AUF1 BINDING-AFFINITY TO A-RICH ELEMENTS CORRELATES WITH RAPID MESSENGER-RNA DEGRADATION(U)

Rapid degradation of many labile mRNAs is regulated in part by an A+U- rich element (ARE) in their 3'-untranslated regions. Extensive mutatio nal analyses of various AREs have identified important components of t he ARE, such as the nonamer motif UUAUUUAUU, two copies of which serve as a potent mRNA destabilizer. To investigate the roles of trans-acti ng factors in ARE-directed mRNA degradation, we previously purified an d molecularly cloned the RNA binding protein AUF1 and demonstrated tha t both cellular and recombinant AUF1 bind specifically to AREs as show n by UV cross-linking assays in vitro. In the present work, we have ex amined the in vitro RNA-binding properties of AUF1 using gel mobility shift assays with purified recombinant His(6)-AUF1 fusion protein. We find that ARE binding affinities of AUF1 correlate with the potency of an ARE to direct degradation of a heterologous mRNA, These results su pport a role for AUF1 in ARE directed mRNA decay that is based upon it s affinity for different AREs.