FIG 4.

Polymerase activity and replication in vitro of H7N9 viruses bearing different NP mutations. (A) Polymerase activities of H7N9 wild-type viruses and NP mutants in a minigenome assay. The values shown are means ± standard deviations (n = 3) and are standardized to the activity of CK/S1220 (100%). (B) Multicycle replication of H7N9 viruses in MDCK cells. MDCK monolayers were inoculated with 10³ EID₅₀ of the indicated viruses, and the culture supernatants were collected at the indicated times and then titrated in eggs. The dashed lines indicate the lower limit of virus detection. The virus titers were compared with those from rCK/S1220-infected cells. Statistical analysis was performed by using one-way ANOVA with GraphPad Prism 6 software. When one-way ANOVA was warranted, the post hoc analysis was performed using Dunnett’s test for multiple comparisons. a, P < 0.01.