A putative RNA-interference-based immune system in prokaryotes: computational analysis of the predicted enzymatic machinery, functional analogies with eukaryotic RNAi, and hypothetical mechanisms of action. Makarova KS, Grishin NV, Shabalina SA, Wolf YI, Koonin EV; Biol Direct. 2006;1:7. PMID:16545108

2: A guild of 45 CRISPR-associated (Cas) protein families and multiple CRISPR/Cas subtypes exist in prokaryotic genomes. Haft DH, Selengut J, Mongodin EF, Nelson KE; PLoS Comput Biol. 2005;1:e60. PMID:16292354

3: Cas6 is an endoribonuclease that generates guide RNAs for invader defense in prokaryotes. Carte J, Wang R, Li H, Terns RM, Terns MP; Genes Dev. 2008;22:3489-3496. PMID:19141480