 Solution

The empty expression plasmid controls for introducing the vector and transfection reagents without adding either TCF transcription factor isoform. It establishes reporter activity supported by endogenous factors and, when used to balance DNA amounts, controls total plasmid load between conditions. Changes relative to this baseline can then be attributed more specifically to the expressed transgene. It is not a substitute for an independent normalization reporter or for checking that the two transgenes produce comparable amounts of functional protein.