The pG5luc Vector contains five GAL4 binding sites upstream of a minimal TATA box, which in turn is upstream of the firefly luciferase gene. The pGAL4 and pVP16 fusion constructs are transfected along with the pG5luc Vector into mammalian cells. Two to three days after transfection, the cells are lysed, and the amount of Renilla luciferase and firefly luciferase are quantitated using the Dual-Luciferase Reporter Assay System. Interaction between the two test proteins, expressed as GAL4 and VP16 fusion constructs, results in an increase in firefly luciferase expression as compared to the negative controls.