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YACOO: Briefly introduction on the induction principle of IPTG

2015-06-09 来源:转载自第三方
Key words: IPTG; Induction principle
IPTG (CAS number: 367-93-1), chemical name is isopropyl-β-D-thiogalactopyranoside, molecular formula: C9H18O5S, molecular weight: 238.30, Yacoo item number: Y0014. IPTG is a β-galactosidase activity inducing substance. Based on this characteristic, when pUC series vector DNA (or other vector carrying lacZ gene) is transformed with lacZ-deficient cells as a host or transfected with M13 phage vector DNA, if X-gal and IPTG was added to the plate medium, gene recombinants can be conveniently selected based on whether white colonies (or plaques) are present due to the a-complement of [beta]-galactosidase. In addition, it can also be used as an expression inducer of an expression vector having a promoter such as lac or tac.
Regarding its induction principle, first of all, the lactose operon of E. coli contains three structural genes of Z, Y and A, encoding galactosidase, dialysase and acetyltransferase, respectively, in addition to a manipulation sequence O, A promoter sequence P and a regulatory gene. The I gene encodes a repressor protein, which binds to the O sequence, blocking the operator (meta) and leaving it off. There is also a catabolite (CAP) binding site upstream of the priming sequence P. By the P sequence, O sequence and CAP binding site together constitute the lac operon regulatory region, the three enzymes encoding genes that are regulated by the same regulatory region, to achieve the coordinated expression of the gene product.
Second, the lac operon (meta) is in a repressed state in the absence of lactose. In this case, the Lac repressor expressed by the I sequence under the PI priming sequence binds to the O sequence, preventing the RNA polymerase from binding to the P sequence and inhibiting the transcription initiation. When there is lactose, lac operon (yuan) can be induced. In this operon (meta) system, the real inducer is not lactose itself. Lactose enters cells and catalyzed by β-galactosidase to convert to isolactose. The latter, as an inducer, binds to the repressor molecule and changes the conformation of the protein, resulting in the dissociation of the repressor protein from the O-sequence and transcription. Isopropylthiogalactoside (IPTG) is the same as lactose, is a highly effective inducer, which is not metabolized by bacteria and very stable, it is widely used in laboratories.
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