Dynamics of chromosomal target search by a membrane-integrated one-component receptor
Fig 2
Dynamics of the target search by CadC.
(A) The target search of membrane-integrated transcription factors is investigated by experimentally measuring the response time of CadC. The molecular model on the right shows CadC in yellow, diffusing in the membrane and forming two dimers to bind to the two CadC binding sites within the cadBA promoter (CadC1 and CadC2), displayed in green. The cadC gene is located upstream of the cadBA operon. (B) Three E. coli strains with different positions of the cadBA promoter: N-PcadBA with the native DNA-binding site close to ori, T-PcadBA with the binding site at the terminus and N+T-PcadBA with both binding sites. (C) Experimental results from CadC spot detection. Fluorescent microscopic images were taken every minute after receptor activation and analyzed for CadC spots for the strains defined in panel B. The plot shows the response R(t), defined as the normalized fraction of cells with fluorescent spots as a function of time t after exposure to acid stress. Error bars correspond to the propagated standard deviation of ν(t) from averaging over multiple data sets. The dashed lines in the plot show a fit of the response function to the CDF of a sequential reversible two-step model with mixed initial condition for N-PcadBA, shown in blue dots and with fixed initial condition for T-PcadBA (orange stars) and N+T-PcadBA (cyan triangles). (D) The fluorescence microscopy images demonstrate how fluorescent spots appear after receptor activation.