A Regulatory Gene Simultaneously Involved in Repression and Induction

A close relationship between enzyme repression and induction has become increasingly apparent. A particularly graphic illustration of this relationship was uncovered (Vogel et al., 1963), when a derivative of strain W of Escherichia coli was isolated which contains an inducible acetylornithine δ-transaminase. The inducibility is enzyme-specific: the transaminase can be induced by arginine while the other enzymes in the arginine pathway are being repressed. The inducible derivative was obtained as a mutant of a strain deficient in the wild-type (repressible) transaminase. The present paper examines two questions: (a) where does the mutation leading to inducibility map? (b) is the Rarg gene (which normally governs the repressibility of the enzymes in the arginine pathway) involved in the inducibility phenomenon?