Conserved tertiary base pairing ensures proper RNA folding and efficient assembly of the signal recognition particle Alu domain

Proper folding of the RNA is an essential step in the assembly of functional ribonucleoprotein complexes. We examined the role of conserved base pairs formed between two distant loops in the Alu portion of the mammalian signal recognition particle RNA (SRP RNA) in SRP assembly and functions. Mutations disrupting base pairing interfere with folding of the Alu portion of the SRP RNA as monitored by probing the RNA structure and the binding of the protein SRP9/14. Complementary mutations rescue the defect establishing a role of the tertiary loop-loop interaction in RNA folding. The same mutations in the Alu domain have no major effect on binding of proteins to the S domain suggesting that the S domain can fold independently. Once assembled into a complete SRP, even particles that contain mutant RNA are active in arresting nascent chain elongation and translocation into microsomes, and, therefore, tertiary base pairing does not appear to be essential for these activities. Our results suggest a model in which the loop-loop interaction and binding of the protein SRP9/14 play an important role in the early steps of SRP RNA folding and assembl

Formation of hot tear under controlled solidification conditions

Aluminum alloy 7050 is known for its superior mechanical properties, and thus finds its application in aerospace industry. Vertical direct-chill (DC) casting process is typically employed for producing such an alloy. Despite its advantages, AA7050 is considered as a "hard-to-cast" alloy because of its propensity to cold cracking. This type of cracks occurs catastrophically and is difficult to predict. Previous research suggested that such a crack could be initiated by undeveloped hot tears (microscopic hot tear) formed during the DC casting process if they reach a certain critical size. However, validation of such a hypothesis has not been done yet. Therefore, a method to produce a hot tear with a controlled size is needed as part of the verification studies. In the current study, we demonstrate a method that has a potential to control the size of the created hot tear in a small-scale solidification process. We found that by changing two variables, cooling rate and displacement compensation rate, the size of the hot tear during solidification can be modified in a controlled way. An X-ray microtomography characterization technique is utilized to quantify the created hot tear. We suggest that feeding and strain rate during DC casting are more important compared with the exerted force on the sample for the formation of a hot tear. In addition, we show that there are four different domains of hot-tear development in the explored experimental window-compression, microscopic hot tear, macroscopic hot tear, and failure. The samples produced in the current study will be used for subsequent experiments that simulate cold-cracking conditions to confirm the earlier proposed model.This research was carried out within the Materials innovation institute (www.m2i.nl) research framework, project no. M42.5.09340

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

The mammalian signal recognition particle : new insights into mechanism and activation of its elongation arrest activity

La particule de reconnaissance du signal (SRP) délivre co-traductionellement les ribosomes synthétisant des protéines secrétées à la membrane du réticulum endoplasmique et arrête l'élongation de la chaîne naissante. En utilisant une approche de cross-linking, nous avons démontré que, durant l'arrêt d'élongation, le domaine Alu de SRP, responsable de l'arrêt d'élongation, est positionné d'une manière stable à proximité du site de liaison des facteurs d'élongation, suggérant un nouveau mécanisme de contrôle de la traduction dans lequel le domaine Alu bloque l'accès des facteurs d'élongation au ribosome. En absence d'arrêt d'élongation, le domaine Alu est déjà à proximité du ribosome, mais dans une position différente. Donc la reconnaissance de la séquence signal influence la position du domaine Alu. Ces approches de cross-linking supportent l'idée que le domaine Alu interagit directement avec le ribosome, probablement par un domaine non défini de SRP9/14 comme suggéré par nos expériences d'interaction in vitro

Signal Recognition Particle Alu Domain Occupies a Defined Site at the Ribosomal Subunit Interface upon Signal Sequence Recognition

The eukaryotic signal recognition particle (SRP) is essential for cotranslational targeting of proteins to the endoplasmic reticulum (ER). The SRP Alu domain is specifically required for delaying nascent chain elongation upon signal sequence recognition by SRP and was therefore proposed to interact directly with ribosomes. Using protein cross-linking, we provide experimental evidence that the Alu binding protein SRP14 is in close physical proximity of several ribosomal proteins in functional complexes. Cross-linking occurs even in the absence of a signal sequence in the nascent chain demonstrating that SRP can bind to all translating ribosomes and that close contacts between the Alu domain and the ribosome are independent of elongation arrest activity. Without a signal sequence, SRP14 cross-links predominantly to a protein of the large subunit. Upon signal sequence recognition, certain cross-linked products become detectable or more abundant revealing a change in the Alu domain-ribosome interface. At this stage, the Alu domain of SRP is located at the ribosomal subunit interface since SRP14 can be cross-linked to proteins from the large and small ribosomal subunits. Hence, these studies reveal differential modes of SRP-ribosome interactions mediated by the Alu domain

Influence of plant genotype and soil on the wheat rhizosphere microbiome: evidences for a core microbiome across eight African and European soils

International audienceHere, we assessed the relative influence of wheat genotype, agricultural practices (conventional vs organic) and soil type on the rhizosphere microbiome. We characterized the prokaryotic (archaea and bacteria) and eukaryotic (fungi and protists) communities in soils from four different countries (Cameroon, France, Italy, Senegal) and determined if a rhizosphere core microbiome existed across these different countries. The wheat genotype had a limited effect on the rhizosphere microbiome (2% of variance) as the majority of the microbial taxa were consistently associated to multiple wheat genotypes grown in the same soil. Large differences in taxa richness and in community structure were observed between the eight soils studied (57% variance) and the two agricultural practices (10% variance). Despite these differences between soils, we observed that 177 taxa (2 archaea, 103 bacteria, 41 fungi and 31 protists) were consistently detected in the rhizosphere, constituting a core microbiome. In addition to being prevalent, these core taxa were highly abundant and collectively represented 50% of the reads in our data set. Based on these results, we identify a list of key taxa as future targets of culturomics, metagenomics and wheat synthetic microbiomes. Additionally, we show that protists are an integral part of the wheat holobiont that is currently overlooked