1. Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
2. Department of Microbiology and Molecular Genetics, McGovern Medical School, Houston, Texas, USA
3. Department of Microbiology and Immunology, University of Minnesota, Minneapolis, Minnesota, USA
4. Wallenberg Centre for Molecular Medicine, Umeå University, Umeå, Sweden