1. Laboratory of Molecular Genetics, Howard Hughes Medical Institute, Rockefeller University, New York, NY 10021, USA.
2. Laboratories of Molecular Biophysics, Howard Hughes Medical Institute, Rockefeller University, New York, NY 10021, USA.
3. Laboratory of Mass Spectrometry, Rockefeller University, New York, NY 10021, USA.
4. Department of Statistics, Columbia University, New York, NY 10027, USA.
5. Brookwood Biomedical Center, Birmingham, AL 35209, USA.