Interaction of VPg-Pro of Turnip mosaic virus with the translation initiation factor 4E and the poly(A)-binding protein in planta

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Abstract
The viral protein linked to the genome (VPg) ofTurnip mosaic virus(TuMV) interactsin vitrowith the translation eukaryotic initiation factor (eIF) 4E. In the present study, we investigated the consequence of TuMV infection on eIF4E expression. Two isomers are present in plants, namely eIF4E and eIF(iso)4E. Expression of the latter was detected in both TuMV-infected and mock-inoculatedBrassica perviridisplants, but expression of eIF4E was found only in infected plants. Membranes from TuMV-infected or mock-inoculated tissues were separated by sucrose gradient centrifugation and fractions were collected. Immunoblot analyses showed that 6K2-VPg-Pro/VPg-Pro polyproteins were associated with endoplasmic reticulum membranes and were the viral forms likely to interact with eIF(iso)4E and eIF4E.In plantainteraction between 6K2-VPg-Pro/VPg-Pro and eIF(iso)4E/eIF4E was confirmed by co-purification by metal chelation chromatography. The poly(A)-binding protein (PABP) was also found to co-purify with VPg-Pro. Direct interaction between VPg-Pro and PABP was shown by an ELISA-based binding assay. These experiments suggest that a multi-protein complex may form around VPg-Pro of TuMV.