GATA-1 can inhibit transactivation by p53 in 6C2 cells. (A) All samples were transfected with 150 ng of CMV Renilla luciferase and 0.5 μg of p53 Luc reporter plasmid; and 0.25 μg of CMV p53 was added to all but the first sample. Increasing amounts of RSV-Cat, empty RSV expression vector, or RSV hGATA-1 were added (1, 2, and 3 μg of DNA). The dual luciferase reporter assay was performed on aliquots of the samples, and firefly luciferase activity normalized to Renilla luciferase is plotted. The error bars indicate the standard deviations and n = 3. Means of the 2 highest DNA concentrations of RSV-Cat and empty vector were compared with means for equal weights of hGATA-1 by Student t test; *P < .05 and **P < .005. (B) RSV-Cat and hGATA-1 were compared in 6 transfections. Results were normalized to Renilla luciferase activity. The firefly luciferase value for 1 μg of RSV-Cat was then set to 100%, and all other values were normalized to this. The error bars indicate the standard deviation and n = 6. We compared means for equal weights of the 2 highest DNA concentrations of the RSV-Cat and hGATA-1 plasmids to test for statistical significance by Student t test; **P < .005. (C) A comparable transfection was performed adding CMV Renilla luciferase, p53 Luc reporter plasmid, and CMV p53 to all samples and cotransfecting increasing amounts of RSV-Cat or RSV hGATA-1. The cells were divided at harvest, and half were used for the dual luciferase reporter assay and half for Western blotting with HRP-conjugated anti-p53 (top) and with anti-GAPDH antibody (bottom).