We have recently shown that influenza virus A infection compromises the expression of host cell mRNAs by: (i) the degradation of newly synthesized polymerase II transcripts in the nucleus; and (ii) the lack of translation of preexisting cellular mRNAs in the cytoplasm. Our objective is to elucidate the mechanism of this selective translation of only influenza viral and not host mRNAs. We will determine whether the block in host cell mRNA translation is at the level of initiation and/or elongation of polypeptide chains, and will assess the role of mRNA competition in the preferential translation of viral mRNAs. We will determine the role of nuclear transport in the host cell shut-off by experiments utilizing influenza virus B, which unlike type A virus causes a minimal suppression of cellular protein synthesis following infection. We intend to exploit the novel system in which we have recently shown that selective translation of influenza viral mRNAs occur, namely adenovirus-infected cells which at late times of infection are superinfected with influenza virus. In these cells, influenza viral mRNA translation, unlike host mRNA translation, occurs at undiminished levels; and this translation, unlike adenoviral translation, is independent of the presence of the adenovirus-encoded VAI RNA, which protects the initiation factor eIF-2 from inactivation via phosphorylation of its Alpha subunit by a protein kinase. We have recently shown that influenza virus superinfection causes a 5 to 10-fold suppression of the kinase induced in cells infected by d1331, the adenovirus mutant defective in VAI RNA synthesis. We intend to identify the influenza viral gene product that suppresses the eIF-2 Alpha kinase and to determine its mode of action. Utilizing cell-free translation extracts, we have obtained evidence that the selective translation of influenza viral nRNAs over adenoviral mRNAs occurring in these doubly-infected cells (d1331 and influenza virus) is due to the presence of limiting amounts of functional eIF-2, a limitation caused by residual kinase. We intend to further assess the role of this mRNA competition in this selective translation. Finally, we will test whether specific sequences in the influenza messages are involved in translational selectivity by experiments in which we insert an influenza viral gene into the adenovirus genome.
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