In Alzheimer's disease, tau pathology is thought to spread via a prion-like manner along connected neuronal networks. For this to occur, the usually cytosolic tau protein must be secreted via an unconventional mechanism prior to uptake into the connected neuron. While secretion of healthy and pathological tau has been documented, it remains under-investigated whether this occurs via overlapping or distinct processes. Here, we established a sensitive bioluminescence-based assay to assess mechanisms underlying the secretion of pseudohyperphosphorylated and wild-type tau in cultured murine hippocampal neurons. We found that under basal conditions, both wild-type and mutant tau are secreted, with mutant tau being more robustly secreted. Pharmacological stimulation of neuronal activity led to a modest increase of wild-type and mutant tau secretion, whereas inhibition of activity had no effect. Interestingly, inhibition of heparin sulfate proteoglycan (HSPG) biosynthesis drastically decreased secretion of both wild-type and mutant tau without affecting cell viability. This shows that native and pathological tau share release mechanisms; both activity-dependent and non-activity-dependent secretion of tau is facilitated by HSPGs.

Background Rapid testing facilitates safe and effective diagnosis, but the true speed of the process is the time from collection of a sample to delivery of an accurate and reliable test result – ‘end-to-end’ time. Transport, unpacking and relaying of information can extend this time considerably beyond the minimum laboratory turnaround times as stipulated by PCR testing protocols. Aim/Objective This study aimed to minimise time needed to ascertain SARS-CoV-2 status prior to treatment in a UK Dental Hospital using a novel, mobile, direct to polymerase chain reaction (PCR) workflow. Methods Process flow analysis and PDSA (Plan, Do, Study, Act) cycles for rapid continuous improvement were employed in a service improvement programme. Primerdesign™ q16 rapid PCR instruments and PROmate® COVID-19 direct assays were used for molecular testing. Findings/Results We showed a reduction in real-world end-to-end time for a diagnostic test from 240 min to 85 min (65% reduction) over a 4-week period. Discussion New rapid technologies have become available that reduce analytical time to under 90 min, but the real-world clinical implementation of the test requires a fully integrated workflow from clinic to reporting.

B-cell receptor (BCR) signaling plays a major role in the pathogenesis of B-cell malignancies and is an established target for therapy, including in chronic lymphocytic leukemia cells (CLL), the most common B-cell malignancy. We previously demonstrated that activation of BCR signaling in primary CLL cells downregulated expression of PDCD4, an inhibitor of the translational initiation factor eIF4A and a potential tumor suppressor in lymphoma. Regulation of the PDCD4/eIF4A axis appeared to be important for expression of the MYC oncoprotein as MYC mRNA translation was increased following BCR stimulation and MYC protein induction was repressed by pharmacological inhibition of eIF4A. Here we show that MYC expression is also associated with PDCD4 down-regulation in CLL cells in vivo and characterize the signaling pathways that mediate BCR-induced PDCD4 down-regulation in CLL and lymphoma cells. PDCD4 downregulation was mediated by proteasomal degradation as it was inhibited by proteasome inhibitors in both primary CLL cells and B-lymphoma cell lines. In lymphoma cells, PDCD4 degradation was predominantly dependent on signaling via the AKT pathway. By contrast, in CLL cells, both ERK and AKT pathways contributed to PDCD4 down-regulation and dual inhibition using ibrutinib with either MEK1/2 or mTORC1 inhibition was required to fully reverse PDCD4 down-regulation. Consistent with this, dual inhibition of BTK with MEK1/2 or mTORC1 resulted in the strongest inhibition of BCR-induced MYC expression. This study provides important new insight into the regulation of mRNA translation in B-cell malignancies and a rationale for combinations of kinase inhibitors to target translation control and MYC expression.

Regulation of mRNA translation is an important mechanism determining the level of expression of proteins in eukaryotic cells. Translation is most commonly initiated by cap-dependent scanning, but many eukaryotic mRNAs contain internal ribosome entry segments (IRESs), providing an alternative means of initiation capable of independent regulation. Here, we show by using dicistronic luciferase reporter vectors that the 5'-UTR of the mRNA encoding human insulin receptor (hIR) contains a functional IRES. RNAi-mediated knockdown showed that the protein PTB was required for maximum IRES activity. Electrophoretic mobility shift assays confirmed that PTB1, PTB2 and nPTB, but not unr or PTB4, bound to hIR mRNA, and deletion mapping implicated a CCU motif 448 nt upstream of the initiator AUG in PTB binding. The IR-IRES was functional in a number of cell lines, and most active in cells of neuronal origin, as assessed by luciferase reporter assays. The IRES was more active in confluent than sub-confluent cells, but activity did not change during differentiation of 3T3-L1 fibroblasts to adipocytes. IRES activity was stimulated by insulin in sub-confluent cells. The IRES may function to maintain expression of IR protein in tissues such as the brain where mRNA translation by cap-dependent scanning is less effective.

