1. INFM and Department of Biology, University of Rome “Tor Vergata”, Rome, Italy; Department of Chemical Science and Technology, University of Rome “Tor Vergata”, Rome, Italy; Radiation and Genome Stability Unit, Medical Research Council, Harwell, Didcot, Oxon OX11 0RD, U.K.; Institute of Biochemical and Pharmacological Sciences, University of Catania, Catania, Italy