Wild-type SIV, SIV Δnef and SIV ΔnefP were tested for virus release in the presence of human tetherin (hBST-2), and three different alleles of rhesus tetherin (rBST-2.1, rBST-2.2 and rBST-2.8, see Figure S1). Virus release is shown at increasing amounts of plasmid DNA for hBST-2 (A), rBST-2.1 (B), rBST-2.2 (C), and rBST-2.8 (D). The amount of virus released into the cell culture supernatant was determined by SIV p27 antigen-capture ELISA 48 hours post-transfection from duplicate transfections, and the mean and standard deviation (+/− error bars) were calculated as a percentage of maximal virus release in the absence of tetherin. (E) The accumulation of virion-associated p27 in the cell culture supernatant was compared to Env and p55 Gag in cell lysates by western blot analysis.