1 Department of Molecular Genetics, National Institute of Genetics and Graduate University for Advanced Studies (SOKENDAI), Mishima, Shizuoka 411-8540, Japan. Electronic address: tfukagaw@lab.nig.ac.jp.
2 Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh, EH9 3JR, UK. Electronic address: bill.earnshaw@ed.ac.uk.