This entry includes animal splicing factor 3B subunit 1 (SF3B1, also known as SAP 155) and its homologues such as Hsh155 from budding yeasts []and Prp10 from fission yeasts []. SF3B1 is a component of the splicing factor SF3B complex, which is important for anchoring the spliceosome to precursor mRNA. SF3B1 binds to pre-mRNA on both sides of the intron branch site region []. This subunit is required for 'A' splicing complex assembly (formed by the stable binding of U2 snRNP to the branchpoint sequence in pre-mRNA) and 'E' splicing complex assembly [].