Gene Regulation in Prokaryotes

Gene regulation in prokaryotes is most extensively observed at the initiation of transcription. Thus, the gene expression during transcription initiation is affected by regulation. The regulation usually takes place in the expression of the RNA polymerase at the promoter site. This affects the accessory proteins which bind to the recognition sites. These accessory proteins can regulate the promoter site in two ways:

Positive regulation by activators

Negative regulation by repressors

In Operons, the operator is situated right next to the promoter where the regulator binds to control its entire functioning.

Lac Operon Model

Regulation in prokaryotescan be explained with the help of Lac Operon model. Here the alteration in physiological and environmental conditions leading to alteration in expression in prokaryotes can be observed. It was observed by Jacob and Monod. The lac operon consists of:

A regulatory genei– It codes for the repressor protein.

zgene – It codes for beta-galactosidase which catalyzes the hydrolysis of lactose into glucose and galactose.

ygene – It codes for permease which regulates the lactose permeability in the cell.

agene – It codes for transacetylase which assists the enzyme beta-galactosidase.

Hence, all thesegeneshelp in the lactose metabolism. In lac operon, lactose acts as an inducer. If lactose is provided in the medium for the bacteria, the regulatory gene is activated. The inducer will bind to the repressor protein and render it inactive which allows transcription of the operon. Thus, lac operon is negatively regulated in this case.