Large Subunit Assembly Research Articles

Complete list of canonical post-transcriptional modifications in the Bacillus subtilis ribosome and their link to RbgA driven large subunit assembly.

Ribosomal RNA modifications in prokaryotes have been sporadically studied, but there is a lack of a comprehensive picture of modification sites across bacterial phylogeny. Bacillus subtilis is a preeminent model organism for gram-positive bacteria, with a well-annotated and editable genome, convenient for fundamental studies and industrial use. Yet remarkably, there has been no complete characterization of its rRNA modification inventory. By expanding modern MS tools for the discovery of RNA modifications, we found a total of 25 modification sites in 16S and 23S rRNA of B. subtilis, including the chemical identity of the modified nucleosides and their precise sequence location. Furthermore, by perturbing large subunit biogenesis using depletion of an essential factor RbgA and measuring the completion of 23S modifications in the accumulated intermediate, we provide a first look at the order of modification steps during the late stages of assembly in B. subtilis. While our work expands the knowledge of bacterial rRNA modification patterns, adding B. subtilis to the list of fully annotated species after Escherichia coli and Thermus thermophilus, in a broader context, it provides the experimental framework for discovery and functional profiling of rRNA modifications to ultimately elucidate their role in ribosome biogenesis and translation.

GTPBP8 plays a role in mitoribosome formation in human mitochondria

Mitochondrial gene expression relies on mitoribosomes to translate mitochondrial mRNAs. The biogenesis of mitoribosomes is an intricate process involving multiple assembly factors. Among these factors, GTP-binding proteins (GTPBPs) play important roles. In bacterial systems, numerous GTPBPs are required for ribosome subunit maturation, with EngB being a GTPBP involved in the ribosomal large subunit assembly. In this study, we focus on exploring the function of GTPBP8, the human homolog of EngB. We find that ablation of GTPBP8 leads to the inhibition of mitochondrial translation, resulting in significant impairment of oxidative phosphorylation. Structural analysis of mitoribosomes from GTPBP8 knock-out cells shows the accumulation of mitoribosomal large subunit assembly intermediates that are incapable of forming functional monosomes. Furthermore, fPAR-CLIP analysis reveals that GTPBP8 is an RNA-binding protein that interacts specifically with the mitochondrial ribosome large subunit 16 S rRNA. Our study highlights the role of GTPBP8 as a component of the mitochondrial gene expression machinery involved in mitochondrial large subunit maturation.

Structural insights into the role of GTPBP10 in the RNA maturation of the mitoribosome

Mitochondria contain their own genetic information and a dedicated translation system to express it. The mitochondrial ribosome is assembled from mitochondrial-encoded RNA and nuclear-encoded ribosomal proteins. Assembly is coordinated in the mitochondrial matrix by biogenesis factors that transiently associate with the maturing particle. Here, we present a structural snapshot of a large mitoribosomal subunit assembly intermediate containing 7 biogenesis factors including the GTPases GTPBP7 and GTPBP10. Our structure illustrates how GTPBP10 aids the folding of the ribosomal RNA during the biogenesis process, how this process is related to bacterial ribosome biogenesis, and why mitochondria require two biogenesis factors in contrast to only one in bacteria.

Hub genes identification and association of key pathways with hypoxia in cancer cells: A bioinformatics analysis

Three human cancer cell lines (A549, HCT116, and HeLa) were used to investigate the molecular mechanisms and potential prognostic biomarkers associated with hypoxia. We obtained gene expression data from Gene Expression Omnibus (GEO) datasets GSE11704, GSE147384, and GSE38061, which included 5 hypoxic and 8 control samples. Using the GEO2R tool and Venn diagram software, we identified common differentially expressed genes (cDEGs). The cDEGs were then subjected to Gene ontology (GO) and Kyoto Encyclopedia of Gene and Genome (KEGG) pathway analysis by employing DAVID. The hub genes were identified from critical PPI subnetworks through CytoHuba plugin and these genes' prognostic significance and expression were verified using Kaplan-Meier analysis and Gene Expression Profiling Interactive Analysis (GEPIA), respectively. The research showed 676 common DEGs (cDEGs), with 207 upregulated and 469 downregulated genes. The STRING analysis showed 673 nodes and 1446 edges in the PPI network. We identified 4 significant modules and 19 downregulated hub genes. GO analysis revealed all of them were majorly involved in ribosomal large subunit assembly and biogenesis, rRNA processing, ribosome biogenesis, translation, RNA & protein binding frequently at the sites of nucleolus and nucleoplasm while11 were significantly associated with a better prognosis of hypoxic tumors. Our research sheds light on the molecular mechanisms that underpin hypoxia in human cancer cell lines and identifies potential prognostic biomarkers for hypoxic tumors.

