Isopropyl-p-D-thiogalactoside

Transcription ofT7 RNA polymerase is induced by addition of isopropyl-p-D-thiogalactoside. The polymerase then directs the transcription of the lipase operon. The lipase is correctly folded and secreted into the bacterial culture supernatant which can subsequently be used to assay lipase activities. 

The lac operon is ordinarily subject to repression and is activated by the presence of an inducer, now known to be allolactose, o-Galp-pi—>6-d-G1c. However, in experimental work artificial inducers such as isopropyl-p-D-thiogalactoside (IPTG) are most often used. Jacob and Monod postulated that the free repressor protein binds to the operator. In the presence of the inducer a conformational change takes place, destroying the affinity of fhe repressor protein for the operator site. Thus, in the presence of inducer fhe operator is not blocked, and the transcription takes place. Such an operon is said to be negatively controlled and inducible. 

IPTG-Xgal mix Mix 1.25 g IPTG (isopropyl p-D-thiogalactoside) and Xgal (5-bromo-4-chloro-3-indolyi p-D-galactoside) in 25 mL dimethyl formamide (DMF). Store the solution in dark at -20 °C. 

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