Department of Microbiology, School of Medicine, University of Washington, Seattle, WA 98195; Department of Microbiology, Arizona State University, Tempe, AZ 85287; Istituto di Ricerche di Biologia Molecolare P. Angeletti, 00040 Pomezia, Rome, Italy; Graduate Degree Program in Molecular and Cellular Biology, Arizona State University, Tempe, AZ 85287; Howard Hughes Medical Institute, Children’s Hospital, and Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115;... (At 1999-05-11)