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DksA and ppGpp directly regulate transcription of the Escherichia coli flagellar cascade
Author(s) -
Lemke Justin J.,
Durfee Tim,
Gourse Richard L.
Publication year - 2009
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 - 10.1111/j.1365-2958.2009.06939.x
Subject(s) - biology , stringent response , flagellum , sigma factor , transcription (linguistics) , gene , plasmid , microbiology and biotechnology , regulation of gene expression , escherichia coli , gene expression , flagellin , promoter , genetics , ribosome , rna , linguistics , philosophy
Summary The components of the Escherichia coli flagella apparatus are synthesized in a three‐level transcriptional cascade activated by the master regulator FlhDC. The cascade co‐ordinates the synthesis rates of a large number of gene products with each other and with nutritional conditions. Recent genome‐wide studies have reported that flagellar transcription is altered in cells lacking the transcription regulators DksA or ppGpp, but some or all reported effects could be indirect, and some are contradictory. We report here that the activities of promoters at all three levels of the cascade are much higher in strains lacking dksA , resulting in overproduction of flagellin and hyperflagellated cells. In vitro , DksA/ppGpp inhibits the flhDC promoter and the σ 70 ‐dependent fliA promoter transcribing the gene for σ 28 . However, DksA and ppGpp do not affect the σ 28 ‐dependent fliA promoter or the σ 28 ‐dependent fliC promoter in vitro , suggesting that the dramatic effects on expression of those genes in vivo are mediated indirectly through direct effects of DksA/ppGpp on FlhDC and σ 28 expression. We conclude that DksA/ppGpp inhibits expression of the flagellar cascade during stationary phase and following starvation, thereby co‐ordinating flagella and ribosome assembly and preventing expenditure of scarce energy resources on synthesis of two of the cell's largest macromolecular complexes.