HuR is a ligand for nuclear mRNAs containing adenylate-uridylate rich elements in the 3'-untranstated region. Once bound to the mRNA, HuR is recognized by adapter proteins which then facilitate nuclear export of the complex. In the cytosol HuR is thought to function to control stability and translation of its ligand message. In the 3T3-L1 cells HuR is constitutively expressed and localized predominantly to the nucleus in the preadipocytes. However within 30 min of exposure to the differentiation stimulus, the HuR content in the cytosol increases consistent with HuR regulating the availability of relevant mRNAs for translation. Using in vitro RNA gel shifts, we have demonstrated that the C/EBP beta message is a ligand for HuR and that the single binding site is an adenylate-uridylate rich element in the 3'-untranslated region. (c) 2007 Elsevier Inc. All rights reserved.