aaRS Genes Research Articles

Coexisting bacterial aminoacyl-tRNA synthetase paralogs exhibit distinct phylogenetic backgrounds and functional compatibility with Escherichia coli.

Aminoacyl-tRNA synthetases (aaRSs) are universally essential enzymes that synthesize aminoacyl-tRNA substrates for protein synthesis. Although most organisms require a single aaRS gene for each proteinogenic amino acid to translate their genetic information, numerous species encode multiple gene copies of an aaRS. Growing evidence indicates that organisms acquire extra aaRS genes to sustain or adapt to their unique lifestyle. However, predicting and defining the function of repeated aaRS genes remains challenging due to their potentially unique physiological role in the host organism and the inconsistent annotation of repeated aaRS genes in the literature. Here, we carried out comparative, phylogenetic, and functional studies to determine the activity of coexisting paralogs of tryptophanyl-, tyrosyl-, seryl-, and prolyl-tRNA synthetases encoded in several human pathogenic bacteria. Our analyses revealed that, with a few exceptions, repeated aaRSs involve paralogous genes with distinct phylogenetic backgrounds. Using a collection of Escherichia coli strains that enabled the facile characterization of aaRS activity in vivo, we found that, in almost all cases, one aaRS displayed transfer RNA (tRNA) aminoacylation activity, whereas the other was not compatible with E. coli. Together, this work illustrates the challenges of identifying, classifying, and predicting the function of aaRS paralogs and highlights the complexity of aaRS evolution. Moreover, these results provide new insights into the potential role of aaRS paralogs in the biology of several human pathogens and foundational knowledge for the investigation of the physiological role of repeated aaRS paralogs across bacteria.

AARS Novel Homozygous Variant in Two Lebanese Siblings with Isolated Transient Neonatal Axial Hypotonia

AARS mutations are associated with many clinical presentations that range from neuropathy to developmental syndromes and have either recessive or dominant patterns of inheritance. Here we present the first reported Lebanese patients with a novel AARS gene variant. The two female patients presented with a transient axial neonatal hypotonia with a muscle biopsy showing secondary mitochondrial dysfunction. The patients’ symptoms showed a benign progression during the first year of life until reaching normal developmental milestones. The present case helps to widen the clinical spectrum of AARS gene mutations in order to include neonatal transient axial hypotonia.

Enzymic recognition of amino acids drove the evolution of primordial genetic codes.

How genetic information gained its exquisite control over chemical processes needed to build living cells remains an enigma. Today, the aminoacyl-tRNA synthetases (AARS) execute the genetic codes in all living systems. But how did the AARS that emerged over three billion years ago as low-specificity, protozymic forms then spawn the full range of highly-specific enzymes that distinguish between 22 diverse amino acids? A phylogenetic reconstruction of extant AARS genes, enhanced by analysing modular acquisitions, reveals six AARS with distinct bacterial, archaeal, eukaryotic, or organellar clades, resulting in a total of 36 families of AARS catalytic domains. Small structural modules that differentiate one AARS family from another played pivotal roles in discriminating between amino acid side chains, thereby expanding the genetic code and refining its precision. The resulting model shows a tendency for less elaborate enzymes, with simpler catalytic domains, to activate amino acids that were not synthesised until later in the evolution of the code. The most probable evolutionary route for an emergent amino acid type to establish a place in the code was by recruiting older, less specific AARS, rather than adapting contemporary lineages. This process, retrofunctionalisation, differs from previously described mechanisms through which amino acids would enter the code.

In Vitro Transcription/Translation-Coupled DNA Replication through Partial Regeneration of 20 Aminoacyl-tRNA Synthetases.

