Participates in the regulation of alternative splicing by modulating the activity of other splice facors. Inhibits the splicing activity of SFRS1, SFRS2 and SFRS6. Augments the splicing activity of SFRS3. Interacts with SREK1IP1 (By similarity). Homodimer. Binds SFRS1, SFRS2, SFRS3 and SFRS6. Interacts with the spliceosome. Ubiquitous. Detected in liver, brain, lung, spleen, testis and pancreas. Belongs to the splicing factor SR family.