Isopropyl β-D-thiogalactoside (IPTG) is widely used in molecular biology as a molecular mimic of allolactose, which induces the expression of genes under the control of the lac operon. It is particularly employed in the induction of protein expression in recombinant DNA technology. When added to bacterial cultures, IPTG binds to the lac repressor, causing it to release from the operator region of the lac operon. This allows RNA polymerase to transcribe the downstream genes, including those encoding recombinant proteins of interest. IPTG is favored for this purpose because it is not metabolized by the cells, ensuring a consistent level of induction over time. It is commonly used in the production of proteins for research, industrial applications, and therapeutic purposes. Additionally, IPTG is utilized in blue-white screening to identify bacterial colonies that have successfully incorporated a plasmid with an insert, as it induces the expression of β-galactosidase, which cleaves X-gal to produce a blue color in colonies lacking the insert.