Fig. 2

Loss of YFP-Vpr after viral fusion mediated by HXB2 envelope glycoprotein. a Snapshots of entry and fusion of an HXB2 Env-pseudotyped particle co-labeled with YFP-Vpr (green) and Gag-imCherry (red). Viruses were pre-bound to CV-1 cells expressing CD4 and CXCR4 and incubated for 1 h at 37 °C to allow fusion, which was manifested by an abrupt loss of the mCherry marker. Post-fusion decay of the YFP-Vpr signal is evident from the lowest image panel. b Single particle tracking of the virus in a, showing a virtually instantaneous loss of mCherry (dark red) followed by a gradual decay of the YFP signal (green). c–e Examples of HXB2 pp fusion (release of mCherry) with subsequent reduction in the YFP-Vpr fluorescence for pseudoviruses produced using pR8ΔEnv (c) and psPAX2 (d, e) vectors