Involved in pre-mRNA splicing as a component of the splicing factor SF3A complex that contributes to the assembly of the 17S U2 snRNP, and the subsequent assembly of the spliceosome. Component of splicing factor SF3A which associates with the splicing factor SF3B and a 12S RNA unit to form the mature 17S U2 small nuclear ribonucleoprotein complex (17S U2 snRNP). Identified in the spliceosome 'E' complex, a precursor of the spliceosome 'A' complex. Identified in the spliceosome 'A' and 'B' complexes. Identified in the spliceosome 'C' complex. Belongs to the SF3A1 family.