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Role of the Nfo (YqfS) and ExoA Apurinic/Apyrimidinic Endonucleases in Protecting Bacillus subtilis Spores from DNA Damage

Institute of Investigation in Experimental Biology, Faculty of Chemistry, University of Guanajuato, P.O. Box 187, Guanajuato, Gto. 36050, Mexico,¹ Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, Farmington, Connecticut 06032²

Received 29 April 2005/ Accepted 29 July 2005

The Bacillus subtilis enzymes ExoA and Nfo (originally termed YqfS) are endonucleases that can repair apurinic/apyrimidinic (AP) sites and strand breaks in DNA. We have analyzed how the lack of ExoA and Nfo affects the resistance of growing cells and dormant spores of B. subtilis to a variety of treatments, some of which generate AP sites and DNA strand breaks. The lack of ExoA and Nfo sensitized spores (termed ^–ß^–) lacking the majority of their DNA-protective /ß-type small, acid-soluble spore proteins (SASP) to wet heat. However, the lack of these enzymes had no effect on the wet-heat resistance of spores that retained /ß-type SASP. The lack of either ExoA or Nfo sensitized wild-type spores to dry heat, but loss of both proteins was necessary to sensitize ^–ß^– spores to dry heat. The lack of ExoA and Nfo also sensitized ^–ß^–, but not wild-type, spores to desiccation. In contrast, loss of ExoA and Nfo did not sensitize growing cells or wild-type or ^–ß^– spores to hydrogen peroxide or t-butylhydroperoxide. Loss of ExoA and Nfo also did not increase the spontaneous mutation frequency of growing cells. exoA expression took place not only in growing cells, but also in the forespore compartment of the sporulating cell. These results, together with those from previous work, suggest that ExoA and Nfo are additional factors that protect B. subtilis spores from DNA damage accumulated during spore dormancy.

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• Ibarra, J. R., Orozco, A. D., Rojas, J. A., Lopez, K., Setlow, P., Yasbin, R. E., Pedraza-Reyes, M. (2008). Role of the Nfo and ExoA Apurinic/Apyrimidinic Endonucleases in Repair of DNA Damage during Outgrowth of Bacillus subtilis Spores. J. Bacteriol. 190: 2031-2038 [Abstract] [Full Text]