Question

Predict what will happen to the expression of β-galactosidase (lacZ gene) in a mutant strain lacking lacY-gene. Remember cells are not able to produce LacY-protein and can not transport lactose:

lacZ gene will be expressed only when both lactose and glucose are present.

lacZ gene will not be expressed.

lacZ gene will be expressed only in the presence of lactose; maximum expression will be observed in the absence of glucose.

lacZ gene will not be repressed; maximum expression will be observed in the absence of glucose.

lacZ gene will not be repressed; maximum expression will be observed in the presence of glucose.

Answer 1

Answer : lacZ gene will not be expressed

As there is Mutation in lacY gene, cell is unable to produce permease, which function is to transport lactose inside the cell. (Remember lactose is the inducer of the Operon, as lactose binds to the lac repressor making repressor inactive) so lactose cannot be transported in this cell. If there is no lactose inside the cell, lac repressor will not be inactivated ever, and will bind to operator, making lac Operon OFF always (Unless lacY gene is complemented).