RNA PolI promoter activities in MDCK, Vero cells, and CEF measured by the expression of a luciferase reporter gene. MDCK, Vero cells, and CEF were transfected with reporter plasmids encoding a firefly luciferase gene inserted between the 3′ and 5′ noncoding regions of the NP segment of A/Puerto Rico/8/34 (PR8) under the control of the canine PolI promoter [pPolIC250-NP(0)Fluc(0) (−250) or pPolIC457-NP(0)Fluc(0) (−457)], the human PolI promoter [pPolI-NP(0)Fluc(0) (human)], or the chicken PolI promoter [pPolGG-NP(0)Fluc(0) (chicken)], or without a PolI promoter [pΔPolIprom-NP(0)Fluc(0) (ΔProm)], together with the four plasmids that express PB2, PB1, PA, and NP from PR8. At 12 h after transfection, cells were subjected to the dual-luciferase assay (Promega). PolI promoter activities, represented as ratios of firefly luciferase to Renilla luciferase (as an internal control), are shown. The data presented are the means ± standard deviations of triplicate samples.