Fig. 1.

The polymerase activity and virus replication of H9N2/Y280 is enhanced by the D253N mutant in PB2. 293T cells were transfected with plasmids containing H9N2/Y280 PB2, PB1, PA, and NP genes plus a control luciferase reporter plasmid and a viral untranslated region-driven luciferase reporter plasmid. Transfected cells were cultured at A 37 °C and B 33 °C for 24 h, and luciferase activity was assayed in cell extracts. Results are the averages of three experiments. The values were statistical analyzed by two-tailed, paired t-tests. *P < 0.05. Primary NHBE cells were infected at an MOI of 0.01 with H9N2/Y280 and the PB2 mutant. The viral titers were measured from the supernatants at 24, 48, and 72 h postinfection using TCID₅₀ assays. C 37 °C, D 33 °C. The data are shown as means of three independent experiments. *P < 0.05.