Influenza mRNA Translation Revisited: Is the eIF4E cap-binding Factor Required for Viral mRNA Translation ?

The influenza virus mRNAs bear a short capped oligonucleotide sequence at their 5´ ends derived from the host cell pre-mRNAs by a "cap-snatching" mechanism, followed immediately by a common viral sequence. At their 3´ends they contain a poly A tail. Although cellular and viral mRNAs are structurally similar, influenza virus promotes selective translation of its mRNAs despite inhibition of host-cell protein synthesis. The viral polymerase performs the "cap-snatching" and binds selectively to the 5´common viral sequence. As viral mRNAs are recognized by their own cap-binding complex, we tested whether viral mRNA translation occurs without the contribution of eIF4E protein, the cellular factor required for cap-dependent translation. Here we show that influenza infection proceeds normally upon different situations of functional impairment of eIF4E factor. In addition, influenza virus polymerase binds to translation preinitiation complexes and furthermore, under conditions of decreased eIF4GI association to cap-structures an increase in eIF4GI binding to these structures was found upon influenza infection. This is the first report providing evidence that influenza mRNA translation proceeds independently of a fully active translation initiation factor (eIF4E). The reported data are in agreement with a role of viral polymerase as substitute of eIF4E factor for viral mRNA translation.