Plays a critical role in both constitutive and enhancer-dependent splicing by mediating protein-protein interactions and protein-RNA interactions required for accurate 3'-splice site selection. Recruits U2 snRNP to the branch point. Directly mediates interactions between U2AF2 and proteins bound to the enhancers and thus may function as a bridge between U2AF2 and the enhancer complex to recruit it to the adjacent intron (By similarity). Identified in the spliceosome C complex. Heterodimer with U2AF2. Interacts with ZRANB2. Interacts (via RS domain) with PHF5A (via N-terminus) (By similarity). Belongs to the splicing factor SR family.