Signaling via the B-cell receptor (BCR) is a key driver and therapeutic target in chronic lymphocytic leukemia (CLL). BCR stimulation of CLL cells induces expression of eIF4A, an initiation factor important for translation of multiple oncoproteins, and reduces expression of PDCD4, a natural inhibitor of eIF4A, suggesting that eIF4A may be a critical nexus controlling protein expression downstream of the BCR in these cells. We, therefore, investigated the effect of eIF4A inhibitors (eIF4Ai) on BCR-induced responses. We demonstrated that eIF4Ai (silvestrol and rocaglamide A) reduced anti-IgM-induced global mRNA translation in CLL cells and also inhibited accumulation of MYC and MCL1, key drivers of proliferation and survival, respectively, without effects on upstream signaling responses (ERK1/2 and AKT phosphorylation). Analysis of normal naïve and non-switched memory B cells, likely counterparts of the two main subsets of CLL, demonstrated that basal RNA translation was higher in memory B cells, but was similarly increased and susceptible to eIF4Ai-mediated inhibition in both. We probed the fate of MYC mRNA in eIF4Ai-treated CLL cells and found that eIF4Ai caused a profound accumulation of MYC mRNA in anti-IgM treated cells. This was mediated by MYC mRNA stabilization and was not observed for MCL1 mRNA. Following drug wash-out, MYC mRNA levels declined but without substantial MYC protein accumulation, indicating that stabilized MYC mRNA remained blocked from translation. In conclusion, BCR-induced regulation of eIF4A may be a critical signal-dependent nexus for therapeutic attack in CLL and other B-cell malignancies, especially those dependent on MYC and/or MCL1.

RNA G-quadruplexes (G4s) are secondary structures proposed to function as regulators of post-transcriptional mRNA localisation and translation. G4s within some neuronal mRNAs are known to control distal localisation and local translation, contributing to distinct local proteomes that facilitate the synaptic remodelling attributed to normal cellular function. In this study, we characterise the G4 formation of a (GGN) 13 repeat found within the 5' UTR of the potassium 2-pore domain leak channel Task3 mRNA. Biophysical analyses show that this (GGN)(13) repeat forms a parallel G4 in vitro exhibiting the stereotypical potassium specificity of G4s, remaining thermostable under physiological ionic conditions. Through mouse brain tissue G4-RNA immuno-precipitation, we further confirm that Task3 mRNA forms a G4 structure in vivo. The G4 is inhibitory to translation of Task3 in vitro and is overcome through activity of a G4-specific helicase DHX36, increasing K+ leak currents and membrane hyperpolarisation in HEK293 cells. Further, we observe that this G4 is fundamental to ensuring delivery of Task3 mRNA to distal primary cortical neurites. It has been shown that aberrant Task3 expression correlates with neuronal dysfunction, we therefore posit that this G4 is important in regulated local expression of Task3 leak channels that maintain K+ leak within neurons.

Triple-negative breast cancer (TNBC) is the most aggressive type of breast cancer that lacks the oestrogen receptor, progesterone receptor and human epidermal growth factor receptor 2, making it difficult to target therapeutically. Targeting synthetic lethality is an alternative approach for cancer treatment. TNBC shows frequent loss of phosphatase and tensin homologue (PTEN) expression, which is associated with poor prognosis and treatment response. To identify PTEN synthetic lethal interactions, TCGA analysis coupled with a whole-genome siRNA screen in isogenic PTEN-negative and -positive cells were performed. Among the candidate genes essential for the survival of PTEN-inactive TNBC cells, WDHD1 (WD repeat and high-mobility group box DNA-binding protein 1) expression was increased in the low vs. high PTEN TNBC samples. It was also the top hit in the siRNA screen and its knockdown significantly inhibited cell viability in PTEN-negative cells, which was further validated in 2D and 3D cultures. Mechanistically, WDHD1 is important to mediate a high demand of protein translation in PTEN-inactive TNBC. Finally, the importance of WDHD1 in TNBC was confirmed in patient samples obtained from the TCGA and tissue microarrays with clinic-pathological information. Taken together, as an essential gene for the survival of PTEN-inactive TNBC cells, WDHD1 could be a potential biomarker or a therapeutic target for TNBC.

