Structure of the human Epo gene. Exons are indicated by solid black boxes; 5′ and 3′ untranslated regions are indicated by open rectangles. Areas of homology between human and murine noncoding sequences are shown with blue rectangles, and the region of liver specific DNase I hypersensitivity is shown with a green rectangle. The 3′ enhancer is expanded for greater detail. Sites that are functionally critical for hypoxic induction are underscored in red. Binding of HIF-1, HNF-4, and p300 is illustrated. As indicated by the arrow, p300 is capable of interacting with the basal transcriptional machinery in the promoter.