122,921 research outputs found
DNA-Binding Activities of the HilC and HilD Virulence Regulatory Proteins of <i>Salmonella enterica</i> Serovar Typhimurium
No full textABSTRACT
The HilC and HilD proteins of
Salmonella enterica
serovar Typhimurium are members of the AraC/XylS family of transcription regulators. They are encoded on
Salmonella
pathogenicity island 1 (SPI1) and control expression of the
hilA
gene, which encodes the major transcriptional activator for many genes encoded on SPI1 and elsewhere that contribute to invasion of host cells. Gel electrophoretic shift and DNase footprinting assays revealed that purified HilC and HilD proteins can bind to multiple regions in the
hilA
and
hilC
promoters and to a single region in the
hilD
promoter. Although both HilC and -D proteins can bind to the same DNA regions, they showed different dependencies on the sequence and lengths of their DNA targets. To identify the binding-sequence specificity of HilC and HilD, a series of single base substitutions changing each position in a DNA fragment corresponding to positions −92 to −52 of the
hilC
promoter was tested for binding to HilC and HilD in a gel shift DNA-binding assay. This mutational analysis in combination with sequence alignments allowed deduction of consensus sequences for binding of both proteins. The consensus sequences overlap but differ so that HilC can bind to both types of sites but HilD only to one. The
hilA
and
hilC
promoters contain multiple binding sites of each type, whereas the
hilD
promoter contains a site that binds HilC but not HilD without additional binding elements. The HilC and HilD proteins had no major effect on transcription from the
hilA
or
hilD
promoters using purified proteins in vitro but changed the choice of promoter at
hilC
. These results are consistent with a model derived from analysis of
lacZ
fusions stating that HilC and HilD enhance
hilA
expression by counteracting a repressing activity.
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Découverte d'une statue d'Athéna à Poitiers
No full textHild J.-A. Découverte d'une statue d'Athéna à Poitiers. In: Comptes rendus des séances de l'Académie des Inscriptions et Belles-Lettres, 46ᵉ année, N. 1, 1902. pp. 30-31
Les Juifs à Rome devant l'opinion et dans la littérature (suite et fin)
No full textHild Joseph-Antoine. Les Juifs à Rome devant l'opinion et dans la littérature (suite et fin). In: Revue des études juives, tome 11, n°21, juillet-septembre 1885. pp. 18-59
Paul Aubin, Plotin et le christianisme. Triade plotinienne et Trinité chrétienne, Paris, Beauchesne, 1992. (= Bibliothèque des Archives de Philosophie, 55)
No full textHild-Capon D. Paul Aubin, Plotin et le christianisme. Triade plotinienne et Trinité chrétienne, Paris, Beauchesne, 1992. (= Bibliothèque des Archives de Philosophie, 55). In: Revue d'histoire et de philosophie religieuses, 73e année n°4, Octobre-décembre 1993. p. 447
Studies on the control and activity of the Salmonella spi-1 regulator HilD
No full textSubmission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2022-04-06 without embargo termsThe student, Marinos Kalafatis, accepted the attached license on 2021-11-29 at 14:29.The student, Marinos Kalafatis, submitted this Dissertation for approval on 2021-11-29 at 14:52.This Dissertation was approved for publication on 2021-12-01 at 15:40.DSpace SAF Submission Ingestion Package generated from Vireo submission #17291 on 2022-04-06 at 17:10:14Made available in DSpace on 2022-04-29T21:34:35Z (GMT). No. of bitstreams: 4
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Previous issue date: 2021-12-01Salmonella Typhimurium utilizes a type three secretion system (T3SS) encoded on the Salmonella pathogenicity island 1 (SPI1) to invade intestinal epithelial cells and induce inflammatory diarrhea. The level of SPI1 T3SS gene expression is controlled by the transcriptional activator HilA, encoded on SPI1. Expression of hilA is controlled by the transcription factors HilD, HilC and RtsA, which act in a complex feed-forward regulatory loop.
The three transcription factors HilD, HilC, and RtsA, belong to the AraC/XylS family and exhibit homology. These regulators also activate the hilD, hilC, and rtsA genes by binding to the same DNA sequences upstream of these promoters. Despite the apparent redundancy in function, HilD has a unique role in SPI1 regulation because the majority of external regulatory inputs act exclusively through HilD. To better understand SPI1 regulation, the nature of interaction between HilD, HilC, and RtsA has been characterized using biochemical and genetic techniques. Our results show that HilD, HilC, and RtsA can form heterodimers as well as homodimers in solution. Comparison with other AraC family members identified a putative α-helix in the N-terminal domain, which acts as the dimerization domain. Alanine substitution in this region results in reduced dimerization of HilD and HilC and also affects their ability to activate hilA expression. The dimer interactions of HilD, HilC, and RtsA add another layer of complexity to the SPI1 regulatory circuit, providing a more comprehensive understanding of SPI1 T3SS regulation and Salmonella pathogenesis.
