SF3b145/SAP145 is a 145 kDa subunit of the splicing factor 3B (SF3B) protein complex. The SF3B complex is composed of at least 8 subunits (SF3B1 through SF3B8). SF3A along with SF3B and a 12S RNA unit are components of the 17S U2 small nuclear ribonucleoprotein complex (U2 snRNP) involved in pre-mRNA splicing. In this complex SF3B2 interacts directly with SF3B4 and associates with the pre-mRNA upstream of the branch site at the anchoring site. SF3A and SF3B may play a role in anchoring the U2 snRNP to the pre-mRNA upstream of the intron’s branch site.