The LSM domain contains Sm proteins as well as other related LSM (Like Sm) proteins. The U1, U2, U4/U6, and U5 small nuclear ribonucleoprotein particles (snRNPs) involved in pre-mRNA splicing contain seven Sm proteins (B/B', D1, D2, D3, E, F and G) in common, which assemble around the Sm site present in four of the major spliceosomal small nuclear RNAs. The U6 snRNP binds to the LSM (Like Sm) proteins [3]. Sm proteins are also found in archaebacteria, which do not have any splicing apparatus suggesting a more general role for Sm proteins. All Sm proteins contain a common sequence motif in two segments, Sm1 and Sm2, separated by a short variable linker. This family also includes the bacterial Hfq (host factor Q) proteins. Hfq are also RNA-binding proteins, that form hexameric rings.

1: snRNP Sm proteins share two evolutionarily conserved sequence motifs which are involved in Sm protein-protein interactions. Hermann H, Fabrizio P, Raker VA, Foulaki K, Hornig H, Brahms H, Luhrmann R EMBO J 1995;14:2076-2088. PMID:7744013

2: Crystal structures of two Sm protein complexes and their implications for the assembly of the spliceosomal snRNPs. Kambach C, Walke S, Young R, Avis JM, de la Fortelle E, Raker VA, Luhrmann R, Li J, Nagai K; Cell 1999;96:375-387. PMID:10025403

3: Characterization of Sm-like proteins in yeast and their association with U6 snRNA. Mayes AE, Verdone L, Legrain P, Beggs JD; EMBO J 1999;18:4321-4331. PMID:10428970

4: Host factor Hfq of Escherichia coli stimulates elongation of poly(A) tails by poly(A) polymerase I. Hajnsdorf E, Regnier P; Proc Natl Acad Sci U S A 2000;97:1501-1505. PMID:10677490

5: Hfq (HF1) stimulates ompA mRNA decay by interfering with ribosome binding. Vytvytska O, Moll I, Kaberdin VR, von Gabain A, Blasi U; Genes Dev 2000;14:1109-1118. PMID:10809669

6: Lsm Proteins are required for normal processing and stability of ribosomal RNAs. Kufel J, Allmang C, Petfalski E, Beggs J, Tollervey D; J Biol Chem 2003;278:2147-2156. PMID:12438310