An extended role for the nucleoid structuring protein H-NS in the virulence gene regulatory cascade of Shigella flexneri.
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.
Beloin
Christophe
C
Department of Microbiology, Moyne Institute of Preventive Medicine, University of Dublin, Dublin2, Ireland.
Dorman
Charles J
CJ
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012763:Shigella flexneri / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D013696:Temperature; D014158:Transcription, Genetic; D014774:Virulence; D037521:Virulence Factors
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; D037521:Virulence Factors