Ribosomal leaky scanning through a translated uORF requires eIF4G2

Abstract

eIF4G2 (DAP5 or Nat1) is a homologue of the canonical translation initiation factor eIF4G1 in higher eukaryotes but its function remains poorly understood. Unlike eIF4G1, eIF4G2 does not interact with the cap-binding protein eIF4E and is believed to drive translation under stress when eIF4E activity is impaired. Here, we show that eIF4G2 operates under normal conditions as well and promotes scanning downstream of the eIF4G1-mediated 40S recruitment and cap-proximal scanning. Specifically, eIF4G2 facilitates leaky scanning for a subset of mRNAs. Apparently, eIF4G2 replaces eIF4G1 during scanning of 5′ UTR and the necessity for eIF4G2 only arises when eIF4G1 dissociates from the scanning complex. In particular, this event can occur when the leaky scanning complexes interfere with initiating or elongating 80S ribosomes within a translated uORF. This mechanism is therefore crucial for higher eukaryotes which are known to have long 5′ UTRs with highly frequent uORFs. We suggest that uORFs are not the only obstacle on the way of scanning complexes towards the main start codon, because certain eIF4G2 mRNA targets lack uORF(s). Thus, higher eukaryotes possess two distinct scanning complexes: the principal one that binds mRNA and initiates scanning, and the accessory one that rescues scanning when the former fails.

Metformin Treatment Modulates Long Non-Coding RNA Isoforms Expression in Human Cells

“…EIF4G2 , previously known as DAP5 , is a homolog of EIF4G1 and is not part of the canonical translation process, even though deletion of this gene disrupts embryogenesis [ 49 , 50 ]. EIF4G2 is related to the alternative scanning of the translation start site by the 40S ribosomal subunit, translation associated with alternative ORFs, and translation under stress [ 51 , 52 ]. EIF4G2 differential expression was previously related to extracellular matrix remodeling [ 53 ].…”

PRRC2 proteins regulate translation initiation by promoting leaky scanning

“…Besides the core regulators of translation initiation (eIF1, eIF1A and eIF5), proteins influencing this process have remained largely elusive. Recently, eIF4G2/NAT1 was implicated in this process (11). We identify PRRC2 proteins as additional promoters of leaky scanning.…”

“…The levels of eIF1 and eIF5 are controlled in negative feedback loops to finetune start codon selection and leaky scanning (8)(9)(10). More recently eIF4G2 (also called NAT1) has also been implicated in facilitating leaky scanning (11).…”

Specific mechanisms of translation initiation in higher eukaryotes: the eIF4G2 story

“…The striking similarity between eIF4G2 and the C-terminal fragment of eIF4G1 formed by picornaviral 2A proteases (p100) (Figure 2A), as well as the inability to pull-down eIF4G2 using m 7 G-sepharose (Liberman et al 2015;Tcherkezian et al 2014) Most of these studies used a DNA bicistronic approach, which leads to artifacts and false positive results, and thus the conclusions drawn from such experiments are not persuasive (Terenin et al 2017;Andreev et al 2009;Kozak 2001;Jackson 2013). Indeed, the monocistronic reporters with CDK1 or eIF4G2 5' UTRs failed to show any dependence on eIF4G2 (Smirnova et al 2022).…”

“…However, this does not necessarily mean that translation of all mentioned mRNAs does not require eIF4G2. For example, eIF4G2 is involved in translation of APAF1 and BCL2 mRNAs (Smirnova et al 2022). Some researchers used A-capped reporter mRNAs to show eIF4G2-dependence of translation, assuming these mRNAs could not be translated in a 5' end-dependent fashion (Liberman et al 2015;Hundsdoerfer et al 2005).…”