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Regulation of finP Transcription by DNA Adenine Methylation in the Virulence Plasmid of Salmonella enterica

Eva M. Camacho,¹ Ana Serna,¹ Cristina Madrid,² Silvia Marqués,^1, Raúl Fernández,³ Fernando de la Cruz,³ Antonio Juárez,^2, and Josep Casadesús^1*

Departamento de Genética, Universidad de Sevilla, Apartado 1095, Seville 41080,¹ Departament de Microbiologia, Universitat de Barcelona, Avda. Diagonal 645, Barcelona 08028,² Departamento de Biología Molecular, Universidad de Cantabria, Avda. Cardenal Herrera Oria s/n, Santander 39011, Spain³

Received 23 March 2005/ Accepted 16 May 2005

DNA adenine methylase (Dam^–) mutants of Salmonella enterica serovar Typhimurium contain reduced levels of FinP RNA encoded on the virulence plasmid. Dam methylation appears to regulate finP transcription, rather than FinP RNA stability or turnover. The finP promoter includes canonical –10 and –35 modules and depends on the ⁷⁰ factor. Regulation of finP transcription by Dam methylation does not require DNA sequences upstream from the –35 module, indicating that Dam acts at the promoter itself or downstream. Unexpectedly, a GATC site overlapping with the –10 module is likewise dispensable for Dam-mediated regulation. These observations indicate that Dam methylation regulates finP transcription indirectly and suggest the involvement of a host factor(s) responsive to the Dam methylation state of the cell. We provide evidence that one such factor is the nucleoid protein H-NS, which acts as a repressor of finP transcription in a Dam^– background. H-NS also restrains transcription of the overlapping traJ gene, albeit in a Dam-independent fashion. Hence, the decreased FinP RNA content found in Dam^– hosts of S. enterica appears to result from H-NS-mediated repression of finP transcription.

Present address: Estación Experimental del Zaidín, C. S. I. C., Profesor Albareda 1, Granada 18008, Spain.

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