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Journal of Bacteriology, June 2009, p. 3706-3711, Vol. 191, No. 11
0021-9193/09/$08.00+0     doi:10.1128/JB.01434-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Chaperone GroESL Enhances the Accumulation of Soluble, Active TraR Protein, a Quorum-Sensing Transcription Factor from Agrobacterium tumefaciens{triangledown}

Yunrong Chai§ and Stephen C. Winans*

Department of Microbiology, Cornell University, Ithaca, New York 14853

Received 13 October 2008/ Accepted 23 March 2009

TraR of Agrobacterium tumefaciens is a LuxR-type quorum-sensing transcription factor that regulates genes required for replication and conjugation of the tumor-inducing (Ti) plasmid. TraR requires its cognate autoinducer N-3-oxooctanoyl-homoserine lactone (OOHL) for resistance of proteolysis in wild-type bacteria and for correct protein folding and solubility when overexpressed in E. coli. In this study, we ask whether GroESL might also play a role in TraR folding, as this molecular chaperone assists many proteins in attaining their native tertiary structure. Expression of E. coli GroESL in a strain expressing TraR increases the solubility of TraR and increases transcriptional activity of a TraR-dependent promoter. Both solubility and activity still require OOHL. We also studied the folding of TraR in the closely related bacterium Sinorhizobium meliloti. A mutation in one groEL gene slightly decreased the expression of a TraR-dependent promoter, strongly decreased the accumulation of TraR in Western immunoblot assays, and also strongly influenced the fate of pulse-labeled TraR.

* Corresponding author. Mailing address: Department of Microbiology, Cornell University, Ithaca, NY 14853. Phone: (607) 255-2413. Fax: (607) 255-3904. E-mail: scw2{at}cornell.edu

{triangledown} Published ahead of print on 27 March 2009.

§ Present address: Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138.

Journal of Bacteriology, June 2009, p. 3706-3711, Vol. 191, No. 11
0021-9193/09/$08.00+0     doi:10.1128/JB.01434-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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