Involved in pre-mRNA splicing as a component of the spliceosome. May play a role in cross-intron bridging of U1 and U2 snRNPs in the mammalian A complex. Component of the spliceosome B complex. Associated with U2 snRNPs. Binds splicing factors SNRPB, SNRPC and SF1 (By similarity). Interacts via the WW domains with the Pro-rich domains of KHDRBS1/SAM68 (By similarity). Interacts via the WW domains with the Pro-rich domains of WBP11 (By similarity). The WW domain recognizes the proline, glycine and methionine-rich (PGM) motif present in the splicing factors, as well as the Arg/Gly-rich-flanked Pro-rich domains found in several WW domain-binding proteins.