Final answer:
When lactose binds to the repressor protein of the lac operon, it causes the repressor to release from the operator, enabling RNA polymerase to transcribe the necessary genes for lactose digestion.
Step-by-step explanation:
In the regulation of an operon, specifically the lac operon in E. coli, when lactose molecules bind to the repressor protein, it causes a conformational change in the repressor.
This change reduces the repressor's affinity for the operator region, leading to its release. With the repressor protein no longer bound to the operator, RNA polymerase can bind to the promoter and transcribe the genes necessary for the digestion of lactose, allowing the bacterium to utilize lactose as an energy source.