Human pathogenic H3N2 influenza A virus strains, Udorn/72 and Beijing/353/89, were cultured in embryonated hen eggs and stored at 270uC. The hemagglutination titer of both influenza virus strains was 256, as measured by standard methods. In infection experiments, virus dose of 2.56 hemagglutination U/ml was used. The experiments were performed with strain Udorn/72 unless otherwise stated. The protein amount of cell lysates was analysed by SDS-PAGE followed by silver-staining and Western blotting to confirm that viral infection did not decrease the total protein expression level in our experiments (Fig. S1E ).