The Lac operator is a protein binding site for the lac operon
repressor which work to regulate the expression of the Lac operon.
In the absence of lactose the repressor binds to the operator
region which leads to the inhibition of the expression of the genes
lacZ-lacY-lacA, which code for the lactose-degrading enzymes of the
operon by hindering RNA polymerase from binding to the Lac
The repressor is inactivated in the presence of lactose which binds
to the repressor. This causes a confomational change that prevents
it from binding to the operator region.