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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13. Gene Regulation in Eukaryotes
GAL Regulation
1:48 minutesProblem 25b
Textbook Question
Regulation of the lac operon in E. coli and regulation of the GAL system in yeast are analogous in that they both serve to adapt cells to growth on different carbon sources. However, the transcriptional changes are accomplished very differently. Consider the conceptual similarities and differences as you address the following.
Compare and contrast the cis-regulatory elements of the lac operon and GAL gene system.
Verified step by step guidance1
Step 1: Define cis-regulatory elements as DNA sequences located near a gene that regulate the transcription of that gene by serving as binding sites for transcription factors or regulatory proteins.
Step 2: Identify the cis-regulatory elements of the lac operon, which include the promoter (where RNA polymerase binds), the operator (where the lac repressor binds), and the CAP binding site (where the catabolite activator protein binds to enhance transcription).
Step 3: Identify the cis-regulatory elements of the GAL gene system in yeast, which include upstream activating sequences (UAS) that serve as binding sites for activator proteins such as Gal4, as well as promoter regions where the general transcription machinery assembles.
Step 4: Compare the lac operon and GAL system cis-elements by noting that both have promoter regions and specific binding sites for regulatory proteins, but the lac operon uses an operator for repressor binding, while the GAL system primarily uses UAS for activator binding.
Step 5: Contrast the two systems by explaining that the lac operon’s cis-elements are organized to allow repression and activation primarily through repressor and CAP binding, whereas the GAL system’s cis-elements are designed to facilitate activation through multiple UAS sites and activator proteins, reflecting different regulatory strategies.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Cis-regulatory Elements
Cis-regulatory elements are DNA sequences located near a gene that regulate its transcription by serving as binding sites for transcription factors. These include promoters, operators, and enhancers, which control gene expression by facilitating or blocking RNA polymerase access. Understanding these elements is essential to compare how the lac operon and GAL system control gene activity.
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Lac Operon Cis-regulatory Elements
The lac operon contains key cis-regulatory elements such as the promoter, operator, and CAP binding site. The operator binds the lac repressor to inhibit transcription in the absence of lactose, while the CAP site binds an activator protein to enhance transcription when glucose is low. These elements enable tight control of lactose metabolism genes in E. coli.
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GAL System Cis-regulatory Elements
The GAL gene system in yeast uses upstream activating sequences (UAS) as cis-regulatory elements, which bind activator proteins like Gal4 to promote transcription. Unlike the lac operon, the GAL system relies heavily on activators and chromatin remodeling, with less emphasis on repressor binding sites, reflecting a different regulatory strategy for adapting to galactose.
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