Inducer
Inmolecular biology,aninduceris amoleculethat regulatesgene expression.[1]An inducer functions in two ways; namely:
- By disablingrepressors.Thegeneis expressed because an inducer binds to the repressor. The binding of the inducer to the repressor prevents the repressor from binding to theoperator.RNA polymerasecan then begin to transcribeoperongenes.
- By binding toactivators.Activators generally bind poorly toactivator DNA sequencesunless an inducer is present. Activator binds to an inducer and the complex binds to the activation sequence and activates target gene.[2]Removing the inducer stops transcription.[2]
Because a small inducer molecule is required, the increased expression of the target gene is calledinduction.[2]The lactose operon is one example of an inducible system.[2]
Function[edit]
Repressor proteins bind to the DNA strand and prevent RNA polymerase from being able to attach to the DNA and synthesize mRNA. Inducers bind to repressors, causing them to change shape and preventing them from binding to DNA. Therefore, they allow transcription, and thus gene expression, to take place.
For ageneto be expressed, itsDNAsequence must be copied (in a process known astranscription) to make a smaller, mobile molecule calledmessenger RNA(mRNA), which carries the instructions for making a protein to the site where the protein is manufactured (in a process known astranslation). Many different types of proteins can affect the level of gene expression by promoting or preventing transcription. Inprokaryotes(such as bacteria), these proteins often act on a portion of DNA known as theoperatorat the beginning of the gene. The promoter is whereRNA polymerase,the enzyme that copies the genetic sequence and synthesizes the mRNA, attaches to the DNA strand.
Some genes are modulated byactivators,which have the opposite effect on gene expression as repressors. Inducers can also bind to activator proteins, allowing them to bind to the operator DNA where they promote RNA transcription.
Ligandsthat bind to deactivate activator proteins are not, in the technical sense, classified as inducers, since they have the effect of preventing transcription.
Examples[edit]
lacoperon[edit]
The inducer in thelacoperonisallolactose.[2]Iflactoseis present in the medium, then a small amount of it will be converted to allolactose by a few molecules ofβ-galactosidasethat are present in the cell.[3]Allolactose binds to the repressor and decreases the repressor's affinity for the operator site.[3]
However, when lactose andglucoseare both available in the system, thelacoperon is repressed. This is because glucose actively prevents the induction oflacZYA.[2]
araoperon[edit]
In thearaoperon(also known as thearaoraraBADoperon),arabinoseacts as both an inducer and a repressor. When arabinose is present, itallostericallybinds to the regulatory protein AraC, which then helps to recruit RNA polymerase for transcription.
Potency[edit]
Index induceror justinducerpredictably induce metabolism via a givenpathwayand are commonly used in prospective clinicaldrug-drug interactionstudies.[4]
Strong, moderate, and weak inducers are drugs that decreases the AUC ofsensitive index substratesof a given metabolic pathway by ≥80%, ≥50% to <80%, and ≥20% to <50%, respectively.[4]
References[edit]
- ^Baraniak, P. R.; Nelson, D. M.; Leeson, C. E.; Katakam, A. K.; Friz, J. L.; Cress, D. E.; Hong, Y; Guan, J; Wagner, W. R. (2011)."Spatial control of gene expression by localized inducer release".Biomaterials.32(11): 3062–71.doi:10.1016/j.biomaterials.2010.12.037.PMC3178343.PMID21269687.
- ^abcdefSlonczewski, Joan, and John Watkins. Foster.Microbiology: An Evolving Science.New York: W.W. Norton &, 2009. Print.[page needed]
- ^abBiology Part 2.Berkeley, CA: Berkeley Review, 1995. Print.[page needed]
- ^ab"Drug Development and Drug Interactions: Table of Substrates, Inhibitors and Inducers".U S Food and Drug Administration Home Page.2009-06-25.Retrieved2019-01-31.
External links[edit]
