FIG. 4.

Complementation for virus-induced cell-to-cell fusion of UL20-null viruses containing syncytial mutations in gK(syn1) or gB(syn3). Vero cells were transfected with plasmids encoding wild-type or mutant UL20 genes and then infected with either the Δ20gKsyn1 or the Δ20gBsyn3 viruses. At 24 h.p.i., cell fusion was determined by visualization of syncytia formation by fluorescence microscopy. The extent of syncytial formation (complementation) obtained with the negative control plasmid, pΔ20NE (A), and positive control plasmid, p20R (B), is shown for reference purposes. Representative images for the CL38, 204t, 211t, and 216t mutants (C, E, G, and I, respectively) and for the CL49, Y49A, S50A, and R51A mutants (D, H, F, and J, respectively) are shown.