Hemagglutinin constructs in fusion with WW linker. (A) Schematic representation of HA precursor gene. (B). Diagrams of HA constructs. WWHA_1 and WWHA_2 contain the complete HA0 gene. Three constructs have N-terminally and three – C-terminally positioned WW domains. WWHA_3 and HAWW_4 contain HA1 and HA2 domains only, while HAWW_5 is devoid of TM and CT domains, and WWHA_6 is devoid of SP.