McFarland2020 - Synthetase sequestration Model:a combined translation and tRNA charging cycle
Ontology highlight
ABSTRACT:
SUBMITTER: 
Ian Stansfield
PROVIDER: MODEL2001080005 | BioModels | 2020-02-05
REPOSITORIES: BioModels
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Project description:In this study, we identify leucyl-tRNA synthetase (LARS) as a breast tumor suppressor. To identify the mechanism underlying LARS-mediated breast tumor suppression, we first conducted charged tRNA profiling to assess charged and total tRNA-Leu expression in cell lines with high and low LARS expression. Expression of select charged and total tRNA-Leu isoacceptors were reduced in cell lines with lower LARS expression. We then conducted RNA-Seq and translation profiling including ribosome profiling (Ribo-Seq), polysome profiling in LARS-depleted cell lines. To test our hypothesis in vivo, we also performed RNA-Seq of ribosome-associated RNAs in Lars depleted PyMT tumors within RiboTag mice. The analyses implicate LARS as a regulator of leucine-rich translation.
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Project description:During mRNA translation, tRNAs are charged by aminoacyl-tRNA synthetases (aaRS) and subsequently used by ribosomes. A multi-enzyme aminoacyl-tRNA synthetase complex (MSC) has long been proposed to increase protein synthesis efficiency by passing charged tRNAs directly to ribosomes. An alternative is that the MSC repurposes specific synthetases for ex-translational functions that are activated by cues that direct specific enzymes to novel targets. To explore this question, we generated mammalian cell clones in which ArgRS and GlnRS were absent from the MSC to give a stable complex lacking the two enzymes (MSCΔRQ). Protein synthesis, under a variety of stress conditions, was unchanged in MSCΔRQ cells. Most strikingly, levels of charged tRNAGln and tRNAArg remained unchanged and no ribosome pausing was observed at codons for Arg and Gln. Thus, increasing or regulating protein synthesis efficiency is not dependent on ArgRS and GlnRS in the MSC. Alternatively, and consistent with previously reported ex-translational roles, we found manipulations that do not affect protein synthesis but instead MSC cellular localization.
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Project description:N6-methyladenosine (m6A) is the most abundant internal messenger (mRNA) modification in mammalian mRNA. This modification is reversible and non-stoichiometric, which potentially adds an additional layer of variety and dynamic control of mRNA metabolism. The m6A-modified mRNA can be selectively recognized by the YTH family “reader” proteins. The preferential binding of m6A-containing mRNA by YTHDF2 is known to reduce the stability of the target transcripts; however, the exact effects of m6A on translation has yet to be elucidated. Here we show that another m6A reader protein, YTHDF1, promotes ribosome loading of its target transcripts. YTHDF1 forms a complex with translation initiation factors to elevate the translation efficiency of its bound mRNA. In a unified mechanism of translation control through m6A, the YTHDF2-mediated decay controls the lifetime of target transcripts; whereas, the YTHDF1-based translation promotion increases the translation efficiency to ensure effective protein production from relatively short-lived transcripts that are marked by m6A. PAR-CLIP and RIP was used to identify YTHDF1 binding sites followed by ribosome profling and RNA seq to assess the consequences of YTHDF1 siRNA knock-down
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Project description:Firczuk2013 - Eukaryotic mRNA translation machinery
This is a model of Saccharomyces cerevisiae
mRNA translation which includes the initiation, elongation and termination phases. The model is for 20 condon mRNAs. The building of a multi-factor complex in initiation and also the different processes in elongation and termination are modelled in detail. The model takes into account that ribosomes cover more than one codon of mRNA so that the movement of ribosomes are effectively blocked by other ribosomes several codons downstream. It is assumed that 15 codons are occupied by each ribosome. This blocking effect is considered in reaction R18 in initiation and also reaction R26, the reaction where translocation of ribosomes takes place in elongation. The kinetic functions of these two reactions are based on MacDonald et al. 1968 and Heinrich & Rapaport 1980. All other kinetic functions follow mass-action kinetics. The concentrations of transfer RNA species (Met-tRNA, aa-tRNA and tRNA in the model) are kept constant, while the other species' concentrations can change in the course of the simulation. The model describes the translation of a short mRNA with 20 codons. Therefore, all reactions in the elongation cycle (R22, R23, R25, R26, R28 and R29) and the corresponding species are replicated accordingly to model the species with ribosomes bound at different positions. In summary, the model contains 165 different species and 141 reactions.
The value of the 56 rate constant parameters were estimated by fitting the model against a series of experimental data consisting of modulation of the various translation factors (Figures 2, 3 and S3). Overall the parameter estimation was carried out over 212 different data points (steady states).
This model is described in the article:
An in vivo control map for the eukaryotic mRNA translation machinery
Helena Firczuk, Shichina Kannambath, Jürgen Pahle, Amy Claydon, Robert Beynon, John Duncan, Hans Westerhoff, Pedro Mendes and John EG McCarthy
Molecular Systems Biology. 9:635
Abstract:
Rate control analysis defines the in vivo control map governing yeast protein synthesis and generates an extensively parameterized digital model of the translation pathway. Among other non-intuitive outcomes, translation demonstrates a high degree of functional modularity and comprises a non-stoichiometric combination of proteins manifesting functional convergence on a shared maximal translation rate. In exponentially growing cells, polypeptide elongation (eEF1A, eEF2, and eEF3) exerts the strongest control. The two other strong control points are recruitment of mRNA and tRNAi to the 40S ribosomal subunit (eIF4F and eIF2) and termination (eRF1; Dbp5). In contrast, factors that are found to promote mRNA scanning efficiency on a longer than-average 5′untranslated region (eIF1, eIF1A, Ded1, eIF2B, eIF3, and eIF5) exceed the levels required for maximal control. This is expected to allow the cell to minimize scanning transition times, particularly for longer 5′UTRs. The analysis reveals these and other collective adaptations of control shared across the factors, as well as features that reflect functional modularity and system robustness. Remarkably, gene duplication is implicated in the fine control of cellular protein synthesis.
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2011-04-30 | BIOMD0000000457 | BioModels