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Journal of Bacteriology, May 2004, p. 2586-2593, Vol. 186, No. 9
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.9.2586-2593.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Evidence for the Active Role of a Novel Nuclease from Helicobacter pylori in the Horizontal Transfer of Genetic Information

Eyleen J. O'Rourke,^1,2,3 A. Viviana Pinto,^1,3 E. Alejandro Petroni,^1, Marcelo E. Tolmasky,⁴ and Luis Ielpi^1*

Fundación Instituto Leloir, University of Buenos Aires and CONICET, C1405BWE-Buenos Aires, Argentina,¹ Unité de Pathogénie Bactérienne des Muqueuses, Institut Pasteur, 75724 Paris,² Département de Radiobiologie et Radiopathologie, CEA, UMR217 CEA/CNRS, F-92265 Fontenay-aux-Roses, France,³ Department of Biological Science, California State University, Fullerton, California⁴

Received 10 November 2003/ Accepted 16 January 2004

Helicobacter pylori is a gram-negative bacterium that colonizes the human stomach, causes gastritis, and is associated with ulcers and gastric cancer. H. pylori is naturally competent for transformation. Natural genetic transformation is believed to be essential for the genetic plasticity observed in this species. While the relevance of horizontal gene transfer in H. pylori adaptiveness and antibiotic resistance is well documented, the DNA transformation machinery components are barely known. No enzymatic activity associated with the transformation process has been determined experimentally and described. We isolated, microsequenced, and cloned a major DNA nuclease from H. pylori. This protein, encoded by the open reading frame hp0323, was expressed in Escherichia coli. The purified protein, NucT, has a cation-independent thermostable nuclease activity that preferentially cleaves single-stranded DNA. NucT is associated with the membrane. NucT-deficient H. pylori strains are one or more orders of magnitude less efficient than the parental strain for transformation with either chromosomal or self-replicating plasmid DNA. To the best of our knowledge, NucT is the first nuclease identified in a gram-negative natural transformation system, and its existence suggests that there is a mechanism of DNA processing and uptake similar to the mechanisms in well-studied gram-positive systems.

Present address: Servicio Antimicrobianos, INEI-ANLIS Dr. Carlos G. Malbrán, C1282AFF-Buenos Aires, and Laboratorio de Retrovirus y Virus Asociados, Fundación de Ayuda al Inmunodeficiente (FUNDAI), Uspallata 2272, C1282AEN-Buenos Aires, Argentina.

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