The in vitro reconstruction of life-like self-reproducing systems is a major challenge in in vitro synthetic biology. Self-reproduction requires regeneration of all molecules involved in DNA replication, transcription, and translation. This study demonstrated the continuous DNA replication and partial regeneration of major translation factors, 20 aminoacyl-tRNA synthetases (aaRS), in a reconstituted transcription/translation system (PURE system) for the first time. First, we replicated each DNA that encodes one of the 20 aaRSs through aaRS expression from the DNA by serial transfer experiments. Thereafter, we successively increased the number of aaRS genes and achieved simultaneous, continuous replication of DNA that encodes all 20 aaRSs, which comprised approximately half the number of protein factors in the PURE system, except for ribosomes, by employing dialyzed reaction and sequence optimization. This study provides a step-by-step methodology for continuous DNA replication with an increasing number of self-regenerative genes toward self-reproducing artificial systems.

Loss of threonyl-tRNA synthetase-like protein Tarsl2 has little impact on protein synthesis but affects mouse development

Aminoacyl-tRNA synthetases (aaRSs) are essential components for mRNA translation. Two sets of aaRSs are required for cytoplasmic and mitochondrial translation in vertebrates. Interestingly, TARSL2 is a recently evolved duplicated gene of TARS1 (encoding cytoplasmic threonyl-tRNA synthetase) and represents the only duplicated aaRS gene in vertebrates. Although TARSL2 retains the canonical aminoacylation and editing activities in vitro, whether it is a true tRNA synthetase for mRNA translation in vivo is unclear. In this study, we showed that Tars1 is an essential gene since homozygous Tars1 knockout mice were lethal. In contrast, when Tarsl2 was deleted in mice and zebrafish, neither the abundance nor the charging levels of tRNAThrs were changed, indicating that cells relied on Tars1 but not on Tarsl2 for mRNA translation. Furthermore, Tarsl2 deletion did not influence the integrity of the multiple tRNA synthetase complex (MSC), suggesting that Tarsl2 is a peripheral member of the MSC. Finally, we observed that Tarsl2-deleted mice exhibited severe developmental retardation, elevated metabolic capacity, and abnormal bone and muscle development after 3 weeks. Collectively, these data suggest that, despite its intrinsic activity, loss of Tarsl2 has little influence on protein synthesis but does affect mouse development.

Aminoacyl-tRNA synthetases in human health and disease.

The Aminoacyl-tRNA Synthetases (aaRSs) are an evolutionarily ancient family of enzymes that catalyze the esterification reaction linking a transfer RNA (tRNA) with its cognate amino acid matching the anticodon triplet of the tRNA. Proper functioning of the aaRSs to create aminoacylated (or "charged") tRNAs is required for efficient and accurate protein synthesis. Beyond their basic canonical function in protein biosynthesis, aaRSs have a surprisingly diverse array of non-canonical functions that are actively being defined. The human genome contains 37 genes that encode unique aaRS proteins. To date, 56 human genetic diseases caused by damaging variants in aaRS genes have been described: 46 are autosomal recessive biallelic disorders and 10 are autosomal dominant monoallelic disorders. Our appreciation of human diseases caused by damaging genetic variants in the aaRSs has been greatly accelerated by the advent of next-generation sequencing, with 89% of these gene discoveries made since 2010. In addition to these genetic disorders of the aaRSs, anti-synthetase syndrome (ASSD) is a rare autoimmune inflammatory myopathy that involves the production of autoantibodies that disrupt aaRS proteins. This review provides an overview of the basic biology of aaRS proteins and describes the rapidly growing list of human diseases known to be caused by genetic variants or autoimmune targeting that affect both the canonical and non-canonical functions of these essential proteins.

Diversification of aminoacyl-tRNA synthetase activities via genomic duplication.

Intricate evolutionary events enabled the emergence of the full set of aminoacyl-tRNA synthetase (aaRS) families that define the genetic code. The diversification of aaRSs has continued in organisms from all domains of life, yielding aaRSs with unique characteristics as well as aaRS-like proteins with innovative functions outside translation. Recent bioinformatic analyses have revealed the extensive occurrence and phylogenetic diversity of aaRS gene duplication involving every synthetase family. However, only a fraction of these duplicated genes has been characterized, leaving many with biological functions yet to be discovered. Here we discuss how genomic duplication is associated with the occurrence of novel aaRSs and aaRS-like proteins that provide adaptive advantages to their hosts. We illustrate the variety of activities that have evolved from the primordial aaRS catalytic sites. This precedent underscores the need to investigate currently unexplored aaRS genomic duplications as they may hold a key to the discovery of exciting biological processes, new drug targets, important bioactive molecules, and tools for synthetic biology applications.

