Pre-mRNA-binding protein required for splicing of both U2- and U12-type introns. Selectively interacts with the 3'-splice site of U2- and U12-type pre-mRNAs and promotes different steps in U2 and U12 intron splicing. Recruited to U12 pre-mRNAs in an ATP-dependent manner and is required for assembly of the prespliceosome, a precursor to other spliceosomal complexes. For U2-type introns, it is selectively and specifically required for the second step of splicing (By similarity). Component of the U11/U12 snRNPs that are part of the U12-type spliceosome. Interacts (via RS domain) with SRSF1 and SRSF2. Interacts with U2AF2/U2AF65 (By similarity). Phosphorylated in the RS domain by SRPK1.