This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This study identified the gene product of SIV that opposes tetherin in rhesus macaques and defined the differences between human and rhesus tetherin that account for species-specific restriction of HIV-1 and SIV.