Unusual Sequence Research Articles

Post-transcriptional methylation of mitochondrial-tRNA differentially contributes to mitochondrial pathology

Human mitochondrial tRNAs (mt-tRNAs), critical for mitochondrial biogenesis, are frequently associated with pathogenic mutations. These mt-tRNAs have unusual sequence motifs and require post-transcriptional modifications to stabilize their fragile structures. However, whether a modification that stabilizes a wild-type (WT) mt-tRNA would also stabilize its pathogenic variants is unknown. Here we show that the N1-methylation of guanosine at position 9 (m1G9) of mt-Leu(UAA), while stabilizing the WT tRNA, has a destabilizing effect on variants associated with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes). This differential effect is further demonstrated, as removal of the m1G9 methylation, while damaging to the WT tRNA, is beneficial to the major pathogenic variant, improving the structure and activity of the variant. These results have therapeutic implications, suggesting that the N1-methylation of mt-tRNAs at position 9 is a determinant of pathogenicity and that controlling the methylation level is an important modulator of mt-tRNA-associated diseases.

Very asymmetric disc edema in fulminant idiopathic intracranial hypertension: A rare and an unusual clinical finding

Fulminant idiopathic intracranial hypertension (IIH) can present as a rapid and severe vision-threatening condition, particularly in young females. We present a distinctive case of fulminant IIH characterized by asymmetrical vision loss with unilateral disc edema with loss of vision in the eye without disc edema. The patient exhibited an unusual serial sequence of radiological signs of raised intracranial pressure, emphasizing the need for emergent treatment. Resolution of the radiological signs was achieved following theco-peritoneal shunt placement. This case highlights the occurrence of fulminant IIH in unilateral disc edema and cause–effect relation between raised intracranial pressure and radiological signs and educative emphasis on the pathophysiology of the condition.

Stereocontrolled Synthesis of Chiral Helicene‐Indenido ansa‐ and Half‐Sandwich Metal Complexes and Their Use in Catalysis

Despite recent tremendous progress in the synthesis of nonplanar chiral aromatics, and helicenes in particular, their conversion to half‐sandwich or sandwich transition metal complexes still lags behind, although they represent an attractive family of modular and underexplored chiral architectures with a potential catalytic use. In this work, starting from various chiral helicene‐indene proligands, we prepared the enantio‐ and diastereopure oxa[6]‐ and oxa[7]helicene‐indenido half‐sandwich RhI and RhIII complexes and oxa[7]helicene‐bisindenido ansa‐metallocene FeII complex. To document their use, oxahelicene‐indenido half‐sandwich RhIII complexes were employed as chiral catalysts in enantioselective C‐H arylation of benzo[h]quinolines with 1‐diazonaphthoquinones to afford a series of axially chiral biaryls in mostly good to high yields and in up to 96 : 4 er. Thus, we developed stereocontrolled synthesis of chiral helicene‐indenido ansa‐ and half‐sandwich metal complexes, successfully demonstrated the first use of such helicene Cp‐related metal complexes in enantioselective catalysis, and described an unusual sequence of efficient central‐to‐helical‐to‐planar‐to‐axial chirality transfer.

Stereocontrolled Synthesis of Chiral Helicene-Indenido ansa- and Half-Sandwich Metal Complexes and Their Use in Catalysis.

Despite recent tremendous progress in the synthesis of nonplanar chiral aromatics, and helicenes in particular, their conversion to half-sandwich or sandwich transition metal complexes still lags behind, although they represent an attractive family of modular and underexplored chiral architectures with a potential catalytic use. In this work, starting from various chiral helicene-indene proligands, we prepared the enantio- and diastereopure oxa[6]- and oxa[7]helicene-indenido half-sandwich RhI and RhIII complexes and oxa[7]helicene-bisindenido ansa-metallocene FeII complex. To document their use, oxahelicene-indenido half-sandwich RhIII complexes were employed as chiral catalysts in enantioselective C-H arylation of benzo[h]quinolines with 1-diazonaphthoquinones to afford a series of axially chiral biaryls in mostly good to high yields and in up to 96 : 4 er. Thus, we developed stereocontrolled synthesis of chiral helicene-indenido ansa- and half-sandwich metal complexes, successfully demonstrated the first use of such helicene Cp-related metal complexes in enantioselective catalysis, and described an unusual sequence of efficient central-to-helical-to-planar-to-axial chirality transfer.

