1. Institut Jacques Monod, Université Paris 6–7, 2 place Jussieu, 75251 Paris Cedex 05, France.
2. Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Konoe, Yoshida, Sakyo, Kyoto 606–8501, Japan.
3. INSERM U571, Faculté de Médecine Necker-Enfants Malades, Université Paris V, 156 rue Vaugirard, 75730 Paris Cedex 15, France.