title: Regulation of transcription by the activity of the Shigella flexneri type III secretion apparatus.
abstract: The virulence plasmid-encoded type III secretion system of Shigella flexneri consists of the Mxi-Spa secretion apparatus, secreted proteins IpaA-D and IpgD involved in entry of bacteria into epithelial cells,cytoplasmic chaperones IpgC and IpgE and 15 other secreted proteins of unknown function, including VirA and members of the IpaH family. The activity of the Mxi-Spa apparatus is regulated by external signals, and transcription of virA and IpaH genes is specifically induced in conditions of active secretion. We present genetic evidence that regulation of these genes involves both MxiE, the transcriptional activator of the AraC family encoded by the mxi operon, and IpgC, the chaperone for IpaB and IpaC. We also show that together MxiE and IpgC are sufficient to activatevirA and IpaH 9.8 promoters in Escherichia coli. InS. flexneri, increasing the expression of IpgC led to a concomitant increase in IpaH production in conditions of non-secretion. This suggests that the activity of secretion is sensed by the presence of free IpgC, which acts as a coactivator to allow MxiE to activate transcription at its target promoters.
authors.affiliation: Unité de Pathogénie Microbienne Moléculaire, INSERM U389, Institut Pasteur, Paris, France.
authors.forename: Maria
authors.initials: M
authors.lastname: Mavris
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Page
authors.forename: Régis
authors.initials: R
authors.lastname: Tournebize
authors.forename: Brigitte
authors.initials: B
authors.lastname: Demers
authors.forename: Philippe
authors.initials: P
authors.lastname: Sansonetti
authors.forename: Claude
authors.initials: C
authors.lastname: Parsot
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D004268:DNA-Binding Proteins; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011817:Rabbits; D012763:Shigella flexneri / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000472:pathogenicity; D014157:Transcription Factors; D014158:Transcription, Genetic; D014774:Virulence / Q000235:genetics; D037521:Virulence Factors
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D018832:Molecular Chaperones; C079724:MxiE protein, Shigella flexneri; D014157:Transcription Factors; D037521:Virulence Factors; C063500:ipaH protein, Shigella flexneri; C094580:IpgC protein, Shigella