Fig. 1.

Impact of endonuclease resistance mutations on the growth of the PR8 influenza virus. A multiplicity of infection (MOI) of 10⁻⁴ of wild-type (A) and PR8 mutant (B–F) viruses was used to infect MDCK cells in the presence (red) or absence (blue) of 10 μM of inhibitory compound L-742,001. Supernatants were collected at 8, 24, 36, 48, 72, and 96 h post inoculation and viral titers determined on MDCK cells by using the Reed–Muench 50% endpoint method (47). Virus titers are displayed as log10 50% tissue culture infectious doses (TCID₅₀). The limit of virus detection was 1.8 log₁₀ TCID₅₀ per mL. Error bars represent SEM derived from three independent experiments. The Student’s t test was used for statistical comparisons (*P < 0.05; ns, not significant).