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Ch. 8 - Molecular Biology of Transcription and RNA Processing
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 8 - Molecular Biology of Transcription and RNA ProcessingProblem 20c
Chapter 8, Problem 20c

Wild-type E. coli grows best at 37°C but can grow efficiently up to 42°C. An E. coli strain has a mutation of the sigma subunit that results in an RNA polymerase holoenzyme that is stable and transcribes at wild-type levels at 37°C. The mutant holoenzyme is progressively destabilized as the temperature is raised, and it completely denatures and ceases to carry out transcription at 42°C. Relative to wild-type growth, characterize the ability of the mutant strain to carry out transcription at 42°C

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Understand the role of the sigma subunit in RNA polymerase: The sigma subunit is a critical component of the RNA polymerase holoenzyme in prokaryotes. It is responsible for recognizing promoter sequences and initiating transcription. A mutation in the sigma subunit can affect the stability and functionality of the holoenzyme.
Analyze the given information about the mutant strain: The mutant RNA polymerase holoenzyme is stable and transcribes at wild-type levels at 37°C. However, as the temperature increases, the mutant holoenzyme becomes progressively destabilized, and at 42°C, it completely denatures and ceases transcription.
Compare the mutant strain to the wild-type strain: Wild-type E. coli can grow efficiently at temperatures up to 42°C, which implies that its RNA polymerase holoenzyme remains stable and functional at this temperature. In contrast, the mutant strain's holoenzyme is unable to maintain stability and function at 42°C.
Characterize the transcriptional ability of the mutant strain at 42°C: Since the mutant holoenzyme completely denatures at 42°C, the mutant strain will be unable to carry out transcription at this temperature. This inability to transcribe genes will prevent the mutant strain from synthesizing essential proteins, ultimately inhibiting its growth.
Conclude the relative ability of the mutant strain: Relative to the wild-type strain, the mutant strain is transcriptionally deficient at 42°C due to the instability of its RNA polymerase holoenzyme. This deficiency highlights the importance of the sigma subunit's stability in maintaining transcriptional activity under elevated temperatures.

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Key Concepts

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

RNA Polymerase Function

RNA polymerase is an essential enzyme responsible for synthesizing RNA from a DNA template during transcription. It forms a holoenzyme complex that includes a sigma factor, which helps the enzyme recognize specific promoter regions on the DNA. Understanding how mutations in the sigma subunit affect the stability and function of RNA polymerase is crucial for analyzing the transcription capabilities of the E. coli strain at different temperatures.
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Temperature Effects on Enzyme Activity

Enzymes, including RNA polymerase, are sensitive to temperature changes, which can affect their stability and activity. Generally, an increase in temperature can enhance enzyme activity up to a certain point, beyond which the enzyme may denature and lose function. In the context of the mutant E. coli strain, recognizing how temperature impacts the stability of the RNA polymerase holoenzyme is vital for understanding its transcriptional capabilities at 42°C.
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Mutations and Phenotypic Expression

Mutations are changes in the DNA sequence that can lead to alterations in protein structure and function. In this case, the mutation in the sigma subunit of E. coli affects the stability of the RNA polymerase holoenzyme, which in turn influences the organism's ability to transcribe RNA at elevated temperatures. Analyzing how this mutation impacts the phenotype, particularly at 42°C, is essential for characterizing the growth and transcription efficiency of the mutant strain.
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Related Practice
Textbook Question

A 1.0-kb DNA fragment from the end of the mouse gene described in the previous problem is examined by DNA footprint protection analysis. Two samples are end-labeled with ³²P and one of the two is mixed with TFIIB, TFIID, and RNA polymerase II. The DNA exposed to these proteins is run in the right-hand lane of the gel shown below and the control DNA is run in the left-hand. Both DNA samples are treated with DNase I before running the samples on the electrophoresis gel.

Explain the role of DNase I.

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Textbook Question

Wild-type E. coli grow best at 37°C but can grow efficiently up to 42°C. An E. coli strain has a mutation of the sigma subunit that results in an RNA polymerase holoenzyme that is stable and transcribes at wild-type levels at 37°C. The mutant holoenzyme is progressively destabilized as the temperature is raised, and it completely denatures and ceases to carry out transcription at 42°C. Relative to wild-type growth, characterize the ability of the mutant strain to carry out transcription at 37°C

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Textbook Question

Wild-type E. coli grows best at 37°C but can grow efficiently up to 42°C. An E. coli strain has a mutation of the sigma subunit that results in an RNA polymerase holoenzyme that is stable and transcribes at wild-type levels at 37°C. The mutant holoenzyme is progressively destabilized as the temperature is raised, and it completely denatures and ceases to carry out transcription at 42°C. Relative to wild-type growth, characterize the ability of the mutant strain to carry out transcription at 40°C

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Textbook Question

Wild-type E. coli grows best at 37°C but can grow efficiently up to 42°C. An E. coli strain has a mutation of the sigma subunit that results in an RNA polymerase holoenzyme that is stable and transcribes at wild-type levels at 37°C. The mutant holoenzyme is progressively destabilized as the temperature is raised, and it completely denatures and ceases to carry out transcription at 42°C. Relative to wild-type growth, characterize the ability of the mutant strain to carry out transcription at What term best characterizes the type of mutation exhibited by the mutant bacterial strain? (Hint: The term was used in Chapter 4 to describe the Himalayan allele of the mammalian C gene.)

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Textbook Question

A mutant strain of Salmonella bacteria carries a mutation of the rho protein that has full activity at 37°C but is completely inactivated when the mutant strain is grown at 40°C. Speculate about the kind of differences you would expect to see if you compared a broad spectrum of mRNAs from the mutant strain grown at 37°C and the same spectrum of mRNAs from the strain when grown at 40°C.

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Textbook Question

A mutant strain of Salmonella bacteria carries a mutation of the rho protein that has full activity at 37°C but is completely inactivated when the mutant strain is grown at 40°C. Are all mRNAs affected by the rho protein mutation in the same way? Why or why not?

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