| Sharma AK and Payne SM. Induction of
expression of hfq by DksA is essential for Shigella flexneri virulence.
Mol Microbiol. 2006 Oct;62(2):469-79.
Hfq plays an important role in cellular physiology by regulating the
expression of several genes. Hfq synthesis in Escherichia coli is subject to
auto-repression at translational level. Studies with Shigella flexneri show
that hfq transcription is regulated by a pleiotropic regulator, DksA.
Comparison of gene expression profiles of wild type and dksA mutant S.
flexneri determined that hfq expression was reduced in the dksA mutant. As
DksA is required for stress resistance and plaque formation in cultured cell
monolayers, a measure of virulence, we assessed the role of Hfq in the dksA
virulence phenotype. Expression of hfq in the dksA mutant restored plaque
formation, and an hfq mutant failed to form plaques. Thus, DksA plays a role
in regulating hfq gene expression and this regulation is important for S.
flexneri virulence. In an in vitro transcription assay, addition of DksA
increased transcription of hfq and this effect was greatest with one of the
known hfq promoters. Addition of ppGpp, a stringent response molecule, along
with DksA in the in vitro transcription assay resulted in a further increase
in transcription of hfq, indicating that DksA is required for maximal
transcription of hfq during both exponential and stringent response growth
conditions.
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