PURIFICATION, CLONING, AND EXPRESSION OF A MURINE PHOSPHOPROTEIN THATBINDS THE KAPPA-B MOTIF IN-VITRO IDENTIFIES IT AS THE HOMOLOG OF THE HUMAN HETEROGENEOUS NUCLEAR RIBONUCLEOPROTEIN K-PROTEIN - DESCRIPTION OF A NOVEL DNA-DEPENDENT PHOSPHORYLATION PROCESS

The kappa B enhancer element regulates expression of many genes involv ed in immune responses and other processes. kappa B motif binds a numb er of proteins, some but not all, are related to the NF-kappa B family of transcription factors. We have previously identified a 65-kDa phos phoprotein that is specifically recognized by the kappa B motif (Ostro wski, J., Sims, J. E., Sibley, C. H., Valentine, M. A., Dower, S. K., Meier, K. E., and Bomsztyk, K. (1991) J. Biol. Chem. 266, 12722-12733) . This protein is closely associated with a serine/threonine kinase th at is responsive to treatment of cells with interleukin-1 and other ag ents. We report here purification, cloning, and expression of this kap pa B motif-binding phosphoprotein. The primary structure deduced from the isolated murine cDNA, identifies the protein as the homolog of the human heterogeneous nuclear ribonucleoprotein K protein. Antipeptide antibodies and expression of the cloned cDNA in Escherichia coli, demo nstrated that the K protein is the authentic phosphoprotein that binds the kappa B motif in vitro. We also demonstrate that the in vitro pho sphorylation of the natural and the recombinant K proteins by the asso ciated kinase is stimulated by the kappa B motif.