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Ch. 18 - Control of Gene Expression in Bacteria
All textbooksFreeman 8th EditionCh. 18 - Control of Gene Expression in BacteriaProblem 14
Chapter 17, Problem 14

LuxR is allosterically regulated by the inducer molecule secreted by V. fischeri. What does it mean that LuxR is allosterically regulated?

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Allosteric regulation refers to the regulation of a protein by binding an effector molecule at a site other than the protein's active site.
The binding of the effector (inducer molecule) causes a conformational change in the protein structure.
This conformational change alters the activity of the protein, which can either enhance or inhibit the protein's function.
In the case of LuxR, a protein involved in the regulation of bioluminescence in V. fischeri, the inducer molecule binds to LuxR at a site different from where DNA would bind.
This binding increases the ability of LuxR to interact with DNA, thereby promoting the expression of genes responsible for light production.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Allosteric Regulation

Allosteric regulation refers to the modulation of a protein's activity through the binding of an effector molecule at a site other than the active site. This binding induces a conformational change in the protein, which can either enhance or inhibit its function. In the case of LuxR, the inducer molecule alters its shape, affecting its ability to bind to DNA and regulate gene expression.
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Inducer Molecule

An inducer molecule is a substance that initiates or enhances the expression of specific genes by binding to regulatory proteins. In the context of LuxR, the inducer secreted by V. fischeri binds to LuxR, promoting its active form. This interaction is crucial for the regulation of bioluminescence in response to environmental signals.
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Quorum Sensing

Quorum sensing is a communication process that bacteria use to detect and respond to cell population density through the release and detection of signaling molecules. LuxR is a key player in this process, as it helps bacteria like V. fischeri coordinate group behaviors, such as bioluminescence, based on the concentration of the inducer molecule in their environment.
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Related Practice
Textbook Question

X-gal is a colorless, lactose-like molecule that can be split into two fragments by ββ-galactosidase. One of these product molecules creates a blue color. The photograph here shows E. coli colonies growing in a medium that contains X-gal. Find three colonies whose cells have functioning copies of ββ-galactosidase. Find three colonies whose cells might have mutations in the lacZ or the lacY genes. Suppose you analyze the protein-coding sequence of the lacZ and lacY genes of cells from the three mutant colonies and find that these sequences are wild type (normal). What other region of the lac operon might be altered to account for the mutant phenotype of these colonies?

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Textbook Question

The light-producing genes of V. fischeri are organized in an operon that is under positive control by an activator protein called LuxR. Would you expect the genes of this operon to be transcribed when LuxR is bound or not bound to a DNA regulatory sequence? Explain.

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Textbook Question

The diagram shown here is a model of the gene regulatory circuit for light production by V. fischeri cells. The lux operon contains genes for luminescence (luxCDABE) and a gene, luxI, that encodes an enzyme that catalyzes the production of an inducer. This inducer easily moves back and forth across the plasma membrane and acts as a signaling molecule. The lux operon is never completely turned off. The luxR gene codes for the activator LuxR. The inducer can bind to LuxR, and when it does, the LuxR–inducer complex can bind to a regulatory site to activate transcription of the lux operon and inhibit transcription of luxR. Explain how this gene regulatory circuit accounts for bacteria emitting light only when they reach a high cell density.

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Textbook Question

What characteristic of the light-producing regulatory circuit is consistent with the idea that it may be a regulon? What characteristic of this circuit stretches the definition for a regulon?

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Textbook Question

Quorum sensing (introduced in Ch. 11, Section 11.4) allows bacteria to detect the number of neighboring cells and to trigger a response only when this number reaches a critical level. Quorum sensing is used by V. fischeri in light production and by many pathogenic bacteria, including Vibrio cholerae, to turn on genes for toxin production only when a critical cell density is reached. Why might quorum sensing be beneficial to pathogenic bacteria?

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