Probably involved in intron recognition and spliceosome assembly. Component of the spliceosome. Interacts with SNRNP35, AFC2, CYP59, RS2Z33 and RNU1 (PubMed:10593939, PubMed:12176998, PubMed:15987817, PubMed:16497658, PubMed:9761791). Interacts with MOS14 (PubMed:21738492). A number of isoforms are produced. According to EST sequences. Expressed in roots, leaves, flowers and siliques. Extensively phosphorylated on serine residues in the RS domain (By similarity). Phosphorylated by AFC2. Belongs to the splicing factor SR family. RSZ subfamily.