coli tat mutants. BK designed and coordinated the study, and drafted the manuscript. All the authors read and approved the final manuscript.”
“Background TTSS plays a major role in virulence determination in pathogenic Shigella. The expression of TTSS is regulated in response to environmental stimuli, such as changes in salt concentration  and growth temperature [2, 3]. This response to environmental factors is appropriate for the life cycle of Shigella, in which the expression of virulence genes is required for invasion and propagation in the host intestinal tract, but might be a potential burden for survival in the natural environment.
The genes this website that encode the components of TTSS in Shigella are located on the virulence plasmid, and are controlled by two regulator proteins, VirF and InvE (VirB) [4, 5]. VirF, an AraC-type transcriptional regulator, activates the transcription of invE (virB) [4, 6–8]. InvE is a homologue of a plasmid-partitioning factor, ParB , and possesses DNA binding activity . InvE activates the transcription of the mxi-spa and ipa genes,
which encode the components of TTSS, through competition with the global repressor H-NS, a histone-like DNA binding protein . Recently, we reported that the temperature-dependent expression of TTSS is controlled at the post-transcriptional level, through the Nepicastat nmr regulation of InvE synthesis . The mRNA of invE is highly stable at 37°C, but stability decreases significantly at 30°C JPH203 supplier where the TTSS synthesis is tightly repressed. Deletion
mutants of hfq, which encodes an RNA-binding protein in Gram-negative bacteria, restores the expression of invE and other TTSS genes at low temperature due to the increased stability of the invE mRNA. To date, a detailed mechanism of osmolarity-dependent Metalloexopeptidase regulation of TTSS expression has yet to be elucidated. In the current study, we examined whether osmotic-dependent changes in TTSS expression involved post-transcriptional regulation. We present several lines of evidence that invE expression is regulated at the post-transcriptional level during TTSS synthesis in Shigella, and that the RNA chaperone Hfq plays a key role in regulating invE mRNA stability. Results Osmolarity and TTSS expression The expression of TTSS in Shigella is markedly reduced in low-salt LB medium . However, it is not clear whether the critical factor for the decreased expression of TTSS in LB medium is low osmolarity or low-salt concentration. We analysed the expression of TTSS in the presence of several different osmolytes, but similar osmotic pressures. There was a difference in the growth rate of S. sonnei in LB medium in the absence (doubling time, 42.1 minutes) and presence (doubling time, 30.6 minutes) of 150 mM NaCl. To control for differences in growth rate in LB medium, we used yeast extract and nutrient broth (YENB) medium , since growth rate in YENB in the absence (doubling time, 32.2 minutes) and presence (doubling time, 31.