N'ime genome nke Escherichia coli bacteria, dịka ọmụmaatụ, enwere usoro nke mkpụrụ ndụ ihe nketa dị mkpa maka synthesis nke amino acid tryptophan. Otú ọ dị, mgbe tryptophan dịlarị na cell, mkpụrụ ndụ ihe nketa ndị a maka synthesis nke tryptophan adịghịzi mkpa. Ọnụnọ nke tryptophan na-emetụta ọrụ nke mkpụrụ ndụ ihe nketa nke mkpụrụ ndụ tryptophan iji gbochie tryptophan (a repressor), na-agbanwe usoro nzaghachi nke transcription, na-egbochi ọtụtụ mkpụrụ ndụ ihe nketa nke na-ejikọta na usoro nhazi nke tryptophan. Ajụjụ: Olee otú ndị na-emepụta tryptophan na-ejikọta?
puku kwuru puku