FAQ: Is T7 expression subject to catabolite repression in BL21(DE3) and derivative strains?

The lambda DE3 prophage carries the T7 RNA polymerase gene (T7gene1). Expression of the T7 RNA Polymerase is controlled by the lacUV5 promoter. Therefore, glucose addition will result in catabolite repression and basal protein expression from T7 promoter vectors will be better controlled when glucose is present in the media. When glycerol is the primary carbon source, there should be no effect on basal T7 expression.