Effect of pre-heating cells on viral infection. 293T cells were incubated at 41°C for 4 h prior to infection with PR8 virus (I Pre) or mock-infection (M Pre), and incubated for 5 h at 37°C. Cells infected (I) or mock-infected (M) and incubated at 37°C or 41°C served as controls. A. Total RNA was isolated and subjected to radiolabelled primer extension analysis to detect segment 5, 7 and 2-specific RNA. B. Cells were fixed at 5 hpi and analysed by confocal microscopy after staining for NP (green) and LAP-2 to delineate the nucleus (red). Bars 10 μm.