Experimental bias in the evaluation of the cellular transient expression in DNA co-transfection experiments

beta-Galactosidase (beta-gal) expressing vectors are commonly used to standardize the transfection efficiency in transient expression experiments. In the Chinese hamster ovary (CHO) cell line, we transfected beta-gal expressing vectors in combination with different plasmid DNAs. We reported here that the presence of specific DNAs led to statistically significant variations in the beta-gal expression level. Therefore, the measure of beta-gal activity is not necessarily an accurate method to monitor transfection efficiency, and its use to normalize the expression from reporter genes could be questionable.