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Isopropyl β-d-1-thiogalactopyranoside (IPTG) 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 .
The tac promoter is, therefore, inducible by IPTG (Isopropyl β-D-1-thiogalactopyranoside), whilst also allowing higher maximum gene expression than either the lac or trp promoters. This makes it suitable for high-efficiency protein production of a recombinant protein. [ 1 ]
IPTG is a reagent which mimics the structure of allolactose, and can therefore bind to the lac repressor and prevent it from inhibiting gene expression. Once enough IPTG is added, the T7 gene is normally transcribed and so transcription of the gene of interest downstream of the T7 promoter also begins. [6]
When referring to a promoter some authors actually mean promoter + operator; i.e., the lac promoter is IPTG inducible, meaning that besides the lac promoter, the lac operon is also present. If the lac operator were not present the IPTG would not have an inducible effect. [citation needed] Another example is the Tac-Promoter system (Ptac ...
pHT01 is a plasmid used as a cloning vector for expressing proteins in Bacillus subtilis.It is 7,956 base pairs in length. [1] pHT01 carries Pgrac, an artificial, strong, IPTG-inducible promoter consisting of the Bacillus subtilis groE promoter, a lac operator, and the gsiB ribosome binding site.
The promoters used in expression vector are normally inducible, meaning that protein synthesis is only initiated when required by the introduction of an inducer such as IPTG. Gene expression however may also be constitutive (i.e. protein is constantly expressed) in some expression vectors.
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IPTG, a molecule similar to lactose, but with a sulfur bond that is not hydrolyzable so that E. coli does not digest it, is used to activate or "induce" the production of the new protein. Once the cells are induced, it is difficult to remove IPTG from the cells and therefore it is difficult to stop expression.