Maintaining accuracy during protein synthesis is crucial to avoid producing misfolded and/or nonfunctional proteins. The target of rapamycin complex 1 (TORC1) pathway and the activity of the protein synthesis machinery are known to negatively regulate lifespan in many organisms, although the precise mechanisms involved remain unclear. Mammalian TORC1 signaling accelerates the elongation stage of protein synthesis by inactivating eukaryotic elongation factor 2 kinase (eEF2K), which, when active, phosphorylates and inhibits eEF2, which mediates the movement of ribosomes along mRNAs, thereby slowing down the rate of elongation. We show that eEF2K enhances the accuracy of protein synthesis under a range of conditions and in several cell types. For example, our data reveal it links mammalian (m) TORC1 signaling to the accuracy of translation. Activation of eEF2K decreases misreading or termination readthrough errors during elongation, whereas knocking down or knocking out eEF2K increases their frequency. eEF2K also promotes the correct recognition of start codons in mRNAs. Reduced translational fidelity is known to correlate with shorter lifespan. Consistent with this, deletion of the eEF2K ortholog or other factors implicated in translation fidelity in Caenorhabditis elegans decreases lifespan, and eEF2K is required for lifespan extension induced by nutrient restriction. Our data uncover a novel mechanism linking nutrient supply, mTORC1 signaling, and the elongation stage of protein synthesis, which enhances the accuracy of protein synthesis. Our data also indicate that modulating translation elongation and its fidelity affects lifespan.

The contribution of epithelial–mesenchymal transition (EMT) to human lung fibrogenesis is controversial. Here we provide evidence that ZEB1-mediated EMT in human alveolar epithelial type II (ATII) cells contributes to the development of lung fibrosis by paracrine signalling to underlying fibroblasts. Activation of EGFR–RAS–ERK signalling in ATII cells induced EMT via ZEB1. ATII cells had extremely low extracellular matrix gene expression even after induction of EMT, however conditioned media from ATII cells undergoing RAS-induced EMT augmented TGFβ-induced profibrogenic responses in lung fibroblasts. This epithelial–mesenchymal crosstalk was controlled by ZEB1 via the expression of tissue plasminogen activator (tPA). In human fibrotic lung tissue, nuclear ZEB1 expression was detected in alveolar epithelium adjacent to sites of extracellular matrix (ECM) deposition, suggesting that ZEB1-mediated paracrine signalling has the potential to contribute to early fibrotic changes in the lung interstitium. Targeting this novel ZEB1 regulatory axis may be a viable strategy for the treatment of pulmonary fibrosis.

http://sro.sussex.ac.uk Spriggs, Keith A, Cobbold, Laura C, Jopling, Catherine L, Cooper, Rebecca E, Wilson, Lindsay A, Stoneley, Mark, Coldwell, Mark J, Poncet, Didier, Shen, Ya-Ching, Morley, Simon, Bushell, Martin and Willis, Anne E (2009) Canonical initiation factor requirements of the Myc family of internal ribosome entry segments. Molecular and Cellular Biology, 29 (6). pp. 1565-1574. ISSN 02707306

Increased mRNA translation drives carcinogenesis and is an attractive target for the development of new anti-cancer drugs. In this work, we investigated effects of phenethylisothiocyanate (PEITC), a phytochemical with chemopreventive and anti-cancer activity, on mRNA translation. PEITC rapidly inhibited global mRNA translation in human breast cancer-derived MCF7 cells and mouse embryonic fibroblasts (MEFs). In addition to the known inhibitory effects of PEITC on mTORC1 activity, we demonstrate that PEITC increased eIF2α phosphorylation. PEITC also increased formation of stress granules which are typically associated with eIF2α phosphorylation and accumulation of translationally stalled mRNAs. Analysis of genetically modified MEFs demonstrated that optimal inhibition of global mRNA translation by PEITC was dependent on eIF2α phosphorylation, but not mTORC1 inhibition. We extended this study into primary leukemic B cells derived from patients with chronic lymphocytic leukaemia (CLL). CLL cells were stimulated in vitro with anti-IgM to mimic binding of antigen, a major driver of this leukemia. In CLL cells, PEITC increased eIF2α phosphorylation, inhibited anti-IgM-induced mTORC1 activation and decreased both basal and anti-IgM-induced global mRNA translation. PEITC also inhibited transcription and translation of MYC mRNA and accumulation of the MYC oncoprotein, in anti-IgM-stimulated cells. Moreover, treatment of CLL cells with PEITC and the BTK kinase inhibitor ibrutinib decreased anti-IgM-induced translation and induced cell death to a greater extent than either agent alone. Therefore, PEITC can inhibit both global and mRNA specific translation (including MYC) via effects on multiple regulatory pathways. Inhibition of mRNA translation may contribute to the chemopreventive and anti-cancer effects of PEITC.

