IkB-alpha protein is a NF-kB inhibitory protein. It binds NF-kB and retains the complex in the cytoplasm, thereby preventing it from entering into nucleus and functioning as a transcription factor. Upon receiving a variety of signals, IkB-alpha undergoes phosphorylation at serine residues by an ubiquitin-dependent protein kinases and finally degraded by the proteasome. Free NF-kB then binds DNA and affects gene expression.