Structural determination in AUF1 required for high affinity binding to A + U-rich elements.

AUF1 is a RNA-binding protein that contains two non-identical RNA recognition motifs (RRMs). AUF1 binds to A + U-rich elements (AREs) with high affinity. The binding of AUF1 to AREs is believed to serve as a signal to a mRNA processing pathway which degrades mRNAs encoding many cytokines, oncoproteins and G protein-coupled receptors. Because the ARE-binding activity of AUF1 appears central to the regulation of many important genes, we analyzed the domains of the protein that are important for this activity. Examination of the binding affinity of various mutants indicates that both RRMs may be required for binding. However, they are not sufficient. Highest affinity binding requires an alanine/glycine-rich region of the N-terminus and a short glutamine-rich region in the C-terminus. The N-terminus is required for dimerization of AUF1. However, AUF1 binds an ARE as a hexameric protein. Thus protein-protein interactions are important for high affinity ARE-binding activity of AUF1.