Protein-DNA interactions at a dioxin-responsive enhancer. Mutational analysis of the DNA-binding site for the liganded Ah receptor.
The liganded Ah receptor activates transcription by binding to a specific DNA-recognition motif within a dioxin-responsive enhancer upstream of the CYP1A1 gene. Analyses of mutant enhancers by gel retardation reveal that each base pair within the domain 5'CGTG(GCAC)3' is essential to the receptor-enhancer interaction. The three base pairs immediately flanking each end of the essential domain contribute less strongly to receptor binding. Analyses of enhancer function by transfection reveal that a mutation in the essential domain, which abolishes receptor-DNA binding, obliterates enhancer function. Mutations outside the essential domain, which diminish, but do not abolish, receptor-DNA binding, also obliterate enhancer function. Additionally, one mutation adjacent to the essential binding motif does not affect receptor-DNA binding, but destroys enhancer activity. These findings imply that transcriptional enhancement by the dioxin-responsive system cannot be predicted solely by the strength of the receptor-enhancer interaction.
Shen
E S
ES
Department of Pharmacology, Stanford University School of Medicine, California 94305-5332.
Whitlock
J P
JP
D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D008024:Ligands; D008969:Molecular Sequence Data; D009154:Mutation; D000072317:Polychlorinated Dibenzodioxins / Q000378:metabolism*; D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug / Q000378:metabolism*
D004268:DNA-Binding Proteins; D008024:Ligands; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug; D004247:DNA