The PEST-like sequence of I kappa B alpha is responsible for inhibition of DNA binding but not for cytoplasmic retention of c-Rel or RelA homodimers.
In most cells, proteins belonging to the Rel/NF-kappa B family of transcription factors are held in inactive form in the cytoplasm by an inhibitor protein, I kappa B alpha. Stimulation of the cells leads to degradation of the inhibitor and transit of active DNA-binding Rel/NF-kappa B dimers to the nucleus. I kappa B alpha is also able to inhibit DNA binding by Rel/NF-kappa B dimers in vitro, suggesting that it may perform the same function in cells when the activating signal is no longer present. Structurally, the human I kappa B alpha molecule can be divided into three sections: a 70-amino-acid N terminus with no known function, a 205-residue midsection composed of six ankyrin-like repeats, and a very acidic 42-amino-acid C terminus that resembles a PEST sequence. In this study we examined how the structural elements of the I kappa B alpha protein correlate with its functional capabilities both in vitro and in vivo. Using a battery of I kappa B alpha mutants, we show that (i) a dimer binds a single I kappa B alpha molecule, (ii) the acidic C-terminal region of I kappa B alpha is not required for protein-protein binding and does not mask the nuclear localization signal of the dimer, (iii) the same C-terminal region is required for inhibition of DNA binding, and (iv) this inhibition may be accomplished by direct interaction between the PEST-like region and the DNA-binding region of one of the subunits of the dimer.
Ernst
M K
MK
Laboratory of Molecular Virology and Carcinogenesis, National Cancer Institute Frederick Cancer Research and Development Center, Maryland 21702-1201.
Dunn
L L
LL
Rice
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D016384:Consensus Sequence; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D020672:I-kappa B Proteins; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D020569:Proto-Oncogene Proteins c-rel; D051996:Transcription Factor RelA; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D046911:Macromolecular Substances; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C000606205:Nfkbia protein, mouse; D009838:Oligodeoxyribonucleotides; D011518:Proto-Oncogene Proteins; D020569:Proto-Oncogene Proteins c-rel; D051996:Transcription Factor RelA; D014157:Transcription Factors; D000072000:NF-KappaB Inhibitor alpha