A new plant protein interacts with eIF3 and 60S to enhance virus-activated translation re-initiation

Abstract

The plant viral re-initiation factor transactivator viroplasmin (TAV) activates translation of polycistronic mRNA by a re-initiation mechanism involving translation initiation factor 3 (eIF3) and the 60S ribosomal subunit (60S). QJ;Here, we report a new plant factor-re-initiation supporting protein (RISP)-that enhances TAV function in re-initiation. RISP interacts physically with TAV in vitro and in vivo. Mutants defective in interaction are less active, or inactive, in transactivation and viral amplification. RISP alone can serve as a scaffold protein, which is able to interact with eIF3 subunits a/c and 60S, apparently through the C-terminus of ribosomal protein L24. RISP pre-bound to eIF3 binds 40S, suggesting that RISP enters the translational machinery at the 43S formation step. RISP, TAV and 60S co-localize in epidermal cells of infected plants, and eIF3-TAV-RISP-L24 complex formation can be shown in vitro. These results suggest that RISP and TAV bridge interactions between eIF3-bound 40S and L24 of 60S after translation termination to ensure 60S recruitment during repetitive initiation events on polycistronic mRNA; RISP can thus be considered as a new component of the cell translation machinery.

Mechanism of Cytoplasmic mRNA Translation

“…Another initiation factor, eIF4B is also involved in the TAV-mediated reinitiation process (see below). A host protein called RISP (reinitiation supporting protein) was described that supports reinitiation during CaMV infection and interacts with eIF3 through the eIF3a and eIF3c subunits (Thiebeauld et al, 2009). TAV binding to the TOR kinase was shown to be critical for the reinitiation event (Schepetilnikov et al, 2011).…”

Translational Regulation of Cytoplasmic mRNAs

“…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).…”

The h subunit of eIF3 promotes reinitiation competence during translation of mRNAs harboring upstream open reading frames

“…One other plant eIF3 subunit, eIF3g, has been linked to reinitiation because it interacts with the cauliflower mosaic virus reinitiation factor, TAV (Park et al 2001. Furthermore, eIF3 and TAV also interact with RPL24 (Park et al 2001) and with a recently discovered cellular protein that is auxiliary to reinitiation (Thiebeauld et al 2009). Taken together, eIF3h appears to be part of a larger functional module that is responsible for efficient reinitiation after uORF translation and that involves cooperation between eIF3 and the large ribosomal subunit.…”