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 40°C

Verified step by step guidance

1. Identify the role of the sigma subunit in the RNA polymerase holoenzyme. It is crucial for the initiation of transcription by facilitating the binding of RNA polymerase to specific promoter regions on the DNA.
2. Understand that the mutation affects the stability of the sigma subunit, which in turn affects the stability of the entire RNA polymerase holoenzyme at higher temperatures.
3. Recognize that at 37°C, the mutant strain transcribes at wild-type levels, indicating that the mutation does not affect transcription at this temperature.
4. Note that as the temperature increases to 42°C, the mutant holoenzyme becomes completely destabilized and ceases transcription, suggesting a progressive loss of function between 37°C and 42°C.
5. Conclude that at 40°C, the mutant strain's ability to carry out transcription is likely reduced compared to wild-type, as the holoenzyme is destabilized but not yet completely non-functional.

Key Concepts

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 at different temperatures.

Temperature Effects on Enzyme Activity

Enzymes, including RNA polymerase, are sensitive to temperature changes, which can affect their stability and activity. Generally, as temperature increases, enzyme activity may rise to an optimal point before denaturing occurs. In this case, the mutant E. coli strain's ability to transcribe at 40°C must be evaluated in light of how the mutation impacts the holoenzyme's stability at elevated temperatures.

Mutations and Phenotypic Expression

Mutations can lead to changes in protein structure and function, which can manifest as altered phenotypes. In this scenario, the mutation in the sigma subunit of E. coli affects the stability of the RNA polymerase holoenzyme, influencing its transcriptional efficiency at varying temperatures. Understanding the relationship between the genetic mutation and its phenotypic consequences is key to characterizing the mutant strain's performance at 40°C.