Binding of lactose to the repressor protein in the lac operon leads to _ of the repressor protein or allosteric regulation of the repressor's protein activity

Conformation change

Explanation:

Repressor protein in the absence of lactose binds to the operator region of the lac operon and does not allow the RNA polymerase to bind to the promoter and start the transcription of lac gene.

In the presence of lactose or allolactose, the repressor protein is not able to bind to the operator region because lactose binds to the active site of repressor protein which results in a conformation change in the repressor protein.

So as the shape of the repressor protein gets changed it do not able to bind to the operon operator and the operon is expressed.