A Model for Sigma Factor Competition in Bacterial Cells
Figure 2
(A) Number of holoenzymes and
as a function of the copy number of alternative sigma factors. Quantities of all molecular species are expressed as absolute numbers per cell. The gray dashed line represents the onset of the competition, when
. The values of the parameters used in the simulations are summarized in Table 1. (B) Determination of the sigma-core dissociation constants for
and
(see Table 2) by fitting the results of binding assays between cores and sigma factors [30], [39]. The number of core-sigma complexes normalized to the maximal number of holoenzymes,
. Stars show the experimental data and lines are due to the fit. (C) Comparison of model predictions (lines) with an in vitro competition experiment [30] with a fixed amount of core and different equimolar amounts of
and
(stars) in the same conditions as in (B). The plot shows the fraction of sigma factors bound in holoenzymes as a function of the total sigma factor concentration,
.