FIG 2.

Infectivity of wild-type virus and FL mutant viruses. (A and B) Spread of WT and FL alanine substitution viruses in DF1 cells over 14 days at 37°C detected by GFP expression. (C) The rate of virus spread for WT and Ala mutants at two temperatures was expressed as the Δln(percent green cells) per day over the period of exponential growth. The dotted line marks the practical limit of accurate rate determination. Spreading rates for mutant viruses at 37°C were compared to those for the WT by one-way analysis of variance (ANOVA), with Bartlett's test used to verify equal variances (***, P < 0.001). For each bar, n = 4. (D) Rate of spread for WT and charge-manipulated viruses in DF1 cells at 37°C. Results for the Ala mutants (hatched bars) are reproduced from panel C for comparison.