Isolation and Classification of Temperature‐Sensitive Mutants of Influenza B Virus

Abstract

We isolated 25 temperature‐sensitive mutants of B/Kanagawa/73 strain generated by mutagenesis with 5‐fluorouracil and classified them into seven recombination groups by pair‐wise crosses. All mutants showed a ratio of plaquing efficiency at the nonpermissive temperature (37.5 C) to 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 neuraminidase (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 × 10–2 and belonged to recombination group VII.

Approach to the Involvement of Influenza B Neuraminidase in the Cleavage of HA by Host Cell Protease Using Low pH‐Induced Cell Fusion Reaction

“…Recently, we have isolated temperature-sensitive (ts) mutants of influenza B/Kanagawa/73 generated by mutagenesis with 5-fluorouracil and classified them into seven recombination groups (13). Mutants ts5 and ts7 had their ts lesions only in the neuraminidase (NA) molecule and lacked its enzymatic activity at the nonpermissive temperature (37.5 C) (10,12).…”