Chapter 8, Problem 20P

Wild-type E. coli grow best at $\text{37°C}$ but can grow efficiently up to $\text{42°C}$. 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 $\text{37°C}$. The mutant holoenzyme is progressively destabilized as the temperature is raised, and it completely denatures and ceases to carry out transcription at $\text{42°C}$. Relative to wildtype growth, characterize the ability of the mutant strain to carry out transcription at

a. $\text{37°C}$

b. $\text{40°C}$

c. $\text{42°C}$

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