Required for pre-mRNA splicing as component of the activated spliceosome (PubMed:11991638, PubMed:28076346, PubMed:28502770, PubMed:28781166, PubMed:29301961, PubMed:29360106, PubMed:30315277, PubMed:30705154). Component of the U5 small nuclear ribonucleoprotein (snRNP) complex and the U4/U6-U5 tri-snRNP complex, building blocks of the spliceosome (PubMed:16723661, PubMed:26912367, PubMed:9774689). As a component of the minor spliceosome, involved in the splicing of U12-type introns in pre-mRNAs (Probable).