scholarly journals Ribosomal protein RACK1 facilitates efficient translation of poliovirus and other viral IRESs

2019 ◽  
Author(s):  
Ethan LaFontaine ◽  
Clare M. Miller ◽  
Natasha Permaul ◽  
Alex G. Johnson ◽  
Elliot T. Martin ◽  
...  
Keyword(s):  
Ribosomal Protein ◽  
Host Cell ◽  
Translation Initiation ◽  
Ribosomal Proteins ◽  
Ribosomal Subunit ◽  
Luciferase Reporter ◽  
Entry Site ◽  
Translational Machinery ◽  
Initiation Factors ◽  
Translation Initiation Factors

AbstractViruses have evolved various strategies to ensure efficient translation using host cell ribosomes and translation factors. In addition to cleaving translation initiation factors required for host cell translation, poliovirus (PV) uses an internal ribosome entry site (IRES) to bypass the need for these translation initiation factors. Recent studies also suggest that viruses have evolved to exploit specific ribosomal proteins to enhance translation of their viral proteins. The ribosomal protein receptor for activated C kinase 1 (RACK1), a protein of the 40S ribosomal subunit, was previously shown to mediate translation of the 5′ cricket paralysis virus and hepatitis C virus IRESs. Here we found that while translation of a PV dual-luciferase reporter shows only a moderate dependence on RACK1, PV translation in the context of a viral infection is drastically reduced. We observed significantly reduced poliovirus plaque size and a delayed host cell translational shut-off suggesting that loss of RACK1 increases the length of the virus life cycle. Our findings further illustrate the involvement of the cellular translational machinery in PV infection and how viruses usurp the function of specific ribosomal proteins.

scholarly journals Dynamic competition between SARS-CoV-2 NSP1 and mRNA on the human ribosome inhibits translation initiation

2021 ◽  
Vol 118 (6) ◽  
pp. e2017715118
Author(s):  
Christopher P. Lapointe ◽  
Rosslyn Grosely ◽  
Alex G. Johnson ◽  
Jinfan Wang ◽  
Israel S. Fernández ◽  
...  
Keyword(s):  
Single Molecule ◽  
Translation Initiation ◽  
Ribosomal Subunit ◽  
Start Codon ◽  
Messenger Rnas ◽  
Eukaryotic Translation ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
40S Ribosomal Subunit ◽  
Eukaryotic Translation Initiation Factors

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a beta-CoV that recently emerged as a human pathogen and is the causative agent of the COVID-19 pandemic. A molecular framework of how the virus manipulates host cellular machinery to facilitate infection remains unclear. Here, we focus on SARS-CoV-2 NSP1, which is proposed to be a virulence factor that inhibits protein synthesis by directly binding the human ribosome. We demonstrate biochemically that NSP1 inhibits translation of model human and SARS-CoV-2 messenger RNAs (mRNAs). NSP1 specifically binds to the small (40S) ribosomal subunit, which is required for translation inhibition. Using single-molecule fluorescence assays to monitor NSP1–40S subunit binding in real time, we determine that eukaryotic translation initiation factors (eIFs) allosterically modulate the interaction of NSP1 with ribosomal preinitiation complexes in the absence of mRNA. We further elucidate that NSP1 competes with RNA segments downstream of the start codon to bind the 40S subunit and that the protein is unable to associate rapidly with 80S ribosomes assembled on an mRNA. Collectively, our findings support a model where NSP1 proteins from viruses in at least two subgenera of beta-CoVs associate with the open head conformation of the 40S subunit to inhibit an early step of translation, by preventing accommodation of mRNA within the entry channel.

Plant translation initiation factors: it is not easy to be green

2004 ◽  
Vol 32 (4) ◽  
pp. 589-591 ◽  
Author(s):  
K.S. Browning
Keyword(s):  
Translation Initiation ◽  
Binding Proteins ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Translational Machinery ◽  
Initiation Factors ◽  
Translation Initiation Factors

Plants have significant differences in some of the ‘parts’ of the translational machinery. There are two forms of eukaryotic initiation factor (eIF) 4F, eIF3 has two novel subunits, eIF4B is poorly conserved, and eIF2 kinases and eIF4E binding proteins (4E-BP) are yet to be discovered. These differences suggest that plants may regulate their translation in unique ways.

scholarly journals Hijacking the translation apparatus by RNA viruses

2002 ◽  
Vol 158 (3) ◽  
pp. 395-399 ◽  
Author(s):  
Martin Bushell ◽  
Peter Sarnow
Keyword(s):  
Host Cell ◽  
Translation Initiation ◽  
Rna Viruses ◽  
Viral Mrnas ◽  
Viral Genomes ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
Translation Apparatus ◽  
Cellular Mrnas ◽  
Successful Amplification

