NF-jB essential modulator (NEMO) plays an essential role in the nuclear factor jB (NF-jB) pathway as a modulator of the two other subunits of the IjB kinase (IKK) complex, . the protein kinases, IKKa and IKKb. Previous reports all envision the IKK complex to be a static entity. Using glycerol-gradient ultracentrifugation, we observed stimulus-dependent dynamic IKK complex assembly.