High growth rate downregulates fumA mRNA transcription but is dramatically compensated by its mRNA stability in Escherichia coli.

Little is known about the association among the transcription, post-transcription, and protein production of the fumA gene. This study demonstrates that increasing growth rate (k) from 0.24/h to 0.96/h causes a marked eightfold reduction in fumA transcription as assessed using the β-galactosidase activity from fumA promoter fused with a lacZ reporter. It was further confirmed using Northern blot analysis. Most interestingly, the FumA protein levels remained unchanged over the growth rate, as indicated by Western blot analysis. Therefore, whether the reduced fumA mRNA expression under the high growth rate can be overcome by increasing the stability of the fumA mRNA was tested. The half-life of fumA mRNA was established to significantly increase by fivefold when the growth rate was increased to 0.96/h. This finding suggests that the cells could turn down the expression of fumA mRNA because of increased stability of its mRNA under the high growth rate. This notion indicates that mRNA stability plays an essential role in maintaining a critical cellular level of a given protein when the mRNA transcript is downregulated by a metabolic event.