Plays a role in pre-mRNA splicing and 3'-end processing (PubMed:17024186). By recruiting PRPF19 and the PRP19C/Prp19 complex/NTC/Nineteen complex to the RNA polymerase II C-terminal domain (CTD), and thereby pre-mRNA, may couple transcription to splicing (PubMed:21536736). Induces cardiac troponin-T (TNNT2) pre-mRNA exon inclusion in muscle. Regulates the TNNT2 exon 5 inclusion through competition with MBNL1. Binds preferentially to a single-stranded structure within the polypyrimidine tract of TNNT2 intron 4 during spliceosome assembly. Required for the export of mRNA out of the nucleus, even if the mRNA is encoded by an intron-less gene. Represses the splicing of MAPT/Tau exon 10. Positively regulates pre-mRNA 3'-end processing by recruiting the CFIm complex to cleavage and polyadenylation signals (PubMed:17024186). Interacts with U2AF1L4 (By similarity). Heterodimer with U2AF1 (PubMed:11551507). Binds unphosphorylated SF1 (PubMed:10449420, PubMed:12718882). Interacts with SCAF11 and SNW1 (PubMed:9447963, PubMed:21460037). Interacts with ZRSR2/U2AF1-RS2. Interacts with RBM17 (PubMed:17589525). Interacts with PRPF19; the interaction is direct. Interacts with POLR2A (via the C-terminal domain); recruits PRPF19 and the Prp19 complex to the pre-mRNA (PubMed:21536736). Interacts with KHDC4 (Isoform 2) (PubMed:19641227). Interacts with ZRSR2 (PubMed:9237760). Interacts with the SF3B complex composed of SF3B1, SF3B2, SF3B3, SF3B4, SF3B5, SF3B6 and PHF5A (PubMed:27720643). Interacts (via N-terminus) with CPSF7 (via C-terminus); this interaction stimulates pre-mRNA 3'-end processing by promoting the recruitment of the CFIm complex to cleavage and polyadenylation signals (PubMed:17024186). Lysyl-hydroxylation at Lys-15 and Lys-276 affects the mRNA splicing activity of the protein, leading to regulate some, but not all, alternative splicing events. Belongs to the splicing factor SR family.