Figure 4

Characteristic sites for human-to-human transmission (H2H) identified in the PB2 protein of the influenza A virus. The sites, whose position is indicated in the circles, are arranged along the length of the protein, with the avian (A2A) variants and the H2H variants indicated above and below the circles respectively. Where multiple variants are present at a site, they are shown in decreasing order of frequency. The coloured lines in the upper part of the figure show the extent of identified PB2 functional domains: the binding regions of PB2 to the PB1 and NP proteins [33] are shown in red and green respectively; the RNA cap binding regions [34, 35] in blue; and the nuclear localization signals (NLS) [32] in orange. Except for site 292, all characteristic sites identified are within one, or two functional domains. The lower part of the figure shows characteristic sites previously identified in other studies [8, 7].