The eukaryotic translation initiation factor eIF2B is a multi-subunit complex with a crucial role in the regulation of global protein synthesis in the cell. The complex comprises five subunits, termed α through ε in order of increasing size, arranged as a heterodecamer with two copies of each subunit. Regulation of the co-stoichiometric expression of the eIF2B subunits is crucial for the proper function and regulation of the eIF2B complex in cells. We have investigated the control of stoichiometric eIF2B complexes through mutual stabilization of eIF2B subunits. Our data show that the stable expression of the catalytic eIF2Bε subunit in human cells requires co-expression of eIF2Bγ. Similarly, stable expression of eIF2Bδ requires both eIF2Bβ and eIF2Bγ+ε. The expression of these subunits decreases despite there being no change in either the levels or the translation of their mRNAs. Instead, these subunits are targeted for degradation by the ubiquitin–proteasome system. The data allow us to propose a model for the formation of stoichiometric eIF2B complexes which can ensure their stoichiometric incorporation into the holocomplex.

There has recently been a huge increase in interest in the formation of stable G-quadruplex structures in mRNAs and their functional significance. In neurons, local translation of mRNA is essential for normal neuronal behaviour. It has been discovered that local translation of specific mRNAs encoding some of the best known synaptic proteins is dependent on the presence of a G-quadruplex. The recognition of G-quadruplexes in mRNAs, their transport as repressed complexes and the control of their translation at their subcellular destinations involves a diversity of proteins, including those associated with disease pathologies. This is an exciting field, with rapid improvements to our knowledge and understanding. Here, we discuss some of the recent work on how G-quadruplexes mediate local translation in neurons.

As the field of molecular biology developed, and the understanding of how inherited genetic material results in the expression of proteins was established, the initial hypothesis was that one gene gave rise to one protein1. As researchers delved deeper into the organization of the genetic code and advances in messenger RNA (mRNA) and protein sequencing were subsequently made, it has become abundantly clear that multiple mechanisms exist meaning that many mRNAs encode more than one version of a protein. Although alternative promoters and alternative splicing play a considerable role in the generation of protein isoforms, in this article we discuss how usage of alternative translation initiation codons in eukaryotes can also lead to an expanded proteome.

ATP-binding cassette 50 (ABC50; also known as ABCF1) binds to eukaryotic initiation factor 2 (eIF2) and is required for efficient translation initiation. An essential step of this process is accurate recognition and selection of the initiation codon. It is widely accepted that the presence and movement of eIF1, eIF1A and eIF5 are key factors in modulating the stringency of start-site selection, which normally requires an AUG codon in an appropriate sequence context. In the present study, we show that expression of ABC50 mutants, which cannot hydrolyse ATP, decreases general translation and relaxes the discrimination against the use of non-AUG codons at translation start sites. These mutants do not appear to alter the association of key initiation factors to 40S subunits. The stringency of start-site selection can be restored through overexpression of eIF1, consistent with the role of that factor in enhancing stringency. The present study indicates that interfering with the function of ABC50 influences the accuracy of initiation codon selection.

