1. Division of Applied Life Science (BK21 program), EB-NCRC, Gyeongsang National University, Jinju 660-701, South Korea, and 12 New Road, Nafferton, Driffield, East Yorkshire YO25 4JP, UK, and Radiation Research Division, Korea Atomic Energy Research Institute, Jeongeup, 580-185, South Korea khpark@gsnu.ac.kr