1. Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224, Novartis Pharmaceuticals Ltd, 4002 Basel, Switzerland, Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland 21205, and Departments of Therapeutic Radiology and Genetics, Yale University School of Medicine, P.O. Box 208040, New Haven, Connecticut 06520-8040