Antigenic stimulation via the B-cell receptor (BCR) is a major driver of the proliferation and survival of chronic lymphocytic leukemia (CLL) cells. However, the precise mechanisms by which BCR stimulation leads to accumulation of malignant cells remain incompletely understood. Here, we investigated the ability of BCR stimulation to increase messenger RNA (mRNA) translation, which can promote carcinogenesis by effects on both global mRNA translation and upregulated expression of specific oncoproteins. Re-analysis of gene expression profiles revealed striking upregulation of pathways linked to mRNA translation both in CLL cells derived from lymph nodes, the major site of antigen stimulation in vivo, and after BCR stimulation in vitro. Anti-IgM significantly increased mRNA translation in primary CLL cells, measured using bulk metabolic labeling and a novel flow cytometry assay to quantify responses at a single-cell level. These translational responses were suppressed by inhibitors of BTK (ibrutinib) and SYK (tamatinib). Anti-IgM-induced mRNA translation was associated with increased expression of translation initiation factors eIF4A and eIF4GI, and reduced expression of the eIF4A inhibitor, PDCD4. Anti-IgM also increased mRNA translation in normal blood B cells, but without clear modulatory effects on these factors. In addition, anti-IgM increased translation of mRNA-encoding MYC, a major driver of disease progression. mRNA translation is likely to be an important mediator of the growth-promoting effects of antigen stimulation acting, at least in part, via translational induction of MYC. Differences in mechanisms of translational regulation in CLL and normal B cells may provide opportunities for selective therapeutic attack.

The C2C12 myoblast cell line has been extensively studied as it has the potential to differentiate from serum-starved confluent monolayer cultures into myotubes, (Fig. 1, upper panel) which can further align and form muscle fibers. Furthermore, C2C12 myoblasts can differentiate into adipose and bone-type lineages, depending on the conditions present. As such the system has to undergo huge changes in both transcription and translation to reflect the different proteomes required for each lineage. Therefore, there must be a great degree of control exerted to ensure the expression of genes involved in the commitment to and progression through myogenesis, to ensure that their temporal and spatial expression is properly regulated. Figure 1. C2C12 myoblasts grown to confluency and starved undergo myogenic differentiation. Allosteric inhibitors of mTORC1 inhibit this process. Availability of eIF4E for mRNA cap-binding in translation is determined by interaction with eIF4E binding proteins ... In their previous work, the Morley group confirmed that the mTORC1 pathway is activated during differentiation in C2C12 cells and that a delay in myogenic differentiation can be caused by allosteric inhibitors of mTORC1 activity, namely rapamycin and RAD001 (everolimus), a rapamycin derivative.1 This rapamycin-sensitive inhibition of myogenesis has been extensively reviewed elsewhere.2 The mTOR kinase is present in the cell within 2 complexes, the rapamycin sensitive mTORC1 which contains Raptor (Fig. 1, lower panel), and the rapamycin insensitive mTORC2 complex which contains Rictor (for a recent review of this vast subject see3). Among many targets, mTORC1 is a master regulator of cap-dependent translation and controls the phosphorylation and the activation of the targets 4E-BP1 (Fig. 1, lower panel) and S6K1. These components are involved in the control of protein synthesis by modulating the availability of the cap-binding protein eIF4E and the activity of the ribosome respectively. In their previous work, the Morley group observed a high level of 4E-BP1 phosphorylation during C2C12 myogenic differentiation, even in the presence of Rad001.1 This contradicts the usual models of eIF4E availability which show that 4E-BP1 phosphorylation is usually downregulated upon mTORC1 inhibition. In their current paper,4 Pollard, Willett and Morley sought to further investigate the role of mTOR kinase signaling pathway during myogenic differentiation, and in particular, the kinases responsible for the phosphorylation of 4E-BP1. The authors show that the phosphorylation is maintained during myogenic differentiation in the presence of RAD001 but is abolished when using direct inhibitors of the mTOR kinase, KU0063794 and Torin1. The ATM kinase, which is thought to phosphorylate 4E-BP1 on other sites was not implicated in this work. In order to clarify the role of the mTORC complexes during myogenic differentiation they used siRNA to knock down the components that are responsible for target specificity. Their targets were either Raptor, a component of the mTORC1 complex, or Rictor from the mTORC2 complex. The separate or combined knockdowns demonstrate that the depletion of raptor or rictor still does not affect the phosphorylation of 4E-BP1. Together, these findings suggest that at least in this system, phosphorylation of 4E-BP1 can be due to mTOR signaling that is not part of the mTORC1 or mTORC2 complexes. While this is unusual, work from the Meyuhas group5 suggests that it is not unprecedented that mTOR may be able to act alone, or in an as yet uncharacterised “mTORC3” complex, both of which would be immune to the presence of rapamycin, but not the direct mTOR kinase inhibitors. The sustained phosphorylation of 4E-BP1 is key to allowing translation to be maintained during the serum starvation required for myogenic differentiation, which would otherwise be inhibitory to the recruitment of eIF4E to the rest of the translation initiation machinery. A secondary effect may also be to help contribute to the selective translation of the subset of mRNAs involved in the differentiation process. The recent advent of ribosomal profiling technologies to examine the translating pool of mRNAs raises the exciting possibility that we may soon be able to understand such key molecular details in this well-studied, but still not fully understood model system.

