The NS1 tails of the displayed influenza A subtypes vary at amino acid positions 217 and 226–229 (boxed). The bona fide H3K4-like sequence in NS1 of the influenza A H3N2 virus (226–229) is shown in yellow. The sumoylation sequence within the NS1 tail of the influenza A H1N1 1918 virus is shown in blue.