Multidimensional Phylogenetic Metrics Identify Class I Aminoacyl-tRNA Synthetase Evolutionary Mosaicity and Inter-Modular Coupling.

The role of aminoacyl-tRNA synthetases (aaRS) in the emergence and evolution of genetic coding poses challenging questions concerning their provenance. We seek evidence about their ancestry from curated structure-based multiple sequence alignments of a structurally invariant “scaffold” shared by all 10 canonical Class I aaRS. Three uncorrelated phylogenetic metrics—mutation frequency, its uniformity, and row-by-row cladistic congruence—imply that the Class I scaffold is a mosaic assembled from successive genetic sources. Metrics for different modules vary in accordance with their presumed functionality. Sequences derived from the ATP– and amino acid– binding sites exhibit specific two-way coupling to those derived from Connecting Peptide 1, a third module whose metrics suggest later acquisition. The data help validate: (i) experimental fragmentations of the canonical Class I structure into three partitions that retain catalytic activities in proportion to their length; and (ii) evidence that the ancestral Class I aaRS gene also encoded a Class II ancestor in frame on the opposite strand. A 46-residue Class I “protozyme” roots the Class I tree prior to the adaptive radiation of the Rossmann dinucleotide binding fold that refined substrate discrimination. Such rooting implies near simultaneous emergence of genetic coding and the origin of the proteome, resolving a conundrum posed by previous inferences that Class I aaRS evolved after the genetic code had been implemented in an RNA world. Further, pinpointing discontinuous enhancements of aaRS fidelity establishes a timeline for the growth of coding from a binary amino acid alphabet.

Prevalence, Virulence Gene Profiling, and Characterization of Enteroaggregative Escherichia coli from Children with Acute Diarrhea, Asymptomatic Nourished, and Malnourished Children Younger Than 5 Years of Age in India

To study the significance of enteroaggregative Escherichia coli (EAEC) as a pathogen causing acute diarrhea and a commensal in healthy nourished and malnourished children younger than five years of age in the Chandigarh region and to address possible traits of EAEC virulence genes, biofilm formation, phylogroups, and antibiotic resistance that would be correlated with diarrhea or carriage. Stool samples were obtained from children with acute diarrhea (n=548), as well as nourished (n=550), and malnourished controls without diarrhea (n=110). E coli isolates were confirmed as EAEC by pCVD432 polymerase chain reaction. Multiplex polymerase chain reactions were used to identify 22 virulence-related genes and phylogeny. Antibiotic susceptibility, adherence, and biofilm-forming potential also were studied. Overall, 16.6% of children were malnourished. EAEC detection was greater among children with acute diarrhea (16%) than nourished (6%) and malnourished nondiarrheal controls (2.7%). We found an association of EAEC infections with age <2years (P=.0001) in the diarrheal group. Adhesive variants adhesion fimbriae IV and adhesion fimbriae II were significantly associated with diarrhea. The aggR and aar genes showed a positive and negative association with the severity of disease (P=.0004 and P=.0003). A high degree of multidrug resistance was found (73.8%) in the diarrheal group. Most EAEC strains from the diarrheal group belonged to B2 and D phylogroups, whereas strains from non-diarrheal groups, which belonged to phylogroup B1. EAEC is a significant contributor to childhood diarrhea, its presence as a commensal, and the significance of the association of various virulence factors among the EAEC isolated from diarrheal and non-diarrheal stools. These data reinforce the importance of aggR and aar as positive and negative regulators and the contribution of AAF/II and AAF/IV fimbria for the pathobiology of EAEC.

