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Identical, Independent, and Opposing Roles of ppGpp and DksA in Escherichia coli

Lisa U. Magnusson,^* Bertil Gummesson, Predrag Joksimovi, Anne Farewell, and Thomas Nyström

Department of Cell and Molecular Biology-Microbiology, Göteborg University, Box 462, 405 30 Göteborg, Sweden

Received 5 March 2007/ Accepted 3 May 2007

The recent discovery that the protein DksA acts as a coregulator of genes controlled by ppGpp led us to investigate the similarities and differences between the relaxed phenotype of a ppGpp-deficient mutant and the phenotype of a strain lacking DksA. We demonstrate that the absence of DksA and ppGpp has similar effects on many of the observed phenotypes but that DksA and ppGpp also have independent and sometimes opposing roles in the cell. Specifically, we show that overexpression of DksA can compensate for the loss of ppGpp with respect to transcription of the promoters P_uspA, P_livJ, and P_rrnBP1 as well as amino acid auxotrophy, cell-cell aggregation, motility, filamentation, and stationary phase morphology, suggesting that DksA can function without ppGpp in regulating gene expression. In addition, ppGpp and DksA have opposing effects on adhesion. In the course of our analysis, we also discovered new features of the relaxed mutant, namely, defects in cell-cell aggregation and motility.

Published ahead of print on 11 May 2007.

L.U.M. and B.G. contributed equally to this study.