FIG 1.

Transcription initiation by the influenza virus RdRp produces three RNA species. (A) Schematic of cap cleavage and transcription initiation with a capped 11-nucleotide-long primer. The duplex of the viral promoter is shaded black, the 3′ end is in orange, and the 5′ end is in gray. The capped primer is shaded red, and the priming loop (PL) is drawn as a dotted line. Alignment of the capped primer to 1U or 2C is also depicted. (B) SDS-PAGE analysis followed by Coomassie staining of purified IAV RdRp. (C) Extension of a radiolabeled, capped, 11-nucleotide-long primer in the presence of four NTPs. The products produced from positions 2C (CP) and 3G (GP) as well as the realignment product (RP) are indicated. The promoter schematic shows the primary initiation site on the wild-type IAV promoter, with colors as described above for panel A. The graph shows the accumulation of the GP, CP, and RP signals as a fraction of the total transcriptional activity. Lines represent fits to an exponential decay of data from one representative experiment. (D) Transcription reaction using β-globin mRNA as the primer donor. (E) Alignment of IAV transcription products present in the GP, CP, or RP band-containing gel fragments as identified by TOPO cloning and Sanger sequencing.