The NF-kappa B p50 precursor, p105, contains an internal I kappa B-like inhibitor that preferentially inhibits p50

EMBO J. 1992 Aug;11(8):3003-9.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Cell Line
  • Electrophoresis, Polyacrylamide Gel
  • Glutathione Transferase / isolation & purification
  • Glutathione Transferase / metabolism
  • Humans
  • Immunoblotting
  • Kinetics
  • Macromolecular Substances
  • Molecular Sequence Data
  • NF-kappa B / genetics*
  • NF-kappa B / isolation & purification
  • NF-kappa B / metabolism*
  • Polymerase Chain Reaction / methods
  • Protein Biosynthesis
  • Protein Precursors / genetics*
  • Protein Precursors / isolation & purification
  • Protein Precursors / metabolism*
  • Recombinant Fusion Proteins / isolation & purification
  • Recombinant Fusion Proteins / metabolism
  • Repetitive Sequences, Nucleic Acid
  • Sequence Homology, Nucleic Acid
  • Transcription, Genetic


  • Macromolecular Substances
  • NF-kappa B
  • Protein Precursors
  • Recombinant Fusion Proteins
  • Glutathione Transferase