Chi hotspot Control of RecBCD Helicase-nuclease: Enzymatic Tests Support the Intramolecular Signal-transduction Model.

Repair of broken DNA is essential for life; the reactions involved can also promote genetic recombination to aid evolution. In Escherichia coli, RecBCD enzyme is required for the major pathway of these events. RecBCD is a complex ATP-dependent DNA helicase with nuclease activity controlled by Chi recombination hotspots (5'-GCTGGTGG-3'). During rapid DNA unwinding, when Chi is in a RecC tunnel, RecB nuclease nicks DNA at Chi. Here, we test our signal transduction model - upon binding Chi (step 1), RecC signals RecD helicase to stop unwinding (step 2); RecD then signals RecB (step 3) to nick at Chi (step 4) and to begin loading RecA DNA strand-exchange protein (step 5). We discovered that ATP-γ-S, like the small molecule RecBCD inhibitor NSAC1003, causes RecBCD to nick DNA, independent of Chi, at novel positions determined by the DNA substrate length. Two RecB ATPase-site mutants nick at novel positions determined by their RecB:RecD helicase rate ratios. In each case, we find that nicking at the novel position requires steps 3 and 4 but not step 1 or 2, as shown by mutants altered at the intersubunit contacts specific for each step; nicking also requires RecD helicase and RecB nuclease activities. Thus, altering the RecB ATPase site, by small molecules or mutation, sensitizes RecD to signal RecB to nick DNA (steps 4 and 3, respecitvely) without the signal from RecC or Chi (steps 1 and 2). These new, enzymatic results strongly support the signal transduction model and provide a paradigm for studying other complex enzymes.

RecBCD enzyme: mechanistic insights from mutants of a complex helicase-nuclease.

SUMMARYRecBCD enzyme is a multi-functional protein that initiates the major pathway of homologous genetic recombination and DNA double-strand break repair in Escherichia coli. It is also required for high cell viability and aids proper DNA replication. This 330-kDa, three-subunit enzyme is one of the fastest, most processive helicases known and contains a potent nuclease controlled by Chi sites, hotspots of recombination, in DNA. RecBCD undergoes major changes in activity and conformation when, during DNA unwinding, it encounters Chi (5'-GCTGGTGG-3') and nicks DNA nearby. Here, we discuss the multitude of mutations in each subunit that affect one or another activity of RecBCD and its control by Chi. These mutants have given deep insights into how the multiple activities of this complex enzyme are coordinated and how it acts in living cells. Similar studies could help reveal how other complex enzymes are controlled by inter-subunit interactions and conformational changes.

Meiotic crossover interference: Methods of analysis and mechanisms of action.

Segregation of chromosomes during meiosis, to form haploid gametes from diploid precursor cells, requires in most species formation of crossovers physically connecting homologous chromosomes. Along with sister chromatid cohesion, crossovers allow tension to be generated when chromosomes begin to segregate; tension signals that chromosome movement is proceeding properly. But crossovers too close to each other might result in less sister chromatid cohesion and tension and thus failed meiosis. Interference describes the non-random distribution of crossovers, which occur farther apart than expected from independence. We discuss both genetic and cytological methods of assaying crossover interference and models for interference, whose molecular mechanism remains to be elucidated. We note marked differences among species.

Meiotic chromosome organization and its role in recombination and cancer.

Chromosomes adopt specific conformations to regulate various cellular processes. A well-documented chromosome configuration is the highly compacted chromosome structure during metaphase. More regional chromatin conformations have also been reported, including topologically associated domains encompassing mega-bases of DNA and local chromatin loops formed by kilo-bases of DNA. In this review, we discuss the changes in chromatin conformation taking place between somatic and meiotic cells, with a special focus on the establishment of a proteinaceous structure, called the chromosome axis, at the beginning of meiosis. The chromosome axis is essential to support key meiotic processes such as chromosome pairing, homologous recombination, and balanced chromosome segregation to transition from a diploid to a haploid stage. We review the role of the chromosome axis in meiotic chromatin organization and provide a detailed description of its protein composition. We also review the conserved and distinct roles between species of axis proteins in meiotic recombination, which is a major factor contributing to the creation of genetic diversity and genome evolution. Finally, we discuss situations where the chromosome axis is deregulated and evaluate the effects on genome integrity and the consequences from protein deregulation in meiocytes exposed to heat stress, and aberrant expression of genes encoding axis proteins in mammalian somatic cells associated with certain types of cancers.

