Mutations in the spike envelope protein from MHV-ExoN(-) P250 increase replicative capacity but do not affect sensitivity to 5-fluorouracil. (A) Replication kinetics of indicated viruses (MOI = 0.01 PFU/cell) plotted as means and standard deviations of results determined with n = 3. (B) Specific infectivity of indicated viruses 12 hpi (MOI = 1 PFU/cell). Data represent means and standard errors of results from n = 6 (two triplicate experiments). (C) Sensitivity of indicated viruses to 5-fluorouracil at MOI = 0.01 PFU/cell, determined as described for Fig. 4. Data represent means and standard errors of results from n = 6 (two triplicate experiments). For panel B, the statistical significance was determined using one-way analysis of variance (ANOVA). For panel C, the statistical significance of changes in the titer of MHV-ExoN(-) spike-P250 relative to MHV-ExoN(-) P3 was determined using the Mann-Whitney test (*, P < 0.05; **, P < 0.01; ***, P < 0.001; ns, not significant).