Isopropyl-β-d-thiogalactopyranoside (IPTG) is a kind of nonmetabolizable analog of lactose widely used for heterogeneous gene expression in Escherichia coli system. Lactose, a natural inducer of β-galactosidase gene, is the most popular substitute for IPTG due to its low cost and nontoxicity.
In blue-white screen, IPTG is used together with X-gal. Blue-white screen allows colonies that have been transformed with the recombinant plasmid rather than a non-recombinant one to be identified in cloning experiments.
Isopropyl β-d-1-thiogalactopyranoside is a molecular biology reagent. This compound is a molecular mimic of allolactose, a lactose metabolite that triggers transcription of the lac operon, and it is therefore used to induce protein expression where the gene is under the control of the lac operator.
When stored as a powder at 4°C or below, IPTG is stable for 5 years. It is significantly less stable in solution; Sigma recommends storage for no more than a month at room temperature.
