Complex formation between potyvirus VPg and translation eukaryotic initiation factor 4E correlates with virus infectivity

The interaction between the viral protein linked to the genome (VPg) of tur nip mosaic potyvirus (TuMV) and the translation eukaryotic initiation facto r eIF(iso)4E of Arabidopsis thaliana has previously been reported. eIF(iso) 4E binds the cap structure (m(7)GpppN, where N is any nucleotide) of mRNAs and has an important role in the regulation in the initiation of translatio n. In the present study, it was shown that not only did VPg bind eIF(iso)4E but it also interacted with the eIF4E isomer of A. thaliana as well as wit h eIF(iso)4E of Triticum aestivum (wheat). The interaction domain on VPg wa s mapped to a stretch of 35 amino acids, and substitution of an aspartic ac id residue found within this region completely abolished the interaction. T he cap analogue m(7)GTP, but not GTP, inhibited VPg-eIF(iso)4E complex form ation, suggesting that VPg and cellular mRNAs compete for eIF(iso)4E bindin g. The biological significance of this interaction was investigated. Brassi ca perviridis plants were infected with a TuMV infectious cDNA (p35Tunos) a nd p35TuD77N, a mutant which contained the aspartic acid substitution in th e VPg domain that abolished the interaction with eIF(iso) IE. After 20 days , plants bombarded with p35Tunos showed viral symptoms, while plants bombar ded with p35TuD77N remained symptomless. These results suggest that VPg-eIF (iso)4E interaction is a critical element for virus production.