Superinduction of CYP1A1 transcription by cycloheximide. Role of the DNA binding site for the liganded Ah receptor.

Nuclear run-off experiments reveal that four distinct DNA domains, each of which contains a binding site for the liganded Ah receptor, can mediate the superinduction of transcription by 2,3,7,8-tetrachlorodibenzo-p-dioxin plus cycloheximide. Superinduction requires substantial inhibition of protein synthesis by cycloheximide. Gel retardation analyses of nuclear extracts and methylation protection studies in intact cells reveal no evidence for cycloheximide-sensitive protein-DNA interactions that might mediate the superinduction response. These observations suggest the existence of a labile protein(s) that acts to inhibit the function of the dioxin-responsive receptor/enhancer regulatory system via protein-protein interactions.