What term best characterizes the type of mutation exhibited by the mutant bacter

Question

What term best characterizes the type of mutation exhibited by the mutant bacterial strain?

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

Explanation / Answer

The core RNA polymerase of the Gram-negative bacterium Escherichia coli requires only four subunits (two ? and one each of ? and ??) to elongate the nascent RNA chain. A sigma subunit is required for initiation of the RNA polymerase holoenzyme (core polymerase with a sigma factor) at a promoter. The sigma factor is released after formation of a productive elongation complex. The essential core subunits of the bacterial RNA polymerase are highly conserved throughout nature.

The sigma subunits of bacterial RNA polymerases are required for the selective initiation of transcription. The mutation that can reduce the efficiency of sigma subunit of RNA polymerase might be grn1 mutation, or grg mutation. These are a kind of single mutations and the mutant cell shows cold-sensitivity. Such cells can no longer transcript at higher temperatures.

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