The prokaryotic CRISPR RNA-Cas protein (Cmr) complex provides protection against mobile genetic elements by cleaving foreign RNA. Its largest subunit is Cmr2. This protein shows a N-terminal HD (histidine-aspartate) domain, two RRM domains resembling adenylate cyclase and two alpha-helical domains. This entry represents the first alpha-helical domain, which is similar to the thumb of DNA polymerases [1-5].

1: Structure of the Cmr2 subunit of the CRISPR-Cas RNA silencing complex. Cocozaki AI, Ramia NF, Shao Y, Hale CR, Terns RM, Terns MP, Li H; Structure. 2012;20:545-553. PMID:22405013

2: Crystal structure of the Cmr2-Cmr3 subcomplex in the CRISPR-Cas RNA silencing effector complex. Osawa T, Inanaga H, Numata T; J Mol Biol. 2013;425:3811-3823. PMID:23583914

3: Crystal structure of Cmr2 suggests a nucleotide cyclase-related enzyme in type III CRISPR-Cas systems. Zhu X, Ye K; FEBS Lett. 2012;586:939-945. PMID:22449983

4: Structure of the Cmr2-Cmr3 subcomplex of the Cmr RNA silencing complex. Shao Y, Cocozaki AI, Ramia NF, Terns RM, Terns MP, Li H; Structure. 2013;21:376-384. PMID:23395183

5: Structural model of a CRISPR RNA-silencing complex reveals the RNA-target cleavage activity in Cmr4. Benda C, Ebert J, Scheltema RA, Schiller HB, Baumgartner M, Bonneau F, Mann M, Conti E; Mol Cell. 2014;56:43-54. PMID:25280103