FIG. 14.

An effective restoring force on protein concentration. The continuous growth model predicts that the time-derivative of protein concentration is linearly dependent on the deviation of the concentration from its steady-state value, see Eq. (29). The figure shows experimental data in E. coli (from Ref. (Tanouchi et al., 2017)), where the concentration of a constitutively expressed (i.e., unregulated) gene, fluorescently labeled, is tracked over time. The red points are binned single-cell data: the time-derivative of the concentration is averaged over many cells with approximately the same concentration, thus suppressing the fluctuations and revealing the underlying linear trend. Adapted from Ref. (Lin and Amir, 2021), with permission.