Question

Which one of the folowing is not true of the attenuation that controls gene expression?

• A. It is seen in tryptophan operon
• B. It is a mechanism whereby transcription is controlled before the initiation of of the mRNA synthesis
• C. Attenuation depends on the stem and loop structures in the mRNA
• D. In eukaryotes, there is no exact equivalent of attenuation as transcription and translation are spatially separated.

Hint:

Remember: Promoter regulation controls transcription initiation, while attenuation controls transcription termination (elongation).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Transcription attenuation is a regulatory mechanism in bacteria that couples translation directly to transcription to control gene expression.

Step 2: Detailed Explanation:
- (A) is true because attenuation was first discovered and characterized in the tryptophan (trp) operon of E. coli.
- (C) is true because the mechanism relies on the formation of alternative hairpin stem-loop structures (terminator vs. anti-terminator loops) in the leader region of the emerging mRNA.
- (D) is true because attenuation requires translation of the leader peptide to occur simultaneously with transcription.
Since eukaryotes contain a nuclear membrane that spatially separates nuclear transcription from cytoplasmic translation, they cannot utilize this mechanism.
- (B) is false because attenuation acts on the transcription elongation complex, terminating transcription prematurely *after* it has already been initiated. It does not regulate transcription *before* mRNA synthesis begins.

Step 3: Final Answer:
The statement that attenuation controls transcription before initiation of mRNA synthesis is not true.