DDX39B and DDX39A inhibit polymerase activity depending on ATP binding and hydrolytic activity.

(A) The protein levels of DDX39B and DDX39A in HEK293T, A549, Vero and DF-1 cells were measured by western blotting. (B) DDX39B-GFP or DDX39A-mCherry was transfected into HEK293T cells, 24 hours after transfection, the cells were then fixed, permeabilized. Cells were stained with the 4, 6-diamidino-2-phenylindole (DAPI) and were examined via fluorescence microscopy. (C) DDX39B-GFP and DDX39A-mCherry were co-transfected into HEK293T cells, 24 hours after transfection, the cells were treated the same as in (B). (D) A549 cells were infected with influenza virus WSN/1933 627K, WSN/1933 627E or recombinant influenza virus WSN-H7 (627K), WSN-H7 (627E) at MOI = 0.5. At 12h, 24h after infection, the cells were lysed and protein levels were measured by western blotting. (E) Polymerase genes (PB2627E), poll-Luc, RL-TK and corresponding HA-tagged mutants of DDX39B or DDX39A or empty pCAGGS vectors were co-transfected into HEK293T cells, 48h after transfection, the polymerase activity is detected. Statistical differences between groups are labeled according to two-way ANOVA. The results are presented as means ± standard deviations. **, P < 0.01; ****, P < 0.0001; ns, no significance.