A ubiquitous factor is required for C/EBP-related proteins to form stable transcription complexes on an albumin promoter segment in vitro.
The liver-enriched transcription factor CCAAT/enhancer binding protein (C/EBP) binds to numerous liver-specific promoters, yet the mechanism by which the protein stimulates transcription has not been described. The serum albumin promoter, which is liver specific, contains a strong C/EBP-binding site tightly juxtaposed to a binding site for the ubiquitous factor nuclear factor-Y (NF-Y). The binding of C/EBP impairs the binding of NF-Y; yet surprisingly, this arrangement leads to strong synergistic activation of a minimal promoter in liver nuclear extracts. Transcriptional synergism is manifested by NF-Y facilitating the ability of C/EBP to form preinitiation complexes that are stable through multiple rounds of transcription. Binding by itself, C/EBP stimulates transcription weakly without forming stable complexes, and moving the NF-Y binding site 10 bp away from the C/EBP site increases NF-Y binding in the presence of C/EBP but reduces the efficiency of stable complex formation and transcriptional synergism. These findings show that C/EBP requires precise positioning next to a ubiquitous factor for optimal formation of stable complexes and provides a model to understand the dramatic activation of the albumin gene in hepatic development.
Milos
P M
PM
Section of Biochemistry, Brown University, Providence, Rhode Island 02912.
Zaret
K S
KS
D000418:Albumins / Q000235:genetics; D001426:Bacterial Proteins; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000235:genetics; D002373:Cyclic AMP Receptor Protein; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D008099:Liver / Q000254:growth & development; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011953:Receptors, Cyclic AMP / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
D000418:Albumins; D001426:Bacterial Proteins; D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D011953:Receptors, Cyclic AMP; D014157:Transcription Factors; D004247:DNA