- The polymerase complex of 6 A / H5N1 strains in this study, possesses amino acid changes at 12 positions, including 4 positions (I504V, Q508R, I675L, A683T) in PB2, 4 positions (L13P, V171M, R198K, H436Y) in PB1 and 4 positions (P224S, S515T, I550L, N615K) in PA protein subunit, as observed in the higly pathogenic avian influenza viruses of A / H5N1 up to date.