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) (PubMed:28781166). Component of the U5 snRNP complex (PubMed:10610776). Component of the U4/U6-U5 tri-snRNP complex (PubMed:26912367). The U4/U6-U5 tri-snRNP complex is a building block of the precatalytic spliceosome (spliceosome B complex) (PubMed:26912367, PubMed:28781166). The U4/U6-U5 tri-snRNP complex is composed of the U4, U6 and U5 snRNAs and at least PRPF3, PRPF4, PRPF6, PRPF8, PRPF31, SNRNP200, TXNL4A, SNRNP40, SNRPB, SNRPD1, SNRPD2, SNRPD3, SNRPE, SNRPF, SNRPG, DDX23, CD2BP2, PPIH, SNU13, EFTUD2, SART1 and USP39, plus LSM2, LSM3, LSM4, LSM5, LSM6, LSM7 and LSM8 (PubMed:16723661, PubMed:26912367, PubMed:28781166). Directly interacts with CD2BP2 (PubMed:17467737, PubMed:24781215). Interacts with HNRPF, HNRPH2, NEDD9 and PQBP1 (PubMed:11054566). Interacts with ERBB4 (PubMed:20858735). The disulfide bond seen in structures determined by X-ray crystallography (PubMed:10610776) and NMR (PubMed:12911302) is not essential for protein folding and function (PubMed:12911302 and PubMed:17467737). The disease is caused by variants affecting the gene represented in this entry. Belongs to the DIM1 family.