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 (By similarity). Interacts (via RS domain) with PHF5A (via N-terminus). Expressed in primary spermatocytes and elongating spermatids (at protein level). The C-terminal SR-rich domain is required for interactions with SR proteins and the splicing regulators TRA and TRA2, and the N-terminal domain is required for formation of the U2AF1/U2AF2 heterodimer. Belongs to the splicing factor SR family.