Why would it be useful to clone a gene into a plasmid under the control of an inducible promoter?
The correct answer and explanation is:
The correct answer is that cloning a gene into a plasmid under the control of an inducible promoter allows controlled expression of the gene, meaning the gene can be turned on or off at will by adding or removing an inducer.
Using an inducible promoter in molecular biology provides researchers with precise control over when and how much of a gene product is produced. Many genes, especially those encoding proteins that might be toxic to the host cells or that could interfere with normal cellular processes, should not be expressed continuously. If such genes were cloned under the control of a constitutive promoter, which is always active, the host cells might suffer growth defects or die because of the constant production of the foreign protein. An inducible promoter solves this by keeping the gene silent until expression is needed.
For example, a common inducible system uses the lac operon in bacteria, which can be activated by adding IPTG, a molecular mimic of allolactose. When IPTG is added to the culture medium, it binds to the repressor protein that normally blocks transcription, freeing the promoter and allowing RNA polymerase to transcribe the gene of interest. This allows researchers to grow the bacterial culture to a desired density before triggering expression, ensuring a high yield of cells before diverting resources to produce the recombinant protein.
Inducible promoters also help optimize experimental conditions. Researchers can test different induction times and inducer concentrations to maximize protein yield or produce enough material for downstream applications like purification or functional studies. This flexibility is valuable in research and industrial biotechnology where large amounts of proteins such as enzymes, vaccines, or therapeutic agents are produced. Overall, an inducible promoter provides both safety for the host organism and practical control for the scientist.