Very similar results were obtained when an empty plasmid (pUC18) was included in the transfection mixture when only one reporter construct was transfected ( Fig. S1A-C) . Thus, the observed differences in firefly luciferase expression do not result from a lower transfection efficiency of the firefly luciferase, but not of the Gaussia luciferase reporter construct, when an additional plasmid was included in the transfection mixture.