A co-transcriptional ribosome assembly checkpoint controls nascent large ribosomal subunit maturation

During transcription of eukaryotic ribosomal DNA in the nucleolus, assembly checkpoints exist that guarantee the formation of stable precursors of small and large ribosomal subunits. While the formation of an early large subunit assembly checkpoint precedes the separation of small and large subunit maturation, its mechanism of action and function remain unknown. Here, we report the cryo-electron microscopy structure of the yeast co-transcriptional large ribosomal subunit assembly intermediate that serves as a checkpoint. The structure provides the mechanistic basis for how quality-control pathways are established through co-transcriptional ribosome assembly factors, that structurally interrogate, remodel and, together with ribosomal proteins, cooperatively stabilize correctly folded pre-ribosomal RNA. Our findings thus provide a molecular explanation for quality control during eukaryotic ribosome assembly in the nucleolus.

Human GTPBP5 is involved in the late stage of mitoribosome large subunit assembly.

Human mitoribosomes are macromolecular complexes essential for translation of 11 mitochondrial mRNAs. The large and the small mitoribosomal subunits undergo a multistep maturation process that requires the involvement of several factors. Among these factors, GTP-binding proteins (GTPBPs) play an important role as GTP hydrolysis can provide energy throughout the assembly stages. In bacteria, many GTPBPs are needed for the maturation of ribosome subunits and, of particular interest for this study, ObgE has been shown to assist in the 50S subunit assembly. Here, we characterize the role of a related human Obg-family member, GTPBP5. We show that GTPBP5 interacts specifically with the large mitoribosomal subunit (mt-LSU) proteins and several late-stage mitoribosome assembly factors, including MTERF4:NSUN4 complex, MRM2 methyltransferase, MALSU1 and MTG1. Interestingly, we find that interaction of GTPBP5 with the mt-LSU is compromised in the presence of a non-hydrolysable analogue of GTP, implying a different mechanism of action of this protein in contrast to that of other Obg-family GTPBPs. GTPBP5 ablation leads to severe impairment in the oxidative phosphorylation system, concurrent with a decrease in mitochondrial translation and reduced monosome formation. Overall, our data indicate an important role of GTPBP5 in mitochondrial function and suggest its involvement in the late-stage of mt-LSU maturation.

Structure of the mature kinetoplastids mitoribosome and insights into its large subunit biogenesis

Kinetoplastids are unicellular eukaryotic parasites responsible for such human pathologies as Chagas disease, sleeping sickness, and leishmaniasis. They have a single large mitochondrion, essential for the parasite survival. In kinetoplastid mitochondria, most of the molecular machineries and gene expression processes have significantly diverged and specialized, with an extreme example being their mitochondrial ribosomes. These large complexes are in charge of translating the few essential mRNAs encoded by mitochondrial genomes. Structural studies performed in Trypanosoma brucei already highlighted the numerous peculiarities of these mitoribosomes and the maturation of their small subunit. However, several important aspects mainly related to the large subunit (LSU) remain elusive, such as the structure and maturation of its ribosomal RNA. Here we present a cryo-electron microscopy study of the protozoans Leishmania tarentolae and Trypanosoma cruzi mitoribosomes. For both species, we obtained the structure of their mature mitoribosomes, complete rRNA of the LSU, as well as previously unidentified ribosomal proteins. In addition, we introduce the structure of an LSU assembly intermediate in the presence of 16 identified maturation factors. These maturation factors act on both the intersubunit and the solvent sides of the LSU, where they refold and chemically modify the rRNA and prevent early translation before full maturation of the LSU.

MitoRibo-Tag Mice Provide a Tool for In Vivo Studies of Mitoribosome Composition

SummaryMitochondria harbor specialized ribosomes (mitoribosomes) necessary for the synthesis of key membrane proteins of the oxidative phosphorylation (OXPHOS) machinery located in the mitochondrial inner membrane. To date, no animal model exists to study mitoribosome composition and mitochondrial translation coordination in mammals in vivo. Here, we create MitoRibo-Tag mice as a tool enabling affinity purification and proteomics analyses of mitoribosomes and their interactome in different tissues. We also define the composition of an assembly intermediate formed in the absence of MTERF4, necessary for a late step in mitoribosomal biogenesis. We identify the orphan protein PUSL1, which interacts with a large subunit assembly intermediate, and demonstrate that it is an inner-membrane-associated mitochondrial matrix protein required for efficient mitochondrial translation. This work establishes MitoRibo-Tag mice as a powerful tool to study mitoribosomes in vivo, enabling future studies on the mitoribosome interactome under different physiological states, as well as in disease and aging.