Crystal Structure of the Native Chromoprotein from Pleurotus salmoneostramineus Provides Insights into the Pigmentation Mechanism.

The pink-colored protein from the fungus Pleurotus salmoneostramineus (PsPCP) possesses unusual primary sequences with little resemblance to those of known proteins and exhibits a red color in aqueous solution. To understand the pigmentation mechanism of PsPCP, we elucidated the X-ray crystal structure of the native PsPCP. We identified a highly conjugated polyene ligand 2-dehydro-3-deoxylaetiporic acid A as a chromophore ligand, whose solution exhibits yellow. The crystal structure of PsPCP indicated that the ligand is secured in the central cavity and anchored at both termini by hydrophilic interactions and that surrounding residues show CH-pi and C-H···O hydrogen bondings. Geometrical analyses of the bound ligand demonstrated that the conjugated C-C and C═C bonds exhibit similar bond distances. The result indicated enhanced electron delocalization within the conjugated CC bond system, resulting in a redshift of the chromophore ligand. The computational estimates of the UV-vis spectra support the view that the electron delocalization within the conjugated CC bonds system of the bound ligand, induced by the specific ligand geometry within a limited space of PsPCP cavity, is responsible for the red pigmentation of PsPCP. Thus, we propose that the coloring mechanism of PsPCP, which constrains the geometry of a highly conjugated polyene ligand, is a novel type of pigment chemistry.

Synthesis and α-Functionalisation of Cyclic Imines

Abstractα-Functionalisation of cyclic imines is explored. The cyclic imine substrates are synthesised from their respective halonitrile precursors using a nucleophilic addition/cyclisation sequence. Selective monohalogenation of the cyclic imines yields α-haloimines, which serve as a platform to obtain various α-hydroxyimine derivatives. In addition, an unusual tautomerisation and oxidation sequence is observed in the attempted preparation of α-hydroxyimines.

Diversity of Unusual Ribosomal Genes and Ecological Origin of Rice (Oryza spp.)

Tandemly organized rRNA genes are a typical example of a multigene family, where individual members evolve co-ordinately within—but independently between—species due to gene conversion and unequal crossing over. More frequently, in eukaryotic species with an interspecies hybrid origin, expression of unhomogenized rRNA genes from one progenitor is epigenetically silenced because of nucleolus dominance, and distinct rRNA genes may lose functionality and evolve faster. Interestingly, we obtained unusual ribosomal gene sequences from Oryza species that showed great diversity and did not appear in the present rice genomic sequence. The diversity of rDNA sequences indicated that the homogenization in rice is incomplete and explains the introgression of distinct rRNA gene families into ancestral rice genomes before speciation and continent separation. The divergent large subunit (LSU) ribosomal genes are expressed, some of them differentially, depending on the N fertilization of plants. Detection of differential transcripts of the rRNA genes suggested that rRNA gene families are not functionally equivalent. Phylogenetic analysis assigned Oryza species branching order to monocots, and monocot lineages probably have the same ecological origin by molecular clock calculation. Therefore, our results suggested that the geographical distances of continent-separation cause barriers to the gene flow and homogenization among Oryza species which requires further explanation.

Unusual Sequence of the Critical Magnetic Fields Hc1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_{c1}$$\\end{document}, Hc2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_{c2}$$\\end{document}, and Hc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_{c}$$\\end{document} in Multicomponent Superconductors

All superconductors in a magnetic field are characterized by three critical magnetic fields: lower critical Hc1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_{c1}$$\\end{document}, upper critical Hc2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_{c2}$$\\end{document} and thermodynamic critical field Hc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_{c}$$\\end{document}. Only two sets of inequalities Hc2>Hc>Hc1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_{c2}>H_c>H_{c1}$$\\end{document} or Hc1>Hc>Hc2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_{c1}>H_c>H_{c2}$$\\end{document} are possible in a single-component superconductor. Here, we report our study of the critical fields in multicomponent superconductors with two superconducting components in the framework of the Ginzburg-Landau functional. We derive the relationship between the phases of the components of the superconducting complex order parameter from the charge conservation law in explicit form and insert it into the Ginzburg-Landau functional. Using the modified Ginzburg-Landau equation, we acquire the single vortex state including the analytical expression for asymptotics. Also, we obtain the analytical form for the state in the upper critical field. We find that in some cases an unusual sequence of critical fields Hc1,Hc2>Hc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_{c1},H_{c2}>H_c$$\\end{document} can be realized in multicomponent superconductors.

