Plays role in pre-mRNA splicing as component of the U5 snRNP and U4/U6-U5 tri-snRNP complexes that are involved in spliceosome assembly, and as component of the precatalytic spliceosome (spliceosome B complex). Component of the precatalytic spliceosome (spliceosome B complex). Component of the U5 snRNP complex. Component of the U4/U6-U5 tri-snRNP complex. Belongs to the DIM1 family.