Resolution:
## Figure 1.
A phosphorylation gradient can be produced by fast asymmetric source and sink activities.A) Schematic of localization of source and sink. B) Mathematical modeling of the spatial asymmetry in phosphorylated response regulator
for different source and sink rates. A substantial gradient is obtained only when
the phosphorylation rate _{σk}and dephosphorylation rate _{σp}are faster than the inverse of the time scale required for diffusion across the cell,
1/τ_{D} = 2D/L^{2}. We model the cell in 1D with length L = 2 μm and poles of extent r_{p} = 0.25 μm. The diffusion constant is D = 2 μm^{2}/s. (Inset) The ratio of R∼P between the two poles ηis virtually independent of the source rate σ._{k}Tropini |