SF3B3 is one of four proteins for SF3B, which is involved in RNA splicing. Introns are removed from nuclear pre-mRNA in 2-step transesterification reactions. Splicing occurred in a large ribonucleoprotein particle, called the spliceosome. Spliceosomal intermediate complexes form on pre-mRNA in the order E, A, B, and C, with the catalytic reactions occurring in complex C. U2 small nuclear ribonucleoproteins are one of the proteins essential for spliceosome assembly and mRNA splicing. Functional U2 snRNP is composed of a 12S unit and 2 splicing factors, SF3A, which is composed of 3 proteins, and SF3B, which composed of 4 proteins. SF3B3 is required for 'A' complex assembly formed by the stable binding of U2 snRNP to the branchpoint sequence(BPS) in pre-mRNA.
