1. Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, California 92697-3900
2. Departments of Neurology and Pathology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033
3. Section of Molecular Genetics and Microbiology and Institute for Cellular and Molecular Biology, University of Texas, Austin, Austin, Texas 78712