Isopropyl β-D-1-thiogalactopyranoside

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Isopropyl β-D-1-thiogalactopyranoside

Identifiers
CAS number	[367-93-1]
PubChem	656894
MeSH	Isopropyl+Thiogalactoside
Properties
Molecular formula	C9H18O5S
Molar mass	238.302
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Isopropyl β-D-1-thiogalactopyranoside, abbreviated IPTG, is a molecular biology reagent.

This compound is used as a molecular mimic of allolactose, a lactose metabolite that triggers transcription of the lac operon. Unlike allolactose, the sulfur (S) atom creates a chemical bond which is non-hydrolyzable by the cell, preventing the cell from "eating up" or degrading the inductant.

IPTG induces the transcription of the gene coding for beta-galactosidase, an enzyme that promotes lactose utilization, by binding and inhibiting the LacI repressor. In cloning experiments, the lacZ gene is replaced with the gene of interest and IPTG is then used to induce gene expression.

Many regulatory elements of the lac operon are used in inducible recombinant protein systems; IPTG is an effective inducer in the concentration range of 100 μM to 1.5 mM.