1. Laboratory of Molecular Genetics, Laboratory of Molecular Biophysics, and Laboratory of Mass Spectrometry and Chemical Physics, The Rockefeller University, 1230 York Avenue, New York, New York 10021, Department of Biology, Brookhaven National Laboratory, Upton, New York 11973, and Department of Biochemistry and Molecular Biology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, New York 10029