Question

If in an experiment you mutate the two trp codons in the attenuator to ala codon what will be the impact on repression?

(a) Repression will be normal

(b) Reduced repression

(c) No repression so the gene would be constitutively turned on

(d) Activation will take place

The question was posed to me in an interview for job.

My doubt is from Operons : Trp in division Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

The correct option is (b) Reduced repression

Explanation: The basis of attenuation at the attenuator is the presence of two trp operon which stalls the RNA polymerase when trp is deficient. Mutating the trp to ala eliminates the attenuator’s mode of repression. However, there is still an intrinsic mode of repression by binding of a repressor, which is still active.