An E. coli strain develops a mutation in the operator region of the lac operon, altering its sequence such that the repressor protein can no longer bind to it. If these bacteria are cultured in a medium completely lacking lactose, what will be the expression status of the operon?

Step-by-step solution

The lac operon is normally under negative regulation. The i gene continuously synthesizes the repressor protein, which binds to the operator region to block RNA polymerase from transcribing the structural genes ( z , y , and a ) when lactose is absent. In this mutant strain, the operator region is altered so the repressor cannot bind to it. Since the repressor cannot block the operator, RNA polymerase will have continuous access to the promoter. This results in the continuous (constitutive) transcription of the z ,