An estimation of the nucleotide substitution rate at defined positions in the influenza virus haemagglutinin gene

Centro Nacional de Biotecnologí (CSIC), Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain The mutation rates to a viable mar (monoclonal antibody-resistant mutant) genotype of wild-type influenza (A/Victoria/3/75; H3N2) virus or its mutator variant strains have been previously determined. In order to estimate the mutation rates per nucleotide position, the sequence alterations present in 44 mar mutants isolated from either the wild-type or the mut43 mutator strain have been determined. These mar mutants were selected with either of two non-overlapping, haemagglutinin-specific, monoclonal antibodies (2G10 and p7). Most of the protein changes were identified as substitutions of large, charged amino acids for glycine residues, as the result of G to A transitions. Particularly interesting amino acid changes, not previously reported, were observed in the p7 monoclonal antibody-specific mutants, in which only Gly to Ser and Gly to Asp at position 226 were detected. The identification of the nucleotide substitutions responsible for the mar phenotype has allowed the calculation of approximate values for the total mutation rates at these positions. Present address: Centro de Biología Molecular (CSIC-UAM), Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain. Received 21 July 1993; accepted 17 September 1993.