Discussion
Which one of the following σ (sigma) factors is responsible for the transcriptional regulation of nitrogen assimilation?
Answer: B
Nitrogen assimilation genes are transcribed with σ 54.
In E. coli, σ54 (RpoN, also called σN) directs RNA polymerase to promoters of nitrogen-regulated genes such as glnA, which encodes glutamine synthetase. Unusually, the σ54 holoenzyme cannot open the promoter on its own; it needs an ATP-hydrolysing enhancer-binding activator, which for nitrogen genes is NtrC, switched on when nitrogen is scarce.
σ70 is the housekeeping factor for most genes in growing cells. σ28 (FliA) transcribes flagellar and chemotaxis genes. σ24 (σE) responds to stress in the cell envelope.
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