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Phenotypic characterization of overexpression or deletion of the Escherichia coli crcA, cspE and crcB genes

Olivier Sand^1,

Nancy Beck^1,

Christine Hall^1,

¹ Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA
² Department of Biological Sciences, Duquesne University, Pittsburgh, PA 15282, USA

Correspondence
Nancy Trun
trun{at}duq.edu

The authors have previously shown that overexpression of the Escherichia coli K-12 crcA, cspE and crcB genes protects the chromosome from decondensation by camphor. In this study they examine the phenotypic consequences of deleting or overexpressing crcA, cspE and crcB. Overexpressing crcA, cspE and crcB increases supercoiling levels of plasmids in wild-type cells and in temperature-sensitive (Ts) gyrase mutants, suppresses the sensitivity of gyrase and topoisomerase IV (topo IV) Ts mutants to nalidixic acid, makes gyrase and topo IV Ts mutants more resistant to camphor and corrects the nucleoid morphology defects in topo IV Ts mutants. Overexpression of crcA, cspE and crcB results in a slight (2·2-fold) activation of the rcsA gene. Deleting crcA, cspE and crcB is not lethal to cells but results in an increase in sensitivity to camphor. Deletion of crcA, cspE and crcB exacerbates the nucleoid morphology defects of the topo IV Ts mutants. When the individual crcA, cspE or crcB genes were tested for their effects on camphor resistance and regulation of rcsA, cspE alone conferred 10-fold camphor resistance and 1·7-fold activation of rcsA. These activities were augmented when crcB was overexpressed with cspE (100-fold camphor resistance and 2·1-fold induction of rcsA).

Present address: Bioinformatics Research Centre, Department of Computing Science, University of Glasgow, Glasgow G12 8QQ, UK.

Present address: Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI 48109, USA.

Present address: Department of Bacteriology, University of Wisconsin, Madison, WI 53706, USA.

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