Affiliation: | a Laboratory of Cell Regulation, Imperial Cancer Research Fund, 44 Lincoln's Inn Fields, London, UK WC2A 3PX b Dept of Biophysics, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan c School of Biological Sciences, 2.205 Stopford Building, Manchester University, Oxford Road, Manchester, UK M13 9PT |