A flexible RecC surface loop required for Chi hotspot control of RecBCD enzyme.

Escherichia coli RecBCD helicase-nuclease promotes vital homologous recombination-based repair of DNA double-strand breaks. The RecB nuclease domain (Nuc) is connected to the RecB helicase domain by a 19-amino-acid tether. When DNA binds to RecBCD, published evidence suggests that Nuc moves ∼50 Šfrom the exit of a RecC tunnel, from which the 3'-ended strand emerges during unwinding, to a distant position on RecC's surface. During subsequent ATP-dependent unwinding of DNA, Nuc nicks the 3'-ended strand near 5'-GCTGGTGG-3' (Chi recombination hotspot). Here, we test our model of Nuc swinging on the tether from the RecC tunnel exit to the RecC distant surface and back to the RecC tunnel exit to cut at Chi. We identify positions in a flexible surface loop on RecC and on RecB Nuc with complementary charges, mutation of which strongly reduces but does not eliminate Chi hotspot activity in cells. The recC loop mutation interacts with recB mutations hypothesized to be in the Chi-activated intramolecular signal transduction pathway; the double mutants, but not the single mutants, eliminate Chi hotspot activity. A RecC amino acid near the flexible loop is also essential for full Chi activity; its alteration likewise synergizes with a signal transduction mutation to eliminate Chi activity. We infer that altering the RecC surface loop reduces coordination among the subunits, which is critical for Chi hotspot activity. We discuss other RecBCD mutants with related properties.

Host nucleases generate prespacers for primed adaptation in the E. coli type I-E CRISPR-Cas system.

CRISPR-Cas systems provide prokaryotes with adaptive immunity against foreign nucleic acids. In Escherichia coli, immunity is acquired upon integration of 33-bp spacers into CRISPR arrays. DNA targets complementary to spacers get degraded and serve as a source of new spacers during a process called primed adaptation. Precursors of such spacers, prespacers, are ~33-bp double-stranded DNA fragments with a ~4-nt 3' overhang. The mechanism of prespacer generation is not clear. Here, we use FragSeq and biochemical approaches to determine enzymes involved in generation of defined prespacer ends. We demonstrate that RecJ is the main exonuclease trimming 5' ends of prespacer precursors, although its activity can be partially substituted by ExoVII. The RecBCD complex allows single strand-specific RecJ to process double-stranded regions flanking prespacers. Our results reveal intricate functional interactions of genome maintenance proteins with CRISPR interference and adaptation machineries during generation of prespacers capable of integration into CRISPR arrays.

RecBCD enzyme and Chi recombination hotspots as determinants of self vs. non-self: Myths and mechanisms.

Bacteria face a challenge when DNA enters their cells by transformation, mating, or phage infection. Should they treat this DNA as an invasive foreigner and destroy it, or consider it one of their own and potentially benefit from incorporating new genes or alleles to gain useful functions? It is frequently stated that the short nucleotide sequence Chi (5' GCTGGTGG 3'), a hotspot of homologous genetic recombination recognized by Escherichia coli's RecBCD helicase-nuclease, allows E. coli to distinguish its DNA (self) from any other DNA (non-self) and to destroy non-self DNA, and that Chi is "over-represented" in the E. coli genome. We show here that these latter statements (dogmas) are not supported by available evidence. We note Chi's wide-spread occurrence and activity in distantly related bacterial species and phages. We illustrate multiple, highly non-random features of the genomes of E. coli and coliphage P1 that account for Chi's high frequency and genomic position, leading us to propose that P1 selects for Chi's enhancement of recombination, whereas E. coli selects for the preferred codons in Chi. We discuss other, previously described mechanisms for self vs. non-self determination involving RecBCD and for RecBCD's destruction of DNA that cannot recombine, whether foreign or domestic, with or without Chi.

Klebsiella pneumoniae Lower Respiratory Tract Infection in a South African Birth Cohort: a Longitudinal Study.

