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

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.