Allolactose, an isomer of lactose, is formed in small amounts from lactose. An E. coli cell is presented for the first time with the sugar lactose (containing allolactose) as a potential food source. Which of the following occurs when lactose enters the cell? Allolactose, an isomer of lactose, is formed in small amounts from lactose. An E. coli cell is presented for the first time with the sugar lactose (containing allolactose) as a potential food source.
Which of the following occurs when lactose enters the cell?

a. Allolactose binds to the regulator gene.
b. Allolactose binds to the repressor protein.
c. RNA polymerase attaches to the regulator.
d. The repressor protein attaches to the regulator.
e. The repressor protein and allolactose bind to RNA polymerase.

Allolactose is an inducer of the lac operon. It binds to the repressor protein and brings about some changes in its confirmation to render it unable to bind to the operator sequence. RNA polymerase enzyme is allowed to transcribe the lac operon. The operator sequence is a binding site for repressor protein and is present near the promoter. When lactose is not present in the medium, repressor protein binds to the operator sequence and does not allow the RNA polymerase to transcribe lac operon.