Plays a role in pre-mRNA splicing and 3'-end processing. 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. Required for the export of mRNA out of the nucleus, even if the mRNA is encoded by an intron-less gene. Positively regulates pre-mRNA 3'-end processing by recruiting the CFIm complex to cleavage and polyadenylation signals. Interacts with U2AF1L4 (PubMed:16819553). Heterodimer with U2AF1. Binds unphosphorylated SF1. Interacts with SCAF11 and SNW1. Interacts with ZRSR2/U2AF1-RS2. Interacts with RBM17. Interacts with PRPF19; the interaction is direct. Interacts with POLR2A (via the C-terminal domain); 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. Interacts with KHDC4 (Isoform 2). Interacts with ZRSR2. Interacts with the SF3B complex composed of SF3B1, SF3B2, SF3B3, SF3B4, SF3B5, SF3B6 and PHF5A (By similarity). 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 (By similarity). 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.