title: The virF promoter in Shigella: more than just a curved DNA stretch.
abstract: In the human enteropathogen Shigella transcription of virF, the primary regulator of the invasion functions, is strictly temperature-dependent and is antagonistically mediated by H-NS and FIS, which bind to specific sites on the virF promoter. Here we report on the relevance of DNA geometry to the thermoregulation of virF and demonstrate that the virF promoter hosts a major DNA bend halfway between two H-NS sites. The bent region has been mutagenized in vitro to mimic temperature-induced changes of DNA curvature. Functional analysis of curvature mutants and of promoter constructs in which the two H-NS sites are phased-out by a half-helix turn reveals that modifying the spatial relationships between these sites severely affects the interaction of H-NS with the virF promoter, as well as its in vivo and in vitro temperature-dependent activity. The role of promoter curvature as thermosensor is also compatible with the present observation that, with increasing temperature, the virF bending centre moves downstream at a rate having its maximum around the transition temperature, abruptly unmasking a binding site for the transcriptional activator FIS.
authors.affiliation: Dip. Biologia Cellulare e dello Sviluppo, University La Sapienza, 00185 Roma, Italy.
authors.forename: Gianni
authors.initials: G
authors.lastname: Prosseda
authors.forename: Maurizio
authors.initials: M
authors.lastname: Falconi
authors.forename: Mara
authors.initials: M
authors.lastname: Giangrossi
authors.forename: Claudio O
authors.initials: CO
authors.lastname: Gualerzi
authors.forename: Gioacchino
authors.initials: G
authors.lastname: Micheli
authors.forename: Bianca
authors.initials: B
authors.lastname: Colonna
mesh_terms: D001483:Base Sequence; D017931:DNA Primers; D004269:DNA, Bacterial / Q000737:chemistry* / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics*; D015183:Restriction Mapping; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D012760:Shigella / Q000235:genetics* / Q000472:pathogenicity*
chemical_list: D017931:DNA Primers; D004269:DNA, Bacterial