1. Laboratoire “Lésions des Acides Nucléiques”, DRFMC/SCIB, UMR-E 3 (CEA/UJF), CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France, and Department of Natural Sciences and Örebro Life Science Center, Örebro University, 701 82 Örebro, Sweden