Accumulation of untranslated lactose-specific messenger ribonucleic acid during catabolite repression in Escherichia coli

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.

A messenger RNA from the lactose operon of Escherichia coli that can not direct the production of functional -galactosidase in absence of exogenous adenosine 3',5-cyclic monophosphate

In a temperature-sensitive mutant of Escherichia coli, beta-galactosidase cannot be induced at the nonpermissive temperature (43 degrees C) without the addition of exogenous 3', 5'-cyclic AMP (cAMP), although the intracellular concentration of this nucleotide is normal. This specific effect of cAMP is probably general in this strain for those operons which are controlled by the cAMP receptor protein and cAMP, but not for other parts of the chromosome. The lac mRNA produced at 43 degrees C in absence of cAMP is transcribed from the correct DNA strand and it directs the synthesis of enzymatically inactive material cross-reacting with beta-galactosidase. Experiments separating transcription from translation by using rifampicin, suggest that cAMP exerts its effect during initiation of transcription or translation of lac mRNA, but does not affect the propagation of either the messenger or of the beta-galactosidase polypeptide chain.