Insight into bovine (Bos indicus) spermatozoal whole transcriptome profile

Mature spermatozoa harbor both coding and non-coding type of RNAs which regulates spermatogenesis, fertilization and early development. Characterization of bovine sperm transcriptome can provide more insight into the molecular mechanisms involved in these processes. Here, we have analyzed whole transcriptome profile of Bos indicus spermatozoa to access the global RNA expression. RNA-Seq analysis identified 14,306 genes expressed with FPKM >0, while 405 genes expressed when threshold increased to FPKM >5. Functional annotations showed that sperm transcripts were associated with molecular processes (translation, ribosomal small and large subunit assembly) and cellular components (cytosolic small and large ribosomal subunit and membranes) related to known sperm functions at fertilization and spermatogenesis. The RNA-Seq data was validated using droplet digital PCR where both highly abundant gene viz. RN7SL1 and less abundant gene viz. ZFP280B were validated. This study may provide future directions in reproductive biology of Bos indicus.

Assembly and early maturation of large subunit precursors

The eukaryotic ribosome is assembled through a complex process involving more than 200 factors. As preribosomal RNA is transcribed, assembly factors bind the nascent pre-rRNA and guide its correct folding, modification, and cleavage. While these early events in the assembly of the small ribosomal subunit have been relatively well characterized, assembly of the large subunit precursors, or pre-60S, is less well understood. Recent structures of nucleolar intermediates of large subunit assembly have shed light on the role of many early large subunit assembly factors, but how these particles emerge is still unknown. Here, we use the expression and purification of truncated pre-rRNAs to examine the initial assembly of pre-60S particles. Using this approach, we can recapitulate the early recruitment of large subunit assembly factors mainly to the domains I, II, and VI of the assembling 25S rRNA.

MTG1 couples mitoribosome large subunit assembly with intersubunit bridge formation.

Mammalian mitochondrial ribosomes (mitoribosomes) synthesize 13 proteins, essential components of the oxidative phosphorylation system. They are linked to mitochondrial disorders, often involving cardiomyopathy. Mitoribosome biogenesis is assisted by multiple cofactors whose specific functions remain largely uncharacterized. Here, we examined the role of human MTG1, a conserved ribosome assembly guanosine triphosphatase. MTG1-silencing in human cardiomyocytes and developing zebrafish revealed early cardiovascular lesions. A combination of gene-editing and biochemical approaches using HEK293T cells demonstrated that MTG1 binds to the large subunit (mtLSU) 16S ribosomal RNA to facilitate incorporation of late-assembly proteins. Furthermore, MTG1 interacts with mtLSU uL19 protein and mtSSU mS27, a putative guanosine triphosphate-exchange factor (GEF), to enable MTG1 release and the formation of the mB6 intersubunit bridge. In this way, MTG1 establishes a quality control checkpoint in mitoribosome assembly. In conclusion, MTG1 controls mitochondrial translation by coupling mtLSU assembly with intersubunit bridge formation using the intrinsic GEF activity acquired by the mtSSU through mS27, a unique occurrence in translational systems.

The polypeptide exit tunnel of the ribosomal large subunit requires assembly factors for proper construction and function