The Unusual Sequence of Lymphomatoid Papulosis Following Hodgkin's Disease: A Case Report

Lymphomatoid papulosis (LyP) is a rare skin disease which is characterised by chronic, recurrent self-healing papulo-nodular skin lesions. It is classified under the group of primary cutaneousCD30+ve lymphoproliferative disorders. It is important to diagnose LyP as it is usually associated with other malignant lymhoproliferative disorders like mycosis fungoides, cutaneous or systemic anaplastic large cell lymphoma and Hodgkin's lymphoma. LyP associated malignancies may occur before, concurrent with or after the onset of LyP. In most of the cases previously described, Hodgkin's disease has developed after, or concurrently with, the onset of LyP. Here we report a case of LyP that developed 5 years after the onset and therapy for Hodgkin's lymphoma.

Perceived Experience and Management of Covid-19 in Southeastern Nigeria

SARS-CoV-2 causes the COVID-19 pandemic. Misconceptions and perceived experience with the onset of the COVID-19 infection are attributed to variations in symptom progression and a lack of timely diagnosis. This study aimed to identify the population of people in South-Eastern Nigeria who had perceived experience with and management of COVID-19. This population-based cross-sectional study of adult patients in South-Eastern Nigeria. Data from questionnaires were collected and statistically analyzed. Four hundred twenty responses were obtained, with 200(47.6%) respondents reporting perceived COVID-19 experience and 220(52.4%) reporting positive COVID-19 test results. The mean age of respondents with perceived experience was 37.61±12.27, while respondents with positive COVID-19 tests had a lower value (40.59±13.42). In comparison, 75.5% of respondents with perceived COVID-19 experience manifested unusual symptoms sequence, whereas this phenomenon was observed in 51.8% of positive COVID-19 patients. The most commonly reported symptoms are fever or chill (100% vs. 100%), cough (86% vs. 82%), and breathing difficulty (86% vs. 82%). Respondents with perceived COVID-19 experience primarily obtain their medication from a drug store (34.0%), whereas positive COVID-19 test respondents primarily obtain their medication from a hospital (64.1%). The study concluded that a lack of testing facilities could increase perceived experience with COVID-19, resulting in fewer people being tested for COVID-19. As a result, it is suggested that government agencies develop strategies to reduce the COVID-19 surge and improve testing facilities in southeastern Nigeria.

Splicing factor Prp18p promotes genome-wide fidelity of consensus 3'-splice sites.

The fidelity of splice site selection is critical for proper gene expression. In particular, proper recognition of 3'-splice site (3'SS) sequences by the spliceosome is challenging considering the low complexity of the 3'SS consensus sequence YAG. Here, we show that absence of the Prp18p splicing factor results in genome-wide activation of alternative 3'SS in S. cerevisiae, including highly unusual non-YAG sequences. Usage of these non-canonical 3'SS in the absence of Prp18p is enhanced by upstream poly(U) tracts and by their potential to interact with the first intronic nucleoside, allowing them to dock in the spliceosome active site instead of the normal 3'SS. The role of Prp18p in 3'SS fidelity is facilitated by interactions with Slu7p and Prp8p, but cannot be fulfilled by Slu7p, identifying a unique role for Prp18p in 3'SS fidelity. This fidelity function is synergized by the downstream proofreading activity of the Prp22p helicase, but is independent from another late splicing helicase, Prp43p. Our results show that spliceosomes exhibit remarkably relaxed 3'SS sequenceusage in the absence of Prp18p and identify a network of spliceosomal interactions centered on Prp18p which are required to promote the fidelity of the recognition of consensus 3'SS sequences.