As invading viruses do not harbor functional ribosomes in their virions, successful amplification of the viral genomes requires that viral mRNAs compete with cellular mRNAs for the host cell translation apparatus. Several RNA viruses have evolved remarkable strategies to recruit the host translation initiation factors required for the first steps in translation initiation by host cell mRNAs. This review describes the ways that three families of RNA viruses effectively usurp limiting translation initiation factors from the host.

scholarly journals Blastocyst implantation failure relates to impaired translational machinery gene expression

Reproduction ◽  
2014 ◽  
Vol 148 (1) ◽  
pp. 87-98 ◽  
Author(s):  
Vicki Plaks ◽  
Eran Gershon ◽  
Amit Zeisel ◽  
Jasmine Jacob-Hirsch ◽  
Michal Neeman ◽  
...  
Keyword(s):  
Embryonic Development ◽  
Ribosomal Proteins ◽  
Oocyte Quality ◽  
Confined Space ◽  
Translational Machinery ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
Developmental Capacity ◽  
Blastocyst Implantation ◽  
And Biological Markers

Oocyte quality is a well-established determinant of embryonic fate. However, the molecular participants and biological markers that affect and may predict adequate embryonic development are largely elusive. Our aim was to identify the components of the oocyte molecular machinery that part take in the production of a healthy embryo. For this purpose, we used an animal model, generated by us previously, the oocytes of which do not express Cx43 (Cx43del/del). In these mice, oogenesis appears normal, fertilisation does occur, early embryonic development is successful but implantation fails. We used magnetic resonance imaging analysis combined with histological examination to characterise the embryonic developmental incompetence. Reciprocal embryo transfer confirmed that the blastocyst evolved from the Cx43del/deloocyte is responsible for the implantation disorder. In order to unveil the genes, the impaired expression of which brings about the development of defective embryos, we carried out a genomic screening of both the oocytes and the resulting blastocysts. This microarray analysis revealed a low expression ofEgr1,Rpl21andEif4a1in Cx43del/deloocytes and downregulation ofRpl15andEif4g2in the resulting blastocysts. We propose that global deficiencies in genes related to the expression of ribosomal proteins and translation initiation factors in apparently normal oocytes bring about accumulation of defects, which significantly compromise their developmental capacity. The blastocysts resulting from such oocytes, which grow within a confined space until implantation, may be unable to generate enough biological mass to allow their expansion. This information could be implicated to diagnosis and treatment of infertility, particularly to IVF.

Reduced dosage of genes encoding ribosomal protein S18 suppresses a mitochondrial initiation codon mutation in Saccharomyces cerevisiae.

Genetics ◽  
1994 ◽  
Vol 137 (2) ◽  
pp. 369-379 ◽  
Author(s):  
L S Folley ◽  
T D Fox
Keyword(s):  
Ribosomal Protein ◽  
Translation Initiation ◽  
Ribosomal Proteins ◽  
Ribosomal Subunit ◽  
Initiation Codon ◽  
Cold Sensitivity ◽  
Mitochondrial Translation ◽  
Ribosomal Subunits ◽  
Translational Accuracy ◽  
Codon Mutation

Abstract A yeast mitochondrial translation initiation codon mutation affecting the gene for cytochrome oxidase subunit III (COX3) was partially suppressed by a spontaneous nuclear mutation. The suppressor mutation also caused cold-sensitive fermentative growth on glucose medium. Suppression and cold sensitivity resulted from inactivation of the gene product of RPS18A, one of two unlinked genes that code the essential cytoplasmic small subunit ribosomal protein termed S18 in yeast. The two S18 genes differ only by 21 silent substitutions in their exons; both are interrupted by a single intron after the 15th codon. Yeast S18 is homologous to the human S11 (70% identical) and the Escherichia coli S17 (35% identical) ribosomal proteins. This highly conserved family of ribosomal proteins has been implicated in maintenance of translational accuracy and is essential for assembly of the small ribosomal subunit. Characterization of the original rps18a-1 missense mutant and rps18a delta and rps18b delta null mutants revealed that levels of suppression, cold sensitivity and paromomycin sensitivity all varied directly with a limitation of small ribosomal subunits. The rps18a-1 mutant was most affected, followed by rps18a delta then rps18b delta. Mitochondrial mutations that decreased COX3 expression without altering the initiation codon were not suppressed. This allele specificity implicates mitochondrial translation in the mechanism of suppression. We could not detect an epitope-tagged variant of S18 in mitochondria. Thus, it appears that suppression of the mitochondrial translation initiation defect is caused indirectly by reduced levels of cytoplasmic small ribosomal subunits, leading to changes in either cytoplasmic translational accuracy or the relative levels of cytoplasmic translation products.

scholarly journals eIF4G-driven translation initiation of downstream ORFs in mammalian cells

