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Infection and Immunity, July 2007, p. 3470-3477, Vol. 75, No. 7
0019-9567/07/$08.00+0 doi:10.1128/IAI.00112-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

University of Texas at Austin, Section of Molecular Genetics and Microbiology, 1 University Station, A5000, Austin, Texas 78712
Received 22 January 2007/ Returned for modification 5 March 2007/ Accepted 6 April 2007
Regulation of bacterial gene expression by small RNA (sRNA) molecules is an increasingly recognized phenomenon but one that is not yet fully understood. We show that the sRNA RyhB suppresses several virulence-associated phenotypes of Shigella dysenteriae, a causative agent of bacillary dysentery in humans. The virulence genes repressed by S. dysenteriae RyhB include those encoding the type III secretion apparatus, its secreted effectors, and specific chaperones. Suppression of Shigella virulence occurs via RyhB-dependent repression of the transcriptional activator VirB, leading to reduced expression of genes within the VirB regulon. Efficient repression of virB is mediated by a single-stranded region of RyhB that is distinct from the region required for repression of Shigella sodB. Regulation of virB by RyhB implicates iron as an environmental factor contributing to the complex regulation of Shigella virulence determinants.
Published ahead of print on 16 April 2007.
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