[1] CSIC, Ctr Nacl Biotecnol, E-28049 Madrid, Spain
[2] European Mol Biol Lab, D-69012 Heidelberg, Germany
[3] Univ Basel, Bioctr, ME Muller Inst Microscop Struct Biol, CH-4056 Basel, Switzerland
[4] CSIC, Ctr Invest & Desarrollo, E-08034 Barcelona, Spain
[5] Adv Technol Ctr Silicon Graph Inc, CH-2016 Cortaillod, Switzerland
[6] Informix Software Ltd, Feltham TW14 8HA, England
[7] European Bioinformat Inst, Cambridge CB10 1SD, England
[8] Univ Oxford, Dept Zool, Oxford OX1 3PS, England