When Escherichia coli cells are cultured in a medium where lactose is absent, the 'i' gene of Lac Operon continues to produce repressor mRNA, because it is
The function of Lac Operon is to control the expression of genes for lactose metabolism. An operon consists of structural genes, operator gene, promoter gene and regulatory gene. The structural genes (lac z, lac y and lac a) code for enzymes responsible for permeability and metabolism of lactose. The operator gene interacts with a protein molecule or regulatory molecule which prevents the transcription of structural genes. The promoter gene has a site where RNA polymerase can attach so that the genes can be transcribed. The regulatory gene produces a repressor protein. It is synthesised all the time from the 'i' gene. Such genes that undergo transcription continuously are called constitutive genes. In the absence of the inducer (lactose) the repressor protein produced from the 'i' gene binds with the operator gene and inhibits the transcription of structural genes. In the presence of the inducer (lactose), the repressor binds with the inducer and does not bind with the operator gene. This results in the transcription of structural genes.