In an inducible operon, what is the role of the inducer?

• A. Binds to repressor to inactivate it, allowing transcription.
• B. Binds to RNA polymerase to start transcription.
• C. Degrades the mRNA after transcription.
• D. Recruits histones to condense chromatin.

Answer: (A)

Inducible operons are controlled by a repressor that sits on the operator to block transcription. The inducer binds to that repressor, changing its shape so it can no longer bind the operator. With the operator unblocked, RNA polymerase can access the promoter and transcribe the genes. This is why the presence of the inducer turns transcription on. A classic example is the lac operon, where allolactose acts as the inducer and inactivates the LacI repressor when lactose is present, allowing expression of the lactose-metabolizing genes. The inducer’s role is not to recruit RNA polymerase or to degrade mRNA, and bacteria don’t use histones to condense DNA, so those ideas don’t fit.