1. Interdisciplinary Center of Neuroscience (IZN), Institute of Neurobiology, University of Heidelberg, INF 364, Heidelberg 69120, Germany.
2. Otto-Meyerhoff-Zentrum, University of Heidelberg, INF 350, Heidelberg 69120, Germany.
3. Institute of Biochemistry, Faculty of Medicine, University of Belgrade, Pasterova 2, Belgrade 11000, Yugoslavia.
4. Electron Microscopy Facility, University of Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany.
5. Institute for Biochemistry and Molecular Biology, University of Bergen, Jonas Lies vei 91, Bergen 5009, Norway.