OBJECTIVES: The role of Klebsiella pneumoniae (KP) in lower respiratory tract infection (LRTI) is not well studied. We longitudinally investigated KP colonization and its association with LRTI in a South African birth cohort. METHODS: We conducted a case-control study of infants who developed LRTI and age-matched controls, followed twice weekly through infancy. Nasopharyngeal swabs taken fortnightly and at LRTI for 33-multipex Quantitative multiplex real-time polymerase chain reaction were tested at LRTI and twice weekly from 90 days preceding LRTI. Controls were tested over the equivalent period. Multivariate models investigated the factors associated with LRTI or with KP-associated LRTI (KP-LRTI). RESULTS: Among 885 infants, there were 439 LRTI episodes, of which 68 (15.5%) were KP-LRTI (OR 1.93; 95% CI 1.25-3.03). Infants with KP-LRTI were younger than those without KP-LRTI (median [IQR] 3.7 [2.1-5.9] vs 4.7 [2.8-7.9] months, P-value=0.009). Clinical features of KP and non-KP-LRTI were similar with 114 (26%) infants hospitalized. Prematurity (adjusted odds ratio [aOR] 11.86; 95% CI 5.22-26.93), HIV exposure (aOR 3.32; 95% CI 1.69-6.53), lower birthweight (aOR 0.68; 95% CI 0.51-0.91), and shorter breastfeeding time (aOR 0.79; 95% CI 0.65-0.96) were associated with KP-LRTI versus non-LRTI. These factors and younger age were associated with KP-LRTI versus non-KP-LRTI. CONCLUSION: KP was associated with a substantial proportion of LRTI, particularly in premature or HIV-exposed infants in whom strategies for treatment and prevention should be strengthened.

Dynamic configurations of meiotic DNA-break hotspot determinant proteins.

Appropriate DNA double-strand break (DSB) and crossover distributions are required for proper meiotic chromosome segregation. Schizosaccharomyces pombe linear element proteins (LinEs) determine DSB hotspots; LinE-bound hotspots form three-dimensional clusters over ∼200 kb chromosomal regions. Here, we investigated LinE configurations and distributions in live cells using super-resolution fluorescence microscopy. We found LinEs form two chromosomal structures, dot-like and linear structures, in both zygotic and azygotic meiosis. Dot-like LinE structures appeared around the time of meiotic DNA replication, underwent dotty-to-linear-to-dotty configurational transitions and disassembled before the first meiotic division. DSB formation and repair did not detectably influence LinE structure formation but failure of DSB formation delayed disassembly. Recombination-deficient LinE missense mutants formed dot-like, but not linear, LinE structures. Our quantitative study reveals a transient form of LinE structures and suggests a novel role for LinE proteins in regulating meiotic events, such as DSB repair. We discuss the relationship of LinEs and the synaptonemal complex in other species. This article has an associated First Person interview with the first author of the paper.

Assessment of Clinical Outcomes Among Children and Adolescents Hospitalized With COVID-19 in 6 Sub-Saharan African Countries.

