Activity of theKCC1gene promoter in erythroid and nonerythroid cell lines in transient transfection assays. Plasmids containing 5′ flanking DNA of the KCC1 gene inserted upstream of the firefly luciferase gene were transfected into K562 or HeLa cells as described in “Materials and methods.” Relative luciferase activity was expressed as that obtained from the test plasmids compared with the activity obtained from the promoterless plasmid pGL2B plasmid, taking into account the transfection efficiency. Data are mean ± SD of at least 6 independent transfection experiments.