Dynamic change in promoter activation during lysine biosynthesis in Escherichia coli cells

We investigated the expression dynamics of genes involved in lysine biosynthesis in Escherichia coli cells to obtain a quantitative understanding of the gene regulatory system. By constructing reporter strains expressing the green fluorescence protein (gfp) gene under the control of the promoter regions of those genes associated with lysine biosynthesis, time-dependent changes in gene expression in response to changes in lysine concentration in the medium were monitored by flow cytometry. Five promoters involved in lysine biosynthesis respond to the changes in lysine concentration in the medium. For these five promoters, time-dependent gene expression data were fitted to a simple dynamical model of gene expression to estimate the parameters of the gene regulatory system. According to the fitting parameters, dapD shows a significantly larger coefficient of repression than the other genes in the lysine synthesis pathway, which indicates the weak binding activity of the repressor to the dapD promoter region. Moreover, there is a trend that the closer an enzyme is to the start of the lysine biosynthesis pathway, the smaller its maximal promoter activity is. The results provide a better quantitative understanding of the expression dynamics in the lysine biosynthesis pathway.