The Trp operon is a coordinately regulated group of genes (trpA-trpE) that are required for tryptophan biosynthesis in E. coli. Based on the figure above, which of the following correctly describes the regulation of the Trp operon?

• In the absence of tryptophan, the repressor is active and binds to the Trp operator, preventing RNA polymerase from transcribing the operon.

• In the presence of tryptophan, the repressor is active and binds to the Trp operator, preventing RNA polymerase from transcribing the operon.

• In the absence of tryptophan, the trpR gene is inactive, preventing the production of the repressor that blocks expression of the operon

• In the presence of tryptophan, the trpR gene is inactive, preventing the production of the repressor that blocks expression of the operon

 

RNA Polymerase Promoter Operator trpE trpD trpC trpB trpA DNA P trpR R Active Repressor 5-- trpR MRNA R Inactive Repressor Active Repressor R = Repressor molecule T= Tryptophan molecule Pg = Promoter for the trpR gene trpR = Repressor gene Operator Binding site for repressor molecule