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Ch. 16 - Regulation of Gene Expression in Bacteria
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 16 - Regulation of Gene Expression in BacteriaProblem 14
Chapter 16, Problem 14

Neelaredoxin is a 15-kDa protein that is a gene product common in anaerobic bacteria. It has superoxide-scavenging activity, and it is constitutively expressed. In addition, its expression is not further induced during its exposure to O₂ or H₂O₂ [Silva, G. et al. (2001). J. Bacteriol. 183:4413 4420]. What do the terms constitutively expressed and induced mean in terms of neelaredoxin synthesis?

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1
Understand the term 'constitutively expressed': This means that the gene responsible for neelaredoxin synthesis is always active, producing the protein continuously, regardless of environmental conditions or external stimuli.
Understand the term 'induced': This refers to a gene whose expression is increased or activated in response to specific environmental conditions or stimuli, such as the presence of O₂ or H₂O₂.
Relate these terms to neelaredoxin: Since neelaredoxin is constitutively expressed, its synthesis occurs at a constant rate and is not dependent on the presence of external factors like O₂ or H₂O₂.
Clarify the lack of induction: The study indicates that neelaredoxin expression does not increase further when exposed to O₂ or H₂O₂, meaning the gene is not inducible under these conditions.
Summarize the synthesis behavior: Neelaredoxin synthesis is regulated in a way that ensures a steady production of the protein, which is essential for its role in superoxide scavenging in anaerobic bacteria.

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Key Concepts

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

Constitutive Expression

Constitutive expression refers to the continuous production of a protein by a gene, regardless of environmental conditions. In the case of neelaredoxin, this means that the protein is synthesized at a constant rate in anaerobic bacteria without the need for specific stimuli. This is crucial for maintaining essential cellular functions, especially in environments where the protein's activity is necessary for survival.
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Inducible Expression

Inducible expression is a regulatory mechanism where the synthesis of a protein is increased in response to specific environmental signals or stressors. For neelaredoxin, the fact that its expression is not induced by O₂ or H₂O₂ indicates that its production is not reliant on these oxidative stress conditions, highlighting its role in the baseline defense against reactive oxygen species in anaerobic bacteria.
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Gene Regulation

Gene regulation encompasses the mechanisms that control the timing and amount of gene expression. It is essential for cellular adaptation to varying environmental conditions. Understanding how neelaredoxin is constitutively expressed versus how other proteins might be induced helps clarify the strategies bacteria use to manage oxidative stress and maintain homeostasis in fluctuating environments.
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Related Practice
Textbook Question

Erythritol, a natural sugar abundant in fruits and fermenting foods, is about 65 percent as sweet as table sugar and has about 95 percent fewer calories. It is 'tooth friendly' and generally devoid of negative side effects as a human consumable product. Pathogenic Brucella strains that catabolize erythritol contain four closely spaced genes, all involved in erythritol metabolism. One of the four genes (eryD) encodes a product that represses the expression of the other three genes. Erythritol catabolism is stimulated by erythritol. Present a simple regulatory model to account for the regulation of erythritol catabolism in Brucella. Does this system appear to be under inducible or repressible control?

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Textbook Question

Describe the role of attenuation in the regulation of tryptophan biosynthesis.

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Textbook Question
Attenuation of the trp operon was viewed as a relatively inefficient way to achieve genetic regulation when it was first discovered in the 1970s. Since then, however, attenuation has been found to be a relatively common regulatory strategy. Assuming that attenuation is a relatively inefficient way to achieve genetic regulation, what might explain its widespread occurrence?
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Textbook Question

The creation of milk products such as cheeses and yogurts is dependent on the conversion by various anaerobic bacteria, including several Lactobacillus species, of lactose to glucose and galactose, ultimately producing lactic acid. These conversions are dependent on both permease and β-galactosidase as part of the lac operon. After selection for rapid fermentation for the production of yogurt, one Lactobacillus subspecies lost its ability to regulate lac operon expression [Lapierre, L., et al. (2002). J. Bacteriol. 184:928–935]. Would you consider it likely that in this subspecies the lac operon is on or off? What genetic events would likely contribute to the loss of regulation as described above?

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Textbook Question

Both attenuation of the trp operon in E. coli and riboswitches in B. subtilis rely on changes in the secondary structure of the leader regions of mRNA to regulate gene expression. Compare and contrast the specific mechanisms in these two types of regulation with those involving short noncoding RNAs (sRNAs).

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Textbook Question

During the reproductive cycle of a temperate bacteriophage, the viral DNA inserts into the bacterial chromosome, where the resultant prophage behaves much like a Trojan horse. It can remain quiescent, or it can become lytic and initiate a burst of progeny viruses. Several operons maintain the prophage state by interacting with a repressor that keeps the lytic cycle in check. Insults (ultraviolet light, for example) to the bacterial cell lead to a partial breakdown of the repressor, which in turn causes the production of enzymes involved in the lytic cycle. As stated in this simple form, would you consider this system of regulation to be operating under positive or negative control?

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