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.

Verified step by step guidance

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.
2. 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.
3. Consider the effect of deleting the entire GAL3 gene: without GAL3 protein, the signal from galactose cannot be properly transmitted to relieve GAL80 repression.
4. Predict that because GAL80 remains bound to GAL4, the transcriptional activation of GAL1 will be impaired or significantly reduced despite the presence of galactose.
5. 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.

Key Concepts

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.

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.

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.