Temperature-sensitive influenza A virus clones originated by a cross between A/Aichi/2/68 (H3N2) and B/Yamagata/1/73

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Abstract
A genetic cross was performed between influenza viruses B/Yamagata/1/73 and clone 6–10, an A type influenza virus derived from a cross between A/Aichi/2/68 (H3N2) and B/Yamagata. Efficiency of plating of B/Yamagata at 39.5° C was less than 10−3 in MDCK cells, while that of clone 6–10 or A/Aichi was higher than 10−1. Four of the 15 clones selected for HA of Aichi serotype from the mixed yield, where type B virus was predominant over type A, were temperature-sensitive(ts), with efficiency of plating at 39.5° C less than 10−2, exceeding the frequency of spontaneousts mutants among clone 6–10 progeny. Thus, co-existing type B virus not only interfered with the replication of type A, but also rendered it temperature-sensitive. Genetic analysis of the 4ts clones using a set ofts mutants of influenza virus A/WSN (H0N1) revealed that these clones, in contrast with the spontaneousts mutant of clone 6–10, withts defect only in NP gene, possessedts lesions in multiple genes including a commonts defect inm. Polyacrylamide gel electrophoresis of viral RNA and proteins of these clones showed an identical gel pattern to that of clone 6–10, although the rate of synthesis of individual viral polypeptide was variable from clone to clone.