InR and DPE are both critical for hKCC1 promoter function. (A) Plasmids containing minimal hKCC1 gene promoter fragments inserted upstream of the firefly luciferase gene were transfected into HeLa cells and luciferase activity was determined as described in “Materials and methods.” Mutations are marked with the letter X. See “Materials and methods” for details. Data are mean ± SD of at least 6 independent transfection experiments. (B) Plasmids containing either a minimal wild-type hTAF_II55 promoter fragment or an hTAF_II55 promoter fragment with the InR and DPE elements replaced by the human KCC1 InR and DPE elements, inserted upstream of the firefly luciferase gene, were transfected into HeLa cells, and luciferase activity was determined as described.