Po The expression of Gene A is up-regulated (increased) by the activator B, whic

Question

Po The expression of Gene A is up-regulated (increased) by the activator B, which binds to the enhancer C upstream (before) of Gene A. Activator B is also activated by the effiector hormone D Once the activator B is bound by the effector D, it binds to the enhancer and recruits RNA polymerase, which binds to the promoter of gene A How many mutations are possible for RNA polymerase that would prevent the gene from turning on? Do not count a mutation that stops its polymerizing activity. How many mutations are possible for the promoter that would prevent the gene from turning on?

Explanation / Answer

The RNA polymerase action depends on two key features. 1. Binding of polymerase to the right promoter. 2. Binding of B activator to the polymerase. Hence these two mutations in the RNA polymerase can prevent gene expression.

The promoter is a set of specific sequence which is detected by the RNA polymerase. Any mutation in the sequence can render the promoter invisible to the polymerase. Thus one mutation in promoter sequence can prevent gene expression.

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