This Article Full Text (PDF) Other Versions of this Article: JB.00315-07v1 189/17/6140    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Jiang, M. Articles by Maddock, J. R. Search for Related Content PubMed PubMed Citation Articles by Jiang, M. Articles by Maddock, J. R.

 Previous Article  |  Next Article 

J. Bacteriol. doi:10.1128/JB.00315-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

G-protein control of the ribosome-associated stress response protein SpoT

Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan, 48109

^* To whom correspondence should be addressed. Email: maddock{at}umich.edu.

	Abstract

The bacterial response to stress is controlled by two proteins, RelA and SpoT. RelA generates the alarmone (p)ppGpp under amino acid starvation, whereas SpoT is responsible for (p)ppGpp hydrolysis and for synthesis of (p)ppGpp under a variety of cellular stress conditions. It is widely accepted that RelA is associated with translating ribosomes. The cellular location of SpoT, however, has been controversial. SpoT physically interacts with the ribosome-associated GTPase, CgtA, and we show here that, under optimized salt condition, SpoT is also associated with a pre-50S particle. Analysis of spoT and cgtA mutants, and strains overexpressing CgtA suggest that the ribosome associations of SpoT and CgtA are mutually independent. The steady state level of (p)ppGpp is increased in a cgtA mutant but the accumulation of (p)ppGpp during amino acid starvation is not affected, providing strong evidence that CgtA regulates the (p)ppGpp level during exponential growth, but not during the stringent response. We show that CgtA is not associated with pre-50S particles during amino acid starvation, indicating that under these conditions in which (p)ppGpp accumulates, CgtA is not bound to either pre-50S particle or to SpoT. We propose that, in addition to its role as a 50S assembly factor, CgtA promotes SpoT (p)ppGpp degradation activity on the ribosome, and the loss of CgtA from the ribosome is necessary for maximal (p)ppGpp accumulation under stress conditions. Intriguingly, we found that in the absence of spoT and relA, cgtA is still an essential gene in E. coli.

This article has been cited by other articles:

• Lesley, J. A., Shapiro, L. (2008). SpoT Regulates DnaA Stability and Initiation of DNA Replication in Carbon-Starved Caulobacter crescentus. J. Bacteriol. 190: 6867-6880 [Abstract] [Full Text]  
• deLivron, M. A., Robinson, V. L. (2008). Salmonella enterica Serovar Typhimurium BipA Exhibits Two Distinct Ribosome Binding Modes. J. Bacteriol. 190: 5944-5952 [Abstract] [Full Text]  
• Shah, S., Das, B., Bhadra, R. K. (2008). Functional Analysis of the Essential GTP-Binding-Protein-Coding Gene cgtA of Vibrio cholerae. J. Bacteriol. 190: 4764-4771 [Abstract] [Full Text]