Figure 12.

Nuclear IκB proteins affect transcription by forming NF-κB:IκB:DNA complexes. Wild type IκBα forms stable binary complexes with NF-κB (top left). Mutations on the acidic IκBα acidic PEST C-terminal domain partially favor ternary complexes with NF-κB and DNA. Such ternary complexes have not been seen in vivo (boxed). Nuclear IκBβ forms ternary complexes with NF-κB and DNA only in its hypo-phosphorylated form. These promoter specific complexes induce gene transcription. Bcl-3:NF-κB:DNA ternary complexes occur only when Bcl-3 is phosphorylated. Unphosphorylated Bcl-3 acts like classical IκB proteins in vitro. It is possible that specific phosphatases exist in vivo that convert Bcl-3 into a classical IκB protein. Finally, IκBζ is known as a transcriptional coactivator by forming ternary complexes. It remains to be determined whether it is regulated similarly to the other nuclear IκB proteins.