Determinants of functional differences between HIV-1 N and SIVcpz Vpus.

<p>(<b>A</b>) Chimeras between the YBF30 (yellow) and EK505 (green) Vpu proteins analyzed. The hydrophobic TMD, the α-helical regions and the position of two serine phosphorylation sites are indicated. Dashes indicate gaps introduced to optimize the alignment. The right panel summarizes the functional activity of the respective wild-type or chimeric Vpu proteins. Abbreviations: −, no; (+) low; +, modest and ++ high activity. The asterisks indicate the Vpus shown in panels <b>B</b> to <b>F</b>. (<b>B</b>) Effect of selected wild-type and mutant YBF30 and EK505 Vpu proteins and the NL4-3 Vpu on infectious virus release in the presence of tetherin. Curves represent the average infection values (n = 3) relative to those obtained in the absence of tetherin. (<b>C</b>) Interaction between tetherin and Vpu detected by BiFC. 293T cells transfected with plasmids expressing tetherin and the indicated Vpu proteins were examined by confocal microscopy. (<b>D</b>) Quantitative BiFC assay. Cells were transfected as described in panel A and analyzed by flow cytometry. Shown is the mean fluorescence intensity (MFI) of Kusabira green relative to the MFI of tetherin (100%). The results represent the means from three independent experiments (±SD). (<b>E–H</b>) Efficiencies of down-modulation of (<b>E</b>) tetherin, (<b>F</b>) CD4, (<b>G</b>) CD1d and (<b>H</b>) NTB-A cell surface expression in the presence of constructs expressing the indicate Vpu proteins relative to those measured in cells transfected with the eGFP control vector. Values are averages (±SD) derived from two independent experiments.