Molecular Landscape of the Ribosome Pre-initiation Complex during mRNA Scanning: Structural Role for eIF3c and Its Control by eIF5

Abstract

Summary During eukaryotic translation initiation, eIF3 binds the solvent-accessible side of the 40S ribosome and recruits the gate-keeper protein eIF1 and eIF5 to the decoding center. This is largely mediated by the N-terminal domain (NTD) of eIF3c, which can be divided into three parts: 3c0, 3c1 and 3c2. The N-terminal part, 3c0, binds eIF5 strongly, but only weakly to the ribosome-binding surface of eIF1, whereas 3c1 and 3c2 form a stoichiometric complex with eIF1. 3c1 contacts eIF1 through Arg-53 and Leu-96, while 3c2 faces 40S protein uS15/S13, to anchor eIF1 to the scanning pre-initiation complex (PIC). We propose that the 3c0:eIF1 interaction diminishes eIF1 binding to the 40S, whereas 3c0:eIF5 interaction stabilizes the scanning PIC by precluding this inhibitory interaction. Upon start codon recognition, interactions involving eIF5, and ultimately 3c0:eIF1 association facilitate eIF1 release. Our results reveal intricate molecular interactions within the PIC, programmed for rapid scanning-arrest at the start codon.

Structural differences in translation initiation between pathogenic trypanosomatids and their mammalian hosts

“…2J). In accord with the earlier yeast data (37,38), the first ~30 residues of the eIF3c-NTD mediate its binding with eIF5, whereas residues 130 through 325 contact eIF1 (Fig. 2J).…”

“…Because the access to the GTP-binding pocket on eIF2γ is in part protected by the zinc-binding domain (ZBD) of the eIF2β-CTD (24,35), it was unclear how eIF1 coordinates the release of free Pi together with the latter factor. Based on biochemical and genetic studies in yeast, eIF2β and eIF3c NTD were implicated in anchoring of eIF1 within the 48S PIC (36)(37)(38)(39), prior to the start codon recognition. However, the molecular basis underlying all these critical interactions remained poorly characterized.…”

“…2I). Besides eIF1, the eIF3c-NTD critically promotes scanning for AUG recognition also through its interaction with the eIF5-CTD, which was so far identified only in yeast S. cerevisiae (37)(38)(39)(40) but was expected to be conserved among all eukaryotes. Surprisingly then, we did not detect any binding between the T. cruzi eIF3c-NTD and eIF5 fused to GST moiety under any experimental conditions that we examined ( Fig.…”

Efficient and Accurate Translation Initiation Directed by TISU Involves RPS3 and RPS10e Binding and Differential Eukaryotic Initiation Factor 1A Regulation

“…This conformational change is facilitated by a new interaction of RPS3 with helix 16 of the 18S rRNA (26). Following AUG recognition via base pairing with Met-tRNA interference (tRNAi) anticodon, eIF1A together with other initiation factors stimulates the reverse conformational change of the 40S rRNA to a "closed" state (26,32,33). Considering the importance of eIF1 and eIF1A in establishing the "open" conformation, we propose that the explicit require- ment for each of these factors for the scanning-free translation directed by TISU may be for the initial opening of the mRNA entry channel latch in the empty 40S subunit to allow mRNA binding.…”

Regulation of translation initiation factor eIF2B at the hub of the integrated stress response

“…The position of eIF5 within the 48S PIC was not well resolved in available structures (Hussain et al, 2014;Llacer et al, 2015;Simonetti et al, 2016). Indeed eIF5 may change position within the complex between scanning and AUG recognition steps prior to its release from initiating ribosomes with eIF2-GDP (Obayashi et al, 2017). eIF5 binds to both eIF2β and γ subunits (Alone & Dever, 2006;Asano, Krishnamoorthy, Phan, Pavitt, & Hinnebusch, 1999;Das, Maiti, Das, & Maitra, 1997;Jennings & Pavitt, 2010a) and with equal affinity for both eIF2-GDP and TC forms (Algire et al, 2005) (Figure 3b).…”