ISOLATION AND CLASSIFICATION OF TEMPERATURE-SENSITIVE MUTANTS OF INFLUENZA-B VIRUS

We isolated 25 temperature-sensitive mutants of B/Kanagawa/73 strain g enerated by mutagenesis with 5-fluorouracil and classified them into s even recombination groups by pairwise crosses. All mutants showed a ra tio of plaquing efficiency at the nonpermissive temperature (37.5 C) t o the permissive temperature (32 C) of 10(-4) or less. At 37.5 C most of group I, II, and III mutants did not produce appreciable amounts of protein, but all other group mutants were protein synthesis-positive. A group VII mutant produced active hemagglutinin (HA) and neuraminida se (NA) at the nonpermissive temperature, but Group V mutants produced only active NA and were defective in the HA molecule. The other group mutants, including group IV mutants with mutation only in the NA gene (8, 10), lacked both activities at the nonpermissive temperature. One of nine influenza B virus isolates in 1989 had EOP 37.5/32 of 1/3 x 1 0(-2) and belonged to recombination group VII.