The nucleoid-associated protein H-NS is a xenogenic silencer that has a major effect on SPI1 expression. In this work, we use genetic techniques to show that disruptions of the chromosomal region surrounding hilD have a cis-effect on H-NS-mediated repression of the hilD promoter; this effect occurs asymmetrically over ~4 kb spanning the prgH-hilD intergenic region. Chloramphenicol acetyltransferase cassettes inserted at various positions in this region are also silenced in relation to the proximity to the hilD promoter. We identify a putative H-NS nucleation site, mutation of which results in de-repression of the locus. Furthermore, we genetically show that HilD abrogates H-NS-mediated silencing to activate the hilD promoter. In contrast, H-NS-mediated repression of the hilA promoter, downstream of hilD, is through its control of HilD, which directly activates hilA transcription. Likewise, activation of the prgH promoter, although in a region silenced by H-NS, is strictly dependent on HilA. In summary, we propose a model in which H-NS nucleates within the hilD promoter region to polymerize and exert its repressive effect. Thus, H-NS-mediated repression of SPI1 is primarily through control of hilD expression, with HilD capable of overcoming H-NS to autoactivate
Competitive infection of <i>S</i>.Tm* and <i>S</i>.Tm*<sup><i>hilD</i></sup> in LCM mice.
No full text(A) Experimental scheme. (B–E) LCM mice were infected with a 100:1 mixture of S.Tm* and the isogenic hilD mutant S.Tm* hilD (5 × 107 CFU, by gavage; n = 7 mice) for 40 days. (B) Total fecal Salmonella loads, as determined using MacConkey plates with selective antibiotics. (C) Fecal S.Tm* and S.Tm* hilD loads, as determined using MacConkey plates with selective antibiotics. (D) Competitive index (C.I.) of S.Tm* hilD vs. S.Tm*, as determined using MacConkey plates with selective antibiotics. The C.I. is normalized to the inoculum. The dotted line indicates a C.I. of 1. (E) Lipocalin-2 ELISA as performed on the feces. We analyzed a minimum n = 3 fecal pellets per time point. Dotted lines indicate the detection limit. Lines connect the median values at the days of analysis. Source data can be found in S1 Data file. Interpretation: In the LCM mice, we observed a selection for the hilD-deficient strain during the first 10 days of the infection. This is likely attributable to the inflamed gut-luminal milieu, which selected for the hilD mutant. Also, the inflammation has likely disturbed the LCM microbiota such that it cannot establish conditions selecting against the hilD mutant during these 10 days. The gut inflammation was apparently resolved by days 20–40, as indicated by the lipocalin-e ELISA data. In this period of the experiment, the selective advantage of the hilD-deficient strain was reversed. We hypothesize that this is attributable to the re-establishment of the LCM microbiota and that this accounts for the 10,000-fold selection of the hilD-proficient over the hilD-deficient strain (C.I. = 102 at day 10; versus C.I. = 10−2 at day 30). (TIF)</p
Conformation of the <i>hilD</i> mRNA alters message stability through binding of SL1 to CsrA.
No full text(A) Mutations within the hilD mRNA alter message stability. Strains of the genotypes shown and with hilD removed from its native expression by fusion to a tetA inducible promoter were assessed by RT-PCR for expression of hilD. Copies of hilD message are shown compared to dnaN. Histograms show mean ±SD for three independent experiments each performed in duplicate (total n = 6). All mutants differed from the wild type at P B) Mutation of the hilD mRNA alters message binding to CsrA. Purified his-tagged CsrA was incubated with 5’-biotinylated RNA probes of the sequence shown, and RNA-protein binding was assessed by blotting the mixture onto nitrocellulose membranes. Binding is shown relative to the wild type, set to 1. The scrambled probe, a randomly generated sequence of the same length and G-C content as the other probes, served as the control. Data show the combined results of three independent experiments, each with five replicates (total n = 15). Histograms show means ±SEM. ***P < 0.001;****P < 0.0001.</p
HilE represses the activity of the Salmonella virulence regulator HilD via a mechanism distinct from that of intestinal long-chain fatty acids
No full textThe expression of virulence factors essential for the invasion of host cells by Salmonella enterica is tightly controlled by a network of transcription regulators. The AraC/XylS transcription factor HilD is the main integration point of environmental signals into this regulatory network, with many factors affecting HilD activity. Long chain fatty acids (LCFAs), which are highly abundant throughout the host intestine directly bind to, and repress HilD, acting as environmental cues to coordinate virulence gene expression. The regulatory protein HilE also negatively regulates HilD activity, through a protein-protein interaction. Both of these regulators inhibit HilD dimerisation, preventing HilD from binding to target DNA. We investigated the structural basis of these mechanisms of HilD repression. LCFAs bind to a conserved pocket in HilD, in a comparable manner to that reported for other AraC/XylS regulators, whereas HilE forms a stable heterodimer with HilD by binding to the HilD dimerisation interface. Our results highlight two distinct, mutually exclusive mechanisms by which HilD activity is repressed, which could be exploited for the development of new antivirulence leads
Tacite, Les Annales, traduction nouvelle, par L. Loiseau, avec préface de J.-A. Hild, 1905
No full textRadet Georges. Tacite, Les Annales, traduction nouvelle, par L. Loiseau, avec préface de J.-A. Hild, 1905. In: Revue des Études Anciennes. Tome 7, 1905, n°1. p. 104
Mémoire de M. Hild sur une inscription trouvée au Peu Berland
No full textBoissier Gaston. Mémoire de M. Hild sur une inscription trouvée au Peu Berland. In: Comptes rendus des séances de l'Académie des Inscriptions et Belles-Lettres, 39ᵉ année, N. 6, 1895. p. 591
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