Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Cysteine Endopeptidases / metabolism*
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DNA-Binding Proteins / isolation & purification
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DNA-Binding Proteins / metabolism*
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HeLa Cells
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Humans
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I-kappa B Proteins*
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Kinetics
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Leupeptins / pharmacology
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Marine Toxins
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Multienzyme Complexes / metabolism*
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Mutagenesis, Site-Directed
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NF-KappaB Inhibitor alpha
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NF-kappa B / antagonists & inhibitors*
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Oxazoles / pharmacology
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Phosphoprotein Phosphatases / antagonists & inhibitors
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Phosphorylation
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Phosphoserine / metabolism
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Proteasome Endopeptidase Complex
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Protein Biosynthesis
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Recombinant Proteins / metabolism
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Ubiquitins / isolation & purification
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Ubiquitins / metabolism*
Substances
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DNA-Binding Proteins
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I-kappa B Proteins
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Leupeptins
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Marine Toxins
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Multienzyme Complexes
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NF-kappa B
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NFKBIA protein, human
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Oxazoles
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Recombinant Proteins
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Ubiquitins
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NF-KappaB Inhibitor alpha
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Phosphoserine
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calyculin A
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Phosphoprotein Phosphatases
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Cysteine Endopeptidases
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Proteasome Endopeptidase Complex
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benzyloxycarbonylleucyl-leucyl-leucine aldehyde