scholarly journals Destabilization of Eukaryote mRNAs by 5′ Proximal Stop Codons Can Occur Independently of the Nonsense-Mediated mRNA Decay Pathway

Cells ◽  
2019 ◽  
Vol 8 (8) ◽  
pp. 800 ◽  
Author(s):  
Barbara Gorgoni ◽  
Yun-Bo Zhao ◽  
J. Krishnan ◽  
Ian Stansfield
Keyword(s):  
Mrna Stability ◽  
Mrna Decay ◽  
Closed Loop ◽  
Stop Codon ◽  
Translation Termination ◽  
Translation System ◽  
Translation Elongation ◽  
Reading Frame ◽  
Stop Codons ◽  
Nonsense Mediated Mrna Decay

In eukaryotes, the binding of poly(A) binding protein (PAB) to the poly(A) tail is central to maintaining mRNA stability. PABP interacts with the translation termination apparatus, and with eIF4G to maintain 3′–5′ mRNA interactions as part of an mRNA closed loop. It is however unclear how ribosome recycling on a closed loop mRNA is influenced by the proximity of the stop codon to the poly(A) tail, and how post-termination ribosome recycling affects mRNA stability. We show that in a yeast disabled for nonsense mediated mRNA decay (NMD), a PGK1 mRNA with an early stop codon at codon 22 of the reading frame is still highly unstable, and that this instability cannot be significantly countered even when 50% stop codon readthrough is triggered. In an NMD-deficient mutant yeast, stable reporter alleles with more 3′ proximal stop codons could not be rendered unstable through Rli1-depletion, inferring defective Rli1 ribosome recycling is insufficient in itself to trigger mRNA instability. Mathematical modelling of a translation system including the effect of ribosome recycling and poly(A) tail shortening supports the hypothesis that impaired ribosome recycling from 5′ proximal stop codons may compromise initiation processes and thus destabilize the mRNA. A model is proposed wherein ribosomes undergo a maturation process during early elongation steps, and acquire competency to re-initiate on the same mRNA as translation elongation progresses beyond the very 5′ proximal regions of the mRNA.

scholarly journals Ribosome recycling factor ABCE1 depletion inhibits nonsense-mediated mRNA decay by promoting stop codon readthrough

2019 ◽  
Author(s):  
Giuditta Annibaldis ◽  
René Dreos ◽  
Michal Domanski ◽  
Sarah Carl ◽  
Oliver Mühlemann
Keyword(s):  
Mrna Decay ◽  
Stop Codon ◽  
Translation Termination ◽  
Ribosome Profiling ◽  
List Type ◽  
Ribosome Recycling Factor ◽  
Stop Codons ◽  
Nonsense Mediated Mrna Decay ◽  
Ribosome Disassembly ◽  
Stop Codon Readthrough

SUMMARYNonsense-mediated mRNA decay (NMD) is an essential post-transcriptional surveillance pathway in vertebrates that appears to be mechanistically linked with translation termination. To gain more insight into this connection, we interfered with translation termination by depleting human cells of the ribosome recycling factor ABCE1, which resulted in an upregulation of many but not all endogenous NMD-sensitive mRNAs. Notably, the suppression of NMD on these mRNAs occurs at a step prior to their SMG6-mediated endonucleolytic cleavage. Ribosome profiling revealed that ABCE1 depletion results in ribosome stalling at stop codons and increased ribosome occupancy in 3’ UTRs, indicative of enhanced stop codon readthrough or re-initiation. Using reporter genes, we further demonstrate that the absence of ABCE1 indeed increases the rate of readthrough, which would explain the observed NMD inhibition, since enhanced readthrough has been previously shown to render NMD-sensitive transcripts resistant to NMD by displacing NMD triggering factors like UPF1 and exon junction complexes (EJCs) from the 3’ UTR. Collectively, our results show that improper ribosome disassembly interferes with proper NMD activation.HighlightsABCE1 knockdown suppresses NMD of many NMD-sensitive mRNAsThe observed NMD inhibition occurs at a stage prior to SMG6-mediated cleavage of the mRNAABCE1 depletion enhances ribosome occupancy at stop codons and in the 3’ UTRABCE1 depletion enhances readthrough of the stop codonEnhanced readthrough inhibits NMD, presumably by clearing the 3’ UTR of NMD factors

scholarly journals Detailed Dissection and Critical Evaluation of the Pfizer/BioNTech and Moderna mRNA Vaccines

