<p>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.</p><p>Lsm (like-Sm) proteins have diverse functions, and are thought to be important modulators of RNA biogenesis and function [<cite idref="PUB00016606"/>, <cite idref="PUB00016607"/>]. 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) [<cite idref="PUB00016608"/>]. All Sm proteins contain a common sequence motif in two segments, Sm1 and Sm2, separated by a short variable linker [<cite idref="PUB00001270"/>]. Other snRNPs, such as U7 snRNP, can contain different Lsm proteins.</p><p>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 are likely to represent the ancestral Lsm domain [<cite idref="PUB00016613"/>].</p>