Translation mechanisms at different stages of the cell cycle have been studied for many years, resulting in the dogma that translation rates are slowed during mitosis, with cap-independent translation mechanisms favored to give expression of key regulatory proteins. However, such cell culture studies involve synchronization using harsh methods, which may in themselves stress cells and affect protein synthesis rates. One such commonly used chemical is the microtubule de-polymerization agent, nocodazole, which arrests cells in mitosis and has been used to demonstrate that translation rates are strongly reduced (down to 30% of that of asynchronous cells). Using synchronized HeLa cells released from a double thymidine block (G 1/S boundary) or the Cdk1 inhibitor, RO3306 (G 2/M boundary), we have systematically re-addressed this dogma. Using FACS analysis and pulse labeling of proteins with labeled methionine, we now show that translation rates do not slow as cells enter mitosis. This study is complemented by studies employing confocal microscopy, which show enrichment of translation initiation factors at the microtubule organizing centers, mitotic spindle, and midbody structure during the final steps of cytokinesis, suggesting that translation is maintained during mitosis. Furthermore, we show that inhibition of translation in response to extended times of exposure to nocodazole reflects increased eIF2α phosphorylation, disaggregation of polysomes, and hyperphosphorylation of selected initiation factors, including novel Cdk1-dependent N-terminal phosphorylation of eIF4GII. Our work suggests that effects on translation in nocodazole-arrested cells might be related to those of the treatment used to synchronize cells rather than cell cycle status.

Large portions of higher eukaryotic proteomes are intrinsically disordered, and abundant evidence suggests that these unstructured regions of proteins are rich in regulatory interaction interfaces. A major class of disordered interaction interfaces are the compact and degenerate modules known as short linear motifs (SLiMs). As a result of the difficulties associated with the experimental identification and validation of SLiMs, our understanding of these modules is limited, advocating the use of computational methods to focus experimental discovery. This article evaluates the use of evolutionary conservation as a discriminatory technique for motif discovery. A statistical framework is introduced to assess the significance of relatively conserved residues, quantifying the likelihood a residue will have a particular level of conservation given the conservation of the surrounding residues. The framework is expanded to assess the significance of groupings of conserved residues, a metric that forms the basis of SLiMPrints (short linear motif fingerprints), a de novo motif discovery tool. SLiMPrints identifies relatively overconstrained proximal groupings of residues within intrinsically disordered regions, indicative of putatively functional motifs. Finally, the human proteome is analysed to create a set of highly conserved putative motif instances, including a novel site on translation initiation factor eIF2A that may regulate translation through binding of eIF4E.

During the initiation stage of eukaryotic mRNA translation, the eIF4G (eukaryotic initiation factor 4G) proteins act as an aggregation point for recruiting the small ribosomal subunit to an mRNA. We previously used RNAi (RNA interference) to reduce expression of endogenous eIF4GI proteins, resulting in reduced protein synthesis rates and alterations in the morphology of cells. Expression of EIF4G1 cDNAs, encoding different isoforms (f-a) which arise through selection of alternative initiation codons, rescued translation to different extents. Furthermore, overexpression of the eIF4GII paralogue in the eIF4GI-knockdown background was unable to restore translation to the same extent as eIF4GIf/e isoforms, suggesting that translation events governed by this protein are different. In the present study we show that multiple isoforms of eIF4GII exist in mammalian cells, arising from multiple promoters and alternative splicing events, and have identified a non-canonical CUG initiation codon which extends the eIF4GII N-terminus. We further show that the rescue of translation in eIF4GI/eIF4GII double-knockdown cells by our novel isoforms of eIF4GII is as robust as that observed with either eIF4GIf or eIF4GIe, and more than that observed with the original eIF4GII. As the novel eIF4GII sequence diverges from eIF4GI, these data suggest that the eIF4GII N-terminus plays an alternative role in initiation factor assembly.