1. Department of Biochemistry, University of Geneva, Sciences II; 30 quai E.Ansermet 1211 Geneva 4 Switzerland
2. Department of Cell Biology, University of Geneva, Sciences III, 30 quai E.Ansermet; 1211 Geneva 4 Switzerland
3. Present address: University of Notre Dame, Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall; Notre Dame IN 46556-5670 USA
4. Centre Medical Universitaire, Departement de Morphologie, 1 rue Michel Servet; 1211 Geneva 4 Switzerland