IMPORTANCE: Little is known about COVID-19 outcomes among children and adolescents in sub-Saharan Africa, where preexisting comorbidities are prevalent. OBJECTIVE: To assess the clinical outcomes and factors associated with outcomes among children and adolescents hospitalized with COVID-19 in 6 countries in sub-Saharan Africa. DESIGN, SETTING, AND PARTICIPANTS: This cohort study was a retrospective record review of data from 25 hospitals in the Democratic Republic of the Congo, Ghana, Kenya, Nigeria, South Africa, and Uganda from March 1 to December 31, 2020, and included 469 hospitalized patients aged 0 to 19 years with SARS-CoV-2 infection. EXPOSURES: Age, sex, preexisting comorbidities, and region of residence. MAIN OUTCOMES AND MEASURES: An ordinal primary outcome scale was used comprising 5 categories: (1) hospitalization without oxygen supplementation, (2) hospitalization with oxygen supplementation, (3) ICU admission, (4) invasive mechanical ventilation, and (5) death. The secondary outcome was length of hospital stay. RESULTS: Among 469 hospitalized children and adolescents, the median age was 5.9 years (IQR, 1.6-11.1 years); 245 patients (52.4%) were male, and 115 (24.5%) had comorbidities. A total of 39 patients (8.3%) were from central Africa, 172 (36.7%) from eastern Africa, 208 (44.3%) from southern Africa, and 50 (10.7%) from western Africa. Eighteen patients had suspected (n = 6) or confirmed (n = 12) multisystem inflammatory syndrome in children. Thirty-nine patients (8.3%) died, including 22 of 69 patients (31.9%) who required intensive care unit admission and 4 of 18 patients (22.2%) with suspected or confirmed multisystem inflammatory syndrome in children. Among 468 patients, 418 (89.3%) were discharged, and 16 (3.4%) remained hospitalized. The likelihood of outcomes with higher vs lower severity among children younger than 1 year expressed as adjusted odds ratio (aOR) was 4.89 (95% CI, 1.44-16.61) times higher than that of adolescents aged 15 to 19 years. The presence of hypertension (aOR, 5.91; 95% CI, 1.89-18.50), chronic lung disease (aOR, 2.97; 95% CI, 1.65-5.37), or a hematological disorder (aOR, 3.10; 95% CI, 1.04-9.24) was associated with severe outcomes. Age younger than 1 year (adjusted subdistribution hazard ratio [asHR], 0.48; 95% CI, 0.27-0.87), the presence of 1 comorbidity (asHR, 0.54; 95% CI, 0.40-0.72), and the presence of 2 or more comorbidities (asHR, 0.26; 95% CI, 0.18-0.38) were associated with reduced rates of hospital discharge. CONCLUSIONS AND RELEVANCE: In this cohort study of children and adolescents hospitalized with COVID-19 in sub-Saharan Africa, high rates of morbidity and mortality were observed among infants and patients with noncommunicable disease comorbidities, suggesting that COVID-19 vaccination and therapeutic interventions are needed for young populations in this region.

Redirecting meiotic DNA break hotspot determinant proteins alters localized spatial control of DNA break formation and repair.

During meiosis, DNA double-strand breaks (DSBs) are formed at high frequency at special chromosomal sites, called DSB hotspots, to generate crossovers that aid proper chromosome segregation. Multiple chromosomal features affect hotspot formation. In the fission yeast S. pombe the linear element proteins Rec25, Rec27 and Mug20 are hotspot determinants - they bind hotspots with high specificity and are necessary for nearly all DSBs at hotspots. To assess whether they are also sufficient for hotspot determination, we localized each linear element protein to a novel chromosomal site (ade6 with lacO substitutions) by fusion to the Escherichia coli LacI repressor. The Mug20-LacI plus lacO combination, but not the two separate lac elements, produced a strong ade6 DSB hotspot, comparable to strong endogenous DSB hotspots. This hotspot had unexpectedly low ade6 recombinant frequency and negligible DSB hotspot competition, although like endogenous hotspots it manifested DSB interference. We infer that linear element proteins must be properly placed by endogenous functions to impose hotspot competition and proper partner choice for DSB repair. Our results support and expand our previously proposed DSB hotspot-clustering model for local control of meiotic recombination.

Global incidence and prevalence of idiopathic pulmonary fibrosis.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a progressive debilitating lung disease with considerable morbidity. Heterogeneity in epidemiologic studies means the full impact of the disease is unclear. METHODS: A targeted literature search for population-based, observational studies reporting incidence and/or prevalence of IPF from January 2009 to April 2020 was conducted. Identified studies were aggregated by country. For countries with multiple publications, a weighted average was determined. Incidence and prevalence data were adjusted for between-study differences where possible. The final model included adjusted estimates of incidence and prevalence per 10,000 of the population with 95% confidence intervals. As prevalence estimates vary depending on the definitions used, estimates were based on a specific case definition of IPF. RESULTS: Overall, 22 studies covering 12 countries met the inclusion criteria, with 15 reporting incidence and 18 reporting prevalence estimates. The adjusted incidence estimates (per 10,000 of the population) ranged from 0.35 to 1.30 in Asia-Pacific countries, 0.09 to 0.49 in Europe, and 0.75 to 0.93 in North America. Unadjusted and adjusted incidence estimates were consistent. The adjusted prevalence estimates ranged from 0.57 to 4.51 in Asia-Pacific countries, 0.33 to 2.51 in Europe, and 2.40 to 2.98 in North America. South Korea had the highest incidence and prevalence estimates. When prevalence estimates were compared to country-specific rare disease thresholds, IPF met the definition of a rare disease in all countries except South Korea. There were notable geographic gaps for IPF epidemiologic data. CONCLUSIONS: Due to differences in study methodologies, there is worldwide variability in the reported incidence and prevalence of IPF. Based on the countries included in our analysis, we estimated the adjusted incidence and prevalence of IPF to be in the range of 0.09-1.30 and 0.33-4.51 per 10,000 persons, respectively. According to these prevalence estimates, IPF remains a rare disease. For consistency, future epidemiologic studies of IPF should take age, sex, smoking status, and the specificity of case definitions into consideration.

