The transcriptional regulator SsrB is involved in a molecular switch controlling virulence lifestyles of Salmonella
Fig 5
SsrB represses hilD by directly acting on its promoter.
Expression of the hilD-cat-108+88 (A), hilD-cat-48+88 (B) and hilD-cat-37+6 (C) transcriptional fusions was tested in the WT S. Typhimurium strain with the vector pMPM-K3, or the plasmid pK3-SsrB, which expresses SsrB from a constitutive promoter. The CAT-specific activity was determined from bacterial cultures grown for 9 h in LB at 37°C. Data represents the mean with standard deviation of three independent experiments. *Statistically different values with respect to the WT strain with pMPM-K3, P < 0.0005. EMSAs were performed to analyze whether SsrB binds to the hilD DNA fragments in the hilD-cat-108+88 (D), hilD-cat-48+88 (E) and hilD-cat-37+6 (F) fusions. The DNA fragments were incubated with increasing concentrations of purified 6H-SsrBc (0, 0.5, 1, 1.5 and 2 μM). DNA-protein complexes are indicated by an asterisk.