Transient expression of luciferase reporter constructs for the ALAS2 promoter. Firefly luciferase activity was normalized to the activity of the Renilla luciferase as described in “Patients and methods” and expressed as the fold change from the normal promoter activity in the same assay. (A) Expression in K562 cells. (B) Expression in 293T cells. Results are the average of 2 independent experiments with each sample assayed in triplicate. Error bars indicate one standard deviation from the mean.