FIG. 4.

Infectivity assays with gL-deficient MHV-68 mutants. A. BHK-21 cells were infected (0.01 PFU/cell, 1 h, 37°C) with wild-type (WT) or gL^-DEL MHV-68. Infectious virus in replicate cultures was determined thereafter by plaque assay. B. BHK-21 cells were exposed to eGFP-expressing wild-type or gL^-DEL MHV-68 (1 PFU/cell) for the times indicated and then washed with PBS and cultured overnight. Viral infection was assayed by flow cytometry for eGFP expression. C. MEFs were exposed to eGFP-expressing wild-type, gL^-DEL, or gL-DEL-STOP MHV-68 (1 PFU/cell) for the times indicated and then washed either with PBS (pH 7.4) or with isotonic (pH 3) buffer (acid wash). Viral infection was assayed by measuring eGFP expression 18 h later as for panel B. D. BHK-21 fibroblasts or NMuMG epithelial cells were infected with eGFP-expressing gL⁻ or gL⁺ viruses as for panel B. The cells were washed with PBS after the time indicated, and eGFP expression was assayed the next day. E. Three different BAC isolates of the gL^-STOP mutant were reconstituted into infectious virus and then compared with the wild type for their capacity to infect BHK-21 cells. F. BHK-21 and Vero cells were exposed to gL⁻ or gL⁺ MHV-68 for different times before being washed with PBS as for panel D.