The effect of 5' deletions on the transcriptional activity of the DRD4 promoter in four different cell lines. Significant difference in promoter activity of pDRD4-A could be observed in each cell line relative to construct B (P < 0.001). Luciferase activity was normalized to the β-galactosidase activity. Data are expressed as fold increments over the pGL3-Basic activity and shown as mean ± SD. Results of a representative experiment are shown as measured in triplicates (*P < 0.05, **P < 0.01, ***P < 0.001 versus the corresponding promoterless vector in each cell type.) Similar data were obtained from three independent transfection experiments.