THE SIGNAL RESPONSE OF I-KAPPA-B-ALPHA IS REGULATED BY TRANSFERABLE N-TERMINAL AND C-TERMINAL DOMAINS

I kappa B alpha retains the transcription factor NF-kappa B in the cyt oplasm, thus inhibiting its function. Various stimuli inactivate I kap pa B alpha by triggering phosphorylation of the N-terminal residues Se r32 and Ser36. Phosphorylation of both serines is demonstrated directl y by phosphopeptide mapping utilizing calpain protease, which cuts app roximately 60 residues from the N terminus, and by analysis of mutants lacking one or both serine residues. Phosphorylation is followed by r apid proteolysis, and the liberated NF-kappa B translocates to the nuc leus, where it activates transcription of its target genes. Transfer o f the N-terminal domain of I kappa B alpha to the ankyrin domain of th e related oncoprotein Bcl-3 or to the unrelated protein glutathione S- transferase confers Signal-induced phosphorylation on the resulting ch imeric proteins. If the C-terminal domain of I kappa B alpha is transf erred as well, the resulting chimeras exhibit both signal-induced phos phorylation and rapid proteolysis. Thus, the signal response of I kapp a B alpha is controlled by transferable N-terminal and C-terminal doma ins.