Operons regulatory gene

Figure 39-2. The positional relationships of the structural and regulatory genes of the lac operon. lacZ encodes 3-galactosidase,/ocT encodes a permease, and lacA encodes a thiogalactoside transacetylase. lad encodes the lac operon repressor protein.

Figure 12-4. The lac operon. A simplified version of the lac operon illustrates how activity is regulated by availability of lactose as the sole carbon source. Repressor is the product of the lad regulatory gene. Lactose in the environment is converted to allolactose, which acts as the inducer. The ON state can only occur in the absence of glucose. With repressor inactive (unbound), RNA polymerase can transcribe the structural genes.

An operon thus consists of a series of functionally related structural genes which are turned on and off together, plus their regulatory gene, the operator. This overall... 

Figure 13.1 Operon model for control of protein synthesis. The example chosen is the lactose (lac) operon. I, regulatory gene p, promoter site o, operator gene z, y, and a represent the structural genes for j8-galactosidase, permease, and transacetylase, respectively.

With an operon, a regulatory gene produces either an inducer or a repressor of the operon. A metabolite acts as a co-inducer or co-repressor to affect the transcription of the structural genes. 

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