PURIFICATION, CHARACTERIZATION, AND CDNA CLONING OF AN AU-RICH ELEMENT RNA-BINDING PROTEIN, AUF1

The degradation of some proto-oncogene and lymphokine mRNAs is control led in part by an AU-rich element (ARE) in the 3' untranslated region. It was shown previously (G. Brewer, Mol. Cell. Biol. 11:2460-2466, 19 91) that two polypeptides (37 and 40 kDa) copurified with fractions of a 130,000 X g postribosomal supernatant (S130) from K562 cells that s electively accelerated degradation of c-myc mRNA in a cell-free decay system. These polypeptides bound specifically to the c-myc and granulo cyte-macrophage colony-stimulating factor 3' UTRs, suggesting they are in part responsible for selective mRNA degradation. In the present wo rk, we have purified the RNA-binding component of this mRNA degradatio n activity, which we refer to as AUF1. Using antisera specific for the se polypeptides, we demonstrate that the 37- and 40-kDa polypeptides a re immunologically cross-reactive and that both polypeptides are phosp horylated and can be found in a complex(s) with other polypeptides. Im munologically related polypeptides are found in both the nucleus and t he cytoplasm. The antibodies were also used to clone a cDNA for the 37 -kDa polypeptide. This cDNA contains an open reading frame predicted t o produce a protein with several features, including two RNA recogniti on motifs and domains that potentially mediate protein-protein interac tions. These results provide further support for a role of this protei n in mediating ARE-directed mRNA degradation.