Signal-induced site-specific phosphorylation targets I kappa B alpha to the ubiquitin-proteasome pathway.
The transcription factor NF-kappa B is sequestered in the cytoplasm by the inhibitor protein I kappa B alpha. Extracellular inducers of NF-kappa B activate signal transduction pathways that result in the phosphorylation and subsequent degradation of I kappa B alpha. At present, the link between phosphorylation of I kappa B ... alpha and its degradation is not understood. In this report we provide evidence that phosphorylation of serine residues 32 and 36 of I kappa B alpha targets the protein to the ubiquitin-proteasome pathway. I kappa B alpha is ubiquitinated in vivo and in vitro following phosphorylation, and mutations that abolish phosphorylation and degradation of I kappa B alpha in vivo prevent ubiquitination in vitro. Ubiquitinated I kappa B alpha remains associated with NF-kappa B, and the bound I kappa B alpha is degraded by the 26S proteasome. Thus, ubiquitination provides a mechanistic link between phosphorylation and degradation of I kappa B alpha.
Mesh Terms:
Cysteine Endopeptidases, DNA-Binding Proteins, Hela Cells, Humans, I-kappa B Proteins, Kinetics, Leupeptins, Multienzyme Complexes, Mutagenesis, Site-Directed, NF-kappa B, Oxazoles, Phosphoprotein Phosphatases, Phosphorylation, Phosphoserine, Proteasome Endopeptidase Complex, Protein Biosynthesis, Recombinant Proteins, Ubiquitins
Cysteine Endopeptidases, DNA-Binding Proteins, Hela Cells, Humans, I-kappa B Proteins, Kinetics, Leupeptins, Multienzyme Complexes, Mutagenesis, Site-Directed, NF-kappa B, Oxazoles, Phosphoprotein Phosphatases, Phosphorylation, Phosphoserine, Proteasome Endopeptidase Complex, Protein Biosynthesis, Recombinant Proteins, Ubiquitins
Genes Dev.
Date: Jul. 01, 1995
PubMed ID: 7628694
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