In the absence of lactose, the lac operon is activated by the binding of the repressor protein to the operator region, allowing RNA polymerase to transcribe the genes.

The lac operon is an example of positive gene regulation only, where the presence of lactose directly stimulates RNA polymerase binding to the promoter without the involvement of any repressor proteins. 

The presence of lactose induces the lac operon by binding to the repressor protein, causing a conformational change that prevents the repressor from binding to the operator region, thereby allowing transcription. 

In the presence of glucose and lactose, the lac operon is fully activated due to the inactivation of the repressor protein and the binding of the catabolite activator protein (CAP) to the promoter region.