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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 20a
Chapter 8, Problem 20a

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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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 function 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. This means that at this temperature, the mutation does not impair the ability of the enzyme to initiate and carry out transcription.
Compare the mutant strain to the wild-type strain at 37°C: Since the mutant holoenzyme is stable and transcribes at wild-type levels at 37°C, the mutant strain should be able to carry out transcription as efficiently as the wild-type strain at this temperature.
Consider the temperature sensitivity of the mutant holoenzyme: The problem specifies that the mutant holoenzyme becomes progressively destabilized as the temperature increases beyond 37°C, eventually ceasing transcription at 42°C. However, this temperature sensitivity does not affect its function at 37°C.
Conclude the transcription ability of the mutant strain at 37°C: Relative to the wild-type strain, the mutant strain is expected to carry out transcription normally at 37°C, as the mutation does not impair the holoenzyme's stability or transcriptional activity at this temperature.

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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. In E. coli, the holoenzyme consists of the core enzyme and a sigma factor that helps initiate transcription at specific promoters. Understanding how mutations in the sigma subunit affect the stability and function of RNA polymerase is crucial for analyzing the transcriptional capabilities of the mutant strain.
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Temperature Effects on Enzyme Activity

Enzymes, including RNA polymerase, have optimal temperature ranges for activity. At temperatures above or below this range, enzyme stability and function can be compromised. In this case, the mutant E. coli strain's ability to transcribe at 37°C compared to its performance at higher temperatures is essential for understanding how temperature influences enzyme activity and overall cellular function.
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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. The specific mutation in the sigma subunit of the E. coli strain affects the stability of the RNA polymerase holoenzyme, which in turn influences transcription efficiency. Analyzing how this mutation impacts the strain's growth and transcription at 37°C relative to wild-type provides insights into the relationship between genotype and phenotype.
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Related Practice
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

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 42°C

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.

What length of DNA is bound by the transcriptional proteins? Explain how the gel results support this interpretation.

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.)

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.

Draw a diagram of this DNA fragment bound by the transcriptional proteins, showing the approximate position of proteins along the fragment.

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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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