1. CRC Cell Cycle Genetics Group, University of Cambridge, Department of Genetics, Downing Site, Tennis Court Road, Cambridge CB2 3EH, UK
2. Department of Chemical Engineering, Instituto Superior Técnico, Av. Rovisco Pais, Lisboa 1049-001, and Cell Division Group, Instituto Gulbenkian de Ciencia, Rua Quinta Grande 6, Oeiras 2780-156, Portugal
3. School of Biological Sciences, 2.205 Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
4. Department of Cell Biology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18a, Martinsried D-82152, Germany