The expression of foreign genes can be regulated by cloning them downstream of the lac operator and promoter. IPTG is commonly used in the lab to induce expression of genes regulated by the lac system. This would permit us to study the regulation of this new gene by monitoring beta-galactosidase levels as we vary relevant physiological conditions. The mal operon is under the same sort of positive regulation as the lac operon - a CAP binding site is found just ahead of the mal promoter. The choice, of course, will depend on what sugar is available to consume - maltose, lactose or something else.
Activator proteins induce expression by assisting RNA polymerase in promoter recognition.
In addition, activator binding sites may be located far away from the genes they activate. This system uses a pair of modular proteins to detect and respond to specific environmental signals. The pair of proteins are a sensor kinase and a response regulator. Each of these proteins is in turn composed of two regions. The phosphate is then transferred to a conserved aspartate residue located in the first domain of the response regulator.