FIG 2.

Nuclear import of PA proteins of H9N2 viruses. (A) Nuclear localization of the PA protein in A549 cells infected with H9N2 viruses. PA proteins in A549 cells infected with the indicated H9N2 viruses at an MOI of 2.0 were localized by immunofluorescence (green) at 4, 6, 8, and 10 hpi. Nuclei were stained with DAPI (blue). (B) Relative nuclear localization of PA protein. A hundred cells (blue nuclei) per microscopic field were randomly selected, from which the percentage of intranuclear PA (green) was determined. Data are presented as means ± standard deviations of results from three independent experiments. * indicates that the value is significantly different from that for the wild-type virus (P < 0.05 as determined by ANOVA). (C) Protein levels of the PA protein in the cytoplasm and nucleus of transfected 293T cells. 293T cells were transfected with a plasmid expressing wild-type PA (PA-WT) or a PA mutant (PA-K356R). Cells were harvested 24 h later, and the expression levels of cytoplasmic and nuclear PA protein were detected by immunoblotting. PA-N and PA-C represent the expression levels of PA in the nucleus and cytoplasm, respectively. The density of each band on the immunoblot was normalized to the density of β-actin in the cytoplasm or PCNA in the nucleus.