Vaccines ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 734
Author(s):  
Xuhua Xia
Keyword(s):  
Codon Usage ◽  
Translation Initiation ◽  
Mrna Stability ◽  
Stop Codon ◽  
Translation Termination ◽  
Critical Evaluation ◽  
Immunization Programs ◽  
Translation Elongation ◽  
Different Types ◽  
Similarities And Differences

The design of Pfizer/BioNTech and Moderna mRNA vaccines involves many different types of optimizations. Proper optimization of vaccine mRNA can reduce dosage required for each injection leading to more efficient immunization programs. The mRNA components of the vaccine need to have a 5’-UTR to load ribosomes efficiently onto the mRNA for translation initiation, optimized codon usage for efficient translation elongation, and optimal stop codon for efficient translation termination. Both 5’-UTR and the downstream 3’-UTR should be optimized for mRNA stability. The replacement of uridine by N1-methylpseudourinine () complicates some of these optimization processes because is more versatile in wobbling than U. Different optimizations can conflict with each other, and compromises would need to be made. I highlight the similarities and differences between Pfizer/BioNTech and Moderna mRNA vaccines and discuss the advantage and disadvantage of each to facilitate future vaccine improvement. In particular, I point out a few optimizations in the design of the two mRNA vaccines that have not been performed properly.

scholarly journals Tpa1p Is Part of an mRNP Complex That Influences Translation Termination, mRNA Deadenylation, and mRNA Turnover in Saccharomyces cerevisiae

2006 ◽  
Vol 26 (14) ◽  
pp. 5237-5248 ◽  
Author(s):  
Kim M. Keeling ◽  
Joe Salas-Marco ◽  
Lev Z. Osherovich ◽  
David M. Bedwell
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mrna Decay ◽  
Potential Role ◽  
Translation Termination ◽  
Tail Length ◽  
Fold Increase ◽  
Reading Frame ◽  
Yeast Strains ◽  
Messenger Ribonucleoprotein ◽  
Nonsense Mediated Mrna Decay

ABSTRACT In this report, we show that the Saccharomyces cerevisiae protein Tpa1p (for termination and polyadenylation) influences translation termination efficiency, mRNA poly(A) tail length, and mRNA stability. Tpa1p is encoded by the previously uncharacterized open reading frame YER049W. Yeast strains carrying a deletion of the TPA1 gene (tpa1Δ) exhibited increased readthrough of stop codons, and coimmunoprecipitation assays revealed that Tpa1p interacts with the translation termination factors eRF1 and eRF3. In addition, the tpa1Δ mutation led to a 1.5- to 2-fold increase in the half-lives of mRNAs degraded by the general 5′→3′ pathway or the 3′→5′ nonstop decay pathway. In contrast, this mutation did not have any affect on the nonsense-mediated mRNA decay pathway. Examination of mRNA poly(A) tail length revealed that poly(A) tails are longer than normal in a tpa1Δ strain. Consistent with a potential role in regulating poly(A) tail length, Tpa1p was also found to coimmunoprecipitate with the yeast poly(A) binding protein Pab1p. These results suggest that Tpa1p is a component of a messenger ribonucleoprotein complex bound to the 3′ untranslated region of mRNAs that affects translation termination, deadenylation, and mRNA decay.

scholarly journals Polypyrimidine tract binding protein 1 protects mRNAs from recognition by the nonsense-mediated mRNA decay pathway

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Zhiyun Ge ◽  
Bao Lin Quek ◽  
Karen L Beemon ◽  
J Robert Hogg
Keyword(s):  
Gene Expression ◽  
Mrna Decay ◽  
Gene Expression Regulation ◽  
Stop Codon ◽  
Binding Protein ◽  
Polypyrimidine Tract ◽  
Polypyrimidine Tract Binding ◽  
Stop Codons ◽  
Polypyrimidine Tract Binding Protein ◽  
Nonsense Mediated Mrna Decay

