1. From Millennium Pharmaceuticals, Inc, Cambridge, Mass (S.A., M.D., J.K., S.S., E.A.W.); the Jean Mayer–US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, Mass (D.O., D.C., J.M.O.); and the Department of Biochemistry and Molecular and Cellular Biology, University of Zaragoza, Zaragoza, Spain (M.P., A.C., P.M.).