The final product of ribosome assembly consists of two ribosomal subunits capable of functioning with high fidelity. In eukaryotes, this process is facilitated by protein assembly factors that can promote proper formation of functional centers through structural probing, functional test‐driving, acting as a scaffold, or protecting the site from premature activity. The polypeptide exit tunnel (PET) of the ribosomal large subunit (LSU) is the conduit through which nascent polypeptide chains are passed as they are synthesized. Protein and RNA components of the PET lumen actively participate in translation by interacting with the nascent chain in order to regulate ribosome stalling events, thus regulating translation speed and gene expression. Recent cryo‐EM structures of immature LSU particles from different stages of assembly spanning the nucleoplasm to the cytoplasm have shown that the PET is sequentially probed by the C‐termini of three assembly factors: first, Nog1, then Rei1, and finally Reh1. The C‐termini of these three assembly factors mimic nascent chains, plugging the PET for almost the entirety of LSU assembly. No biological function, however, has been assigned to this redundant occupation of the PET. Here, we show that truncating PET‐inclusive residues from the C‐terminus of Nog1 causes LSU assembly defects that are exacerbated by analogous truncations to one or both of the Rei1 and Reh1 C‐termini. These defects manifest in processing of late immature ribosomal RNA intermediates. Interestingly, these assembly defects are further exacerbated at lower temperatures. Despite these mutants displaying slow growth at permissive temperatures, however, mature ribosomes are produced that may be defective in translation. Our data supports the model that Nog1 is necessary for efficient construction of the PET during early stages of assembly while Rei1 and Reh1 carry out checkpoints during later stages.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Yeast Mitoribosome Large Subunit Assembly Proceeds by Hierarchical Incorporation of Protein Clusters and Modules on the Inner Membrane

Mitoribosomes are specialized for the synthesis ofhydrophobic membrane proteins encoded by mtDNA, all essential for oxidative phosphorylation. Despite their linkage to human mitochondrial diseases and the recent cryoelectron microscopy reconstruction of yeast and mammalian mitoribosomes, how they are assembled remains obscure. Here, we dissected the yeast mitoribosome large subunit (mtLSU) assembly process by systematic genomic deletion of 44 mtLSU proteins (MRPs). Analysis of the strain collection unveiled 37 proteins essential for functional mtLSU assembly, three of which are critical for mtLSU 21S rRNA stability. Hierarchical cluster analysis of mtLSU subassemblies accumulated in mutant strains revealed co-operative assembly of protein sets forming structural clusters and preassembled modules. It also indicated crucial roles for mitochondrion-specific membrane-binding MRPs in anchoring newly transcribed 21S rRNA to the inner membrane, where assembly proceeds. Our results define the yeast mtLSU assembly landscape invivo and provide a foundation for studies of mitoribosome assembly across evolution.

Ribosome Biogenesis Controls Erythroid Differentiation Via a p53-Dependent Transcriptional Checkpoint and Its Limitation By RPS14 Haploinsufficiency Results in Selective Defects in Translation

Haploinsufficiency in genes encoding ribosomal proteins (RP) or ribosome-associated proteins either by mutation or deletion leads to a predominant erythroid phenotype. In acquired 5q- myelodysplasic syndrome (MDS), the macrocytic anemia has been linked to the monoallelic deletion of RPS14 gene which results in altered ribosome biogenesis. Because of the defective maturation of the small 40S ribosome subunit, the RPL5/RPL11/5SrARN complex, normally involved in the assembly of the large 60S subunit assembly, accumulates and inhibits E3-ligase-HDM2 leading to the stabilization and activation of p53 resultig in cell cycle arrest, increased apoptosis and defective differentiation of maturing erythroblasts. In the present work, we hypothesized that p53 could play a key role in the control of normal erythroid differentiation by ribosome biogenesis and we further investigated the involvement of the decreased pool of ribosome on erythroid defects in the 5q- syndrome.To investigate the first hypothesis, we studied the kinetics of ribosome biogenesis in human primary erythroblasts by mass spectrometry after pulse-SILAC. We noted that ribosome renewal collapses begining at the polychromatophilic erythroblast stage. We subsequently used the pharmacological agent CX-5461 to inhibit RNA polymerase I. When ribosome biogenesis in proerythroblasts is blocked by CX-5461, p53 is activated and proerythroblasts enter the terminal differentiation by expressing GATA1-erythroid target genes without apoptosis. By ChIP-seq in primary erythroblasts, we demonstrated that p53 binds to 1289 genes including 263 genes specifically activated by CX-5461, 6 of them being upregulated during CX-5461-induced erythroid differentiation and 3 of them being known GATA1 targets. We further used an shRNA strategy to demonstrate that one of these genes is required to permit entry into terminal erythroid differentiation when ribosome biogenesis is abrogated. We thus showed that normal erythroid differentiation is controlled by ribosome biogenesis through a p53-dependent checkpoint.In 5q- syndrome, ribosome biogenesis is continuously decreased along all stages of erythropoiesis and in contrast to the normal conditions, erythroid differentiation is defective with an excess of apoptosis affecting mature erythroblasts. We previously reported that GATA1 is targeted by a caspase-dependent cleavage since GATA1 is not protected by its chaperone HSP70 in the nucleus of MDS erythroblasts. We confirmed that GATA1 protein is decreased in 5q- primary erythroblasts and in RPS14 shRNA-expressing normal erythroblasts. To obtain further insights into the defective erythroid maturation of RPS14-deleted erythroblasts, we developed an inducible shRNA to RPS14 in the UT7/Epo cell line. Polysome profiling confirmed the decrease of 40S subunit and absolute quantification of RP by deep proteomics demonstrated a 50% decrease of RPS in conjunction with 50% reduction of ribosome content in these cells. GATA1 expression was decreased and was only partially rescued by treatment with either caspase inhibitor qVD or proteasome inhibitor, bortezomib. We then tested the hypothesis of a decrease in GATA1 translation, as previously shown in a shRNA RPS19 Diamond-Blackfan model, by analyzing and comparing the global transcriptome and the translatome corresponding to transcripts present in high molecular weight polysomes using Affymetrix HTA 2.0 microarrays. We observed a decoupling between transcriptome and translatome suggesting a selectivity of translational defects. Thermodynamic characteristics i.e. the fold energy, energy per base and length of the 3'UTR and the energy per base of the 5'UTR (Vienna RNA Package, UCSC genome browser) were the determinants of transcript selection on the polysome. The shortest transcripts with a highly structured 3'UTR including GATA1 were the transcripts which were less effectively translated. Consistently, the diminution of GATA1 protein was associated with a decrease of its target genes. Our results suggest that GATA1 is a potentially interesting therapeutic target.In summary, our results show that ribosome biogenesis controls erythroid differentiation via a p53-dependent transcriptional regulation and that a reduction of the ribosome pool leads to a selective translation at the expense of erythroid master gene GATA1. DisclosuresFontenay:Celgene: Research Funding.

