Question

Sigma 54 has a safety check that prevents it from continuously expressing the glutamine synthase gene. What is the basis for this control?

A. DNA looping and ATP hydrolysis inhibit sigma 54 from activating NIF genes under control conditions.

B. Sigma 54 is unable to melt the promoter without added ATP and a helper protein NtrC bound to the enhancer element at least 70 bp away.

C. Negative factor NtrC inhibits transcription regulated by sigma 54 under control conditions.

D. GreA and GreB proteins are necessary to activate sigma 54.

Answer 1

Sigma 54 requires ATP and a helper protein bound to an enhancer element to initiate transcription of the glutamine synthase gene, ensuring controlled gene expression.

Step-by-step explanation:

The safety check that prevents Sigma 54 from continuously expressing the glutamine synthase gene is based on the requirement of added ATP and a helper protein, such as NtrC, bound to the enhancer element at least 70 bp away from the promoter. This necessity for an activator protein and the hydrolysis of ATP ensures that sigma 54 cannot initiate transcription on its own.

Therefore, to correctly answer the student's question, the basis for the control preventing the continuous expression of the glutamine synthase gene lies in the requirement of both ATP hydrolysis and a distant bound activator to facilitate promoter melting and transcription initiation by sigma 54.