Stationary phase, amino acid limitation and recovery from stationary phase modulate the stability and translation of chloramphenicol acetyltransferase mRNA and total mRNA in Escherichia coli

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Abstract
The functional stability of the chloramphenicol acetyltransferase (cat) mRNA, as well as the functional stability of the total mRNA pool, change during the course ofEscherichia coliculture growth. mRNA half-lives are long during lag phase, decrease during the exponential phase and increase again during the stationary phase of the bacterial growth cycle. The half-lives ofcatmRNA and total mRNA also increase three- to fourfold during amino acid starvation when compared to exponential culture growth. Even though the stability of thecatmessage changes about fourfold during culture growth, the amount ofcatmRNA per cell mass does not vary significantly between the culture growth phases, indicating that there are compensating changes incatgene transcription. Translation ofcatmRNA also changes during culture growth. In exponential phase, the rate ofcattranslation is about 14-fold higher than when the culture is in stationary phase. This is in contrast to the fourfold increase in stability ofcatmRNA in the stationary-phase culture compared to the exponentially growing culture and indicates that active translation is not correlated with increased mRNA stability. When a stationary-phase culture was diluted into fresh medium, there was a five- to sevenfold increase in CAT synthesis and a threefold increase in total protein synthesis in the presence or absence of rifampicin. These results suggest that while mRNA becomes generally more stable and less translated in the stationary-phase culture, the mRNA is available for immediate translation when nutrients are provided to the culture even when transcription is inhibited.