Unusual stability and translation kinetics of an Escherichia coli lac messenger RNA synthetized during amino-acids deprivation.

Escherichia coli, cultured on minimal medium and deprived of its required amino-acids, was induced for lac genes transcription. After inducer removal and restoration of growth, beta-galactosidase synthesis was measured. Two different kinetics of enzyme synthesis were observed depending on the starvation conditions employed during the induction period: 1. beta-galactosidase synthesis was immediately obtained and a plateau was reached, in 20 min after restoration of growth, when cells had been induced during deprivation of amino-acids and carbon source. 2. beta-galactosidase displayed an unusually long rate of synthesis, and plateau was not reached before two doubling times, when cells had been induced during the deprivation of the sole amino-acids. The latter result points out a problem of messenger stability during those long translation kinetics and led us to study the behaviour of strains carrying lac genetic determinants on different replicative structures; chromosomic and plasmidic. In those two situations, induction of lac messenger RNA was obtained and ratify our previous observations. However, their translation kinetics suggest a DNA linkage of this induced messenger.