Figure 2. SPI1 gene expression is induced by a step increase in P_hilD promoter activity.

(A) Comparison of time-course dynamics for P_hilD (pSS074) promoter activities in wild type (black) and a ΔhilD mutant (JS253, red) as determined using luciferase transcriptional reporters. (B) Comparison of P_hilD (pSS072) promoter activity in wild type (black) and a ΔhilD mutant (JS253, grey) as determined using GFP transcriptional reporters and flow cytometry. Note that the activation of the P_hilD promoter is switch-like both in wild type and the ΔhilD mutant. Experiments were performed as described in Figure 1 .