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 second alpha-helical domain. It is similar to the small subunit Cmr5, which contains six alpha-helices and two helical insertions that fold into a single globular structure [1-5]. This domain is also found in Cas10 proteins from bacteria [6].

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

6: Mycobacterium tuberculosis CRISPR/Cas system Csm1 holds clues to the evolutionary relationship between DNA polymerase and cyclase activity. Zhang S, Li T, Huo Y, Yang J, Fleming J, Shi M, Wang Y, Wei W, Gu S, Bi L, Jiang T, Zhang H; Int J Biol Macromol. 2021;170:140-149. PMID:33352158