The NF-kappa B p50 precursor, p105, contains an internal I kappa B-like inhibitor that preferentially inhibits p50.
The p50 subunit of NF-kappa B is apparently synthesized as a precursor molecule of 105 kDa (p105); subsequent processing releases the amino-terminal p50 polypeptide with rel homology, DNA binding activity and transcriptional activation potential. The carboxy-terminal region of p105 contains seven copies of an ankyrin-related sequence previously found in several genes involved in differentiation and cell cycle control. Two proteins with I kappa B activity, MAD-3 and pp40, have been cloned and found to contain five obvious ankyrin repeats that align with those in the carboxy-terminus of p105. Both proteins target their inhibitory activity to the p65 subunit of NF-kappa B and to c-rel. Here we show that the bacterially expressed and purified carboxy-terminal region (CTR) of p105 abolishes the binding of p50 homodimers to a kappa B motif but minimally affects the binding of p65 homodimers and NF-kappa B. By contrast, MAD-3 inhibits the binding of p65 and NF-kappa B but not p50. Both the CTR and MAD-3 interact with their respective targets through physical association both in vitro and in vivo. The CTR can be expressed as an independent entity and thus may play two roles, as a cis inhibitor built into the p105 molecule and as a trans regulator of p50.
Liou
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Rockefeller University, New York, NY 10021.
Nolan
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Ghosh
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Fujita
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Baltimore
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D000595:Amino Acid Sequence; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D005982:Glutathione Transferase / Q000302:isolation & purification / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007700:Kinetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D016133:Polymerase Chain Reaction / Q000379:methods; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
D046911:Macromolecular Substances; D016328:NF-kappa B; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; D005982:Glutathione Transferase