Effect of in vitro methylation on the activity of human AC133 promoters. AC133 promoter 1 (–1100/+10) and promoter 2 luciferase constructs were mock methylated or methylated with SssI methylase. Both methylated and mock-methylated constructs were transiently transfected into the Caco-2 cell line, and luciferase activity was measured and normalized to the activity of the methylated and mock-methylated pGL3-enhancer vector, respectively. All data represent the mean of 3 independent experiments. Error bars represent standard deviation.