1. Division of Genetics and Mutagenesis National Institute of Health Sciences Tokyo 158‐8501 Japan
2. Division of Medical Nutrition Tokyo Health Care University Tokyo 154‐8568 Japan
3. Unité Mixte de Recherche 7258 CRCM Genome Instability and Carcinogenesis Centre National de la Recherche Scientifique Marseille F‐13009 France