Figure 2. The abundance of host proteins in influenza virions.

Protein abundance in purified virions was determined by SINQ. A threshold was set at one tenth the abundance of the least abundant polymerase subunit, and any protein of lower abundance was assigned this value. Proteins were matched to their human orthologs to allow comparisons between virions from different host species. (a) Principal co-ordinates analysis of log₁₀(protein abundance/a.u.) for 548 protein orthologs (goodness of fit = 0.795). (b) Log₁₀(abundance/a.u.) of proteins in virions from mammalian cells and in virions from avian cells; mean and s.d. of four combinations of viruses and mammalian hosts, and four combinations of viruses and avian hosts (Table 1). (c) The core and host-dependent features of influenza virions. The maximum copy number of proteins in virions is shown, calculated by assuming that an average virion incorporates no more than eight viral polymerases. Viral proteins are shown as red lines, and host proteins with a mean copy number greater than one are shown as bars. Host proteins are only shown if detected in all four combinations of virus and host with both mammalian hosts (green bars) and avian hosts (blue bars); the mean and s.d. is indicated. The core architecture of a spherical influenza virion consists of the viral proteins (red lines) and those host proteins found in all hosts (yellow background). Additional host proteins are found only in virions from mammalian hosts (green background) or from avian hosts (blue background).