1. Institut Curie, Section Recherche, UMR 144 du CNRS, 26 rue d'Ulm, 75248 Paris Cedex 05, France.
2. Department of Cell Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
3. Zellbiologie, Adolf-Butenandt-Institut, Ludwig-Maximilians-Universität, D-80336 München, Germany.