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Journal of Bacteriology, August 2004, p. 5249-5257, Vol. 186, No. 16
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.16.5249-5257.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

The Escherichia coli GTPase CgtA_E Cofractionates with the 50S Ribosomal Subunit and Interacts with SpoT, a ppGpp Synthetase/Hydrolase

P. Wout, K. Pu, S. M. Sullivan, V. Reese, S. Zhou, B. Lin, and J. R. Maddock^*

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

Received 1 March 2004/ Accepted 18 May 2004

CgtA_E/Obg_E/YhbZ is an Escherichia coli guanine nucleotide binding protein of the Obg/GTP1 subfamily whose members have been implicated in a number of cellular functions including GTP-GDP sensing, sporulation initiation, and translation. Here we describe a kinetic analysis of CgtA_E with guanine nucleotides and show that its properties are similar to those of the Caulobacter crescentus homolog CgtA_C. CgtA_E binds both GTP and GDP with moderate affinity, shows high guanine nucleotide exchange rate constants for both nucleotides, and has a relatively low GTP hydrolysis rate. We show that CgtA_E is associated predominantly with the 50S ribosomal subunit. Interestingly, CgtA_E copurifies with SpoT, a ribosome-associated ppGpp hydrolase/synthetase involved in the stress response. The interaction between CgtA_E and SpoT was confirmed by reciprocal coprecipitation experiments and by two-hybrid assays. These studies raise the possibility that the ribosome-associated CgtA_E is involved in the SpoT-mediated stress response.

Present address: NABI Biopharmaceuticals, Rockville, MD 20852.

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