Nuclear factor κB(NF-κB) is an important transcriptional factor and maintains in a cytoplasmically localized inactive state by the inhibitory protein κB(IκB). Following stimulation, NF-κB and IκB import into nucleus through nuclear pore complexes(NPC),mediated by nuclear localization signal(NLS), respectively. In nucleus, IκB binds to NF-κB again. Dependent on the CRM1 pathway, the complexes export from nucleus to cytoplasm, mediated by nuclear export signal(NES). Nucleocytoplasmic transport of complexes is an energy-dependent process which involves small Ran protein and several soluble factors.