Required for pre-mRNA splicing as component of the spliceosome, including pre-catalytic, catalytic and post-catalytic spliceosomal complexes (By similarity). Component of the U5 snRNP and the U4/U6-U5 tri-snRNP complex, a building block of the spliceosome (By similarity). Component of the U5 snRNP and the U4/U6-U5 tri-snRNP complex, a building block of the spliceosome (By similarity). 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, DDX23, CD2BP2, PPIH, SNU13, EFTUD2, SART1 and USP39 (By similarity). Component of the pre-catalytic, catalytic and post-catalytic spliceosome complexes (By similarity). Interacts with ERBB4 and PRPF8 (By similarity). Interacts with PIH1D1 (By similarity). Interacts with RPAP3 and URI1 in a ZNHIT2-dependent manner (By similarity). Interacts with NRDE2 (By similarity). Interacts with FAM50A (By similarity). Belongs to the TRAFAC class translation factor GTPase superfamily. Classic translation factor GTPase family. EF-G/EF-2 subfamily.