VP1, the RNA-dependent RNA polymerase and genome-linked protein of infectious bursal disease virus, interacts with the carboxy-terminal domain of translational eukaryotic initiation factor 4AII

Infectious bursal disease virus (IBDV), a member of the family Birnaviridae, is a non-enveloped, double-stranded RNA virus. Viral protein 1 (VP1), the putative RNA-dependent RNA polymerase, occurs in virions both as a free polypeptide and as a genome-linked protein, called VPg. To gain more insight in its function, we initiated a yeast two-hybrid screen. With this approach we identified the carboxy-terminal domain of eukaryotic translation initiation factor 4AII (eIF4AII) as an interactor for VP1. The association between these molecules was confirmed by co-immunoprecipitation analyses. eIF4A plays an essential role in the initiation of translation of both capped and uncapped mRNAs. Its association with IBDV VP1 suggests an involvement of this viral protein in IBDV mRNA translation. An interaction between VP1 and full-length eIF4AII was, however, not observed. In view of the known two-domain structure of eIF4AII it is conceivable that the interaction of VP1 with full-length eIF4AII requires collaborating proteins that open up its structure and expose the VP1-binding site in the carboxy-terminal domain. The biological relevance of the potential VP1-eIF4AII interaction is discussed.