2020 ◽  
Vol 48 (18) ◽  
pp. 10441-10455
Author(s):  
Risa Nobuta ◽  
Kodai Machida ◽  
Misaki Sato ◽  
Satoshi Hashimoto ◽  
Yasuhito Toriumi ◽  
...  
Keyword(s):  
Translation Initiation ◽  
Mammalian Cells ◽  
Open Reading Frames ◽  
Translation System ◽  
Entry Site ◽  
Internal Ribosome Entry ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
Genome Wide

Abstract Comprehensive genome-wide analysis has revealed the presence of translational elements in the 3′ untranslated regions (UTRs) of human transcripts. However, the mechanisms by which translation is initiated in 3′ UTRs and the physiological function of their products remain unclear. This study showed that eIF4G drives the translation of various downstream open reading frames (dORFs) in 3′ UTRs. The 3′ UTR of GCH1, which encodes GTP cyclohydrolase 1, contains an internal ribosome entry site (IRES) that initiates the translation of dORFs. An in vitro reconstituted translation system showed that the IRES in the 3′ UTR of GCH1 required eIF4G and conventional translation initiation factors, except eIF4E, for AUG-initiated translation of dORFs. The 3′ UTR of GCH1-mediated translation was resistant to the mTOR inhibitor Torin 1, which inhibits cap-dependent initiation by increasing eIF4E-unbound eIF4G. eIF4G was also required for the activity of various elements, including polyU and poliovirus type 2, a short element thought to recruit ribosomes by base-pairing with 18S rRNA. These findings indicate that eIF4G mediates translation initiation of various ORFs in mammalian cells, suggesting that the 3′ UTRs of mRNAs may encode various products.

scholarly journals Translation Initiation Factor eIF4B Interacts with a Picornavirus Internal Ribosome Entry Site in both 48S and 80S Initiation Complexes Independently of Initiator AUG Location

1999 ◽  
Vol 73 (9) ◽  
pp. 7505-7514 ◽  
Author(s):  
Kerstin Ochs ◽  
RenéC. Rust ◽  
Michael Niepmann
Keyword(s):  
Translation Initiation ◽  
Internal Ribosome Entry Site ◽  
Ribosomal Subunit ◽  
Translation Initiation Factor ◽  
Entry Site ◽  
Small Ribosomal Subunit ◽  
Internal Ribosome Entry ◽  
Initiation Factors ◽  
Mouth Disease Virus ◽  
Energy Dependent

ABSTRACT Most eukaryotic initiation factors (eIFs) are required for internal translation initiation at the internal ribosome entry site (IRES) of picornaviruses. eIF4B is incorporated into ribosomal 48S initiation complexes with the IRES RNA of foot-and-mouth disease virus (FMDV). In contrast to the weak interaction of eIF4B with capped cellular mRNAs and its release upon entry of the ribosomal 60S subunit, eIF4B remains tightly associated with the FMDV IRES during formation of complete 80S ribosomes. Binding of eIF4B to the IRES is energy dependent, and binding of the small ribosomal subunit to the IRES requires the previous energy-dependent association of initiation factors with the IRES. The interaction of eIF4B with the IRES in 48S and 80S complexes is independent of the location of the initiator AUG and thus independent of the mechanism by which the small ribosomal subunit is placed at the actual start codon, either by direct internal ribosomal entry or by scanning. eIF4B does not greatly rearrange its binding to the IRES upon entry of the ribosomal subunits, and the interaction of eIF4B with the IRES is independent of the polypyrimidine tract-binding protein, which enhances FMDV translation.

scholarly journals Insights from a Paradigm Shift: How the Poly(A)-Binding Protein Brings Translating mRNAs Full Circle

2014 ◽  
Vol 2014 ◽  
pp. 1-16 ◽  
Author(s):  
Daniel R. Gallie
Keyword(s):  
Translation Initiation ◽  
Paradigm Shift ◽  
Binding Protein ◽  
Ribosomal Subunit ◽  
Physical Interaction ◽  
New Paradigm ◽  
Initiation Factors ◽  
Full Circle ◽  
Translation Initiation Factors ◽  
Cap Binding Complex

In recent years, our thinking of how the initiation of protein synthesis occurs has changed dramatically. Initiation was thought to involve only events occurring at or near the 5′-cap structure, which serves as the binding site for the cap-binding complex, a group of translation initiation factors (eIFs) that facilitate the binding of the 40 S ribosomal subunit to an mRNA. Because the poly(A)-binding protein (PABP) binds the poly(A) tail present at the 3′-terminus of an mRNA, it was long thought to play no role in translation initiation. In this review, I present evidence from my laboratory that has contributed to the paradigm shift in how we think of mRNAs during translation. The depiction of mRNAs as straight molecules in which the poly(A) tail is far from events occurring at the 5′-end has now been replaced by the concept of a circular mRNA where the interaction between PABP and the cap-binding complex bridges the termini of an mRNA and promotes translation initiation. The research from my laboratory supports the new paradigm that translation of most mRNAs requires a functional and physical interaction between the termini of an mRNA.

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