We are testing various promoters in a dual luciferase assay. Surprisingly, a promoter expected to be strong shows very low luminescence for both the test construct AND the control (the levels of BOTH drop about 90% compared to the promoters which are expected to be weaker). Is it possible that a very strong promoter somehow extinguishes cellular resources, or that a very strong luciferase expression is somehow toxic, causing this phenomenon? It's not only saturation, as the sum of the control and test luminescence is much less than with the other test constructs.