1. Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27514, USA.
2. Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC 27514, USA.
3. Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27514, USA.
4. Curriculum in Bioinformatics and Computational Biology, University of North Carolina, Chapel Hill, NC 27514, USA.
5. Department of Biology, University of North Carolina, Chapel Hill, NC 27514, USA.
6. Department of Applied Physical Sciences, University of North Carolina, Chapel Hill, NC 27514, USA.
7. Viral Diseases Branch, Walter Reed Army Institute of Research, Silver Spring, MD 20910, USA.