I have been doing research to design a reporter assay (with luciferase as my reporter). I see that renilla is typically a control as part of a dual luciferase system. To me, it seems that both genes should be on a single plasmid but most often it seems that people are co-transfecting two separate plasmids. Is this correct? Which is the preferred method? If both genes are on one vector what vector would you recommend (I want to do enhancer and promoter assays)?