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Influenza virus attaches on the sialic acid on cellular membrane through it's HA protein and enters cytoplasm by receptor-mediated endocytosis, then move from endocytic vesicles to early endosomes and late endosome where the influenza viruses fuse with the endosomal membrane to release viral genome followed to transport the genome to nuclei where virus replicate their genome. Previously we found that host cell protein Ebpl (ErbB3 binding protein 1) interacted with the catalytic subunit PB1 of influenza virus RNA dependent RNA polymerase and interfered with its function. Ebpl expression is regulated by cell cycle, showing high level expression especially in Gl to S phase. Recently we identified another host protein (PA4c9) interacts with subunit PA of influenza virus RNA polymerase. Again PA4c9 is one of the cell cycle dependent proteins. These findings encouraged us to investigate the host cell cycle dependency of influenza infection. To identify the cell phase at which influenza virus attach most efficiently, the cells were treated with the fluorescent-labeled influenza viruses for 5-15 minutes and fixed with paraformaldehyde followed by observation under the confocal microscope. In parallel, attempts were made to manipulate a single particle of fluorescent-labeled virus using laser manipulator for infection onto a single cell at different phase. The results altogether indicated that influenza virus preferred the membrane of stable cell phase (G0/G1) to attach for infection.