1. Department of Microbiology, University of Regensburg, Universitaetsstr. 31, D-93053 Regensburg, Germany
2. Department of Biochemistry, A 214 Life Sciences Building, The University of Georgia, Athens, Georgia 30602-7229
3. Division of Biological Sciences, University of California—San Diego, 9500 Gilman Drive, La Jolla, California 92093-0634