THE P50 SUBUNIT OF NF-KAPPA-B ASSOCIATES WITH THE NF-IL6 TRANSCRIPTION FACTOR

The NF-kappa-B-p50 polypeptide, a member of the Rel family of transcription factors, was produced as a fusion protein containing amino-terminal peptide additions that facilitate purification and detection with a monoclonal antibody and specific radiolabeling by phosphorylation in vitro. The P-32-labeled NF-kappa-B-p50 fusion polypeptide was used as the probe in Western blotting experiments and in screenings of a bacteriophage expression library to isolate cDNAs encoding interacting protein domains. As expected, cDNAs encoding proteins of the Rel family were identified. Surprisingly, the P-32-labeled NF-kappa-B protein also specifically bound to proteins encoded by cDNAs for the human NF-IL6 transcription factor. The NF-kappa-B-p50 and NF-IL6 proteins directly interact, and the Rel homology domain and leucine-zipper motif, respectively, are important for this interaction. Since induction of the NF-kappa-B and NF-IL6 factors are important events in immune and acute-phase responses, this interaction could permit coregulation of genes.