Read the following statement regarding the regulation of the lac operon in E. coli and select the correct option to fill in the blanks. "Lactose is transported into the cell by the action of [X], and it then induces the operon by binding to the [Y]."

Step-by-step solution

The y gene of the lac operon codes for permease, which increases the permeability of the cell to -galactosides (lactose), allowing its transport into the cell. Thus, [X] is permease. Once inside the cell, lactose (or its isomer allolactose) acts as an inducer. It binds to the active repressor protein, altering its structure so that it can no longer bind to the operator region. This allows RNA polymerase to access the promoter and transcribe the operon. Thus, [Y] is the repressor protein. Selecting -galactosidase fo