Diagnostic utility of exome sequencing for inherited peripheral neuropathies

Introduction. Hereditary motor and sensory neuropathies, a highly genetic heterogeneous group of disorders, have a phenotype caused by peripheral nerve damage.Purpose of the study – to assess the extent of genetic heterogeneity of hereditary motor and sensory neuropathies in Russian patients and to evaluate the diagnostic effectiveness of using full-exome research methods to find the genetic cause of hereditary motor and sensory neuropathies.Materials and methods. The material for the study was DNA samples from 51 patients and their family members referred for whole exome sequencing to the DNA-diagnostics laboratory of Research Centre for Medical Genetics in 2017–2019. Methods: whole exome sequencing, Sanger sequencing, restriction fragment length polymorphism.Results. Whole exome sequencing in combination with segregation analysis of the pathogenic variants in families allowed to determine the cause of the disease in 41 % of cases. In another 16 % of cases, candidate genetic variants as a possible cause of the disease were revealed, but additional studies are needed to confirm it. The most frequently mutated gene was MFN2 caused neuropathy in 6 unrelated families. MPZ gene mutations were detected in two families, AARS gene mutations were revealed in another two families, and mutations in GJB1, HINT1, INF2, LRSAM1, LITAF, MME, NEFL, WWOX were detected once. Among the causal variants, mutations in B4GALNT1 caused spastic paraplegia, in COL6A1 led to Bethlem’s congenital muscular dystrophy, and in SYT2 caused congenital myasthenic syndrome indicating difficulties in differential diagnosis of inherited neuromuscular disorders. A PMP22 duplication was detected in 2 families prior to whole exome sequencing.Conclusion. Whole exome sequencing is very important for finding the molecular cause of hereditary motor and sensory neuropathies. In most cases, additional methods should be used to clarify the pathogenicity of variants detected by whole exome sequencing. However, it is necessary to remember that the most common cause of the disease is a large duplication of the region 17p11.2.

Expression of genes for selected plant aminoacyl-tRNA synthetases in the abiotic stress

Plants, as sessile organisms, have evolved intricate mechanisms to adapt to various environmental changes and challenges. Because various types of stress trigger significant decrease in global translation rates we examined the stress-related expression of aminoacyl-tRNA synthetases (aaRSs), enzymes that participate in the first step of protein biosynthesis. We have analyzed promoters of genes encoding cytosolic seryl-tRNA synthetase (SerRS), cytosolic aspartyl-tRNA synthetase (AspRS) and cytosolic cysteinyl-tRNA synthetase (CysRS) in Arabidopsis thaliana L., and examined SerRS, AspRS and CysRS gene expression in seedlings exposed to different abiotic stressors. Although global translation levels are repressed by stress, our results show that plant aaRSs expression is not decreased by osmotic, salt and heavy metal/cadmium stress. Moreover, during exposure to stress conditions we detected increased AspRS and CysRS transcript levels. SerRS gene expression did not change in stress conditions although participation of SerRS in stress response could be regulated at the protein level. Expression of the examined aaRS genes under stress correlated well with the length of their predicted promoters and the number of available binding sites for the stress related transcription factors. It thus appears that during stress it is important to keep steady state levels of aaRSs for translation of specific stress-related mRNAs and furthermore to rapidly continue with translation when stress conditions cease. Importantly, increased levels of plant aaRSs during stress may serve as a pool of aaRS proteins that can participate directly in stress responses through their noncanonical activities.

Plant-Specific Domains and Fragmented Sequences Imply Non-Canonical Functions in Plant Aminoacyl-tRNA Synthetases.

