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A Model for Sigma Factor Competition in Bacterial Cells

Figure 4

Effect of non-specific binding of holoenzymes and cores to DNA.

(A) Formation of holoenzymes in the presence of one type of sigma factor in the absence of DNA (no non-specific binding, dashed line), in the presence of DNA with equal non-specific binding affinities of cores and holoenzymes ( M, dotted line) and with different non-specific binding affinities ( M, M, solid line). (B) Number of free cytoplasmic holoenzymes and (upper row) and total number of holoenzymes (free and non-specifically bound, , lower row) as functions of the copy number of alternative sigma factors for three different combinations of non-specific binding affinities: in (i) and (ii) all non-specific dissociation constant are equal ( M), in (iii) and (iv) the non-specific dissociation constant for the core is smaller than for the holoenzymes ( M, M), in (v) and (vi) the non-specific dissociation constant for the is smaller than for and core ( M, M). The dashed lines in all panels shows the reference case without DNA (no non-specific binding).

doi: https://doi.org/10.1371/journal.pcbi.1003845.g004