Fig. S1.

(A) Immunoblotting of X4 HIV-1*GFP virions for incorporated epitope-tagged Vpx proteins from SIVmac239 (WT and Q76A mutant; myc), SIVmnd-2 or SIVrcm (WT and corresponding H72A and Q75A mutant, respectively; both flag). HIV-1 p24CA served as a loading control. The use of different tags precluded quantitative comparisons of virion incorporation of these Vpx variants. myc-Vpx–tagged and flag-Vpx–tagged virions were run on the same membrane, respectively, and unrelated samples are not shown. (B) Quantification of physical particles via p24CA ELISA, RT activity via SG-PERT, and determination of the infectious titer on TZM-bl reporter cells via blue cell assay of sucrose-pelleted virions. Depicted is the mean ± SEM of two (p24CA ELISA) or three (RT activity and blue cell assay) independently produced virus stocks.