STRUCTURAL DETERMINANTS IN AUF1 REQUIRED FOR HIGH-AFFINITY BINDING TOA-RICH ELEMENTS(U)

AUF1 is an RNA binding protein that contains two nonidentical RNA reco gnition motifs (RRMs), AUF1 binds to A + U-rich elements (AREs) with h igh affinity. The binding of AUF1 to AREs is believed to serve as a si gnal to an mRNA-processing pathway that degrades mRNAs encoding many c ytokines, oncoproteins, and G protein-coupled receptors, Because the A RE binding activity of AUF1 appears central to the regulation of many important genes, we analyzed the domains of the protein that are impor tant for this activity. Examination of the RNA binding affinity of var ious AUF1 mutants suggests that both RRMs may be required for binding to the human c-fos ARE. However, the two RRMs together are not suffici ent, Highest affinity binding of AUF1 to an ARE requires an alanine-ri ch region of the N terminus and a short glutamine-rich region in the C terminus. In addition, the N terminus is required for dimerization of AUF1, However, AUF1 binds an ARE as a hexameric protein. Thus, protei n-protein interactions are important for high affinity ARE binding act ivity of AUF1.