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Ch. 17 - Transcriptional Regulation in Eukaryotes
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 17 - Transcriptional Regulation in EukaryotesProblem 22b
Chapter 17, Problem 22b

Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.
A deletion of the entire GAL3 gene.

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1
Understand the role of the GAL3 gene in the regulation of the GAL1 gene. GAL3 encodes a protein that acts as a sensor and inducer in the presence of galactose, facilitating transcription activation of GAL1.
Recognize that in the presence of galactose, the GAL3 protein binds galactose and interacts with the GAL80 repressor, relieving its inhibition on the GAL4 activator, which then promotes transcription of GAL1.
Consider the effect of deleting the entire GAL3 gene: without GAL3 protein, the signal from galactose cannot be properly transmitted to relieve GAL80 repression.
Predict that because GAL80 remains bound to GAL4, the transcriptional activation of GAL1 will be impaired or significantly reduced despite the presence of galactose.
Conclude that the deletion of GAL3 leads to a failure in induction of GAL1 transcription in response to galactose, resulting in low or no expression of the GAL1 gene under inducing conditions.

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Key Concepts

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

Role of GAL3 in Galactose Signaling

GAL3 encodes a sensor protein that binds galactose and ATP, triggering a signal that relieves repression of GAL gene transcription. Without GAL3, the cell cannot effectively detect galactose, preventing activation of GAL1 transcription despite galactose presence.
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GAL Regulation

Regulation of GAL1 Gene Transcription

The GAL1 gene is regulated by a network of proteins including GAL4 (activator), GAL80 (repressor), and GAL3 (inducer). In the presence of galactose, GAL3 binds GAL80, freeing GAL4 to activate GAL1 transcription. Disruption in this pathway affects GAL1 expression.
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Impact of Gene Deletion on Regulatory Pathways

Deleting the GAL3 gene removes a critical component of the galactose induction pathway, leading to failure in signal transduction. This results in continued repression of GAL1 transcription, demonstrating how gene deletions can disrupt regulatory networks and gene expression.
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Related Practice
Textbook Question

DNA supercoiling, which occurs when coiling tension is generated ahead of the replication fork, is relieved by DNA gyrase. Supercoiling may also be involved in transcription regulation. Researchers discovered that enhancers operating over a long distance (2500 bp) are dependent on DNA supercoiling, while enhancers operating over shorter distances (110 bp) are not so dependent [Liu et al. (2001). Proc. Natl. Acad. Sci. USA 98:14,883–14,888]. Using a diagram, suggest a way in which supercoiling may positively influence enhancer activity over long distances.

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Textbook Question

Because the degree of DNA methylation appears to be a relatively reliable genetic marker for some forms of cancer, researchers have explored the possibility of altering DNA methylation as a form of cancer therapy. Initial studies indicate that while hypomethylation suppresses the formation of some tumors, other tumors thrive. Why would one expect different cancers to respond differently to either hypomethylation or hypermethylation therapies?

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Textbook Question

Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.

A deletion within the GAL4 gene that removes the region encoding amino acids 1 to 100.

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Textbook Question

Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.

A mutation within the GAL80 gene that blocks the ability of Gal80 protein to interact with Gal3p.

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Textbook Question

Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.

A deletion of one of the four UASG elements upstream from the GAL1 gene.

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Textbook Question

Explain how the following mutations would affect transcription of the yeast GAL1 gene in the presence of galactose.

A point mutation in the GAL1 core promoter that alters the sequence of the TATA box.

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