The corepressor of tryptophan biosynthesis in the trp operon
     The corepressor of tryptophan biosynthesis in the trp operon of E. coli is  the cAMP-CRP complex  tryptophan  the attenuator  lactose  the trp tRNA 
  
  Solution
11. tryptophan
A corepressor downregulates the expression of genes by binding to and activating a repressor transcription factor. The molecule that functions as a corepressor for the trp operon is tryptophan.

