FIG. 4.

Time course of proteinase K and bafilomycin A1 sensitivity of viral entry. (A) HCVpp, (B) SFVpp, or (C) VSVpp were prebound to Huh7 cells at 4°C for 1 h. Entry was initiated by shifting cells to 37°C. At the indicated time points, cells were treated with proteinase K (50 μg/ml) at 4°C for 1 h (dotted line). Cells were washed, resuspended in fresh medium, and reseeded. Alternatively, bafilomycin A1 (25 nM) was added at the indicated time points (solid line). After 3 h, the drug was removed by a change of medium. Luciferase activity was measured in cellular extracts 48 h postinfection. The percent entry was calculated relative to the 3-h time point, and values are means of at least three independent experiments ± standard deviations.