Isopropyl β-D-1-thiogalactopyranoside

Isopropyl β-D-1-thiogalactopyranoside (IPTG) is a synthetic analog of lactose that is widely used in molecular biology and biotechnology for the induction of gene expression where the lac operon is under control of the lac repressor. IPTG is not hydrolyzed by the β-galactosidase enzyme, making it an efficient inducer that is not consumed or depleted during the process. This property makes IPTG extremely useful in the field of recombinant protein production, particularly in the expression of cloned genes in Escherichia coli and other bacteria.

Structure and Function

IPTG mimics the structure of lactose, allowing it to bind to the lac repressor with high affinity. When IPTG is present, it binds to the lac repressor, causing a conformational change that releases the repressor from the lac operator. This derepression allows for the transcription of the operon's genes, including those coding for β-galactosidase, permease, and transacetylase. Unlike lactose, IPTG is not a substrate for β-galactosidase, so it remains in the cell to continuously induce expression.

Applications in Molecular Biology

IPTG is extensively used in cloning and protein expression protocols. It is particularly valuable in the production of recombinant proteins where tight control of gene expression is necessary. By adding IPTG to the growth medium of bacteria carrying a plasmid with an IPTG-inducible promoter, researchers can precisely control the timing and level of gene expression. This is crucial for producing high yields of protein while minimizing the metabolic burden on the host cells.

Preparation and Usage

IPTG is typically used at concentrations ranging from 0.1 to 1 mM in culture media. The exact concentration and induction time can vary depending on the host strain, target protein, and expression system. It is soluble in water, and stock solutions are usually prepared at high concentrations (e.g., 1 M) and stored at -20°C for long-term use.

Safety and Handling

While IPTG is generally considered safe for laboratory use, it should be handled with care. Appropriate personal protective equipment, such as gloves and goggles, should be worn to avoid skin and eye contact. Waste disposal should follow institutional guidelines and regulations.

See Also

• Lac operon
• Gene expression
• Recombinant DNA
• Escherichia coli