Aminoacyl-tRNA synthetases (aaRSs) play essential roles in protein translation. In addition, numerous aaRSs (mostly in vertebrates) have also been discovered to possess a range of non-canonical functions. Very few studies have been conducted to elucidate or characterize non-canonical functions of plant aaRSs. A genome-wide search for aaRS genes in Arabidopsis thaliana revealed a total of 59 aaRS genes. Among them, asparaginyl-tRNA synthetase (AsnRS) was found to possess a WHEP domain inserted into the catalytic domain in a plant-specific manner. This insertion was observed only in the cytosolic isoform. In addition, a long stretch of sequence that exhibited weak homology with histidine ammonia lyase (HAL) was found at the N-terminus of histidyl-tRNA synthetase (HisRS). This HAL-like domain has only been seen in plant HisRS, and only in cytosolic isoforms. Additionally, a number of genes lacking minor or major portions of the full-length aaRS sequence were found. These genes encode 14 aaRS fragments that lack key active site sequences and are likely catalytically null. These identified genes that encode plant-specific additional domains or aaRS fragment sequences are candidates for aaRSs possessing non-canonical functions.

The molecular aetiology of tRNA synthetase depletion: induction of a GCN4 amino acid starvation response despite homeostatic maintenance of charged tRNA levels.

During protein synthesis, charged tRNAs deliver amino acids to translating ribosomes, and are then re-charged by tRNA synthetases (aaRS). In humans, mutant aaRS cause a diversity of neurological disorders, but their molecular aetiologies are incompletely characterised. To understand system responses to aaRS depletion, the yeast glutamine aaRS gene (GLN4) was transcriptionally regulated using doxycycline by tet-off control. Depletion of Gln4p inhibited growth, and induced a GCN4 amino acid starvation response, indicative of uncharged tRNA accumulation and Gcn2 kinase activation. Using a global model of translation that included aaRS recharging, Gln4p depletion was simulated, confirming slowed translation. Modelling also revealed that Gln4p depletion causes negative feedback that matches translational demand for Gln-tRNAGln to aaRS recharging capacity. This maintains normal charged tRNAGln levels despite Gln4p depletion, confirmed experimentally using tRNA Northern blotting. Model analysis resolves the paradox that Gln4p depletion triggers a GCN4 response, despite maintenance of tRNAGln charging levels, revealing that normally, the aaRS population can sequester free, uncharged tRNAs during aminoacylation. Gln4p depletion reduces this sequestration capacity, allowing uncharged tRNAGln to interact with Gcn2 kinase. The study sheds new light on mutant aaRS disease aetiologies, and explains how aaRS sequestration of uncharged tRNAs can prevent GCN4 activation under non-starvation conditions.

Characterization of Aminoacyl-tRNA Synthetases in Chromerids.

Aminoacyl-tRNA synthetases (AaRSs) are enzymes that catalyze the ligation of tRNAs to amino acids. There are AaRSs specific for each amino acid in the cell. Each cellular compartment in which translation takes place (the cytosol, mitochondria, and plastids in most cases), needs the full set of AaRSs; however, individual AaRSs can function in multiple compartments due to dual (or even multiple) targeting of nuclear-encoded proteins to various destinations in the cell. We searched the genomes of the chromerids, Chromera velia and Vitrella brassicaformis, for AaRS genes: 48 genes encoding AaRSs were identified in C. velia, while only 39 AaRS genes were found in V. brassicaformis. In the latter alga, ArgRS and GluRS were each encoded by a single gene occurring in a single copy; only PheRS was found in three genes, while the remaining AaRSs were encoded by two genes. In contrast, there were nine cases for which C. velia contained three genes of a given AaRS (45% of the AaRSs), all of them representing duplicated genes, except AsnRS and PheRS, which are more likely pseudoparalogs (acquired via horizontal or endosymbiotic gene transfer). Targeting predictions indicated that AaRSs are not (or not exclusively), in most cases, used in the cellular compartment from which their gene originates. The molecular phylogenies of the AaRSs are variable between the specific types, and similar between the two investigated chromerids. While genes with eukaryotic origin are more frequently retained, there is no clear pattern of orthologous pairs between C. velia and V. brassicaformis.

