A plant viral "reinitiation" factor interacts with the host translational machinery

The cauliflower mosaic virus transactivator, TAV, controls translation rein itiation of major open reading frames on polycistronic RNA. We show here th at TAV function depends on its association with polysomes and eukaryotic in itiation factor eIF3 in vitro and in vivo. TAV physically interacts with eI F3 and the 60S ribosomal subunit. Two proteins mediating these interactions were identified: eIF3g and 60S ribosomal protein L24. Transient expression of eIF3g and L24 in plant protoplasts strongly affects TAV-mediated reinit iation activity. We demonstrate that TAV/eIF3/40S and eIF3/TAV160S ternary complexes form in vitro, and propose that TAV mediates efficient recruitmen t of eIF3 to polysomes, allowing translation of polycistronic mRNAs by rein itiation, overcoming the normal cell barriers to this process.