1. Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996-0845
2. Department of Pharmaceutical Sciences, University of Tennessee Medical Health Center, Memphis, Tennessee 38163
3. Stout Neuroscience Laboratory, University of Tennessee, Memphis, Tennessee 38163
4. Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3004
5. Department of Biology, University of Virginia, Charlottesville, Virginia 22904-4328