Plays role in pre-mRNA splicing as component of the U4/U6-U5 tri-snRNP complex that is involved in spliceosome assembly, and as component of the precatalytic spliceosome (spliceosome B complex). The heptameric LSM2-8 complex binds specifically to the 3'-terminal U-tract of U6 snRNA. Component of the precatalytic spliceosome (spliceosome B complex). Component of the U4/U6-U5 tri-snRNP complex, a building block of the precatalytic spliceosome (spliceosome B complex). LSM2, LSM3, LSM4, LSM5, LSM6, LSM7 and LSM8 form a heptameric, ring-shaped subcomplex (the LSM2-8 complex) that is part of the U4/U6-U5 tri-snRNP complex and the precatalytic spliceosome. Belongs to the snRNP Sm proteins family.