InterPro domain: IPR009145

The U2 small nuclear ribonucleoprotein auxiliary factor (U2AF) is aheterodimeric splicing factor composed of a large and a small subunit [ 1 ]. Thelarge U2AF subunit recognises the intronic polypyrimidine tract, asequence located adjacent to the 3' splice site that serves as an importantsignal for both constitutive and regulated pre-mRNA splicing. The smallsubunit interacts with the 3' splice site dinucleotide AG and is essentialfor regulated splicing. The subunits shuttle continuously between thenucleus and the cytoplasm via a mechanism that involves carrier receptors and is independent of binding to mRNA. Both subunits contain an arginine/serine-rich (RS) domain, which acts as a nuclear localisation signal.Furthermore, the presence of an RS domain on either subunit is sufficient to trigger the nucleocytoplasmic import of the heterodimeric complex [ 2 , 3 , 4 ].

The human form of the U2 auxiliary factor small subunit, hU2AF35, containsa degenerate RNA recognition motif (RRM) and a C-terminal RS domain. Themurine form has been shown to be genomically imprinted with monoallelicexpression from the paternal allele. However, this is not the case inhumans [ 5 ].

1. Pre-spliceosome formation in S.pombe requires a stable complex of SF1-U2AF(59)-U2AF(23). EMBO J. 21, 5516-26
2. Biochemical characterization of U2 snRNP auxiliary factor: an essential pre-mRNA splicing factor with a novel intranuclear distribution. EMBO J. 10, 207-14
3. Identification, purification, and biochemical characterization of U2 small nuclear ribonucleoprotein auxiliary factor. Proc. Natl. Acad. Sci. U.S.A. 86, 9243-7
4. RNA binding activity of heterodimeric splicing factor U2AF: at least one RS domain is required for high-affinity binding. Mol. Cell. Biol. 18, 4004-11
5. Absence of imprinting in U2AFBPL, a human homologue of the imprinted mouse gene U2afbp-rs. Biochem. Biophys. Res. Commun. 222, 171-7