1. Howard Hughes Medical Institute and Department of Biological Chemistry,University of California, Los Angeles, CA 90095-1662, USA
2. Victor Goodhill Ear Center, Head and Neck Surgery Division, University of California, Los Angeles, CA 90095-1794, USA
3. Department of Cell Biology, Duke University Medical Center, Durham, NC 272710,USA
4. Samuel Lunenfeld Research Institute, Mount Sinai Hospital, University of Toronto, Toronto, M5G 1X5, Canada