NaCl concentration (150 mM, 0 mM), selleckchem strains (Wild-type strain MS390; Δhfq, MS4831) and time after rifampicin treatment (0, 2, 4, 6, 8, or 32 min) are indicated above the panels. Primers used in the experiments are indicated on the right side of the

panels. B. Decay curves of invE mRNAs. Total RNA (100 ng) was subjected to real-time PCR analysis. The amount of RNA was normalized to an internal control (6S RNA) and expression was expressed relative to expression at time 0, which was set as 1.0. The X-axis indicates time after rifampicin treatment (0 to 8 min). Presence or absence www.selleckchem.com/products/psi-7977-gs-7977.html of 150 mM NaCl (plus, minus) and strains (Wt, wild-type strain MS390; Δhfq, MS4831) are indicated on the right side of the graph. Hfq-invE mRNA interaction in vitro under low-salt conditions In low osmotic conditions, bacteria maintain intracellular osmotic homeostasis through the rapid release of small intracellular molecules, such as ions and amino acids [17]. Since potassium ion is a major cation in bacteria [18], we measured intracellular K+ concentrations in S. sonnei under low osmotic conditions. In S. sonnei strain MS506 grown in the absence

and presence of 150 mM NaCl, the intracellular K+ concentration was 131 ± 4 mmoles/mg cell and 316 ± 0 mmoles/mg cell, respectively. These results indicated that K+ concentration under low osmotic conditions decreases to nearly 40% of that Belnacasan chemical structure seen under physiological osmotic conditions. Since interactions between proteins and nucleic acids are influenced by salt concentration, we examined the effect of salt concentration on the interaction of Hfq and invE RNA in vitro, using an RNA gel-shift assay and surface plasmon resonance (Biacore analysis). Hfq-invE RNA complex formation was examined by gel-shift assay using a binding buffer that contained 100 mM NH4Cl [19]. To control for the decrease in intracellular K+ concentration in the absence of physiological concentrations of NaCl, we also performed the gel-shift assay in buffer that

contained 40 mM NH4Cl. The RNA probe (2 nM) was mixed with increasing concentrations either of purified Hfq hexamer complex (from 1–16 nM) at 37°C for 10 min. In the presence of 40 mM NH4Cl, we observed an initial shift of the RNA probe upon the addition of 1 nM Hfq hexamer (Fig. 5A, lane 1), whereas the corresponding shift in the presence of 100 mM NH4Cl required 8 nM hexamer (Fig. 5A, lane 11). The apparent binding constant, as determined by the disappearance of half of the free RNA probe, was 1.7 nM Hfq in the presence of 40 mM NH4Cl and 6.2 nM in the presence of 100 mM NH4Cl. Figure 5 A. Gel-shift analysis in the presence of 40 mM or 100 mM NH 4 Cl. A 5′-end labelled invE RNA probe (2 nM) was mixed with Hfq protein and then incubated at 37°C for 10 min. Electrophoresis was carried out at 37°C. Concentration of NH4Cl (40 mM, 100 mM) and Hfq protein are indicated above the panels.