Child mortality associated with maternal HIV status: a retrospective analysis in Rwanda, 2005-2015.

INTRODUCTION: Child mortality remains highest in regions of the world most affected by HIV/AIDS. The aim of this study was to assess child mortality rates in relation to maternal HIV status from 2005 to 2015, the period of rapid HIV treatment scale-up in Rwanda. METHODS: We used data from the 2005, 2010 and 2015 Rwanda Demographic Health Surveys to derive under-2 mortality rates by survey year and mother's HIV status and to build a multivariable logistic regression model to establish the association of independent predictors of under-2 mortality stratified by mother's HIV status. RESULTS: In total, 12 010 live births were reported by mothers in the study period. Our findings show a higher mortality among children born to mothers with HIV compared with HIV negative mothers in 2005 (216.9 vs 100.7 per 1000 live births) and a significant reduction in mortality for both groups in 2015 (72.0 and 42.4 per 1000 live births, respectively). In the pooled reduced multivariable model, the odds of child mortality was higher among children born to mothers with HIV, (adjusted OR, AOR 2.09; 95% CI 1.57 to 2.78). The odds of child mortality were reduced in 2010 (AOR 0.69; 95% CI 0.59 to 0.81) and 2015 (AOR 0.35; 95% CI 0.28 to 0.44) compared with 2005. Other independent predictors of under-2 mortality included living in smaller families of 1-2 members (AOR 5.25; 95% CI 3.59 to 7.68), being twin (AOR 4.93; 95% CI 3.51 to 6.92) and being offspring from mothers not using contraceptives at the time of the survey (AOR 1.6; 95% CI 1.38 to 1.99). Higher education of mothers (completed primary school: (AOR 0.74; 95% CI 0.64 to 0.87) and secondary or higher education: (AOR 0.53; 95% CI 0.38 to 0.74)) was also associated with reduced child mortality. CONCLUSIONS: This study shows an important decline in under-2 child mortality among children born to both mothers with and without HIV in Rwanda over a 10-year span.

How COVID-19 has fundamentally changed clinical research in global health.

COVID-19 has had negative repercussions on the entire global population. Despite there being a common goal that should have unified resources and efforts, there have been an overwhelmingly large number of clinical trials that have been registered that are of questionable methodological quality. As the final paper of this Series, we discuss how the medical research community has responded to COVID-19. We recognise the incredible pressure that this pandemic has put on researchers, regulators, and policy makers, all of whom were doing their best to move quickly but safely in a time of tremendous uncertainty. However, the research community's response to the COVID-19 pandemic has prominently highlighted many fundamental issues that exist in clinical trial research under the current system and its incentive structures. The COVID-19 pandemic has not only re-emphasised the importance of well designed randomised clinical trials but also highlighted the need for large-scale clinical trials structured according to a master protocol in a coordinated and collaborative manner. There is also a need for structures and incentives to enable faster data sharing of anonymised datasets, and a need to provide similar opportunities to those in high-income countries for clinical trial research in low-resource regions where clinical trial research receives considerably less research funding.

Diatomite encapsulated AgNPs as novel hair dye cosmetics: Preparation, performance, and toxicity.

