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 42°C

Key Concepts

RNA Polymerase Function

RNA polymerase is an essential enzyme responsible for synthesizing RNA from a DNA template during transcription. It forms a holoenzyme complex that includes a sigma factor, which helps the enzyme recognize specific promoter regions on the DNA. Understanding how mutations in the sigma subunit affect the stability and function of RNA polymerase is crucial for analyzing the transcription capabilities of the E. coli mutant strain at elevated 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 but can lead to denaturation beyond that point. In the case of the E. coli mutant strain, the progressive destabilization of the holoenzyme at higher temperatures illustrates how temperature can limit transcriptional efficiency and overall cellular function.

Mutations and Phenotypic Expression

Mutations are changes in the DNA sequence that can alter the function of genes and their corresponding proteins. In this scenario, the mutation in the sigma subunit of E. coli affects the stability of the RNA polymerase holoenzyme, leading to a phenotypic expression characterized by reduced transcriptional capability at higher temperatures. Understanding the relationship between genetic mutations and their phenotypic outcomes is essential for evaluating the growth and survival of the mutant strain under stress conditions.