The lac operon (lactose operon) is an essential operon used for the transport and metabolism of lactose in Escherichia coli and some enteric bacteria. It has three adjacent structural genes, lacZ, lacY and lacA. The lacZ gene encodes β-galactosidase. Escherichia coli β-galactosidase is mostly used as a reporter enzyme. It is produced under oxidizing conditions in the cytoplasm of an Origami strain. β-galactosidase occurs in a disulfide bond. at the active site of β-galactosidase a loop opens and closes during catalysis.
