1. Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
2. Department of Chemistry, University of California, Berkeley, CA 94720, USA.
3. Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
4. Department of Regulation in Infection Biology, Helmholtz Centre for Infection Research, D-38124 Braunschweig, Germany.
5. Laboratory for Molecular Infection Medicine Sweden, Umeå Centre for Microbial Research, Department of Molecular Biology, Umeå University, S-90187 Umeå, Sweden.
6. Hannover Medical School, D-30625 Hannover, Germany.