The E. coli chromosome contains the malanose operon (shown below). The malanose
ID: 212588 • Letter: T
Question
The E. coli chromosome contains the malanose operon (shown below). The malanose operon has a "strong promoter," which is negatively regulated by MalX transcription factor. MalX protein exerts its influence by binding to a regulatory element called the MalX RE 23) RE gene B An E. coli strain is isolated that has a mutation prevents the production of the MalX protein. What effect will this mutation have on transcription of the malanose operon (genes A and B)? D8.5, L104, L105 A. Transcription of the malanose operon will occur. B. Transcription of the malanose operon will be completely shut down. C. The cell will not be able to turn the malanose operon OFF using Malx. D. A and B E. A and C Could you imagine how this question might look if the promoter was weak and the transcription factor controlled the gene by positive regulation?Explanation / Answer
Q.23
Option: E.
Transcription of the malanose operon will occur and also the cell will not be able to turn the malanose operon off using MalX.
MalX has negative regulation on this operon. Presence of this regulatory protein will lead to its binding on the MalX RE. This prevents the RNA polymerase from transcribing the gene. It is because the MalX is blocking the movement of RNA polymerase by binding to the MalX RE.
Consider the promotor was weak and the TF has positive regulation on the operon. According to the question there is mutation which prevents the production of Positive regulator TF.
In this case the transcription of malanose operon will never occur. And the transcription of the malanose operon will be completely shut down. Since the TF has positive regulation on the gene, its presence is very crucial for the RNA polymerase to transcribe the gene. In its absence the transcription won’t proceed.
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