Eucaryotic initiation factor 4B controls eIF3-mediated ribosomal entry of viral reinitiation factor

Abstract

The cauliflower mosaic virus reinitiation factor TAV interacts with host translation initiation factor 3 (eIF3) and the 60S ribosomal subunit to accomplish translation of polycistronic mRNAs. Interaction between TAV and eIF3g is critical for the reinitiation process. Here, we show that eIF4B can preclude formation of the TAV/eIF3 complex via competition with TAV for eIF3g binding; indeed, the eIF4B-and TAV-binding sites on eIF3g overlap. Our data indicate that eIF4B interferes with TAV/eIF3/40S ribosome complex formation during the first initiation event. Consequently, overexpression of TAV in plant protoplasts affects only second initiation events. Transient overexpression of eIF4B in plant protoplasts specifically inhibits TAVmediated reinitiation of a second ORF. These data suggest that TAV enters the host translation machinery at the eIF4B removal step to stabilize eIF3 on the translating ribosome, thereby allowing translation of polycistronic viral RNA.

Translational Regulation of Cytoplasmic mRNAs

“…Different client specificities are also apparent for isoforms of eIF4B (Park et al, 2004;Mayberry et al, 2009). Therefore any changes in the relative cellular abundance of these eIF isoforms may alter the translation states of different mRNAs in the cell.…”

“…A viral gene product, named transactivator (TAV), which is expressed from a monocistronic (single-ORF) mRNA, is required (Bonneville et al, 1989). TAV binds to polysomes in virus infected cells and directly interacts with the g subunit of eIF3 and with the RPL24 protein in a manner that is sensitive to eIF4B (Park et al, 2001;Park et al, 2004). Remarkably, TAV can stimulate the association of the eIF3 complex with the 80S ribosome, an event predicted by many models of translation reinitiation (Park et al, 2001;Park et al, 2004;Ryabova et al, 2006).…”

“…TAV binds to polysomes in virus infected cells and directly interacts with the g subunit of eIF3 and with the RPL24 protein in a manner that is sensitive to eIF4B (Park et al, 2001;Park et al, 2004). Remarkably, TAV can stimulate the association of the eIF3 complex with the 80S ribosome, an event predicted by many models of translation reinitiation (Park et al, 2001;Park et al, 2004;Ryabova et al, 2006). TAV does not act alone to stimulate translation reinitiation, but in association with a host factor, re-initiation supporting protein (RISP), whose biochemical interactions suggest that it can bridge between RPL24 on the 60S large subunit and eIF3, which is typically bound to the 40S small subunit (Thiebeauld et al, 2009).…”

Mechanism of Cytoplasmic mRNA Translation

“…The 5' leader of this viral mRNA is long, highly structured and contains several short ORFs. A viral encoded protein called TAV (transactivation/viroplasmin) interacts with eIF3 through eIF3g to retain eIF3 on ribosomes and promote reinitiation at the initiation codon of the first long viral ORF (Park et al, 2001;Park et al, 2004). Another initiation factor, eIF4B is also involved in the TAV-mediated reinitiation process (see below).…”

Apoptosis‐inducing factor (AIF) inhibits protein synthesis by interacting with the eukaryotic translation initiation factor 3 subunit p44 (eIF3g)

“…eIF3g, the p44 subunit of the eIF3 complex, has been reported to strongly associate with eIF3a (p170) and bind to rRNA through a RRM domain at the C-terminal region [21]. In S. cerevisiae yeast, it has been demonstrated that eIF3g interacts with eIF4B, and that the central part of eIF3g spanning amino-acids 66-173 is involved in binding to eIF4B or eIF3i (p36), whereas the C-terminal part of eIF3g contributes to neither eIF4B nor eIF3i binding [26]. Moreover, it was reported that eIF3g interacts directly with erythroid protein 4.1 (4.1R), and that the RRM of eIF3g is involved in this binding [27].…”