| Summary: | The aim of this project was to investigate the role of PA in the virus life cycle. Firstly, four archived A/FPV/Rostock/34 (FPV) temperature sensitive (ts) mutants were analysed. Duplicate cDNA clones of each PA gene were sequenced and all but one had single amino-acid mutations compared to wild-type PA. One clone of ts30 PA (ts30.2) had two amino acid changes, the other only one. Two viruses (ts45 and tsmN4) were defective in plaque formation at the non-permissive temperature (NPT), while two (ts30 and ts29) were not, possibly due to reversion. All viruses synthesised normal amounts of protein at the NPT, but ts45 did not shut off host cell protein synthesis effectively. Mutants ts45 and tsmN4 failed to synthesise vRNA at the NPT. Recombinant RNPs containing ts45, mN4 or ts30.2 PA were ts for viral gene expression; both mutations seen in ts30.2 were necessary to confer this defect. In a recombinant system, ts45 displayed a specific defect in synthesis of vRNA from a cRNA template, consistent with its failure to accumulate vRNA in the authentic viral background. However, tsmN4 was unable to synthesis either vRNA or mRNA in this system. Overall these data show that PA is an essential component of the polymerase but do not support the hypothesis that it is only required for genome replication. We propose the novel hypothesis that PA induces RNAse activity that contributes to host-cell shut off and interferon antagonism.
|
|---|
