1. Department of Cell and Developmental Biology, Biocenter of the University of Würzburg, D-97074 Würzburg, Germany
2. Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037
3. Institute for Clinical and Molecular Virology, University Erlangen-Nürnberg, D-91054 Erlangen, Germany
4. Max-Planck-Institute for Biochemistry, D-82152 Martinsried, Germany
5. Cell Biology, Zoological Institute, Technical University of Braunschweig, D-38092 Braunschweig, Germany