Which operon is usually off?

An inducible operon is one that is usually off; a molecule called an inducer inactivates the repressor and turns on transcription​ EXAMPLE OF INDUCIBLE OPERON: The lac operon, it contains genes that code for enzymes used in the hydrolysis and metabolism of lactose​. The entire transcription unit is under the control of one main operator and promoter​. A regulatory gene, lacI, located outside the operon encodes a repressor protein that can switch off the operon​. By itself, the lac repressor is active and switches the lac operon off​. A molecule called an inducer inactivates the repressor to turn the lac operon on​. In the case of the lac operon, the inducer is allolactose, an isomer of lactose. Allolactose binds the repressor protein, altering its shape of the repressor so it can no longer bind to the operator sequence​.