This domain, approximately 150 residues, is mainly found in several uncharacterized proteins in various Prochlorococcus and Synechococcus species. The crystal structure of ECX21941 reveals unexpected similarity to Sm/LSm proteins, which are important RNA-binding proteins, despite no detectable sequence similarity [1]. The specific function of this family is unknown, but the structure analysis of ECX21941 indicates nucleic acid-binding capabilities and suggests a role in RNA and/or DNA processing [1].

1: Crystal structure of a novel Sm-like protein of putative cyanophage origin at 2.60 A resolution. Das D, Kozbial P, Axelrod HL, Miller MD, McMullan D, Krishna SS, Abdubek P, Acosta C, Astakhova T, Burra P, Carlton D, Chen C, Chiu HJ, Clayton T, Deller MC, Duan L, Elias Y, Elsliger MA, Ernst D, Farr C, Feuerhelm J, Grzechnik A, Grzechnik SK, Hale J, Han GW, Jaroszewski L, Jin KK, Johnson HA, Klock HE, Knuth MW, Kumar A, Marciano D, Morse AT, Murphy KD, Nigoghossian E, Nopakun A, Okach L, Oommachen S, Paulsen J, Puckett C, Reyes R, Rife CL, Sefcovic N, Sudek S, Tien H, Trame C, Trout CV, van den Be, Weekes D, White A, Xu Q, Hodgson KO, Wooley J, Deacon AM, Godzik A, Lesley SA and Wilson IA. Proteins 75 (2), 296-307 (2009) PMID:19173316