Question

Which of these systems give the best mode for turning trp operon off?

(a) Repressor

(b) Attenuator

(c) Repressor with a downstream poly A tail

(d) Repressor with an attenuator

I had been asked this question in unit test.

Asked question is from Operons : Trp topic in division Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

Right answer is (d) Repressor with an attenuator

To explain: A repressor provides 70 fold lowering of expression while an attenuator provided an additional 10 fold lowering of expression. Together they have a net effect of 700 fold repression over the trp operon.