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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 21a
Chapter 8, Problem 21a

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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1
Understand the role of the rho protein in transcription termination: Rho is a termination factor in prokaryotes that helps stop transcription at specific sites. When rho is functional, it ensures that transcription ends properly, preventing the production of excessively long or unnecessary mRNA transcripts.
Analyze the effect of temperature on rho activity: At 37°C, the rho protein is fully active, meaning transcription termination occurs normally. At 40°C, the rho protein is completely inactivated, leading to a failure in rho-dependent termination of transcription.
Predict the differences in mRNA profiles: At 37°C, the mRNA spectrum will include transcripts of normal length, as rho ensures proper termination. At 40°C, without rho activity, transcription may continue past normal termination sites, resulting in longer mRNA transcripts and potentially the inclusion of downstream, unintended sequences.
Consider the impact on gene expression: The longer mRNAs produced at 40°C may include additional coding or non-coding regions, potentially leading to the production of aberrant proteins or untranslated regions. This could disrupt normal cellular processes and gene regulation.
Summarize the expected differences: The mRNA spectrum at 37°C will reflect normal transcription termination, while at 40°C, the spectrum will likely show an increase in longer mRNAs due to the failure of rho-dependent termination. This difference highlights the critical role of rho in maintaining proper transcriptional regulation.

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Key Concepts

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

Rho Protein Function

The Rho protein is a transcription termination factor in bacteria that plays a crucial role in regulating gene expression. It facilitates the termination of transcription by recognizing specific RNA sequences, allowing the RNA polymerase to detach from the DNA. In the context of the mutant strain, the activity of the Rho protein at different temperatures can significantly influence the levels of mRNA produced, affecting overall gene expression.
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Temperature Effects on Protein Activity

Temperature can greatly influence protein structure and function, as proteins are sensitive to thermal changes. At optimal temperatures, proteins like Rho maintain their functional conformation, while deviations can lead to denaturation or loss of activity. In this case, the Rho protein's full activity at 37°C versus its inactivation at 40°C suggests that temperature affects the stability and functionality of the protein, which in turn impacts mRNA synthesis and stability.
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mRNA Profiling

mRNA profiling involves analyzing the expression levels of various mRNAs within a cell under specific conditions. This technique can reveal differences in gene expression patterns, indicating which genes are upregulated or downregulated in response to environmental changes, such as temperature. By comparing mRNA profiles from the mutant strain at 37°C and 40°C, one can infer the impact of Rho protein activity on transcriptional regulation and identify specific genes affected by the temperature-induced mutation.
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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

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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 42°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. Are all mRNAs affected by the rho protein mutation in the same way? Why or why not?

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Textbook Question

The human β-globin wild-type allele and a certain mutant allele are identical in sequence except for a single base-pair substitution that changes one nucleotide at the end of intron 2. The wild-type and mutant sequences of the affected portion of pre-mRNA are

Speculate about the way in which this base substitution causes mutation of β-globin protein.

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Textbook Question

The human β-globin wild-type allele and a certain mutant allele are identical in sequence except for a single base-pair substitution that changes one nucleotide at the end of intron 2. The wild-type and mutant sequences of the affected portion of pre-mRNA are

This is one example of how DNA sequence change occurring somewhere other than in an exon can produce mutation. List other kinds of DNA sequence changes occurring outside exons that can produce mutation. In each case, characterize the kind of change you would expect to see in mutant mRNA or mutant protein.

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