Figure 3.

In vivo TSC-induced co-regulation of adjacent genes on the Escherichia coli chromosome. (A) The expression of the inducible tetP promoter (by increasing tet inducer concentration or absence of tet repressor) progressively activates a divergent promoter (tufB) (14). This effect is reproduced semi-quantitatively in our simulations by only changing the tetP basal initiation rate; small discrepancies with the data may reflect a different SC-sensitivity of the two promoters (see text). (B) The gyrA promoter is activated by the expression of the upstream isodirectional gene uidA, almost independently of the distance between the two genes (from 0 to 6 kb) (16). This observation is fully consistent with our hypothesis of fast diffusion of SC over kilobase distances. A reversed promoter activation curve was used here to account for the unusual properties of the gyrA promoter (see text and Supplementary Figure S2B). (C) Simulations (without insert) show that the gyrA activation factor is strongly dependent on the expression strength of the uidA gene.