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Ch. 17+18 - Transcriptional Regulation in Eukaryotes
All textbooksKlug 12th EditionCh. 17+18 - Transcriptional Regulation in EukaryotesProblem 25
Chapter 17, Problem 25

Regulation of the lac operon in E. coli (see Chapter 16) 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.

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span>Identify the cis-regulatory elements of the lac operon in E. coli. These include the promoter (P), operator (O), and the CAP binding site.</span
span>Identify the cis-regulatory elements of the GAL gene system in yeast. These include the UAS (Upstream Activating Sequence) and the promoter regions.</span
span>Compare the function of the operator in the lac operon with the UAS in the GAL system. The operator is a binding site for the repressor protein, while the UAS is a binding site for activator proteins.</span
span>Contrast the role of the CAP binding site in the lac operon with the regulatory sequences in the GAL system. The CAP site enhances transcription in the presence of cAMP, whereas the GAL system relies on the presence of galactose to activate transcription through different regulatory proteins.</span
span>Discuss how the presence or absence of specific sugars (lactose for the lac operon and galactose for the GAL system) influences the binding of regulatory proteins to these cis-regulatory elements, leading to transcriptional activation or repression.</span

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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 regions of non-coding DNA that regulate the transcription of nearby genes. They include promoters, enhancers, and silencers, which interact with transcription factors to control gene expression. In the context of the lac operon and GAL system, these elements play crucial roles in determining how genes respond to environmental signals, such as the presence of specific sugars.
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Human Transposable Elements

Lac Operon

The lac operon is a well-studied example of gene regulation in E. coli, consisting of genes required for the metabolism of lactose. It is regulated by the presence of lactose and glucose, involving a promoter and an operator where the repressor protein binds. When lactose is present, it binds to the repressor, allowing transcription to occur, showcasing a classic example of negative regulation.
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Lac Operon Overview

GAL Gene System

The GAL gene system in yeast regulates the metabolism of galactose and involves a different set of cis-regulatory elements compared to the lac operon. It includes a promoter and upstream activating sequences that interact with specific transcription factors, such as Gal4. The system exemplifies positive regulation, where the presence of galactose activates transcription, highlighting the diversity in regulatory mechanisms across different organisms.
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Related Practice
Textbook Question

Much of what we know about gene interactions in development has been learned using nematodes, yeast, flies, and bacteria. This is due, in part, to the relative ease of genetic manipulation of these well-characterized genomes. However, of great interest are gene interactions involving complex diseases in humans. Wang and White [(2011). Nature Methods 8(4):341–346] describe work using RNAi to examine the interactive proteome in mammalian cells. They mention that knockdown inefficiencies and off-target effects of introduced RNAi species are areas that need particular improvement if the methodology is to be fruitful.

Comment on how 'knockdown inefficiencies' and 'off-target effects' would influence the interpretation of results.

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Textbook Question

In this chapter, we discussed several specific cis-elements in mRNAs that regulate splicing, stability, decay, localization, and translation. However, it is likely that many other uncharacterized cis-elements exist. One way in which they may be characterized is through the use of a reporter gene such as the gene encoding the green fluorescent protein (GFP) from jellyfish. GFP emits green fluorescence when excited by blue light. Explain how one might be able to devise an assay to test for the effect of various cis-elements on posttranscriptional gene regulation using cells that transcribe a GFP mRNA with genetically inserted cis-elements.

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Textbook Question

Regulation of the lac operon in E. coli (see Chapter 16) 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 roles of the lac operon inducer in bacteria and Gal3p in eukaryotes in the regulation of their respective systems.

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Textbook Question

Regulation of the lac operon in E. coli (see Chapter 16) 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 how these two systems are negatively regulated such that they are downregulated in the presence of glucose.

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Textbook Question

Incorrectly spliced RNAs often lead to human pathologies. Scientists have examined cancer cells for splice-specific changes and found that many of the changes disrupt tumor-suppressor gene function [Xu and Lee (2003). Nucl. Acids Res. 31:5635–5643]. In general, what would be the effects of splicing changes on these RNAs and the function of tumor-suppressor gene function? How might loss of splicing specificity be associated with cancer?

284
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Textbook Question

Mutations in the low-density lipoprotein receptor (LDLR) gene are a primary cause of familial hypercholesterolemia. One such mutation is a SNP in exon 12 of the LDLR. In premenopausal women, but not in men or postmenopausal women, this SNP leads to skipping of exon 12 and production of a truncated nonfunctional protein. It is hypothesized that this SNP compromises a splice enhancer [Zhu et al. (2007). Hum Mol Genet. 16:1765–1772]. What are some possible ways in which this SNP can lead to this defect, but only in premenopausal women?

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