This animation shows how lac operon works.-galactosidase is also found in many other microorganisms, plants and animals, including humans. ß-galactosidase catalyzes the breakdown of the substrate lactose into two products, galactose and glucose. An operon is a cluster of bacterial genes along with an adjacent promoter that controls the transcription of those genes. The operator is a short region of DNA that lies partially within the promoter and that interacts with a regulatory protein that controls the transcription of the operon. The regulatory gene lacI produces an mRNA that produces a Lac repressor protein, which can bind to the operator of the lac operon.