Fig. 3

Biological characteristics of the recombinant viruses. A The multistep growth kinetics (MOI = 0.01) of rSG10* and rSG10*-F/L537A in DF1 or BSR-T7/5 cells. The supernatants of infected cells were collected at the indicated time point, and the viral loads were quantified as the TCID₅₀ values. B Replication levels of rSG10* and rSG10*-F/L537A in DF1 or BSR-T7/5 cells. The total RNA levels of the NP gene in monolayer cells were determined by RT-qPCR. RNA levels were normalized to β-actin (in BSR-T7/5 cells) or GAPDH (in DF-1 cells). The total RNA levels of the NP gene are expressed as percentages of the levels for rSG10*, which were set at 100%. C The F protein expression levels of rSG10* and rSG10*-F/L537A. BSR-T7/5 cells were infected with virus at an MOI of 0.01 and cell lysates were collected at the indicated times. The F protein expression was analyzed by western blotting using anti-F antibodies. F protein expression levels are expressed as percentages of the levels for rSG10*, which were set at 100%. D The sizes of syncytium induced by BSR-T7/5 cells infected with rSG10* or rSG10*-F/L537A. After infection with the viruses, the cells were stained with Giemsa solution to determine the size of the syncytium. The syncytium diameter are expressed as percentages of the levels for rSG10*, which were set as 100% and the ratio was expressed as the fusion index. The average syncytium diameters of rSG10* infected group was set at 100%, and the syncytium diameter of rSG10*-F/L537A infected group were expressed as fusion index, which means the relative percentages to the rSG10* group. P values were calculated with a two-way ANOVA; n = 3; *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001