Primary structure of the gene coding for the haemagglutinin of influenza virus A/Leningrad/385/80(H3N2): detection of a point mutation responsible for the antigenic drift.

Primary structure of the gene coding for haemagglutinin (HA-gene) of influenza virus A/Leningrad/385/80(H2N2) isolated during the epidemics of influenza in Leningrad in 1980 was determined. The close relationship of HA gene of this virus to the corresponding gene of the virus A/Bangkok/1/79(H3N2) was confirmed. It was shown that a single mutation in an antigenic site (the change from isoleucine to leucine at position 51 of HA1 gene) caused an antigenic drift. One silent mutation was detected (nucleotide 428 of HA1 gene) which points at the relatedness of strains A/Leningrad/385/80 with A/Bangkok/2/79 and with other more recent strains. These data allowed to determine the position of the strain A/Leningrad/385/80 HA gene regarding to the evolutionary relationships of HA genes of influenza A (H3N2 subtype) viruses. The branch leading to the above-mentioned strain is supposed to start from a point common for strains isolated following A/Bangkok/1/79. The mutations of HA genes presented in this subgroup were analysed supporting the notion on limited evolutionary potential of the subtype H3N2 influenza viruses.