The cAMP receptor protein (CRP) is the factor that mediates the inhibition of the Pu promoter in E. coli.

*The β-galactosidase activity in LB medium with an addition of 0.2 mmol/L mMBA as the inducer was assayed after growing cells at 30°C. Mean values and standard deviations from three independent experiments are shown.†Exogenous cAMP was at a final concentration of 2 mmol/L when added.* 将细胞于30℃下培养后，对添加有0.2 mmol/L mMBA作为诱导剂的LB培养基中的β-半乳糖苷酶（β-galactosidase）活性进行测定。结果展示了三次独立实验的平均值与标准差。†：当添加外源性cAMP（cyclic adenosine monophosphate）时，其终浓度为2 mmol/L。