1. Istituto di Genetica Molecolare IGM‐CNR, Consiglio Nazionale delle Ricerche via Abbiategrasso 207 I‐27100 Pavia Italy
2. Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique 205 route de Narbonne 31077 Toulouse Cedex France
3. Institute of Veterinary Biochemistry and Molecular Biology IVB‐MB, University of Zürich Winterthurerstrasse 190 CH‐8057 Zürich Switzerland