1. Department of Biochemistry and Molecular Biophysics; Columbia University; New York New York 10032
2. Department of Biochemistry and Molecular Biophysics; Howard Hughes Medical Institute; Columbia University; New York New York 10032
3. Division of Infectious Diseases; New York State Department of Health; Wadsworth Center; Albany New York 12201
4. Department of Biological Sciences; Columbia University; New York New York 10027