Figure 2.

TOR activates translation reinitiation mechanisms. A, The pattern of reinitiation after short uORF translation. TOR is activated in response to various stimuli. For example, TOR can be activated by auxin, which acts on TOR through GTP-bound ROP2. TOR-P binds polysomes to maintain the high phosphorylation status of S6K1 and thus the eIF3 subunit h (3h), which promotes the reinitiation event. eIF3, together with other eIFs, remains associated with the translating ribosome during the short elongation event to form reinitiation-competent ribosomal complexes capable of resuming scanning, as well as recruiting ternary complex (TC) and the 60S ribosomal subunit. B, The pattern of virus-activated reinitiation after long ORF translation. TAV binds and activates TOR (TOR-P). TAV retains eIF3/RISP on the translating ribosome during the long elongation event, likely by transferring to the rear side of the 60S subunit through association with eL18 or eL24 in the 60S subunit (Park et al., 2001; Thiébeauld et al., 2009). TOR-P associates with polysomes, where it maintains high RISP phosphorylation status. During translation termination and release of 60S, eIF3/TAV/RISP-P might be transported back to 40S and assist in 60S/TC recruitment. C, Sequence features of mRNA 5′-UTRs that might influence translation initiation.