Question

You are examining the Psf gene and it is known that Psf is normally produced when cells are exposed to high levels of both Ca^2+ and Mg^2+. MetA, MetB, and MetC are important for binding to the promoter of the Psf gene and are involved in regulating its transcription. MetA binds to the A site in the promoter region, MetB binds to the B site, and MetC to the C site. You create binding site mutations in the A,B, and C sites and observe what happens to transcription of the Psf gene. Your results are summarized in a table pictured.

Which transcription factors are normally bound to the Psf promoter in the presence of both Mg2+ and Ca2+?
(a) MetA and MetB
(b) MetB and MetC
(c) MetA and MetC
(d) all of them

Answer 1

The transcription factors MetA, MetB, and MetC are all important for the normal expression of the Psf gene in the presence of both Mg2+ and Ca2+. Therefore, the answer to which transcription factors are normally bound to the Psf promoter under these conditions is (d) all of them.

Step-by-step explanation:

The question is asking which transcription factors are normally bound to the Psf promoter in the presence of both Mg2+ and Ca2+. Based on the context provided, MetA, MetB, and MetC are all important for binding to the promoter of the Psf gene and are involved in regulating its transcription. When mutations are made to the promoter's binding sites, the rate and occurrence of transcription of the Psf gene is affected, which indicates the involvement of these factors in the gene's expression in normal conditions.

Mutated promoters can either increase or decrease the rate of transcription depending on whether they enhance or impede the binding of transcription factors. In the scenario where all factors MetA, MetB, and MetC are required for transcription, mutating their respective binding sites would likely lead to a decrease in transcription. Therefore, if the presence of both Mg2+ and Ca2+ normally induces the expression of the Psf gene, it suggests that all three transcription factors MetA, MetB, and MetC are required to bind to their respective sites (A, B, and C) in the promoter region, implicating the answer (d) all of them as normally being bound to the Psf promoter.