Which of the following occurs when the cellular level of tryptophan decreases in E.coli?
A)Tryptophan-bound Trp repressor associates with trp operator.
B)Trp apo-repressor has lowered affinity for trp promoter,allowing RNA polymerase binding and transcription of the trp operon.
C)Tryptophan binds trp inducer to promote positive control of trp promoter.
D)Trp repressor has a greater affinity for trp operator.

Question

Quizplus · Accepted Answer

When the cellular level of tryptophan decreases in E. coli, the Trp apo-repressor (a form of the repressor protein without tryptophan bound) has a lowered affinity for the trp operator, not the promoter as stated, which allows RNA polymerase to bind to the promoter and initiate transcription of the trp operon. This process is part of a negative feedback mechanism where the operon is turned on (transcribed) when tryptophan levels are low to synthesize more tryptophan.

Which of the Following Occurs When the Cellular Level of Tryptophan