Plays role in pre-mRNA splicing as core component of precatalytic, catalytic and postcatalytic spliceosomal complexes (PubMed:28502770, PubMed:28781166, PubMed:29361316, PubMed:30315277, PubMed:29360106, PubMed:29301961, PubMed:30728453, PubMed:30705154). Involved in spliceosome assembly, activation and disassembly. Mediates changes in the dynamic network of RNA-RNA interactions in the spliceosome. Catalyzes the ATP-dependent unwinding of U4/U6 RNA duplices, an essential step in the assembly of a catalytically active spliceosome. ATP + H2O = ADP + H(+) + phosphate Component of a core complex containing at least PRPF8, SNRNP200, EFTUD2 and SNRNP40. Component of the U5 snRNP and U4/U6-U5 tri-snRNP complexes, building blocks of the spliceosome. Component of the U4/U6-U5 tri-snRNP complex composed of the U4, U6 and U5 snRNAs and at least PRPF3, PRPF4, PRPF6, PRPF8, PRPF31, SNRNP200, TXNL4A, SNRNP40, DDX23, CD2BP2, PPIH, SNU13, EFTUD2, SART1 and USP39 (PubMed:16723661, PubMed:8670905, PubMed:26912367). Component of precatalytic, catalytic and postcatalytic spliceosomal complexes (PubMed:11991638, PubMed:28502770, PubMed:28781166, PubMed:29361316, PubMed:30315277, PubMed:29360106, PubMed:29301961, PubMed:30728453, PubMed:30705154). Widely expressed. Contains two helicase domains. The N-terminal helicase domain has catalytic activity by itself, contrary to the C-terminal helicase domain that may have a regulatory role and enhance the activity of the first helicase domain. The disease is caused by variants affecting the gene represented in this entry. Belongs to the helicase family. SKI2 subfamily. Truncated N-terminus.