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Figure 1: PARP1 is required for optimal activity of the influenza A virus RNA-dependent RNA polymerase. (a) Host factors are required for influenza A virus polymerase function. For minigenome reporter assays, cDNA encoding influenza polymerase proteins (PB1, PB2, PA, and NP), a firefly luciferase reporter driven by a virus RdRP-binding site promoter, and a constitutive Renilla luciferase internal reference were transfected into human HEK 293T cells targeted with siRNA against human PARP1, Ku70, and Ku80/86 (Ku70-86), or scrambled siRNA control (Nontgt), in duplicate. Polymerases from influenza A virus strains included human A/WSN/33 (H1N1) (WSN), human A/PR/8/34 (H1N1) (PR8), A/swine/Texas/4199-2/98 (H3N2) (swTX98), human A/California/04/09 (pdmH1N1) (CA0409), or avian-derived A/Viet Nam/1203/04 (H5N1) (VN1203). Polymerase activity of the negative control was normalized for each strain to 1.0. (b) Immunoblot showing PARP1 protein depletion with GAPDH protein as internal reference. Cellular RNA polymerase II-mediated expression of plasmid encoding Renilla luciferase (c) and (d) cell viability assays measuring ATP availability (CellTiter-Glo, CTG) and apoptosis by caspase activation (Csp3/7), in 293T cells targeted with siRNA. Significance estimated by 2-tailed t-test, with p values p<0.05 () or p<0.1 () indicated.