Abstract 4156: Multiple rare germline variants in a thyroid cancer family

Abstract Thyroid cancer is the 12th most common cancer in the USA. Four main types exist: the majority (85-90%) is papillary thyroid cancer (PTC). Familial form of PTC represents 5 to 15 % of all thyroid cancers. We have access to 155 PTC families including clinical data and biological samples. Our aim was to search for highly penetrant gene variants in 17 PTC families. Data from one of the families in which PTC is segregating in three generations are described here. Whole genome sequencing was performed in three family members affected by PTC. Sanger sequencing at germline DNA and RNA levels followed by TOPO cloning was used to study the effects of mutations. We found 4 different either novel or ultra-rare mutations in the ITGAD, AARS and PDPR genes on chromosome 16 (Table). All mutations segregated perfectly with PTC in family members (n=4) and were absent in unaffected members (n=3). We Sanger sequenced cDNA from two of the PTC patients and cloned the products into the pCR 2.1-® TOPO vector. Based on the cDNA sequencing and cloning results, all of the mutations will create a premature stop codon leading to a truncated protein. We will verify the effects of the mutations by protein analysis as well. In addition, structural variation analysis will be done to exclude large genomic rearrangements. The germline events leading to PTC are neither well known nor extensively researched. When occurring in families PTC regularly shows autosomal dominant inheritance with incomplete penetrance. Only a few of probable mutations have been reported. Nevertheless, our finding of the truncating mutations in 3 genes on chromosome 16 that are cosegregating with PTC in a 3-generation family is surprising. Even more so: is the localization of the three genes in one chromosome coincidental? Preliminary findings in some of the other 16 PTC families suggest that the occurrence of more than one truncating mutation is not a unique event. We look forward to answer the question whether combination of two or more mutant genes can be responsible for one disease segregating in families. Citation Format: Taina T. Nieminen, Daniel F. Comiskey, Yanqiang Wang, Sandya Liyanarachchi, Pamela Brock, Paivi Peltomaki, Huiling He, Albert de la Chapelle. Multiple rare germline variants in a thyroid cancer family [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4156.

Compositional dynamics and codon usage pattern of BRCA1 gene across nine mammalian species

The BRCA1 gene is located on the human chromosome 17q21.31 and plays important role in biological processes. The aminoacyl-tRNA synthetases (AARS) are a family of heterogenous enzymes responsible protein synthesis and whose secondary functions include a role in autoimmune myositis. Our findings reveal that the compositional constraint and the preference of more A/T –ending codons determine the codon usage patterns in BRCA1 gene while more G/C-ending codons influence the codon usage pattern of AARS gene among mammals. The codon usage bias in BRCA1 and AARS genes is low. The codon CGC encoding arginine amino acid and the codon TTA encoding leucine were uniformly distributed in BRCA1 and AARS genes, respectively in mammals including human. Natural selection might have played a major role while mutation pressure might have played a minor role in shaping the codon usage pattern of BRCA1 and AARS genes.

Clinico-Electrophysiological and Genetic Overlaps and Magnetic Resonance Imaging Findings in Charcot-Marie- Tooth Disease: A Pilot Study from Western India.

Background:Charcot–Marie–Tooth (CMT) disease is clinically and genetically heterogeneous. There are no published series describing clinical, electrophysiological, and genetic information on CMT from the Indian subcontinent. Magnetic resonance imaging (MRI) neurography technique provides useful information about the plexus and roots and can be employed in patients with CMT.Settings and Design:A prospective, observational study carried out at a tertiary care hospital in Western India.Subjects and Methods:CMT patients fulfilling the UK Genetic Testing Network criteria were included. They underwent clinical, electrophysiological, radiological, and multigene panel testing.Results:Totally 22 patients (19 males, 3 females; 18 sporadic and 4 familial cases) were studied. Pes cavus (19), hammer toes (16), and scoliosis was seen in 1 patient. Electrophysiology revealed motor predominant neuropathy with 15 demyelinating (10 uniform and 5 multifocal) and 7 axonal patterns. Thickened lumbosacral plexuses on MRI neurography were evident in 6/10 studied patients, all 6 having demyelinating neuropathy. Genetic analysis identified PMP22, GJB1, SH3TC2, HSPB1, SPTLC2, MPZ, AARS, and NEFH gene mutations.Conclusions:This small series documents the pattern of CMT neuropathies as seen in Western India. Clinico-electrophysiological and genetic diagnosis showed general concordance some overlaps and reiterated advantages of gene panel testing in this heterogeneous group of neuropathies. MRI neurography was useful as an additional investigation to detect nerve enlargement in patients with demyelinating neuropathies.

