Sm

snRNP Sm proteins
Sm
SMART accession number:SM00651
Description: small nuclear ribonucleoprotein particles (snRNPs) involved in pre-mRNA splicing
Interpro abstract (IPR006649):

This family is found in Lsm (like-Sm) proteins, which have a core structure consisting of an open beta-barrel with an SH3-like topology.

Lsm (like-Sm) proteins have diverse functions, and are thought to be important modulators of RNA biogenesis and function [(PUBMED:10801455), (PUBMED:12438310)]. The Sm proteins form part of specific small nuclear ribonucleoproteins (snRNPs) that are involved in the processing of pre-mRNAs to mature mRNAs, and are a major component of the eukaryotic spliceosome. Most snRNPs consist of seven Sm proteins (B/B', D1, D2, D3, E, F and G) arranged in a ring on a uridine-rich sequence (Sm site), plus a small nuclear RNA (snRNA) (either U1, U2, U5 or U4/6) [(PUBMED:15130578)]. All Sm proteins contain a common sequence motif in two segments, Sm1 and Sm2, separated by a short variable linker [(PUBMED:7744013)]. Other snRNPs, such as U7 snRNP, can contain different Lsm proteins.

Lsm proteins are also found in archaebacteria, which do not have any splicing apparatus, suggesting a more general role for Lsm proteins. Archaeal Lsm proteins have been shown to bind to small RNAs and are probably involved in many cellular processes [(PUBMED:20826804)]. Archaeal Lsm proteins are likely to represent the ancestral Lsm domain [(PUBMED:11399068)].

Family alignment:
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There are 13152 Sm domains in 7148 proteins in SMART's nrdb database.

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