Unusual Magnetospheric Dynamics During Intense Substorm Initiated by Strong Magnetospheric Compression

AbstractWe investigate an unusual sequence and peculiar features of magnetotail changes during a storm‐range substorm initiated by the interplanetary shock. Auroral observations and measurements at several favorably distributed magnetospheric spacecraft allowed the construction of an adaptive time‐dependent magnetospheric model to quantitatively characterize the configurational changes and mapping variations. Several passages of low‐altitude spacecraft in polar orbits near midnight help reveal the magnetic configuration of the nightside tail‐dipole transition region. In this event, an intense auroral and convection activity (accompanied by an up to 1,500 nT increase in the SuperMag AL‐index index) emerged in the highly compressed magnetosphere after the passage of interplanetary shock followed by strongly southward interplanetary magnetic field (IMF). This directly driven phase of the activity continued for an hour and resulted in the formation of a hybrid magnetic configuration with dipolarized midtail and stretched field lines in the transition region. Observations of energetic particle isotropy boundary latitudes near midnight are consistent with the modeled magnetic configuration. In concert with a downward turn of the solar wind (SW) flow, and weakening of the IMF driver and convection, an unusual stretching signature of the inner magnetosphere magnetic field was observed as close as at r ∼ 5 to 7 Re; which resulted mostly from an increasing downward tilt of the thin azimuthal current. Classic substorm breakup signatures commenced at fairly low, ∼60° magnetic latitude, deep in the closed field line region, in association with the current sheet upward motion. It was followed by strong stepwise poleward auroral expansion. We discuss how these signatures deviate from standard substorm scenarios and may be potentially imparted by the aforementioned changes in SW flow direction and pressure.

Zinc chloride-catalyzed cyclizative 1,2-rearrangement enables facile access to morpholinones bearing aza-quaternary carbons

Morpholines and morpholinones are important building blocks in organic synthesis and pharmacophores in medicinal chemistry, however, C3-disubstituted morpholines/morpholinones are extremely difficult to access. Here we show the ZnCl2-catalyzed cyclizative 1,2-rearrangement for the efficient synthesis of morpholinones bearing aza-quaternary stereocenters. A series of structurally diverse C3-disubstituted morpholin-2-ones which are difficultly accessible by existing methods were efficiently constructed from readily available two achiral linear compounds. Notably, mechanistic studies reveal that this reaction proceeds via an unusual sequence of direct formal [4 + 2] heteroannulation regioselectively delivering specific α-iminium/imine hemiacetals followed by a 1,2-esters or amides shift process, which is different from the reported mechanism of the aza-benzilic ester rearrangements.

Unraveling the Evolution of an Unusually Active Earthquake Sequence Near Sheldon, Nevada

One of most universal statistical properties of earthquakes is the tendency to cluster in space and time. Yet while clustering is pervasive, individual earthquake sequences can vary markedly in duration, spatial extent, and time evolution. In July 2014, a prolific earthquake sequence initiated within the Sheldon Wildlife Refuge in northwest Nevada, USA. The sequence produced 26 M4 earthquakes and several hundred M3s, with no clear mainshock or obvious driving force. Here we combine a suite of seismological analysis techniques to better characterize this unusual earthquake sequence. High-precision relocations reveal a clear, east dipping normal fault as the dominant structure that intersects with a secondary, subvertical cross fault. Seismicity occurs in burst of activity along these two structures before eventually transitioning to shallower structures to the east. Inversion of hundreds of moment tensors constrain the overall normal faulting stress regime. Source spectral analysis suggests that the stress drops and rupture properties of these events are typical for tectonic earthquakes in the western US. While regional station coverage is sparse in this remote study region, the timely installation of a temporary seismometer allows us to detect nearly 70,000 earthquakes over a 40-month time period when the seismic activity is highest. Such immense productivity is difficult to reconcile with current understanding of crustal deformation in the region and may be facilitated by local hydrothermal processes and earthquake triggering at the transitional intersection of subparallel fault systems.

Sequential order dependent dark-exciton modulation in bi-layered TMD heterostructure

We report the emergence of dark-excitons in transition-metal-dichalcogenide (TMD) heterostructures that strongly rely on the stacking sequence, i.e., momentum-dark K-Q exciton located exclusively at the top layer of the heterostructure. The feature stems from band renormalization and is distinct from those of typical neutral excitons or trions, regardless of materials, substrates, and even homogeneous bilayers, which is further confirmed by scanning tunneling spectroscopy. To understand the unusual stacking sequence, we introduce the excitonic Elliot formula by imposing strain exclusively on the top layer that could be a consequence of the stacking process. We further find that the intensity ratio of Q- to K-excitons in the same layer is inversely proportional to laser power, unlike for conventional K-K excitons. This can be a metric for engineering the intensity of dark K-Q excitons in TMD heterostructures, which could be useful for optical power switches in solar panels.

