The figure below shows the mechanism of transcription termination at the trp att

Question

The figure below shows the mechanism of transcription termination at the trp attenuator in wild-type E. coli cell. Select one of the following responses regarding the trp operon system

If you introduced mutations in region 1 to eliminate Trp codons from the leader peptide, what type of response would you expect from this mutant E. coli strain?

A- Transcription is terminated at the trp operon attenuator only at high concentration of Trp

B- Transcription is terminated at the trp operon attenuator only at low concentration of Trp

C- Transcription is terminated at the trp operon attenuator at both high and low concentrations of Trp

D- Transcription is not terminated at the trp operon attenuator at any concentration of Trp

a high tryptophan leader peptide coding region b low tryptophan leader peptide trp operon mRNA tryptophan codons C no protein synthesis Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Explanation / Answer

Important points to be consider:

* If trp is high in the medium, ribosome translates leader sequence, hence transcription termination occurs --------Tryptophan turned off

* If trp is low in the medium, ribosome stalls on the leader sequence, hence transcription termination does not occur because of trp regulated genes--------Tryptophan turned on

Mutants cannot be fully induced/repressed by the trptophan

If we introduce mutations in region 1 to eliminate Trp codons from the leader peptide in E.Coli strain then,

D- Transcription is not terminated at the trp operon attenuator at any concentration of Trp.

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