FIG 3 .
Polymerase activity and receptor specificity of H1N1 influenza viruses. (A) Polymerase activity of ribonucleoprotein complexes of TN/560, G1, and G2 (H1N1) viruses as determined by a dual-luciferase reporter assay in three independent experiments. 293T cells were transfected in triplicate with luciferase and Renilla reporter plasmids, together with plasmids expressing PB2, PB1, PA, and NP from either TN/560, G1, or G2 viruses. Cells were incubated at 33°C (orange bars), 37°C (red bars), or 39°C (purple bars) for 24 h, and cell lysates were analyzed to measure firefly luciferase and Renilla activities. The latter was used to normalize transfection efficiency. Values shown represent the activities of each ribonucleoprotein (RNP) complex relative to that of TN/560. *, P < 0.05; °, P <0.01 compared with the value for TN/560 virus (one-way ANOVA). (B) Receptor specificity of NJ/15, TN/560, G1, and G2 (H1N1) influenza viruses. Association constants (Kass) of virus complexes with “human-type” sialylglycopolymers conjugated to 6′-SL and 6′-SLN are shown. Higher Kass values indicate stronger binding. Values are the means from four independent experiments. *, P < 0.05; °, P <0.01 compared with the value for TN/560 virus (one-way ANOVA).