1. Department of Molecular and Cell Biology, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, UK
2. Department of Chromosome Science, National Institute of Genetics, Research Organization of Information and Systems (ROIS), Yata 1111, Mishima, Shizuoka 411-8540, Japan
3. Department of Genetics, SOKENDAI, Mishima, Shizuoka 411-8540, Japan
4. Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan