Extended Data Figure 5: NTP and template tunnels in PB1.

a, View straight along the putative NTP entrance tunnel towards the putative priming loop (magenta) in the internal cavity. The NTP channel is lined with basic residues from the fingertips (Lys 235, Lys 237 and Arg 239, blue), fingers (Arg 45, cyan) and palm (Lys 308, Lys 480 and Lys 481, red) that are absolutely conserved in all influenza strains. The fingertips are in close proximity to PA helices α20 and α21 and to the loop of the 5′ hook. b, Surface view as in a showing that the putative priming loop in the interior cavity is visible through the NTP tunnel. c, View straight along the template entrance tunnel towards the priming loop (magenta) in the internal cavity. The tunnel is lined by residues conserved in all influenza strains and from all three subunits, Arg 507 and Asp 509 from PA (green), Tyr 30, Arg 126, Met 227, Lys 229 and Asp 230 from PB1 (cyan), and Arg 38, Lys 41 and Asn 42 from PB2 (red). d, Surface view as in c showing that the internal priming loop is visible through the template tunnel.