Identification of two polypeptide segments of CCAAT/enhancer-binding protein required for transcriptional activation of the serum albumin gene.
We used molecular genetic methods to generate systematically altered forms of CCAAT/enhancer-binding protein (C/EBP). The aim of our experiments was to identify regions of C/EBP that contribute to its capacity to activate transcription from the promoter of the serum albumin gene in cultured hepatoma cells. Earlier experiments had shown that the DNA-binding domain must remain intact for C/EBP to activate albumin transcription. We now provide evidence of two additional elements of C/EBP that are required for its gene-activating role. One such element occurs within a 28-residue region located close to the amino terminus of the protein. The other maps to a broader, more internal region of the protein and appears to exhibit functional redundancy. These newly defined elements of C/EBP exhibit two characteristics of "activation" domains delineated in studies of other gene regulatory proteins. First, they play no obvious role in the capacity of C/EBP to bind to its DNA substrate. Second, they retain function after being appended onto the DNA-binding domain of a different protein. Neither of these putative activating elements is characterized by overt distinction in either charge or preponderance of any particular amino acid. The more amino-terminal element does, however, exhibit several features suggesting that it may assume an alpha-helical structure. These studies offer observations and reagents that will be valuable for future studies concerning the physiologic function of C/EBP.
Friedman
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Howard Hughes Research Laboratories, Department of Embryology, Carnegie Institution of Washington, Baltimore, Maryland 21210.
McKnight
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D000595:Amino Acid Sequence; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D005796:Genes; D006801:Humans; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D012709:Serum Albumin / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D012709:Serum Albumin; D014157:Transcription Factors