Summary of in vivo footprints of the γ-globin gene promoter observed with butyrate treatment. Canonical elements are boxed. Closed and stippled symbols are for sickle cell anemia and β-thalassemia, respectively. Symbols: circles, footprinted G residues; triangles, G residues hyperreactive to DMS. Asterisks indicate sites of mutations that result in HPFH. The transcriptional start site of the γ-globin gene is denoted by the arrow.