1. Advanced BioScience Laboratories-Basic Research Program1 and
2. Department of Microbiology, Michigan State University, East Lansing, Michigan 48824-11012; and
3. Intramural Research Support Program, SAIC Frederick, and Laboratory of Molecular Immunoregulation, Division of Basic Sciences,3 National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, Maryland 21702-1201;
4. Engelhardt Institute of Molecular Biology, Russian Academy of Sciences and Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia4