You are comparing transcription of gene X in a normal strain of E. coli cells an

Question

You are comparing transcription of gene X in a normal strain of E. coli cells and a strain of that has been mutated. You observe that in the mutant cells gene X is not transcribed. What mutation in could explain this observation?

a. The sigma subunit of RNA polymerase is non functional.

b. There is a mutation within the protein coding sequence of gene X that causes the production of a non functional protein.

c. There is a mutation in the-10 TATaaT promoter sequence for gene X.

d. There is a mutation in the start codon for gene X.

Explanation / Answer

Correct option. C. Mutation in -10 promotor region.

Ans. #A. Sigma factor binds to the promotor and recruits RNA pol to it during imitation of transcription. Once promotor clearance is done, sigma factor dissociates. Rest of the transcription process (elongation and termination) is mediated by RNA polymerase. A mutated sigma factor is often functional with change in its relative activity and response to environmental stimuli to which the native sigma factor responded to. So, there is possibility of getting the transcribes product- mRNA.

#C. The -10 promotor region interacts with other regulatory elements (say, enhancers) simultaneously with interacting with sigma factor during initiation of transcription. A mutation in promotor region results no interaction with the regulatory elements of the gene- so, transcription can’t be initiated in absence of proper stimuli. Moreover, it also may hinder the binding of sigma factor- leading to no recruitment of RNA pol. Under these circumstances, the gene will not be transcribed.

Therefore, it is the mutation in the promotor that inhibits the transcription of gene X.

#B and #D. The codon come in play during translation after the mRNA has been produced (i.e. gene has already been transcribed). Mutation in codons does NOT affect gene transcription- however translation may or may not give functional protein depending on the type of mutation.

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