1. Department of Microbiology and Molecular Genetics, University of California, Los Angeles, CA 90024.
2. Howard Hughes Medical Institute, University of California, Los Angeles, CA 90024.
3. Mammalian Genetics Laboratory, ABL-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, MD 21702.
4. DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, CA 94304.