title: A multifactor regulatory circuit involving H-NS, VirF and an antisense RNA modulates transcription of the virulence gene icsA of Shigella flexneri.
abstract: The icsA gene of Shigella encodes a structural protein involved in colonization of the intestinal mucosa by bacteria. This gene is expressed upon invasion of the host and is controlled by a complex regulatory circuit involving the nucleoid protein H-NS, the AraC-like transcriptional activator VirF, and a 450 nt antisense RNA (RnaG) acting as transcriptional attenuator. We investigated on the interplay of these factors at the molecular level. DNase I footprints reveal that both H-NS and VirF bind to a region including the icsA and RnaG promoters. H-NS is shown to repress icsA transcription at 30°C but not at 37°C, suggesting a significant involvement of this protein in the temperature-regulated expression of icsA. We also demonstrate that VirF directly stimulates icsA transcription and is able to alleviate H-NS repression in vitro. According to these results, icsA expression is derepressed in hns- background and overexpressed when VirF is provided in trans. Moreover, we find that RnaG-mediated transcription attenuation depends on 80 nt at its 5'-end, a stretch carrying the antisense region. Bases engaged in the initial contact leading to sense-antisense pairing have been identified using synthetic RNA and DNA oligonucleotides designed to rebuild and mutagenize the two stem-loop motifs of the antisense region.
authors: Laboratory of Molecular Genetics, School of Bioscience and Biotechnology., University of Camerino, 62032 Camerino (MC), Italy.
authors: Chi Nhan
authors: CN
authors: Tran
authors: Mara
authors: M
authors: Giangrossi
authors: Gianni
authors: G
authors: Prosseda
authors: Anna
authors: A
authors: Brandi
authors: Maria Letizia
authors: ML
authors: Di Martino
authors: Bianca
authors: B
authors: Colonna
authors: Maurizio
authors: M
authors: Falconi
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D016372:RNA, Antisense / Q000737:chemistry / Q000378:metabolism*; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D037521:Virulence Factors / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; D016372:RNA, Antisense; D012329:RNA, Bacterial; D015534:Trans-Activators; D014157:Transcription Factors; D037521:Virulence Factors; C058483:virG protein, Shigella flexneri