The nonsense-mediated mRNA decay (NMD) pathway degrades mRNAs containing long 3'UTRs to perform dual roles in mRNA quality control and gene expression regulation. However, expansion of vertebrate 3'UTR functions has required a physical expansion of 3'UTR lengths, complicating the process of detecting nonsense mutations. We show that the polypyrimidine tract binding protein 1 (PTBP1) shields specific retroviral and cellular transcripts from NMD. When bound near a stop codon, PTBP1 blocks the NMD protein UPF1 from binding 3'UTRs. PTBP1 can thus mark specific stop codons as genuine, preserving both the ability of NMD to accurately detect aberrant mRNAs and the capacity of long 3'UTRs to regulate gene expression. Illustrating the wide scope of this mechanism, we use RNA-seq and transcriptome-wide analysis of PTBP1 binding sites to show that many human mRNAs are protected by PTBP1 and that PTBP1 enrichment near stop codons correlates with 3'UTR length and resistance to NMD.

scholarly journals New insights into the interplay between the translation machinery and nonsense-mediated mRNA decay factors

2018 ◽  
Vol 46 (3) ◽  
pp. 503-512 ◽  
Author(s):  
Etienne Raimondeau ◽  
Joshua C. Bufton ◽  
Christiane Schaffitzel
Keyword(s):  
Mrna Decay ◽  
Stop Codon ◽  
Translation Termination ◽  
Premature Stop Codon ◽  
Molecular Function ◽  
Translation Machinery ◽  
New Findings ◽  
Nascent Chain ◽  
Nonsense Mediated Mrna Decay

Faulty mRNAs with a premature stop codon (PTC) are recognized and degraded by nonsense-mediated mRNA decay (NMD). Recognition of a nonsense mRNA depends on translation and on the presence of NMD-enhancing or the absence of NMD-inhibiting factors in the 3′-untranslated region. Our review summarizes our current understanding of the molecular function of the conserved NMD factors UPF3B and UPF1, and of the anti-NMD factor Poly(A)-binding protein, and their interactions with ribosomes translating PTC-containing mRNAs. Our recent discovery that UPF3B interferes with human translation termination and enhances ribosome dissociation in vitro, whereas UPF1 is inactive in these assays, suggests a re-interpretation of previous experiments and modification of prevalent NMD models. Moreover, we discuss recent work suggesting new functions of the key NMD factor UPF1 in ribosome recycling, inhibition of translation re-initiation and nascent chain ubiquitylation. These new findings suggest that the interplay of UPF proteins with the translation machinery is more intricate than previously appreciated, and that this interplay quality-controls the efficiency of termination, ribosome recycling and translation re-initiation.

scholarly journals Nonsense mRNA suppression via nonstop decay

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Joshua A Arribere ◽  
Andrew Z Fire
Keyword(s):  
Mrna Decay ◽  
Stop Codon ◽  
Premature Stop Codon ◽  
Nonsense Mediated Decay ◽  
Stop Codons ◽  
Nonstop Mrna Decay ◽  
Rna Fragments ◽  
Nonsense Mediated Mrna Decay ◽  
Key Steps

Nonsense-mediated mRNA decay is the process by which mRNAs bearing premature stop codons are recognized and cleared from the cell. While considerable information has accumulated regarding recognition of the premature stop codon, less is known about the ensuing mRNA suppression. During the characterization of a second, distinct translational surveillance pathway (nonstop mRNA decay), we trapped intermediates in nonsense mRNA degradation. We present data in support of a model wherein nonsense-mediated decay funnels into the nonstop decay pathway in Caenorhabditis elegans. Specifically, our results point to SKI-exosome decay and pelota-based ribosome removal as key steps facilitating suppression and clearance of prematurely-terminated translation complexes. These results suggest a model in which premature stop codons elicit nucleolytic cleavage, with the nonstop pathway disengaging ribosomes and degrading the resultant RNA fragments to suppress ongoing expression.

