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An extended role for the nucleoid structuring protein H‐NS in the virulence gene regulatory cascade of Shigella flexneri
Author(s) -
Beloin Christophe,
Dorman Charles J.
Publication year - 2003
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2003.03347.x
Subject(s) - promoter , biology , repressor , shigella flexneri , gene , derepression , transcription factor , transcription (linguistics) , virulence , regulation of gene expression , genetics , nucleoid , dna binding protein , microbiology and biotechnology , gene expression , psychological repression , escherichia coli , linguistics , philosophy
Summary The H‐NS nucleoid structuring protein has been shown previously to play a negative role in controlling virulence gene expression in Shigella flexneri by repressing transcription of the virF and virB regulatory genes and the VirF‐dependent icsA structural gene under non‐permissive growth conditions. Here, we show that H‐NS also acts at the promoters of the VirB‐dependent structural genes in the regulatory cascade. H‐NS protein binds to the promoter regions in vivo and in vitro . The promoters were shown physically and by in silico analysis to contain regions of DNA curvature, a feature of H‐NS binding sites. H‐NS binding sites were determined by DNase I footprinting at the icsB and the virA promoters. The locations of these sites were consistent with a role for H‐NS as a transcription repressor. The VirB‐dependent structural gene promoters were found to respond directly to the H‐NS repressor, revealing a level of control that is additional to that exerted by the H‐NS‐dependent virB activator gene. Moreover, the promoters were sensitive to the level of VirB protein in the cell, requiring a threshold level of VirB to be reached before becoming active. A model is discussed in which the levels of expression of the structural genes reflect the outcome of competition between the countervailing regulatory activities of the H‐NS and VirB proteins.