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Journal of Bacteriology, October 2004, p. 6824-6829, Vol. 186, No. 20
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.20.6824-6829.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Replicon-Specific Regulation of Small Heat Shock Genes in Agrobacterium tumefaciens

Sylvia Balsiger,^1, Curdin Ragaz,^1, Christian Baron,² and Franz Narberhaus^1,3*

Institut für Mikrobiologie, Eidgenössische Technische Hochschule, Zürich, Switzerland,¹ Department of Biology, McMaster University, Hamilton, Ontario, Canada,² Lehrstuhl für Biologie der Mikroorganismen, Fakultät für Biologie, Ruhr-Universität Bochum, Bochum, Germany³

Received 8 April 2004/ Accepted 14 July 2004

Four genes coding for small heat shock proteins (sHsps) were identified in the genome sequence of Agrobacterium tumefaciens, one on the circular chromosome (hspC), one on the linear chromosome (hspL), and two on the pAT plasmid (hspAT1 and hspAT2). Induction of sHsps at elevated temperatures was revealed by immunoblot analyses. Primer extension experiments and translational lacZ fusions demonstrated that expression of the pAT-derived genes and hspL is controlled by temperature in a regulon-specific manner. While the sHsp gene on the linear chromosome turned out to be regulated by RpoH (³²), both copies on pAT were under the control of highly conserved ROSE (named for repression of heat shock gene expression) sequences in their 5' untranslated region. Secondary structure predictions of the corresponding mRNA strongly suggest that it represses translation at low temperatures by masking the Shine-Dalgarno sequence. The hspC gene was barely expressed (if at all) and not temperature responsive.

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* Corresponding author. Mailing address: Lehrstuhl für Biologie der Mikroorganismen, Fakultät für Biologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany. Phone: 49 (234) 32 23100. Fax: 49 (234) 32 14620. E-mail: franz.narberhaus{at}rub.de.

S.B. and C.R. contributed equally to this work.

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Journal of Bacteriology, October 2004, p. 6824-6829, Vol. 186, No. 20
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.20.6824-6829.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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