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Gene expression is a strictly regulated process that is altered in response to developmental cues, therapeutic drugs, environmental changes, or diseases. Gene regulation is critical for an organism to optimize their metabolic activity and respond to changes in various extracellular and intracellular signals. The pioneering work by Francois Jacob and Jacques Monod in 1961 depicted a classic example of how genetic mechanisms can be altered in response to changing environmental stimulants to regulate bacterial metabolic activities. The operon model depicting this phenomenon was based on lactose metabolism in Escherichia coli.[1] Genes involved in bacterial metabolic pathways are clustered together and coordinately transcribed under a common promoter. These structural genes, the promoter, and additional sequences that regulate their expression are called operons. Clustering allows coordinated regulation and expression of the genes and provides rapid adaptation to various environmental changes. An inducible operon is one whose expression increases quantitatively in response to an enhancer, an inducer, or a positive regulator. The lac operon is a classic example of an inducible operon. It is induced by lactose and its structural analogs: isopropyl beta-D-1 thiogalactopyranoside (IPTG) and thiomethyl galactoside (TMG) (See Video. Lac Operon and its Regulatory Elements).[2][3] Many other inducible operons have been identified since the introduction of the operon model, which plays a key role in bacterial metabolism and survival against host defense mechanisms. Examples include the gal operon regulating galactose metabolism induced in the presence of D-galactose and the L-arabinose operon metabolizing arabinose and induced by it.[4][5]