Theoretical work suggests that a slow promoter-binding of the central transcription factor ComK leads to stochastic phenotype switching in the bacterium Bacillus subtilis. We identify the source of noise by probing the fluctuations of endogeneously expressed fluorescent proteins under the control of the major competence promoter using single-molecule live cell imaging. A key parameter that determines the speed of ComK-DNA-binding is the intracellular diffusion coefficient of ComK. We use in vivo single-molecule tracking to identify the timescale for the promoter binding of ComK in live bacterial cells. Our study revisits key assumptions behind genetic network models to improve the design of genetic circuits with new functionalities.
Stochastic fluctuations in promoter activity (top) and diffusion of single transcription factors (bottom, left) will be monitored using our new objective-based TIRF microscope.