An influenza virus temperature-sensitive mutant defective in the nuclear-cytoplasmic transport of the negative-sense viral RNAs.

An influenza A virus mutant ts-51, which contains a temperature-sensitive (ts) defect in the genome encoding the M1 and M2 proteins, was characterized. Nucleotide sequencing of the M segment revealed a predicted single amino acid change of phenylalanine to serine at amino acid position 79 in the M1 protein. The nuclear-cytoplasmic transport of the negative-sense viral RNAs (vRNAs) was then investigated using an in situ hybridization technique. At 6 hr after the ts-51 virus infection, approximately 95% of the vRNAs were accumulated in the nucleus at a non-permissive temperature, when approximately 50% of the vRNAs were transported into the cytoplasm in the wild-type virus-infected cells. The M1 protein of the ts-51 virus was also accumulated in the nucleus under the same conditions. Therefore, the M1 protein of the ts-51 virus may be associated with the vRNPs, but the possible M1-vRNP complex thus formed was defective in the nuclear-cytoplasmic transport and the single amino acid change in the M1 protein was responsible for this defect.