This gene encodes subunit 1 of the splicing factor 3a protein complex. The splicing factor 3a heterotrimer includes subunits 1, 2 and 3 and is necessary for the in vitro conversion of 15S U2 snRNP into an active 17S particle that performs pre-mRNA splicing. Subunit 1 belongs to the SURP protein family; named for the SURP (also called SWAP or Suppressor-of-White-APricot) motifs that are thought to mediate RNA binding. Subunit 1 has tandemly repeated SURP motifs in its amino-terminal half while its carboxy-terminal half contains a proline-rich region and a ubiquitin-like domain. Binding studies with truncated subunit 1 derivatives demonstrated that the two SURP motifs are necessary for binding to subunit 3 while contacts with subunit 2 may occur through sequences carboxy-terminal to the SURP motifs. Alternative splicing results in multiple transcript variants encoding different isoforms.