Next, to analyze whether the observed difference in luciferase protein levels results from differences at the RNA level, we performed a quantitative RT-PCR analysis of the mRNA levels [19] . The results are shown in Figure 2D . The mRNA levels of the Gaussia reporter gene were not affected by co-transfection of the other reporter construct. However, co-transfection of the Gaussia luciferase construct significantly affected mRNA levels of the firefly luciferase gene. From these results we conclude that the observed inhibitory effect of co-transfection of the Gaussia luciferase construct on the firefly luciferase activity is a reflection of lower firefly luciferase mRNA levels.