U2 auxiliary factor (U2AF),comprising a large and a small subunit,is a non-snRNP protein required for the binding of U2 snRNP to the pre-mRNA branch site. U2 (RNU2) small nuclear RNA auxiliary factor 1 (U2AF1,synonyms: RN,FP793,U2AF35,U2AFBP,RNU2AF1)is the small subunit which plays a critical role in both constitutive and enhancer-dependent RNA splicing by directly mediating interactions between the large subunit and proteins bound to the enhancers. The U2AF1 gene is localized to chromosome 21q22.3,which is the critical region for three diseases,progressive myoclonus epilepsy,autoimmune polyglandular disease type 1,and one form of bipolar affective disorder.