InterPro domain: IPR034101

This entry represents Sm-like protein Lsm4. It could be found in the nuclear Lsm2-8 complex or in the cytoplasmic Lsm1-7 complex.

The Lsm2-8 complex associates with multiple snRNP complexes containing the U6 snRNA (U4/U6 snRNP, U4/U6.U5 snRNP, and free U6 snRNP). It binds and stabilizes the 3'-terminal poly(U) tract of U6 snRNA and facilitates the assembly of U4-U6 di-snRNP and U4-U6-U5 tri-snRNP [ 1 , 2 , 3 ]. The Lsm1-7 complex associates with deadenylated mRNA and promotes decapping in the 5'-3' mRNA decay pathway [ 4 , 4 ].

The Sm and the Lsm proteins, characterised by the Sm-domain, have RNA-related functions. The Sm heptamer ring associates with four (U1, U2, U4, U5) snRNPs, while Lsm2-8 heptamer associates with the U6 snRNP. Another Lsm heptameric complex, Lsm1-7, which differs from Lsm2-8 by one Lsm protein, functions in mRNA decapping, a crucial step in the mRNA degradation pathway [ 5 ].

1. Crystal structures of Lsm3, Lsm4 and Lsm5/6/7 from Schizosaccharomyces pombe. PLoS ONE 7, e36768
2. Lsm proteins and RNA processing. Biochem. Soc. Trans. 33, 433-8
3. Crystal structures of the Lsm complex bound to the 3' end sequence of U6 small nuclear RNA. Nature 506, 116-20
4. Functions of Lsm proteins in mRNA degradation and splicing. Curr. Opin. Cell Biol. 12, 346-50
5. Crystal structure and biochemical analysis of the heptameric Lsm1-7 complex. Cell Res. 24, 497-500