IPTG

IPTG, or isopropyl β-D-1-thiogalactopyranoside, is a synthetic thiogalactoside that acts as a gratuitous inducer of the lac operon. It binds with high affinity to the lac repressor (LacI), preventing repression of lac-, lacUV5-, and tac-based promoters and allowing transcription of downstream genes. Unlike the natural inducer lactose, IPTG is not readily metabolized by Escherichia coli, so it provides sustained induction even in the presence of the inducer.

In molecular biology, IPTG is widely used to initiate expression of recombinant proteins in bacterial systems, particularly with vectors that place the gene under control of lac-based promoters or the T7 expression system. It is typically added to cultures at concentrations ranging from about 0.1 to 1 mM, with common working concentrations around 0.1–0.5 mM. IPTG stocks are usually prepared in water and added to the culture at the chosen growth stage, often during mid-log phase to balance cell health and expression levels.

Limitations and considerations include variability in induction strength due to promoter variants, plasmid copy number, host strain, and growth conditions. High-level expression can cause cellular stress or formation of inclusion bodies; reducing induction temperature or using gradual or lower-concentration induction can improve protein solubility. As a non-metabolizable inducer, IPTG remains effective for sustained expression, but researchers should optimize conditions for each system. Safety and handling are in line with standard laboratory chemical reagents.