Cauliflower mosaic virus (CaMV) upregulates translation reinitiation of its pregenomic polycistronic 35S RNA via interaction with the cell’s translation machinery

Caulimoviruses have evolved very unusual mechanisms of translation initiation to express the multiple genes in their very compact genomes. Most of the icosahedral Caulimoviridae (caulimo-, soymo-, and probably cavemovirus) produce polycistronic mRNAs that are translated via reinitiation—a mechanism normally prohibited in eukaryotes—enabled by the action of a viral transactivator of translation reinitiation. The mechanism of virus-induced polycistronic translation was first discovered and characterized for Cauliflower mosaic virus (CaMV), which produces transactivator/viroplasmin TAV to allow translation of its 35S pregenomic RNA via recruitment of multiple host factors—mainly components of the host’s translation machinery. The details of this close cooperation between CaMV and the host translation machinery is discussed here and is compared to related processes in other viruses and cells. CaMV is the first plant or mammalian virus shown to interact physically with the target-of-rapamycin (TOR) protein kinase and to activate the TOR signaling pathway. We pay special attention to the physical and functional interactions between CaMV TAV, translation initiation factor 3 (eIF3), reinitiation-supporting factor (RISP), and TOR that are able to overcome cellular barriers to reinitiation.