Wing and tail feather damage in Western Common Kingfishers Alcedo atthis ispida in relation to moult

ABSTRACT Feathers have to be moulted to repair sustained damage. Our objective is to understand the relationship between the frequency of feather damage, feather sturdiness and moult sequence. Damage was recorded in five flight feather tracts for over 2000 Common Kingfishers Alcedo atthis ispida captured during a population study in northwestern Germany. We found that, of the feather tracts studied before the first moult, the tail feathers sustained most wear and damage, especially the more sturdily built outermost ones. Nevertheless, the probability of moulting a rectrix decreased from the central pair to the outside, while the damage risk increased. The sturdy distal primaries and the more lightly built innermost secondaries were the remiges with the highest frequency of damage, but not the most severe damage, while a row of midwing secondaries and primaries had the lowest damage risk. Where remiges had been retained when moult was suspended at the beginning of winter, about 75% of unmoulted feathers belonged to this low-risk group. The distal alula feather and the outermost primary covert had damage rates comparable to the low-risk row of remiges. Feather damage in the wings does not accumulate evenly over time, but increased markedly from March to April, coinciding with courtship and nest excavation, especially in females. Ultraviolet light seems to be an important factor for the observed feather deterioration, but is not the only one. The Kingfisher’s unusual moult sequence of remiges and primary coverts matches the distribution pattern of feather damage, but the sequence of the first tail-feather moult does not. Very few previous studies have investigated the relationship between patterns of feather damage and moult sequence. We hope this work encourages more investigation of this subject.

Twin anemia polycythemia sequence in discordant dichorionic twins.

A 23-year-old primiparous woman with spontaneous dichorionic pregnancy was diagnosed by early ultrasonography. She developed hypertensive disorder of pregnancy at 27 weeks of gestation. At 29 weeks and 3 days of gestation, she was transferred to our perinatal center due to increasing discrepancy between the fetal weights (fetus A 1203 g, fetus B 989 g). Notably, polyhydramnios-oligohydramnios sequence was not observed. An emergency cesarean section was performed at 31 weeks 1 day of gestation because of elevated liver enzyme levels. Two male neonates were delivered with birth weights of 1413 and 1098 g, respectively. At birth, twin A was peripherally cyanotic with hemoglobin of 26.4 g/dL and a reticulocyte count of 4.1%. He was treated using partial exchange transfusion for polycythemia. Twin B was pale with hemoglobin of 7.8 g/dL and a reticulocyte count of 20.5%; thus, an emergent red blood cell transfusion was performed for anemia. Based on their hematological values, the twins were diagnosed with twin anemia polycythemia sequence (TAPS). A marked difference in the coloration of the maternal surface was observed in the two placentas on a macroscopic examination (Fig. 1); however, no vascular anastomosis was detected during dye studies. Microscopic histopathology revealed two amniotic layers and two chorionic layers, which confirmed dichorionicity. Recent literature reviews reported that twin-to-twin transfusion syndrome (TTTS) or TAPS occurs in dichorionic twin placentas with evidence of vascular anastomoses, although it is extremely rare.1Kanagaretnam D. Nayyar R. Zen M. Twin anemia polycythemia sequence in dichorionic diamniotic twins: a case report and review of the literature.Clin Case Rep. 2021; 9e04184Crossref Scopus (1) Google Scholar, 2Lanna M. Faiola S. Casati D. Rustico M.A. Twin-twin transfusion syndrome in dichorionic twin pregnancy: rare but not impossible.Ultrasound Obstet Gynecol. 2019; 54: 412-418Crossref Scopus (2) Google Scholar, 3Zilliox M. Koch A. Farve R. Sananes N. Unusual twin anemia-polycythemia sequence in a dichorionic diamniotic pregnancy.J Gynecol Obstet Hum Reprod. 2019; 48: 359-361Crossref Scopus (4) Google Scholar Miniscule anastomoses undetectable by a dye study may have been present in our dichorionic twins. Prenatal diagnosis, close monitoring, appropriate early delivery, and postnatal management are necessary to improve the outcomes of TTTS and TAPS. Thus, this report highlights the importance of prenatal recognition and postnatal confirmation of TTTS or TAPS, regardless of chorionicity. S.H. and S.I. drafted the initial manuscript. S.H., S.I. and S.T. treated the patient, and contributed to the acquisition of clinical data and imaging. M.Y. performed pathological evaluation. S. Y. supervised the manuscript. All authors approved the final manuscript. The authors have no conflicts of interest to declare. We thank the patient's parents for their kind cooperation. We also thank Dr. Chizen Tarui, Department of Neonatology, and Dr. Tomoko Kibara and Megumi Kaneko, Department of Obstetrics, in Hyogo Prefectural Kobe Children's Hospital for their support.

