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 What term best characterizes the type of mutation exhibited by the mutant bacterial strain? (Hint: The term was used in Chapter 4 to describe the Himalayan allele of the mammalian C gene.)

Key Concepts

Mutation Types

Mutations can be classified into several types, including missense, nonsense, and silent mutations. A missense mutation results in a single amino acid change in a protein, while a nonsense mutation introduces a premature stop codon, leading to truncated proteins. Silent mutations do not affect the amino acid sequence. Understanding these types is crucial for characterizing the effects of mutations on protein function.

Temperature Sensitivity

Temperature sensitivity refers to the ability of an organism or its components, such as proteins, to function optimally within a specific temperature range. In the context of E. coli, the mutant strain's RNA polymerase holoenzyme is stable at 37°C but becomes progressively destabilized at higher temperatures, illustrating how temperature can influence protein stability and function, which is critical for understanding the mutant's growth characteristics.

Phenotypic Expression

Phenotypic expression is the observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences. In this case, the mutant strain's ability to transcribe RNA at varying temperatures reflects its phenotypic expression, which is influenced by the mutation in the sigma subunit. This concept is essential for understanding how genetic mutations can lead to changes in organism behavior and physiology.