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Journal of Bacteriology, April 2003, p. 2493-2502, Vol. 185, No. 8
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.8.2493-2502.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Geobacter sulfurreducens Has Two Autoregulated lexA Genes Whose Products Do Not Bind the recA Promoter: Differing Responses of lexA and recA to DNA Damage

Mónica Jara,1 Cinthia Núñuz,2,3 Susana Campoy,1 Antonio R. Fernández de Henestrosa,1 Derek R. Lovley,2 and Jordi Barbé1,4*

Department of Genetics and Microbiology, Universitat Autònoma de Barcelona,1 Centre de Recerca en Sanitat Animal, Universitat Autònoma de Barcelona-Institut de Recerca i Tecnologia Agroalimentària, Bellaterra, 08193 Barcelona, Spain,4 Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003,2 Departamento de Microbiologia Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62251, Mexico3

Received 15 November 2002/ Accepted 23 January 2003

The Escherichia coli LexA protein was used as a query sequence in TBLASTN searches to identify the lexA gene of the {delta}-proteobacterium Geobacter sulfurreducens from its genome sequence. The results of the search indicated that G. sulfurreducens has two independent lexA genes designated lexA1 and lexA2. A copy of a dinB gene homologue, which in E. coli encodes DNA polymerase IV, is present downstream of each lexA gene. Reverse transcription-PCR analyses demonstrated that, in both cases, lexA and dinB constitute a single transcriptional unit. Electrophoretic mobility shift assays with purified LexA1 and LexA2 proteins have shown that both proteins bind the imperfect palindrome GGTTN2CN4GN3ACC found in the promoter region of both lexA1 and lexA2. This sequence is also present upstream of the Geobacter metallireducens lexA gene, indicating that it is the LexA box of this bacterial genus. This palindrome is not found upstream of either the G. sulfurreducens or the G. metallireducens recA genes. Furthermore, DNA damage induces expression of the lexA-dinB transcriptional unit but not that of the recA gene. However, the basal level of recA gene expression is dramatically higher than that of the lexA gene. Likewise, the promoters of the G. sulfurreducens recN, ruvAB, ssb, umuDC, uvrA, and uvrB genes do not contain the LexA box and are not likely to bind to the LexA1 or LexA2 proteins. G. sulfurreducens is the first bacterial species harboring a lexA gene for which a constitutive expression of its recA gene has been described.

* Corresponding author. Mailing address: Department of Genetics and Microbiology, Universitat Autònoma de Barcelona, Bellaterra, 08193 Barcelona, Spain. Phone: 34-93-581-1837. Fax: 34-93-581-2387. E-mail: jordi.barbe{at}uab.es.

Journal of Bacteriology, April 2003, p. 2493-2502, Vol. 185, No. 8
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.8.2493-2502.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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