The adenosine-uridine binding factor recognizes the AU-rich elements of cytokine, lymphokine, and oncogene mRNAs.

Selective mRNA degradation is an important control point in the transient expression of a variety of mRNAs coding for growth regulators. A variety of labile mRNAs coding for lymphokines, cytokines, and oncogenes contain within their 3'-untranslated region an AU-rich region shown to destabilize these messages. We recently identified a cytosolic protein, adenosine-uridine binding factor (AUBF), which complexes with four tandem AUUUA reiterations of a synthetic RNA transcript. We now show that AUBF forms RNase T1-resistant band-shifted complexes with a variety of in vitro transcribed mRNAs including granulocyte-macrophage colony-stimulating factor, interferon-gamma, interleukin-3, c-fos, and v-myc. Formation of complexes was specifically inhibited by AUUUA containing RNA, but not by irrelevant RNA. After brief ultraviolet light-induced cross-linking, AUBF.RNA complexes with the exception of c-fos comigrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Mutations within the AUUUA motifs demonstrate that both nucleotide sequence and secondary structure are important in AUBF.AUUUA RNA complex formation. Based upon these data, we suggest AUBF may interact with a variety of labile mRNAs with multiple AUUUA reiterations or single reiterations within an AU-rich 3'-untranslated region.