Functional interaction between ribosomal protein L6 and RbgA during ribosome assembly.

RbgA is an essential GTPase that participates in the assembly of the large ribosomal subunit in Bacillus subtilis and its homologs are implicated in mitochondrial and eukaryotic large subunit assembly. How RbgA functions in this process is still poorly understood. To gain insight into the function of RbgA we isolated suppressor mutations that partially restored the growth of an RbgA mutation (RbgA-F6A) that caused a severe growth defect. Analysis of these suppressors identified mutations in rplF, encoding ribosomal protein L6. The suppressor strains all accumulated a novel ribosome intermediate that migrates at 44S in sucrose gradients. All of the mutations cluster in a region of L6 that is in close contact with helix 97 of the 23S rRNA. In vitro maturation assays indicate that the L6 substitutions allow the defective RbgA-F6A protein to function more effectively in ribosome maturation. Our results suggest that RbgA functions to properly position L6 on the ribosome, prior to the incorporation of L16 and other late assembly proteins.

How to avoid undesirable interactions during ribosome assembly?

Ribosome subunit assembly in bacteria is assisted by several non-ribosomal proteins, the absence of which leads to assembly defects. The two DEAD-box RNA helicases SrmB and DeaD/CsdA are required for efficient assembly of the ribosome large subunit, in particular at low temperature, but their sites of action on rRNA were not known until now. In this issue of Molecular Microbiology, Proux et al. show that SrmB acts far away from its tethering site on the assembly intermediate particle. A genetic screen identified mutations in complementary sequences of 23S and 5S rRNA that help to bypass SrmB deficiency, partially correcting the large subunit assembly defect. The results suggest that 5S rRNA and 23S rRNA can interact via base-pairing, forming a non-native structure that needs to be corrected. The authors discuss attractive hypotheses on SrmB acts during large subunit assembly.

The role of disordered ribosomal protein extensions in the early steps of eubacterial 50 S ribosomal subunit assembly.

Although during the past decade research has shown the functional importance of disorder in proteins, many of the structural and dynamics properties of intrinsically unstructured proteins (IUPs) remain to be elucidated. This review is focused on the role of the extensions of the ribosomal proteins in the early steps of the assembly of the eubacterial 50 S subunit. The recent crystallographic structures of the ribosomal particles have revealed the picture of a complex assembly pathway that condenses the rRNA and the ribosomal proteins into active ribosomes. However, little is know about the molecular mechanisms of this process. It is thought that the long basic r-protein extensions that penetrate deeply into the subunit cores play a key role through disorder-order transitions and/or co-folding mechanisms. A current view is that such structural transitions may facilitate the proper rRNA folding. In this paper, the structures of the proteins L3, L4, L13, L20, L22 and L24 that have been experimentally found to be essential for the first steps of ribosome assembly have been compared. On the basis of their structural and dynamics properties, three categories of extensions have been identified. Each of them seems to play a distinct function. Among them, only the coil-helix transition that occurs in a phylogenetically conserved cluster of basic residues of the L20 extension appears to be strictly required for the large subunit assembly in eubacteria. The role of α helix-coil transitions in 23 S RNA folding is discussed in the light of the calcium binding protein calmodulin that shares many structural and dynamics properties with L20.

