1. Department of Molecular Microbiology and Immunology, Brown University, Providence, Rhode Island, USA
2. Department of Microbiology, University of California, San Francisco, San Francisco, California, USA
3. Department of Mathematics, MIT, Cambridge, Massachusetts, USA
4. Institut für Molekulare Infektionsbiologie, Universität Würzburg, Würzburg, Germany
5. Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, California, USA