Signal-induced degradation of I kappa B alpha requires site-specific ubiquitination

Proc Natl Acad Sci U S A. 1995 Nov 21;92(24):11259-63. doi: 10.1073/pnas.92.24.11259.


The inhibitor protein I kappa B alpha controls the nuclear import of the transcription factor NF-kappa B. The inhibitory activity of I kappa B alpha is regulated from the cytoplasmic compartment by signal-induced proteolysis. Previous studies have shown that signal-dependent phosphorylation of serine residues 32 and 36 targets I kappa B alpha to the ubiquitin-proteasome pathway. Here we provide evidence that lysine residues 21 and 22 serve as the primary sites for signal-induced ubiquitination of I kappa B alpha. Conservative Lys-->Arg substitutions at both Lys-21 and Lys-22 produce dominant-negative mutants of I kappa B alpha in vivo. These constitutive inhibitors are appropriately phosphorylated but fail to release NF-kappa B in response to multiple inducers, including viral proteins, cytokines, and agents that mimic antigenic stimulation through the T-cell receptor. Moreover, these Lys-->Arg mutations prevent signal-dependent degradation of I kappa B alpha in vivo and ubiquitin conjugation in vitro. We conclude that site-specific ubiquitination of phosphorylated I kappa B alpha at Lys-21 and/or Lys-22 is an obligatory step in the activation of NF-kappa B.

Publication types

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

MeSH terms

  • Arginine / chemistry
  • Base Sequence
  • Cell Compartmentation
  • Cell Nucleus / metabolism
  • Cells, Cultured
  • Cysteine Endopeptidases / metabolism
  • DNA Primers / chemistry
  • Humans
  • Lymphocyte Activation
  • Lysine / chemistry
  • Molecular Sequence Data
  • Multienzyme Complexes / metabolism
  • NF-kappa B / metabolism*
  • Phosphorylation
  • Phosphoserine / metabolism
  • Proteasome Endopeptidase Complex
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-rel
  • Structure-Activity Relationship
  • Transcription Factor RelB
  • Transcription Factors*
  • Ubiquitins / metabolism*


  • DNA Primers
  • Multienzyme Complexes
  • NF-kappa B
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-rel
  • RELB protein, human
  • Transcription Factors
  • Ubiquitins
  • Transcription Factor RelB
  • Phosphoserine
  • Arginine
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • Lysine