Ribosome assembly in Escherichia coli strains lacking the RNA helicase DeaD/CsdA or DbpA

Ribosome subunit assembly in bacteria is a fast and efficient process. Among the nonribosomal proteins involved in ribosome biogenesis are RNA helicases. We describe ribosome biogenesis in Escherichia coli strains lacking RNA helicase DeaD (CsdA) or DbpA. Ribosome large subunit assembly intermediate particles (40S) accumulate at 25 degrees C and at 37 degrees C in the absence of DeaD but not without DbpA. 23S rRNA is incompletely processed in the 40S and 50S particles of the DeaD(-) strain. Pulse labeling showed that the 40S particles are converted nearly completely into functional ribosomes. The rate of large ribosomal subunit assembly was reduced about four times in DeaD-deficient cells. Functional activity tests of the ribosomal particles demonstrated that the final step of 50S assembly, the activation step, was affected when DeaD was not present. The results are compatible with the model that predicts multiple DeaD-catalyzed structural transitions of the ribosome large subunit assembly.

Importance of Transient Structures During Post-transcriptional Refolding of the Pre-23 S rRNA and Ribosomal Large Subunit Assembly

An important step of ribosome assembly is the folding of the rRNA into a functional structure. Despite knowledge of the folded state of rRNA in the ribosomal subunits, there is very little information on the rRNA folding pathway. We are interested in understanding how the functional structure of rRNA is formed and whether the rRNA folding intermediates have a role in ribosome assembly. To this end, transient secondary structures around both ends of pre-23S rRNA were analyzed by a chemical probing approach, using pre-23S rRNA transcripts. Metastable hairpin loop structures were found at both ends of 23S rRNA. The functional importance of the transient structures around the ends of 23S rRNA was tested by mutations that alter only the transient structure. The effect of mutations on 23S rRNA folding was tested in vitro and in vivo. It was found that both stabilization and destabilization of the transient structure around the 5' end of 23S rRNA inhibits post-transcriptional refolding in vitro and ribosome formation in vivo. The data suggest that the transient structure of rRNA has a function during 23S rRNA folding and thereby in ribosome assembly.

A Fistful of Factors

BIOCHEMISTRY One of the familiar leitmotifs of biological regulation is a cascade of switches aimed at a crucial go-no go control point. The initiation of protein synthesis is one such point, and assembly of the translational machine, the ribosome, on the messenger RNA (mRNA) is a carefully thought-out decision. In the developing Drosophila oocyte, oskar mRNA is donated by the surrounding nurse cells, and posterior patterning of the oocyte requires spatially restricted translation of oskar mRNA. Wilhelm et al . show that the protein Cup binds to eukaryotic initiation factor 4E (eIF4E), which sits at the capped 5' end of the mRNA. Cup acts to recruit oskar mRNA to the posterior region and to keep it translationally inactive until it gets there. Nelson et al. show that the Oskar protein appears to exercise a similar regulatory oversight of nanos mRNA, whose translation is inhibited by the interaction between Smaug and Cup, which is in contact with eIF4E bound at the 5' end of the nanos mRNA. Oskar binds to Smaug, and this may result in disruption of the Cup-eIF4E interaction. Why is it so crucial to control access to eIF4E? Gross et al. describe the structure of the complex between eIF4E and eIF4G. The 4G factor is itself part of a multiprotein complex that serves as a platform for integrating kinase-communicated signals and the subsequent steps of small and large ribosome subunit assembly. The contact between these two factors encompasses a large surface area formed by threading the bracelet-like eIF4G onto the initially unfolded N-terminal α-helix of eIF4E, which then organizes into a fist-like domain, locking eIF4G into place. — GJC J. Cell Biol. 163 , 1197 (2003); EMBO J. 10.1038/sj.emboj.7600026 (2003); Cell 115 , 739 (2003)