Fig. 2.

Fig. 2. The D614G mutation may have the determining role in the increase of viral infectivity. Pseudoviruses containing one or more mutations in the spike protein were generated as described in the Materials and Methods and infected into Hcc15-ACE2 cells, which stably express human ACE2. At 72 h post-infection, cells were lysed for the luciferase assay. The luciferase activity was normalized to that of the WT spike, and the fold difference in relative luciferase units (RLU) compared to those of WT is plotted. One representative data from three independent experiments is shown (top panel). The expression of the spike protein was analyzed by Western blotting (bottom panel). EV indicates the empty vector transfected control. The size of the full-length spike protein and the S2 cleavage product are depicted on the right. *, p < 0.05; **, p < 0.02; ***, p < 0.001.

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