It has been reported that NA gene of some H1N1 Influenza A virus strains isolated since 1933 is characterized by a deletion of 11 to 16 amino acids in the stalk.The spontaneous mutant in NA stalk of H1N1 virus lacks enzyme activity with large substrate(fetuin) but not with small substrate(sialyllactose).Recently,H5N1 virus also has been found that NA has the same unique mutation in the stalk,a deletion of 15 to 20 amino acids.However,biological significance of this mutation has not yet been reported.In order...

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