Polyuridylated mRNA synthesized by a recombinant. influenza virus is defective in nuclear export

The poly(A) tail of influenza virus mRNA is synthesized by reiterative copy ing of a Il track near the 5' end of the virion RNA (vRNA) template by the viral RNA polymerase. We have engineered a novel influenza A/WSN/33 virus w hich contains a neuraminidase (NA) vRNA with its U track mutated into an A track Instead of synthesizing poly(A)-tailed NA mRNA, this navel virus synt hesizes poly(U)-tailed NA mRNA. In infected cells, most poly(U)-tailed NA m RNA was retained in the nucleus, while most control polyadenylated NA mRNA was transported to the cytoplasm. These results suggest that the poIy(A) ta il is important for efficient nuclear export of NA mRNA The mutant virus pr oduced a reduced amount of NA and showed an attenuated phenotype, suggestin g that poly(A) signal mutants of this type might be useful as potential liv e attenuated virus vaccines. In addition, this virus mutant might provide a useful model to further elucidate the basic mechanisms of mRNA nuclear exp ort.