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Characterization of a New LexA Binding Motif in the Marine Magnetotactic Bacterium Strain MC-1

Antonio R. Fernández de Henestrosa,^1, Jordi Cuñé,¹ Gerard Mazón,¹ Bradley L. Dubbels,² Dennis A. Bazylinski,² and Jordi Barbé^1,3*

Departament Genètica i Microbiologia,¹ Centre de Recerca en Sanitat Animal (CReSA), Universitat Autònoma de Barcelona, Bellaterra, 08193 Barcelona, Spain,³ Department of Microbiology, Iowa State University, Ames, Iowa 50011²

Received 6 December 2002/ Accepted 23 April 2003

MC-1 is a marine, magnetotactic bacterium that is phylogenetically associated with the alpha subclass of the Proteobacteria and is the first and only magnetotactic coccus isolated in pure culture to date. By using a TBLASTN search, a lexA gene was identified in the published genome of MC-1; it was subsequently cloned, and the protein was purified to >90% purity. Results from reverse transcription-PCR analysis revealed that the MC-1 lexA gene comprises a single transcriptional unit with two open reading frames encoding proteins of unknown function and with a rumA-like gene, a homologue of the Escherichia coli umuD gene. Mobility shift assays revealed that this LexA protein specifically binds both to its own promoter and to that of the umuDC operon. However, MC-1 LexA does not bind to the promoter regions of other genes, such as recA and uvrA, that have been previously reported to be regulated by LexA in bacterial species belonging to the alpha subclass of the Proteobacteria. Site-directed mutagenesis of both the lexA and umuDC operator regions demonstrated that the sequence CCTN₁₀AGG is the specific target motif for the MC-1 LexA protein.

Present address for Antonio R. Fernández de Henestrosa: Centro de Biología Molecular Severo Ochoa (CSIC), Cantoblanco, 28049 Madrid, Spain. Phone: 34 91 397 3981. Fax: 34 91 397 4799. E-mail: arfernandez{at}cbm.uam.es

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