Control of cytochrome P1-450 gene expression: analysis of a dioxin-responsive enhancer system.

We analyzed the function and sequence of a dioxin-responsive genomic element flanking the 5' end of the cytochrome P1-450 gene in high-activity variant mouse hepatoma cells. The element can regulate the mouse mammary tumor virus promoter. The element retains responsiveness to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) when the distance, the 5' or 3' position, and/or the 5' or 3' orientation with respect to the promoter are varied. The function of the element requires TCDD-receptor complexes. The element remains responsive to TCDD when transfected into cells from either a heterologous mouse tissue or a heterologous species (human). The DNA element and TCDD receptors together constitute a dioxin-responsive enhancer system.