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 37°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.

Temperature Effects on Enzyme Activity

Enzymes, including RNA polymerase, are sensitive to temperature changes, which can affect their stability and activity. Typically, enzymes have an optimal temperature range where they function best. In this case, the wild-type E. coli grows optimally at 37°C, and understanding how the mutant strain's transcriptional activity is influenced by temperature is key to characterizing its growth relative to the wild-type.

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, leading to a decrease in transcription efficiency at elevated temperatures. Analyzing how this mutation impacts the strain's ability to transcribe at 37°C compared to wild-type is essential for understanding its overall growth and survival.