Naturally-occurring diatomite has been successfully utilised as a unique encapsulating material to obtain a highly dispersed suspension of uniformly-sized silver nanoparticles (AgNPs). Plant derived gallic acid was used as the reducing and capping agent. High-resolution scanning and transmission electron microscopy results confirmed the attachment of AgNPs on the surface of diatom frustule and maintained an excellent dispersion stability against particle aggregation. The AgNPs obtained were employed for the colouration of bleached human hair owing to the local surface plasmonic absorption (LSPR) of the AgNPs. The effects of Ag/diatomite concentration, dyeing pH, temperature and time on the produced colour were investigated. Hair fibres treated under optimised conditions display good colour fastness toward solar radiation. The morphology and chemical composition of AgNP-dyed hair were determined by energy-dispersive spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses. The biocompatibility of the Ag/diatomite composite, AgNPs, and the dyebaths were confirmed by in vitro acute dermal and ocular toxicity tests. The diatomite supporting AgNPs therefore hold good promise and enormous potential to be exploited for sustainable dyeing of human hair.

Activation of meiotic recombination by nuclear import of the DNA break hotspot-determining complex in fission yeast.

Meiotic recombination forms crossovers important for proper chromosome segregation and offspring viability. This complex process involves many proteins acting at each of the multiple steps of recombination. Recombination initiates by formation of DNA double-strand breaks (DSBs), which in the several species examined occur with high frequency at special sites (DSB hotspots). In Schizosaccharomyces pombe, DSB hotspots are bound with high specificity and strongly activated by linear element (LinE) proteins Rec25, Rec27 and Mug20, which form colocalized nuclear foci with Rec10, essential for all DSB formation and recombination. Here, we test the hypothesis that the nuclear localization signal (NLS) of Rec10 is crucial for coordinated nuclear entry after forming a complex with other LinE proteins. In NLS mutants, all LinE proteins were abundant in the cytoplasm, not the nucleus; DSB formation and recombination were much reduced but not eliminated. Nuclear entry of limited amounts of Rec10, apparently small enough for passive nuclear entry, can account for residual recombination. LinE proteins are related to synaptonemal complex proteins of other species, suggesting that they also share an NLS, not yet identified, and undergo protein complex formation before nuclear entry.This article has an associated First Person interview with Mélody Wintrebert, joint first author of the paper.

Reporting and design of randomized controlled trials for COVID-19: A systematic review.

BACKGROUND: The novel coronavirus 2019 (COVID-19) pandemic has mobilized global research at an unprecedented scale. While challenges associated with the COVID-19 trial landscape have been discussed previously, no comprehensive reviews have been conducted to assess the reporting, design, and data sharing practices of randomized controlled trials (RCTs). PURPOSE: The purpose of this review was to gain insight into the current landscape of reporting, methodological design, and data sharing practices for COVID-19 RCTs. DATA SOURCES: We conducted three searches to identify registered clinical trials, peer-reviewed publications, and pre-print publications. STUDY SELECTION: After screening eight major trial registries and 7844 records, we identified 178 registered trials and 38 publications describing 35 trials, including 25 peer-reviewed publications and 13 pre-prints. DATA EXTRACTION: Trial ID, registry, location, population, intervention, control, study design, recruitment target, actual recruitment, outcomes, data sharing statement, and time of data sharing were extracted. DATA SYNTHESIS: Of 178 registered trials, 112 (62.92%) were in hospital settings, median planned recruitment was 100 participants (IQR: 60, 168), and the majority (n = 166, 93.26%) did not report results in their respective registries. Of 35 published trials, 31 (88.57%) were in hospital settings, median actual recruitment was 86 participants (IQR: 55.5, 218), 10 (28.57%) did not reach recruitment targets, and 27 trials (77.14%) reported plans to share data. CONCLUSIONS: The findings of our study highlight limitations in the design and reporting practices of COVID-19 RCTs and provide guidance towards more efficient reporting of trial results, greater diversity in patient settings, and more robust data sharing.

Alpine Ski Motion Characteristics in Slalom.

