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
Table of contents
- 1. Introduction to Genetics51m
- 2. Mendel's Laws of Inheritance3h 37m
- 3. Extensions to Mendelian Inheritance2h 41m
- 4. Genetic Mapping and Linkage2h 28m
- 5. Genetics of Bacteria and Viruses1h 21m
- 6. Chromosomal Variation1h 48m
- 7. DNA and Chromosome Structure56m
- 8. DNA Replication1h 10m
- 9. Mitosis and Meiosis1h 34m
- 10. Transcription1h 0m
- 11. Translation58m
- 12. Gene Regulation in Prokaryotes1h 19m
- 13. Gene Regulation in Eukaryotes44m
- 14. Genetic Control of Development44m
- 15. Genomes and Genomics1h 50m
- 16. Transposable Elements47m
- 17. Mutation, Repair, and Recombination1h 6m
- 18. Molecular Genetic Tools19m
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
10. Transcription
Transcription in Prokaryotes
Problem 21b
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?

1
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.
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Proteins
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.
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Mutations and Phenotypes
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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mRNA Processing
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