Aminoacyl-tRNA Synthetases in the Bacterial World.

Aminoacyl-tRNA synthetases (aaRSs) are modular enzymes globally conserved in the three kingdoms of life. All catalyze the same two-step reaction, i.e., the attachment of a proteinogenic amino acid on their cognate tRNAs, thereby mediating the correct expression of the genetic code. In addition, some aaRSs acquired other functions beyond this key role in translation. Genomics and X-ray crystallography have revealed great structural diversity in aaRSs (e.g., in oligomery and modularity, in ranking into two distinct groups each subdivided in 3 subgroups, by additional domains appended on the catalytic modules). AaRSs show huge structural plasticity related to function and limited idiosyncrasies that are kingdom or even species specific (e.g., the presence in many Bacteria of non discriminating aaRSs compensating for the absence of one or two specific aaRSs, notably AsnRS and/or GlnRS). Diversity, as well, occurs in the mechanisms of aaRS gene regulation that are not conserved in evolution, notably between distant groups such as Gram-positive and Gram-negative Bacteria. The review focuses on bacterial aaRSs (and their paralogs) and covers their structure, function, regulation, and evolution. Structure/function relationships are emphasized, notably the enzymology of tRNA aminoacylation and the editing mechanisms for correction of activation and charging errors. The huge amount of genomic and structural data that accumulated in last two decades is reviewed, showing how the field moved from essentially reductionist biology towards more global and integrated approaches. Likewise, the alternative functions of aaRSs and those of aaRS paralogs (e.g., during cell wall biogenesis and other metabolic processes in or outside protein synthesis) are reviewed. Since aaRS phylogenies present promiscuous bacterial, archaeal, and eukaryal features, similarities and differences in the properties of aaRSs from the three kingdoms of life are pinpointed throughout the review and distinctive characteristics of bacterium-like synthetases from organelles are outlined.

Dual Organellar Targeting of Aminoacyl-tRNA Synthetases in Diatoms and Cryptophytes.

The internal compartmentation of eukaryotic cells not only allows separation of biochemical processes but it also creates the requirement for systems that can selectively transport proteins across the membrane boundaries. Although most proteins function in a single subcellular compartment, many are able to enter two or more compartments, a phenomenon known as dual or multiple targeting. The aminoacyl-tRNA synthetases (aaRSs), which catalyze the ligation of tRNAs to their cognate amino acids, are particularly prone to functioning in multiple subcellular compartments. They are essential for translation, so they are required in every compartment where translation takes place. In diatoms, there are three such compartments, the plastid, the mitochondrion, and the cytosol. In cryptophytes, translation also takes place in the periplastid compartment (PPC), which is the reduced cytoplasm of the plastid’s red algal ancestor and which retains a reduced red algal nucleus. We searched the organelle and nuclear genomes of the cryptophyte Guillardia theta and the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana for aaRS genes and found an insufficient number of genes to provide each compartment with a complete set of aaRSs. We therefore inferred, with support from localization predictions, that many aaRSs are dual targeted. We tested four of the predicted dual targeted aaRSs with green fluorescent protein fusion localizations in P. tricornutum and found evidence for dual targeting to the mitochondrion and plastid in P. tricornutum and G. theta, and indications for dual targeting to the PPC and cytosol in G. theta. This is the first report of dual targeting in diatoms or cryptophytes.

Early onset epileptic encephalopathy and deficient myelination as a result of autosomal recessive mutations in the AARS gene (S22.007)

Early onset epileptic encephalopathy and deficient myelination as a result of autosomal recessive mutations in the AARS gene (S22.007)