A role for H-NS in the regulation of the virF gene of Shigella and enteroinvasive Escherichia coli

Prosseda, Gianni; Fradiani, Piera Assunta; Lorenzo, Manuela Di; Falconi, Maurizio; Micheli, Gioacchino; Casalino, Maria Assunta; Nicoletti, Mauro; Colonna, Bianca

doi:10.1016/s0923-2508(97)83619-4

Cited by 73 publications

(82 citation statements)

References 37 publications

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“…This is similar to the situation observed in the VirF-VirB regulatory cascade of S. flexneri (38). The toxT, tcpA, and ctx promoters possess characteristics that have been correlated with H-NS binding.…”

Section: Discussionsupporting

confidence: 82%

Vibrio cholerae H-NS Silences Virulence Gene Expression at Multiple Steps in the ToxR Regulatory Cascade

et al. 2000

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H-NS is an abundant nucleoid-associated protein involved in the maintenance of chromosomal architecture in bacteria. H-NS also has a role in silencing the expression of a variety of environmentally regulated genes during growth under nonpermissive conditions. In this study we demonstrate a role for H-NS in the negative modulation of expression of several genes within the ToxR virulence regulon of Vibrio cholerae. Deletion of hns resulted in high, nearly constitutive levels of expression of the genes encoding cholera toxin, toxin-coregulated pilus, and the ToxT virulence gene regulatory protein. For the cholera toxin-and ToxT-encoding genes, elevated expression in an hns mutant was found to occur in the absence of the cognate activator proteins, suggesting that H-NS functions directly at these promoters to decrease gene expression. Deletion analysis of the region upstream of toxT suggests that an extensive region located far upstream of the transcriptional start site is required for complete H-NS-mediated repression of gene expression. These data indicate that H-NS negatively influences multiple levels of gene expression within the V. cholerae virulence cascade and raise the possibility that the transcriptional activator proteins in the ToxR regulon function to counteract the repressive effects of H-NS at the various promoters as well as to recruit RNA polymerase.

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Section: Discussionsupporting

confidence: 82%

Vibrio cholerae H-NS Silences Virulence Gene Expression at Multiple Steps in the ToxR Regulatory Cascade

et al. 2000

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“…The results obtained at pH 8 are shown in Figure 3D. These results were consistent with studies in Shigella and enteroinvasive Escherichia coli, where H-NS repressed virF expression at low temperature and low pH (Prosseda et al 1998). Although the in vivo responses to temperature and pH may be more complex, our results highlight the importance of the stiffening mode of H-NS binding in the regulation of virulence gene expression.…”

Section: Two Modes Of H-ns Binding To Dna Genes and Development 341supporting

confidence: 90%

“…The importance of the stiffening mode in gene silencing is further supported by its direct susceptibility to temperature and pH (Fig. 3A-C), since these stimuli are known modulators of H-NS activity (Atlung and Ingmer 1997;Williams and Rimsky 1997;Prosseda et al 1998;McLeod and Johnson 2001). In addition to these environmental factors, numerous regulators are involved in derepressing the genes silenced by H-NS (Stoebel et al 2008).…”

Section: Mechanisms Of H-ns-mediated Dna Stiffening and Dna Foldingmentioning

confidence: 90%

A divalent switch drives H-NS/DNA-binding conformations between stiffening and bridging modes

Liu¹,

Chen²,

Kenney³

et al. 2010

Genes Dev.

220

314

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Heat-stable nucleoid structuring protein (H-NS) is an abundant prokaryotic protein that plays important roles in organizing chromosomal DNA and gene silencing. Two controversial binding modes were identified. H-NS binding stimulating DNA bridging has become the accepted mechanism, whereas H-NS binding causing DNA stiffening has been largely ignored. Here, we report that both modes exist, and that changes in divalent cations drive a switch between them. The stiffening form is present under physiological conditions, and directly responds to pH and temperature in vitro. Our findings have broad implications and require a reinterpretation of the mechanism by which H-NS regulates genes.

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“…At temperatures less than 32 uC, expression of virulence genes is negatively regulated; derepression occurs at the permissive temperature of 37 u C (Colonna et al, 1995;Dorman et al, 1990;Falconi et al, 1998;Gardel & Mekalanos, 1994;Hromockyj et al, 1992;Maurelli & Sansonetti, 1988;Nye et al, 2000;Porter & Dorman, 1994;Prosseda et al, 1998). These findings are consistent with the bacterium expressing a critical virulence factor when present within the mammalian host (37 u C) and downregulating expression under growth conditions outside the host.…”

Section: Discussionmentioning

confidence: 79%

Differential regulation of the Proteus mirabilis urease gene cluster by UreR and H-NS

Poore

Mobley

2003

Microbiology

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Proteus mirabilis, a cause of catheter-associated urinary tract infection, relies on several virulence factors to colonize the urinary tract. Among these, urease contributes to the development of urinary stones resulting from the increase in local pH due to urease-mediated hydrolysis of urea to NH 3 and CO 2 . UreR, an AraC-like transcriptional activator, activates transcription of the genes encoding the urease subunits and accessory proteins (ureDABCEFG) in the presence of urea. UreR also initiates transcription of its own gene in a urea-inducible manner by binding to the intergenic region between ureR and ureD. The intergenic region contains poly(A) tracts that appear to be the target of H-NS. It has been shown that Escherichia coli and P. mirabilis H-NS acts to repress transcription of ureR in an E. coli model system. It was hypothesized that H-NS represses urease gene expression in the absence of UreR and urea by binding to the intergenic region. To demonstrate this the P. mirabilis hns gene was cloned and the 15?6 kDa H-NS was overexpressed and purified as a myc-His tail fusion. Using a gel shift assay, purified H-NS-myc-His bound preferentially to a 609 bp DNA fragment containing the entire ureR-ureD intergenic region. H-NS and UreR were able to displace each other from the ureR-ureD intergenic region. Circular permutation analysis revealed that the intergenic region is bent. Moreover, H-NS recognizes this curvature, binds the DNA fragment and induces further bending of the DNA as shown by a circular ligation assay. The effects of H-NS, urea and temperature (25 vs 37 6C) on urease expression were shown in E. coli containing an hns knockout and P. mirabilis where expression was increased at 37 6C. Increased transcription from p ureR was seen in the E. coli hns knockout when temperature was increased from 25 to 37 6C. These findings suggest H-NS and UreR differentially regulate urease in a negative and positive manner, respectively.

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A role for H-NS in the regulation of the virF gene of Shigella and enteroinvasive Escherichia coli

Cited by 73 publications

References 37 publications

Vibrio cholerae H-NS Silences Virulence Gene Expression at Multiple Steps in the ToxR Regulatory Cascade

Vibrio cholerae H-NS Silences Virulence Gene Expression at Multiple Steps in the ToxR Regulatory Cascade

A divalent switch drives H-NS/DNA-binding conformations between stiffening and bridging modes

Differential regulation of the Proteus mirabilis urease gene cluster by UreR and H-NS

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