1. From the Departments of Medicine (H.T., S.V.N.P., R.J.L., H.A.R.), Cell Biology (H.A.R.), Molecular Genetics (H.A.R.), and Surgery (W.J.K.), and the Howard Hughes Medical Institute (R.J.L.), Duke University Medical Center, Durham, NC. Dr Koch is now at the Center for Translational Medicine, Jefferson Medical College, Philadelphia, Pa.