Protein-DNA Interactions at Recognition Sites for the Dioxin-Ah Receptor Complex

Gel retardation analyses reveal a cluster of six binding sites for the liganded Ah receptor within a 700-base pair DNA domain upstream of the mouse CYP1A1 gene. The nucleotide sequences of the binding sites define a consensus recognition motif for the liganded receptor. The consensus motif is not symmetric. Alteration of the consensus motif produces a decrease in the receptor-DNA interaction. The ligand receptor binds as a monomer to its recognition motif and preferentially binds to double-stranded DNA. These observations reveal apparent differences between 2,3,7,8-tetrachlorodibenzo-p-dioxin and steroid hormones in their respective mechanisms of action.