FIG 3.

RNP polymerase activities of wild-type and mutant H9N2 influenza viruses. Polymerase activities in 293T cells (A) or DF-1 cells (B) were determined by minigenome replication assays and are expressed as mean percent activities ± standard deviations, with the activity of the corresponding wild-type PA protein being set at 100% from three independent experiments. Western blotting was performed on protein lysates from 293T or DF-1 cells transfected with wild-type and mutant polymerase plasmids (PA and PB2). The density of each band on the immunoblot was normalized to the density of β-actin. * indicates that the value is significantly different from that for the wild-type virus (P < 0.05 as determined by ANOVA), and # indicates that the value is significantly different from that for the virus with single mutation PB2-E627K (P < 0.05 as determined by ANOVA).