1. Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, CA 94143.
2. Department of Biochemistry, University of Illinois, Urbana, IL 61801, USA.
3. Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA 02254, USA.
4. Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115, USA.