Summary auto-generated
This study examined how mRNA stability and translation change during different growth phases of Escherichia coli and in response to nutrient starvation. Researchers measured the functional half-life of chloramphenicol acetyltransferase (cat) mRNA and total cellular mRNA using rifampicin-mediated transcription inhibition combined with pulse-labeling of newly synthesized proteins. The results showed that cat mRNA had a short half-life of 0.7 minutes during exponential growth but increased approximately fourfold to 2.8 minutes during lag and stationary phases. Total mRNA showed a similar pattern, with longer half-lives during nutrient-poor conditions (lag and stationary phases) compared to exponential growth. During leucine starvation, both cat and total mRNA stability increased threefold to fourfold relative to exponential phase. Despite substantial changes in mRNA stability, the amount of cat mRNA per cell mass remained relatively constant across growth phases, suggesting compensatory changes in transcription rates. Translation rates showed an inverse relationship with mRNA stability: cat mRNA translation was 14-fold higher during exponential phase than stationary phase. When stationary-phase cultures were diluted into fresh medium, CAT synthesis increased 5-7 fold even without new transcription, indicating that mRNAs accumulated during stationary phase are available for rapid translation upon nutrient availability.
Key findings
- mRNA stability increases 3-4 fold during stationary phase and amino acid starvation compared to exponential growth
- Translation rates and mRNA stability are inversely correlated; increased mRNA stability does not correlate with increased translation
- Constant cat mRNA levels across growth phases despite 4-fold changes in stability suggest transcription rates adjust reciprocally with mRNA decay rates
- Stationary-phase mRNAs can be rapidly translated following nutrient replenishment without requiring new transcription initiation
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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 of Escherichia coli culture 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 of cat mRNA and total mRNA also increase three- to fourfold during amino acid starvation when compared to exponential culture growth. Even though the stability of the cat message changes about fourfold during culture growth, the amount of cat mRNA per cell mass does not vary significantly between the culture growth phases, indicating that there are compensating changes in cat gene transcription. Translation of cat mRNA also changes during culture growth. In exponential phase, the rate of cat translation is about 14- fold higher than when the culture is in stationary phase. This is in contrast to the fourfold increase in stability of cat mRNA 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.