A Model for Sigma Factor Competition in Bacterial Cells
Figure 3
(A) Normalized transcription rate (Equation 12) for a σ70-dependent promoter as a function of the number of alternative sigma factors. The numbers of
and cores are fixed. The blue line is for a saturated promoter (with
M) and the cyan line for an unsaturated promoter (with
M). (B) Comparison of model predictions (lines) with an in vitro competition experiment [29] with a fixed amount of core and σH and different amounts of
(stars). The plot shows the transcription rate of a σH-dependent gene (normalized to the maximal value) as a function of the concentration
. (C) The sigma-core and the holoenzyme-promoter dissociation constants (see Table 2) are determined by fitting the results of transcription rate experiments with a fixed amount of cores in the same conditions as in (B) without competition in the presence of a DNA template containing σH- and σ70-driven genes [29], [32]. (D) When a σ70-dependent promoter also binds another type of holoenzyme or overlaps to another promoter,
also acts as a repressor of the σ70-dependent transcription. (E) Normalized transcription rate of a saturated and unsaturated σ70-dependent promoter as a function of the number of
(blue and cyan solid lines with
M and
M, respectively). The dashed line show the corresponding results in the absence of repression by promoter sharing or overlapping.