Misacylation of tRNA with methionine in Saccharomyces cerevisiae

Accurate transfer RNA (tRNA) aminoacylation by aminoacyl-tRNA synthetases controls translational fidelity. Although tRNA synthetases are generally highly accurate, recent results show that the methionyl-tRNA synthetase (MetRS) is an exception. MetRS readily misacylates non-methionyl tRNAs at frequencies of up to 10% in mammalian cells; such mismethionylation may serve a beneficial role for cells to protect their own proteins against oxidative damage. The Escherichia coli MetRS mismethionylates two E. coli tRNA species in vitro, and these two tRNAs contain identity elements for mismethionylation. Here we investigate tRNA mismethionylation in Saccharomyces cerevisiae. tRNA mismethionylation occurs at a similar extent in vivo as in mammalian cells. Both cognate and mismethionylated tRNAs have similar turnover kinetics upon cycloheximide treatment. We identify specific arginine/lysine to methionine-substituted peptides in proteomic mass spectrometry, indicating that mismethionylated tRNAs are used in translation. The yeast MetRS is part of a complex containing the anchoring protein Arc1p and the glutamyl-tRNA synthetase (GluRS). The recombinant Arc1p-MetRS-GluRS complex binds and mismethionylates many tRNA species in vitro. Our results indicate that the yeast MetRS is responsible for extensive misacylation of non-methionyl tRNAs, and mismethionylation also occurs in this evolutionary branc

Bridging the gap between ribosomal and nonribosomal protein synthesis

Aminoacyl-tRNA synthetases (aaRSs) are the enzymes normally responsible for the attachment of amino acids (aa) to tRNAs. Numerous paralogous proteins of aaRSs have been identified in a wide range of organisms, but the functions of most of these aaRS-like proteins are yet to be determined. In PNAS, the study by Mocibob et al. (1) identifies a paralog of seryl-tRNA synthetase that does not aminoacylate a tRNA, but instead, aminoacylates an aa carrier protein. This exciting discovery provides an unforeseen function for the aaRS architecture and also uncovers a possible evolutionary link between ribosome-catalyzed translation and nonribosomal peptide synthesis

Kinematic assessment of subject personification of human body models (THUMS)

The goal of this study was to quantify the effect of improving the geometry of a human body model on the accuracy of the predicted kinematics for 4 post-mortem human subject sled tests. Three modifications to the computational human body model THUMS were carried out to evaluate if subject personification can increase the agreement between predicted and measured kinematics of post-mortem human subjects in full frontal and nearside oblique impacts. The modifications consisted of: adjusting the human body model mass to the actual subject mass, morphing it to the actual anthropometry of each subject and finally adjustment of the model initial position to the measured position in selected post-mortem human subject tests. A quantitative assessment of the agreement between predicted and measured response was carried out by means of CORA analysis by comparing the displacement of selected anatomical landmarks (head CoG, T1 and T8 vertebre and H-Point). For all three scenarios, the more similar the human body model was to the anthropometry and posture of the sled tested post-mortem human subject, the more similar the predictions were to the measured responses of the post-mortem human subject, resulting in higher CORA score

Analysis of occupant kinematics and dynamics in nearside oblique impacts

Objective: The objective of this article is to analyze the kinematics and dynamics of restrained postmortem human surrogates (PMHS) exposed to a nearside oblique impact and the injuries that were found after the tests.Methods: Three male PMHS of similar age (64 4years) and anthropometry (weight: 61 9.6kg; stature: 172 +/- 2.7cm) were exposed to a 30 degrees nearside oblique impact at 34km/h. The test fixture approximated the seating position of a front seat occupant. A rigid seat was designed to match the pelvic displacement in a vehicle seat. Surrogates were restrained by a 3-point seat belt consisting of a 2kN pretensioner (PT), 4.5kN force-limiting shoulder belt, and a 3.5kN PT lap belt. The shoulder belt PT was not fired in one of the tests. Trajectories of the head, shoulder, and hip joint (bilaterally) were recorded at 1,000Hz by a 3D motion capture system. The 3D acceleration and angular rate of the head, T1, and pelvis, and the 3D acceleration of selected spinal locations was measured at 10,000Hz. Seat belt load cells measured the belt tension at 4 locations. PMHS donation and handling were performed with the approval of the relevant regional ethics review board.Results: Activation of the shoulder PT reduced substantially the peak forward excursion of the head but did not influence the lateral displacement of the head center of gravity (CG). In all 3 subjects, the lateral excursion of the head CG (291.1, 290, 292.1mm) was greater than the forward displacement (271.4, 216.7, 171.5mm). The hip joint excursion of the PMHS that was not exposed to the shoulder PT seat belt was twice the magnitude observed for the other 2 subjects. The 3 PMHS sustained clavicle fractures on the shoulder loaded by the seat belt and 2 of them were diagnosed atlantoaxial subluxation in the radiologist examination. Avulsion fractures of the right lamina of T1, T2, T3, and T4 were found when the PT was not used. The 3 PMHS received multiple fractures spread over both aspects of the rib cage and involving the posterior aspect of it.Conclusion: In this study of nearside oblique impact loading, the PMHS exhibited kinematics characterized by reduced torso pitching and increased lateral head excursion as compared to previous frontal impact results. These kinematics resulted in potential cervical and thoracic spinal injuries and in complete, displaced fractures of the lateral and posterior aspects of the rib cage. Though this is a limited number of subjects, it shows the necessity of further understanding of the kinematics of occupants exposed to this loading mode

Crystal structure of a transfer-ribonucleoprotein particle that promotes asparagine formation

A small number of aminoacyl-tRNAs are synthesized by an indirect mechanism that involves initial mischarging of the tRNA with a chemically related amino acid followed by the enzymatic conversion into the cognate amino acid. This study provides structural insight into the ribonucleoprotein complex that catalyses both steps of asparaginyl-tRNA synthesis

Expression of Nuclear and Mitochondrial Genes Encoding ATP Synthase Is Synchronized by Disassembly of a Multisynthetase Complex

In eukaryotic cells, oxidative phosphorylation involves multisubunit complexes of mixed genetic origin. Assembling these complexes requires an organelle independent synchronizing system for the proper expression of nuclear and mitochondrial genes. Here we show that proper expression of the F1FO ATP synthase (complex V) depends on a cytosolic complex (AME) made of two aminoacyl-tRNA synthetases (cERS and cMRS) attached to an anchor protein, Arc1p. When yeast cells adapt to respiration the Snf1/4 glucose-sensing pathway inhibits ARC1 expression triggering simultaneous release of cERS and cMRS. Free cMRS and cERS relocate to the nucleus and mitochondria, respectively, to synchronize nuclear transcription and mitochondrial translation of ATP synthase genes. Strains releasing asynchronously the two aminoacyl-tRNA synthetases display aberrant expression of nuclear and mitochondrial genes encoding subunits of complex V resulting in severe defects of the oxidative phosphorylation mechanism. This work shows that the AME complex coordinates expression of enzymes that require intergenomic control