A multifactor regulatory circuit involving H-NS, VirF and an antisense RNA modulates transcription of the virulence gene icsA of Shigella flexneri.

Chi Nhan Tran (1) , Mara Giangrossi (1) , Gianni Prosseda (2) , Anna Brandi (1) , Maria Letizia Di Martino (2) , Bianca Colonna (2) , Maurizio Falconi (1)

1 Laboratory of Molecular Genetics, School of Bioscience and Biotechnology
2 Department of Biology and Biotechnology "Charles Darwin"

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.

Domaines: Microbiologie et Parasitologie

Chi Nhan Tran, Mara Giangrossi, Gianni Prosseda, Anna Brandi, Maria Letizia Di Martino, et al.. A multifactor regulatory circuit involving H-NS, VirF and an antisense RNA modulates transcription of the virulence gene icsA of Shigella flexneri.. Nucleic Acids Research, 2011, 39 (18), pp.8122-34. ⟨10.1093/nar/gkr521⟩. ⟨pasteur-00975905⟩