Important insight into ski function, and ultimately skier technique and tactics, can be gained by studying how measured ski trajectories compare to predictions based on theoretical models of ski-snow interaction mechanics. The aim of this investigation was to use a 3D kinematic data set collected on highly-skilled skiers during slalom race simulations to quantify ski motion characteristics and to compare these measures with theoretical predictions based primarily on ski geometrical characteristics. For slalom turns on moderate steepness (19°), ski edging angles reached maximum values of 65.7 ± 1.7° and 71.0 ± 1.9° for 10 and 13 m gate spacings. Turn radii reached minimum values of 3.96 ± 0.23 and 4.94 ± 0.59 m for the 10 and 13 m courses. These values were in good agreement with theoretical predictions by Howe (2001) of turn radius based on edging angle. Other results of the study support recent developments in understanding of the role which the ski shovel plays in groove formation during carving, and also point to the need for further study of how ski geometrical and physical characteristics interact to determine the ski's trajectory, particularly at low edge angles. These results have important implications for understanding the consequences that ski design can have for skier technique and tactics in competitive slalom skiing.

The Landscape of Emerging Randomized Clinical Trial Evidence for COVID-19 Disease Stages: A Systematic Review of Global Trial Registries.

PURPOSE: A multitude of randomized controlled trials (RCTs) have emerged in response to the novel coronavirus disease (COVID-19) pandemic. Understanding the distribution of trials among various settings is important to guide future research priorities and efforts. The purpose of this review was to describe the emerging evidence base of COVID-19 RCTs by stages of disease progression, from pre-exposure to hospitalization. METHODS: We collated trial data across international registries: ClinicalTrials.gov; International Standard Randomised Controlled Trial Number Registry; Chinese Clinical Trial Registry; Clinical Research Information Service; EU Clinical Trials Register; Iranian Registry of Clinical Trials; Japan Primary Registries Network; German Clinical Trials Register (up to 7 October 2020). Active COVID-19 RCTs in international registries were eligible for inclusion. We extracted trial status, intervention(s), control, sample size, and clinical context to generate descriptive frequencies, network diagram illustrations, and statistical analyses including odds ratios and the Mann-Whitney U-test. RESULTS: Our search identified 11503 clinical trials registered for COVID-19 and identified 2388 RCTs. After excluding 45 suspended RCTs and 480 trials with unclear or unreported disease stages, 1863 active RCTs were included and categorized into four broad disease stages: pre-exposure (n=107); post-exposure (n=208); outpatient treatment (n=266); hospitalization, including the intensive care unit (n=1376). Across all disease stages, most trials had two arms (n=1500/1863, 80.52%), most often included (hydroxy)chloroquine (n=271/1863, 14.55%) and were US-based (n=408/1863, 21.90%). US-based trials had lower odds of including (hydroxy)chloroquine than trials in other countries (OR: 0.63, 95% CI: 0.45-0.90) and similar odds of having two arms compared to other geographic regions (OR: 1.05, 95% CI: 0.80-1.38). CONCLUSION: There is a marked difference in the number of trials across settings, with limited studies on non-hospitalized persons. Focus on pre- and post-exposure, and outpatients, is worthwhile as a means of reducing infections and lessening the health, social, and economic burden of COVID-19.

Chi hotspot control of RecBCD helicase-nuclease by long-range intramolecular signaling.

Repair of broken DNA by homologous recombination requires coordinated enzymatic reactions to prepare it for interaction with intact DNA. The multiple activities of enterobacterial RecBCD helicase-nuclease are coordinated by Chi recombination hotspots (5' GCTGGTGG 3') recognized during DNA unwinding. Chi is recognized in a tunnel in RecC but activates the RecB nuclease, > 25 Ǻ away. How the Chi-dependent signal travels this long distance has been unknown. We found a Chi hotspot-deficient mutant in the RecB helicase domain located > 45 Ǻ from both the Chi-recognition site and the nuclease active site. This unexpected observation led us to find additional mutations that reduced or eliminated Chi hotspot activity in each subunit and widely scattered throughout RecBCD. Each mutation alters the intimate contact between one or another pair of subunits in crystal or cryoEM structures of RecBCD bound to DNA. Collectively, these mutations span a path about 185 Ǻ long from the Chi recognition site to the nuclease active site. We discuss these surprising results in the context of an intramolecular signal transduction accounting for many previous observations.