FIG 4.
Effects of nucleotide substitutions at 3′-end positions 13 to 15 and 5′-end positions 14′ to 16′ on virus replication efficiency. (A to D) Growth curves of the wild-type WSN virus and recombinant viruses with the indicated mutation(s). A total of 5 × 105 MDCK cells were infected with the indicated viruses at an MOI of 0.001. The numbers of infectious particles in supernatants were determined at the indicated time points by plaque assay in MDCK cells. The data represent means ± standard deviations of three independent experiments.