Ch. 8 - Molecular Biology of Transcription and RNA Processing

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 8 - Molecular Biology of Transcription and RNA Processing

Problem 21b

Chapter 8, Problem 21b

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?

Verified step by step guidance

Understand the role of the rho protein: The rho protein is involved in transcription termination in prokaryotes. It helps to stop RNA synthesis at specific termination sites by interacting with the RNA and the RNA polymerase.

Recognize the mutation's effect: The mutant rho protein is temperature-sensitive, functioning normally at 37°C but becoming completely inactive at 40°C. This means that at 40°C, rho-dependent termination will not occur.

Differentiate between rho-dependent and rho-independent termination: Not all mRNAs rely on rho protein for termination. Some genes use rho-independent termination, which relies on specific sequences in the RNA that form a hairpin structure followed by a poly-U tail to terminate transcription without rho.

Analyze the impact on mRNAs: Only mRNAs that require rho-dependent termination will be affected by the mutation at 40°C. These mRNAs may be transcribed beyond their normal termination sites, potentially leading to longer transcripts.

Conclude the reasoning: Since not all mRNAs use rho-dependent termination, the mutation will not affect all mRNAs in the same way. Rho-independent mRNAs will terminate normally, while rho-dependent mRNAs will exhibit altered termination at 40°C.

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Key Concepts

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

Rho Protein Function

Rho protein is a transcription termination factor in bacteria that facilitates the release of RNA polymerase from the DNA template once transcription is complete. It recognizes specific sequences in the mRNA and binds to them, promoting the dissociation of the RNA transcript from the transcription complex. Understanding its role is crucial to determine how mutations may affect mRNA processing.

Temperature Sensitivity in Mutations

Temperature-sensitive mutations are genetic alterations that result in a functional protein at one temperature but inactive at another. In this case, the rho protein retains its function at 37°C but loses it at 40°C. This concept is essential for understanding how environmental conditions can influence the expression and functionality of proteins, including their effects on mRNA.

mRNA Diversity and Rho Dependency

Not all mRNAs are equally dependent on rho protein for termination. Some mRNAs may have intrinsic termination signals that allow them to terminate transcription independently of rho. Therefore, the impact of the rho protein mutation on mRNA stability and processing can vary, leading to different outcomes for different mRNAs in the mutant strain.

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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 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. 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

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

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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Textbook Question

Microbiologists describe the processes of transcription and translation as 'coupled' in bacteria. This term indicates that a bacterial mRNA can be undergoing transcription at the same moment it is also undergoing translation.

How is coupling of transcription and translation possible in bacteria?

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