Kinetic enhancement of NF-κB·DNA dissociation by IκBα

Abstract

A hallmark of the NF-κB transcription response to inflammatory cytokines is the remarkably rapid rate of robust activation and subsequent signal repression. Although the rapidity of postinduction repression is explained partly by the fact that the gene for IκBα is strongly induced by NF-κB, the newly synthesized IκBα still must enter the nucleus and compete for binding to NF-κB with the very large number of κB sites in the DNA. We present results from real-time binding kinetic experiments, demonstrating that IκBα increases the dissociation rate of NF-κB from the DNA in a highly efficient kinetic process. Analysis of various IκB mutant proteins shows that this process requires the C-terminal PEST sequence and the weakly folded fifth and sixth ankyrin repeats of IκBα. Mutational stabilization of these repeats reduces the efficiency with which IκBα enhances the dissociation rate.