1. Department of Molecular Biology and Microbiology1 and
2. Avian Disease and Oncology Laboratory, U.S. Department of Agriculture, Agricultural Research Station, East Lansing, Michigan 488232;
3. Department of Pathology, Baylor College of Medicine, Houston, Texas 770303; and
4. Institute of Pathology,4 School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106;
5. University of California Davis Cancer Center, Sacramento, California 958175