Part of pre- and post-splicing multiprotein mRNP complexes. Involved in numerous pre-mRNA processing events. Promotes constitutive and exonic splicing enhancer (ESE)-dependent splicing activation by bridging together sequence-specific (SR family proteins, SFRS4, SFRS5 and TRA2B/SFRS10) and basal snRNP (SNRP70 and SNRPA1) factors of the spliceosome. Stimulates mRNA 3'-end cleavage independently of the formation of an exon junction complex. Binds both pre-mRNA and spliced mRNA 20-25 nt upstream of exon-exon junctions. Binds RNA and DNA with low sequence specificity and has similar preference for either double- or single-stranded nucleic acid substrates. Identified in the spliceosome C complex. Found in a pre-mRNA splicing complex with SFRS4, SFRS5, SNRP70, SNRPA1, SRRM1 and SRRM2. Found in a pre-mRNA exonic splicing enhancer (ESE) complex with SNRP70, SNRPA1, SRRM1 and TRA2B/SFRS10. Found in a mRNA splicing-dependent exon junction complex (EJC) with DEK, PRPF8, NCBP1, RBM8A, RNPS1, SRRM1 and ALYREF/THOC4. Interacts with DDX39B, CPSF1, RBM8A, RNPS1, and ALYREF/THOC4. Seems to be a compound of RNA export complexes that are released from speckles in a ATP-dependent manner. Phosphorylated on multiple serine and threonine residues by DYRK3 during the G2-to-M transition, after the nuclear-envelope breakdown (PubMed:29973724). Phosphorylation by DYRK3 promotes disassembly of nuclear speckles (PubMed:29973724). Citrullinated by PADI4. Belongs to the splicing factor SR family.