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Schematic of influenza virus HA and HA2 sequences. EHA2 (E. coli-expressed HA2 residues 23–185) is the protein structure determined here. TM, transmembrane anchor; S—S, interchain disulfide bond from HA1 Cys-14 to HA2 Cys-137; Flag octapeptide (in F185), bold.
