1. Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093
2. Howard Hughes Medical Institute, Chevy Chase, MD 20815
3. Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, CA 92093
4. The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 043210
5. Department of Molecular Genetics, The Ohio State University, Columbus, OH 043210