The HA Protein of Influenza A and B Viruses

HA of influenza B viruses has not been characterized to the same extent as the corresponding protein of influenza A viruses. The amino acid sequences deduced from the nucleotide suquence of different strains indicate that the amino acid identity between HAs of type A and B influenza viruses is about 30% with most of the cysteine residues being conserved (Lamb, 1989). It is expected that the main structural features are very similar in both proteins. 

Influenza C viruses differ from influenza A and B viruses by containing only a single type of surface glycoprotein, the HEF protein (reviewed by Herrler and Klenk, 1991). The three-letter designation HEF indicates that the protein has three activities receptor-binding (/lemagglutination), receptor-inactivation (es- 

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