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Journal of Bacteriology, August 2002, p. 4455-4465, Vol. 184, No. 16
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.16.4455-4465.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

DksA Affects ppGpp Induction of RpoS at a Translational Level

Larissa Brown,1 Daniel Gentry,1,{dagger} Thomas Elliott,2 and Michael Cashel1*

Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, Bethesda, Maryland 20892,1 Department of Microbiology, Immunology and Cell Biology, West Virginia University Health Sciences Center, Morgantown, West Virginia 265062

Received 28 January 2002/ Accepted 17 May 2002

The RpoS sigma factor (also called {sigma}S or {sigma}38) is known to regulate at least 50 genes in response to environmental sources of stress or during entry into stationary phase. Regulation of RpoS abundance and activity is complex, with many factors participating at multiple levels. One factor is the nutritional stress signal ppGpp. The absence of ppGpp blocks or delays the induction of rpoS during entry into stationary phase. Artificially inducing ppGpp, without starvation, is known to induce rpoS during the log phase 25- to 50-fold. Induction of ppGpp is found to have only minor effects on rpoS transcript abundance or on RpoS protein stability; instead, the efficiency of rpoS mRNA translation is increased by ppGpp as judged by both RpoS pulse-labeling and promoter-independent effects on lacZ fusions. DksA is found to affect RpoS abundance in a manner related to ppGpp. Deleting dksA blocks rpoS induction by ppGpp. Overproduction of DksA induces rpoS but not ppGpp. Deleting dksA neither alters regulation of ppGpp in response to amino acid starvation nor nullifies the inhibitory effects of ppGpp on stable RNA synthesis. Although this suggests that dksA is epistatic to ppGpp, inducing ppGpp does not induce DksA. A dksA deletion does display a subset of the same multiple-amino-acid requirements found for ppGpp0 mutants, but overproducing DksA does not satisfy ppGpp0 requirements. Sequenced spontaneous extragenic suppressors of dksA polyauxotrophy are frequently the same T563P rpoB allele that suppresses a ppGpp0 phenotype. We propose that DksA functions downstream of ppGpp but indirectly regulates rpoS induction.

* Corresponding author. Mailing address: Building 6B, Room 3B-314, National Institutes of Health, Bethesda, MD 20892. Phone: (301) 496-0619. Fax: (301) 496-0423. E-mail: mcashel{at}nih.gov.

{dagger} Present address: SmithKline Beecham Pharmaceuticals, Collegeville, PA 19426.

Journal of Bacteriology, August 2002, p. 4455-4465, Vol. 184, No. 16
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.16.4455-4465.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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