1. Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158
2. Zellbiologie/Elektronenmikroskopie, Universität Bayreuth, 95440 Bayreuth, Germany
3. Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan
4. Department of Cell Biology and Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605