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Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
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Tutti i libri di testoSanders 3rd EditionCh. 12 - Regulation of Gene Expression in Bacteria and BacteriophageProblema 25b
Capitolo 12, Problema 25b

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.
Region 4 is deleted.

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Understand the role of the trpL region in attenuation control: The trpL region is part of the leader sequence of the trp operon and contains four regions (1, 2, 3, and 4) that can form stem-loop structures in the mRNA. These structures influence whether transcription continues or terminates based on tryptophan levels.
Recognize the function of Region 4: Region 4 is critical for forming the terminator stem-loop structure (between Regions 3 and 4). This structure causes RNA polymerase to terminate transcription when tryptophan levels are high.
Analyze the effect of deleting Region 4: Without Region 4, the terminator stem-loop cannot form. This means attenuation control is disrupted, and transcription of the trp operon genes will likely continue regardless of tryptophan levels.
Consider the physiological implications: If transcription is not terminated, the trp operon genes will be expressed even when tryptophan is abundant, leading to unnecessary synthesis of tryptophan and inefficient use of cellular resources.
Summarize the reasoning: The deletion of Region 4 removes the ability to form the terminator stem-loop, effectively disabling attenuation control and causing constitutive expression of the trp operon genes.

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Attenuation in Gene Regulation

Attenuation is a regulatory mechanism in prokaryotes, particularly in the trp operon, that controls gene expression based on the availability of tryptophan. It involves the formation of specific RNA structures during transcription that can either promote or inhibit the continuation of transcription depending on the cellular conditions.
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Trp Attenuation

trp Operon Structure

The trp operon is a cluster of genes in bacteria that encode enzymes for tryptophan biosynthesis. It includes regulatory regions such as the leader sequence (trpL) that contains sequences capable of forming alternative secondary structures, which play a crucial role in the attenuation process by determining whether transcription will proceed or terminate.
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Trp Attenuation

Role of Region 4 in Attenuation

Region 4 of the trpL sequence is essential for the formation of a transcription terminator structure. If Region 4 is deleted, the ability of the RNA to form this terminator is compromised, which can lead to increased transcription of the trp operon genes, as the attenuation mechanism is disrupted, allowing for continued expression even in high tryptophan conditions.
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Trp Attenuation
Pratica correlata
Domanda del libro di testo

A repressible operon system, like the trp operon, contains three genes, G, Z, and W. Operon genes are synthesized when the end product of the operon synthesis pathway is absent, but there is no synthesis when the end product is present. One of these genes is an operator, one is a regulatory protein, and the other is a structural enzyme involved in synthesis of the end product. In the table below, '+' indicates that the enzyme is synthesized by the operon and '−' means that no enzyme synthesis occurs. Use this information to determine which gene corresponds to each operon function.

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Domanda del libro di testo

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

Two nucleotides are inserted into the trpL region immediately after the polypeptide stop codon.

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Domanda del libro di testo

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

Region 3 is deleted.

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Domanda del libro di testo

What is a riboswitch? Describe the riboswitch mechanism that regulates transcription of the thi operon in B. subtilus. What parallels can you see between this mechanism and the regulation of transcription of the trp operon in E. coli?

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Domanda del libro di testo

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

The start (AUG) codon of the trpL polypeptide is deleted.

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Domanda del libro di testo

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

The entire trpL region is deleted.

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