A regulator gene-minus strain of E. coli is constitutive for expression of the lac-operon because the repressor cannot bind tothe operator region even when lactose is present. By bacterialconjugation, it is possible to introduce into the regulator-minusstrain a wild type or regulator-plus gene, which can betranscribed.

What effect does lactose have on expression of the lac-operon in the bacteria containing both types of regulator genes? Explain youranswer.