passages.id: split_1_test_2948_passage
passages.type: progene_text
passages.text: The need for two specific inducing signals , one for ChbR to activate the expression of the operon and a second for NagC to relieve its repression , ensure that the chb operon is only induced when there is sufficient flux through the combined chb - nag metabolic pathway to activate expression of both the chb and nag operons .