InterPro domain: IPR034098

This entry represents the small nuclear ribonucleoprotein G.

The eukaryotic Sm proteins (B/B', D1, D2, D3, E, F and G) assemble into a hetero-heptameric ring around the Sm site of the 2,2,7-trimethyl guanosine (m3G) capped U1, U2, U4 and U5 snRNAs (Sm snRNAs) forming the core of the snRNP particle [ 1 ]. The snRNP particle, in turn, assembles with other components onto the pre-mRNA to form the spliceosome which is responsible for the excision of introns and the ligation of exons. Members of this family share a highly conserved Sm fold containing an N-terminal helix followed by a strongly bent five-stranded antiparallel beta-sheet [ 2 ]. Sm subunit G binds subunits E and F to form a trimer which then assembles onto snRNA along with the D1/D2 and D3/B heterodimers forming a seven-membered ring structure [ 3 , 4 , 5 ].

1. Sm protein-Sm site RNA interactions within the inner ring of the spliceosomal snRNP core structure. EMBO J. 20, 187-96
2. Crystal structures of two Sm protein complexes and their implications for the assembly of the spliceosomal snRNPs. Cell 96, 375-87
3. Sm and Sm-like proteins assemble in two related complexes of deep evolutionary origin. EMBO J. 18, 3451-62
4. The Sm domain is an ancient RNA-binding motif with oligo(U) specificity. Proc. Natl. Acad. Sci. U.S.A. 98, 3685-9
5. Structural Basis of Assembly Chaperone- Mediated snRNP Formation. Mol. Cell 49, 692-703