1. Laboratory of Microbiology, Rockefeller University, New York, NY 10021.
2. Department of Microbiology, UmeåUniversity, S90187 Umeå, Sweden.
3. Department of Molecular Microbiology, Washington University, St. Louis, MO 63110.
4. Department of Biochemistry, Michigan State University-NIH Mass Spectrometry Facility, East Lansing, MI 48824.