title: Integration host factor alleviates H-NS silencing of the Salmonella enterica serovar Typhimurium master regulator of SPI1, hilA.
abstract: Coordination of the expression of Salmonella enterica invasion genes on Salmonella pathogenicity island 1 (SPI1) depends on a complex circuit involving several regulators that converge on expression of the hilA gene, which encodes a transcriptional activator (HilA) that modulates expression of the SPI1 virulence genes. Two of the global regulators that influence hilA expression are the nucleoid-associated proteins Hha and H-NS. They interact and form a complex that modulates gene expression. A chromosomal transcriptional fusion was constructed to assess the effects of these modulators on hilA transcription under several environmental conditions as well as at different stages of growth. The results obtained showed that these proteins play a role in silencing hilA expression at both low temperature and low osmolarity, irrespective of the growth phase. H-NS accounts for the main repressor activity. At high temperature and osmolarity, H-NS-mediated silencing completely ceases when cells enter the stationary phase, and hilA expression is induced. Mutants lacking IHF did not induce hilA in cells entering the stationary phase, and this lack of induction was dependent on the presence of H-NS. Band-shift assays and in vitro transcription data showed that for hilA induction under certain growth conditions, IHF is required to alleviate H-NS-mediated silencing.
authors.affiliation: Departament de Microbiologia, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal, 645, 08028 Barcelona, Spain.
authors.forename: Mário H
authors.initials: MH
authors.lastname: Queiroz
authors.affiliation: Departament de Microbiologia, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal, 645, 08028 Barcelona, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Madrid
authors.affiliation: Departament de Microbiologia, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal, 645, 08028 Barcelona, Spain.
authors.forename: Sònia
authors.initials: S
authors.lastname: Paytubi
authors.affiliation: Departament de Microbiologia, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal, 645, 08028 Barcelona, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Balsalobre
authors.affiliation: Institut de Bioenginyeria de Catalunya (IBEC), Parc Científic de Barcelona, Baldiri Reixach, 15-21, 08028 Barcelona, Spain.|Departament de Microbiologia, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal, 645, 08028 Barcelona, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Juárez
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D020868:Gene Silencing; D044404:Genomic Islands / Q000235:genetics*; D034982:Integration Host Factors / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009994:Osmolar Concentration; D011401:Promoter Regions, Genetic; D012486:Salmonella typhimurium / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D013696:Temperature; D015534:Trans-Activators / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; C102236:HilA protein, Salmonella; D034982:Integration Host Factors; D015534:Trans-Activators