scholarly journals Eukaryotic ribosome recognizes 3 context and stimulates stop codon readthrough

2021 ◽  
Author(s):  
Elizaveta Sokolova ◽  
Tatiana Egorova ◽  
Alexey Shuvalov ◽  
Elena Alkalaeva
Keyword(s):  
18S Rrna ◽  
Stop Codon ◽  
Translation Termination ◽  
Translation System ◽  
Stop Codons ◽  
Nucleotide Context ◽  
The One ◽  
A Site ◽  
Stop Codon Readthrough ◽  
Cognate Trna

It is known that the nucleotide context surrounding stop codons significantly affects the efficiency of translation termination. In eukaryotes, various 3 contexts have been described that are unfavourable for translation termination; however, the exact molecular mechanism that mediates their effect remains unknown. In this study, we used a reconstituted mammalian translation system to examine the efficiency of stop codons in different contexts, including several previously described weak 3 stop codon contexts. Our results revealed that ribosomes can independently recognize certain contexts and ignore stop codons that are followed by these sequences. Moreover, the efficiency of translation termination at the weak 3 contexts was almost equal to the one at the standard context. We propose that weak 3 contexts interact with the 18S rRNA provoking a conformational change in the U-turn-like structure of the stop codon in the A site of ribosome. This change makes incorporation of the near-cognate tRNA more preferable than recognition of the stop codon by the release factors and increases readthrough.

scholarly journals Mechanisms that ensure speed and fidelity in eukaryotic translation termination

2021 ◽  
Author(s):  
Michael R Lawson ◽  
Laura N Lessen ◽  
Jinfan Wang ◽  
Arjun Prabhakar ◽  
Nicholas C Corsepius ◽  
...  
Keyword(s):  
Single Molecule ◽  
Translation Termination ◽  
Translation System ◽  
Single Molecule Fluorescence ◽  
Translation Elongation ◽  
Eukaryotic Translation ◽  
Stop Codons ◽  
Release Factors ◽  
Molecular Events

Translation termination, which liberates a nascent polypeptide from the ribosome specifically at stop codons, must occur accurately and rapidly. We established single molecule fluorescence assays to track the dynamics of ribosomes and two requisite release factors (eRF1 and eRF3) throughout termination using an in vitro reconstituted yeast translation system. We found that the two eukaryotic release factors bind together to recognize stop codons rapidly and elicit termination via a tightly regulated, multi-step process that resembles tRNA selection during translation elongation. Because the release factors are conserved from yeast to humans, the molecular events that underlie yeast translation termination are likely broadly fundamental to eukaryotic protein synthesis.

scholarly journals A UPF1 variant drives conditional remodeling of nonsense-mediated mRNA decay

2021 ◽  
Author(s):  
Sarah E. Fritz ◽  
Soumya Ranganathan ◽  
J. Robert Hogg
Keyword(s):  
Gene Expression ◽  
Mrna Decay ◽  
Gene Expression Regulation ◽  
Translation Termination ◽  
Translational Repression ◽  
The Core ◽  
Human Genes ◽  
Rna Quality Control ◽  
Nonsense Mediated Mrna Decay

AbstractThe nonsense-mediated mRNA decay (NMD) pathway monitors translation termination to degrade transcripts with premature stop codons and regulate thousands of human genes. Due to the major role of NMD in RNA quality control and gene expression regulation, it is important to understand how the pathway responds to changing cellular conditions. Here we show that an alternative mammalian-specific isoform of the core NMD factor UPF1, termed UPF1LL, enables condition-dependent remodeling of NMD specificity. UPF1LL associates more stably with potential NMD target mRNAs than the major UPF1SL isoform, expanding the scope of NMD to include many transcripts normally immune to the pathway. Unexpectedly, the enhanced persistence of UPF1LL on mRNAs supports induction of NMD in response to rare translation termination events. Thus, while canonical NMD is abolished by translational repression, UPF1LL activity is enhanced, providing a mechanism to rapidly rewire NMD specificity in response to cellular stress.

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