Lac repressor can bind to 

Lac repressor is an allosteric protein. It can reversibly bind to both operator (DNA sequence) and to the disaccharide lactose. It has operator binding site and lactose binding site. When bound to lactose, it shows conformational change at the operator binding site and can not bind to or detach from operator. In lactose free conditions, it can bind to operator to prevent transcription of structural genes cluster.