RNA-binding protein that acts as a pre-mRNA splicing factor. Acts by promoting exon inclusion via regulation of exon cassette splicing (By similarity). Also acts as a transcriptional coactivator for steroid nuclear receptors ESR1/ER-alpha and ESR2/ER-beta, and JUN/AP-1, independently of the pre-mRNA splicing factor activity (By similarity). Interacts with NCOA6 and JUN. Interacts with ESR1 and ESR2, in the presence of estradiol (E2). Interacts with RSRC1 (via Arg/Ser-rich domain). Interacts with SF3B1. Interacts with ZNF106 (via N-terminus). Concentrated in nuclear speckles. Colocalizes with the core spliceosomal snRNP proteins (By similarity). Belongs to the splicing factor SR family.