1. Center for Retrovirus Research, Ohio State University, Columbus, OH 43210, USA.
2. Department of Veterinary Biosciences, Ohio State University, Columbus, OH 43210, USA.
3. Virus-Cell Interaction Section, HIV Dynamics and Replication Program, National Cancer Institute, Frederick, Frederick, MD 21702, USA.
4. Department of Microbial Infection and Immunity, Ohio State University, Columbus, OH 43210, USA.
5. Viruses and Emerging Pathogens Program, Infectious Diseases Institute, Ohio State University, Columbus, OH 43210, USA.