The nucleotide sequence of the gene coding for the large subunit of influenza virus hemagglutinin (HA1) was determined for strains A/NT/60/68, A/Eng/878/ 69, and A/Qu/7/70, three early isolates of the Hong Kong subtype. Sequences were obtained by the dideoxy chain termination method, using reverse transcriptase to synthesize partial DNA copies of the RNA gene. HAl amino acid sequences predicted from the gene sequences were compared with published data for strains A/Aichi/2/68 and A/Vic/3/75.

more »

... pared with earlier strains, the HAls of A/Eng/878/69 and A/Qu/7/70 each contained three amino acid changes. Some of these were also found in A/Vic/3/75, but some were unique to the particular strain. When all of the strains were titrated with a panel of monoclonal antibodies directed against A/NT/60/68, alterations in viral antigenicity could be correlated with particular amino acid changes. The existence of multiple pathways for viral evolution during antigenic drift is discussed. MATERIALS AND METHODS Purification of virus and viral RNA. Influenza strains Eng69 and Qu7O (kindly supplied by W. G. Laver) and Aichi68, A/Vic/3/75 (Vic75), and NT68 and its derivatives 29C, 34C, and 375/17 (obtained from S. Fazekas de St. Groth and C. Hannoun [7]) were grown and purified, and the RNA was extracted as described previously (20) .