The star in RNO 54: A possible post-FUor with a short faint jet

Aims. The aim of the present study is to analyze the spectra of an unusual pre-main sequence star in the cometary nebula RNO 54, which is suspected by several researchers to be a FUori-like object. Methods. We performed long-slit spectroscopy of the star using the 6m telescope with the SCORPIO-2 multi-mode focal reducer. Results. We discover a short (~4″ or ~6000 AU) and faint emission shock-excited jet from this star, probably oriented toward the long axis of the nebular ellipse. The spectral type of the star is estimated as G0-2 II; we confirm the split of the Li I absorption line, which is a typical sign indicating a FUori-like spectrum. Our analysis of the available data reveals an almost null photometric variability over at least the last 20 years. The lower limit of the bolometric luminosity of the star is estimated as 300 L⊙. Our study supports the classification of RNO 54 as a FUor-like star in the long post-outburst stage.

Telomerase RNA gene paralogs in plants - the usual pathway to unusual telomeres.

Telomerase, telomeric DNA and associated proteins together represent a complex, finely tuned and functionally conserved mechanism that ensures genome integrity by protecting and maintaining chromosome ends. Changes in its components can threaten an organism's viability. Nevertheless, molecular innovation in telomere maintenance has occurred multiple times during eukaryote evolution, giving rise to species/taxa with unusual telomeric DNA sequences, telomerase components or telomerase-independent telomere maintenance. The central component of telomere maintenance machinery is telomerase RNA (TR) as it templates telomere DNA synthesis, its mutation can change telomere DNA and disrupt its recognition by telomere proteins, thereby leading to collapse of their end-protective and telomerase recruitment functions. Using a combination of bioinformatic and experimental approaches, we examine a plausible scenario of evolutionary changes in TR underlying telomere transitions. We identified plants harbouring multiple TR paralogs whose template regions could support the synthesis of diverse telomeres. In our hypothesis, formation of unusual telomeres is associated with the occurrence of TR paralogs that can accumulate mutations, and through their functional redundancy, allow for the adaptive evolution of the other telomere components. Experimental analyses of telomeres in the examined plants demonstrate evolutionary telomere transitions corresponding to TR paralogs with diverse template regions.

Structural basis of regioselective tryptophan dibromination by the single-component flavin-dependent halogenase AetF.

The flavin-dependent halogenase (FDH) AetF successively brominates tryptophan at C5 and C7 to generate 5,7-dibromotryptophan. In contrast to the well studied two-component tryptophan halogenases, AetF is a single-component flavoprotein monooxygenase. Here, crystal structures of AetF alone and in complex with various substrates are presented, representing the first experimental structures of a single-component FDH. Rotational pseudosymmetry and pseudomerohedral twinning complicated the phasing of one structure. AetF is structurally related to flavin-dependent monooxygenases. It contains two dinucleotide-binding domains for binding the ADP moiety with unusual sequences that deviate from the consensus sequences GXGXXG and GXGXXA. A large domain tightly binds the cofactor flavin adenine dinucleotide (FAD), while the small domain responsible for binding the nicotinamide adenine dinucleotide (NADP) is unoccupied. About half of the protein forms additional structural elements containing the tryptophan binding site. FAD and tryptophan are about 16 Å apart. A tunnel between them presumably allows diffusion of the active halogenating agent hypohalous acid from FAD to the substrate. Tryptophan and 5-bromotryptophan bind to the same site but with a different binding pose. A flip of the indole moiety identically positions C5 of tryptophan and C7 of 5-bromotryptophan next to the tunnel and to catalytic residues, providing a simple explanation for the regioselectivity of the two successive halogenations. AetF can also bind 7-bromotryptophan in the same orientation as tryptophan. This opens the way for the biocatalytic production of differentially dihalogenated tryptophan derivatives. The structural conservation of a catalytic lysine suggests a way to identify novel single-component FDHs.