Role of genes 4 and 6 for the expression of some biological properties of influenza virus A/PR/8/34.

Genetic composition and biological properties of influenza virus recombinants A/PR/8/34 (H1N1) and A/Greifswald/6/74 (H3N2) were analysed. The haemagglutinin (HA) gene of the strain A/PR/8/34 was shown an important part of the gene complex determining the virulence for mice, the yield of HA and the plaque forming capacity. The exchange of the HA gene with that of an another strain led to a drastic reduction of these properties. On the other hand, the introduction of the HA gene of A/PR/8/34 strain into the genome of an another strain, did not render the latter virulent for mice. The production of H3 HA proceeded at an about 5-fold higher extent when the H3-gene was cooperating with the genes of A/PR/8/34 in contrast to the genes of A/Greifswald/6/74.