| Summary: | 碩士 === 國立交通大學 === 生物科技研究所 === 89 === Abstract
Escherichia coli contains three biochemically distinct fumarases to catalyze the interconversion of fumarate to L-malate in the tricarboxylic acid (TCA) cycle. In order to study how the fumA and fumC genes are regulated by different air saturation and cell growth rates, we examined the fumarase activity of fumA, fumB and fumC mutants in continuous cultures. The results showed that the fumarase activity of three mutants are regulated by the rate of cell growth as they shown in wild type strain. However, it showed that there is feedback regulation on fumA and fumC genes . At transcriptional level, there are the same variation of fumA and fumC genes between the amount of mRNA and the enzyme activity. In addition, when the specific cell growth rate increase from 0.48/h to 1.2/h, the amount of fumC mRNA decrease 2.3 fold, while the stability of fumC mRNA increase 2.5 fold and the expression of FumC enzyme activity decrease 2.4 fold. Therefore, it showed that expression are dependent on cell growth rate at (post-) transcriptional and translational level. In addition, the regulation of the stability of fumC mRNA are carbon source dependent. The results showed that the growth rate-dependent regulation of fumA and fumC genes was affected by oxygen level and carbon source utilization at both transcriptional and translational levels.
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