InterPro domain: IPR027141

This entry represents a group of LSM domain containing proteins functioning in RNA processing, including U6 snRNA-associated Sm-like protein LSm4 and small nuclear ribonucleoproteins Sm D1 and D3.

LSm4 is a component of LSm protein complexes, which are involved in RNA processing and may function in a chaperone-like manner. It binds specifically to the 3'-terminal U-tract of U6 snRNA [ 1 , 2 ].

SmD1 is involved in pre-mRNA splicing. It binds snRNA U1, U2, U4 and U5, which contain a highly conserved structural motif called the Sm binding site. It also binds telomerase RNA and is required for its accumulation [ 3 , 4 ].

SmD3 is a core protein of small nuclear ribonucleoprotein (snRNP) essential for splicing of primary transcripts [ 5 ]. It appears to function in the U7 snRNP complex that is involved in histone 3'-end processing. It binds to the downstream cleavage product (DCP) of histone pre-mRNA in a U7 snRNP dependent manner [ 6 ].

1. A Sm-like protein complex that participates in mRNA degradation. EMBO J. 19, 1661-71
2. Lsm proteins are required for normal processing of pre-tRNAs and their efficient association with La-homologous protein Lhp1p. Mol. Cell. Biol. 22, 5248-56
3. Convergent transcripts of the yeast PRP38-SMD1 locus encode two essential splicing factors, including the D1 core polypeptide of small nuclear ribonucleoprotein particles. Proc. Natl. Acad. Sci. U.S.A. 90, 848-52
4. Saccharomyces cerevisiae telomerase is an Sm small nuclear ribonucleoprotein particle. Nature 401, 177-80
5. Knock-out mutations of Arabidopsis SmD3-b induce pleotropic phenotypes through altered transcript splicing. Plant Sci. 180, 661-71
6. Purified U7 snRNPs lack the Sm proteins D1 and D2 but contain Lsm10, a new 14 kDa Sm D1-like protein. EMBO J. 20, 5470-9