1. Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7090;
2. Departments of Cell Biology,
3. Biochemistry and Molecular Genetics, and
4. Department of Physiology, University College London, London, United Kingdom; and
5. Neurobiology, University of Alabama at Birmingham, Birmingham, Alabama 35294;
6. Howard Hughes Medical Institute, Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710