1. Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA
2. Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
3. Institute for Molecular Virology, University of Minnesota, Minneapolis, Minnesota, USA
4. Department of Chemistry and Biochemistry, University of San Diego, La Jolla, California, USA
5. Howard Hughes Medical Institute, University of Minnesota, Minneapolis, Minnesota, USA