Analysis of fluctuation in protein abundance without promoter regulation based on Escherichia coli continuous culture.

Fluctuation of protein abundance of isogenic Escherichia coli cells in uniform environment was studied. Based on a continuous culture system, which provides homogeneous culture environment, we investigated the fluctuation in GlnA protein abundance regardless of known glnALG promoter regulation. As results by flow cytometer, we found that the GlnA protein abundance in the cells exhibit a large fluctuation, even though GlnA protein is an essential factor for cell growth and the environment is homogeneous. Furthermore, among several steady states, transient processes of such heterogeneous cell population were investigated, by changing the environmental conditions. The results showed that the expression of GlnA protein can be controlled, depending on its necessity, even though there is no known regulatory machinery. These results may provide a clue to understand the nature of regulation of protein expression dynamics with the stochastic fluctuation.