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

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 degrees 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 degrees C less than 10(-2), exceeding the frequency of spontaneous ts 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 of ts mutants of influenza virus A/WSN (H0N1) revealed that these clones, in contrast with the spontaneous ts mutant of clone 6-10, with ts defect only in NP gene, possessed ts lesions in multiple genes including a common ts defect in M. 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.