The lactose operon repressor is a DNA binding protein that
functions to regulate the expression of the Lac operon.
In the absence of lactose it inhibits the expression of the genes
lacZ-lacY-lacA which code for the lactose-degrading enzymes of the
operon by binding to the operator region of the Lac operon, thus
hindering RNA polymerase from binding to the Lac promoter.
The repressor is inactivated by lactose which binds to the
repressor. This causes a confomational change that prevents it from
binding to the operator region.