Nascent ribosomal and messenger RNA in DNA-membrane-complexes of Escherichia coli

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.

Catabolite translational effects on the lac messenger RNA of Escherichia coli K12

The transcriptional and translational events occurring during the induction of the lac operon, were separated by blocking the translational step, either by aminoacid starvation or by addition of chloramphenicol. It was found that the carbon source used during the subsequent translation, affected the rate of beta-galactosidase synthesis. A decoordination effect on the production of enzymes of the lac system was also observed in high catabolite repression media, as well as in nitrogen limiting conditions. These findings suggested a similarity with the polarity phenomenon. In order to test this similarity, polarity suppressors of a Z- polar mutant were isolated. In one of these mutants, probably suA like, no carbon source effect was observed during the translational step. The induction kinetics in different media, after distinct pregrowth conditions, supported the idea that this mutant could be considered catabolite repression resistant only in certain restrictive conditions.