Question

Which segments of the attenuator together form the repression loop?

(a) Segment 1-2

(b) Segment 2-3

(c) Segment 3-4

(d) Segment 1-4

The question was posed to me during an interview for a job.

My question is based upon Operons : Trp topic in division Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

The correct choice is (b) Segment 2-3

For explanation I would say: In the absence of tryptophan when the RNA polymerase stalls at segment 1 of the attenuator it hinders the formation of loop 1-2. The alternate loop so formed is loop 2-3 which is the attenuation loop.