Kinetic of induced enzyme synthesis determination of the mean life of galactosidase-specific messenger RNA

Abstract

The induced synthesis of β-galactosidase (β-d-galactoside galactohydrolase, EC 3.2.1.23) in Escherichia coli has been studied initially after addition of the inducer and terminally after removal of the inducer. A method of giving short pulses of inducer allowed the identification of inducer-dependent and inducer-independent processes, the first including the inactivation of the repressor and the synthesis of messenger RNA, the second including protein synthesis. Various inhibitors help distinguish these processes. The following conclusions have been reached. The inactivation of the repressor and the start of messenger RNA synthesis followed the addition of inducer without delay. The rate of synthesis of messenger RNA was constant frrm its onset. Messenger RNA was transcribed into polypeptide but completed polypeptide chains did not appear before 1.5 min, the absolute lag. Messenger RNA was inactivated according to first-order kinetics with a half-life of 1 min during enzyme synthesis as well as during inhibition of protein synthesis. The steady-state amount of messenger RNA was equivalent to some 1.5 min-maximal synthesis. The time constant of its accumulation agree with the time constant of its decay. An absolute lag of 1.5 min plus an acceleration of 1.5 min in enzyme synthesis agreed with the previously observed 3-min lag. An experimental scheme has been designed to distinguish between inhibitors of the first and the second transcription. As an example, the glucose effect is shown to be an inhibition of only the first transcription.