D1thiogalactopyranoside

Isopropyl β-D-1-thiogalactopyranoside, commonly known as IPTG, is a synthetic inducer used to activate gene expression in bacteria. It is a non-metabolizable analog of lactose and a thiogalactoside; IPTG binds the lac repressor LacI with high affinity, causing a conformational change that releases repression at the operator and enables transcription of downstream genes. Because IPTG is not hydrolyzed by β-galactosidase, it remains in the culture and provides a stable induction signal.

IPTG is widely used with lac-based promoters, including lac, lacUV5, and lac-controlled T7 expression systems. Induction is typically achieved by adding IPTG to mid-log phase cultures at final concentrations around 0.1–1 mM, with the exact amount chosen based on promoter strength and desired expression level. Its non-metabolizable nature generally yields more uniform induction than lactose.

Chemical handling and storage: IPTG is usually supplied as a solid or as an aqueous stock solution (for example, 0.5 M). Stocks are stored at 4°C for short-term use or at −20°C for long-term storage, and should be protected from light. Working solutions are prepared as needed and used with standard laboratory PPE. Safety data should be consulted for specific precautions.

Applications: IPTG is a standard tool in molecular biology for controlled expression of recombinant proteins and other genes in bacteria, contributing to cloning workflows and protein production pipelines where predictable, tunable induction is required.