Testimony of Demetrios G. Papademetriou, MPI President, before the Subcommittee on Immigration and Border Security, Committee on the Judiciary, U.S. House of Representatives.

That’s what Pakistan can become, warns Patrick French. (Via Nikhil Mehra.)

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The U.K. company planning the world’s first tidal-lagoon power station said its next plant may generate electricity at almost half the price.

Japan anticipates that by 2030 clean energy such as solar and hydro will generate slightly more of the nation’s electricity than nuclear power plants.

Japan anticipates that by 2030 clean energy such as solar and hydro will generate slightly more of the nation’s electricity than nuclear power plants.

Iran wants to work toward a draft agreement on a comprehensive solution to a lingering nuclear row with Western powers, the foreign minister said Tuesday.

Iran's deputy foreign minister said nuclear negotiations in Vienna were useful and another round of talks was scheduled over the course of three days in April.

There's a chance for Iran to reach a comprehensive nuclear agreement that would benefit its people if the rights steps are taken, President Obama said Thursday.

Researchers at Johns Hopkins University said Thursday work was ongoing at North Korean nuclear and missile sites, but no imminent threat is apparent.

This woman took a truly nuclear revenge against a company that was up to all kinds of no good. The best part about this revenge, other than the fact that she brought justice to the company, was her added touch of subscribing everyone at the company to hundreds of different email alerts. She left the operation in complete and utter chaos. 

NEED POWER PLANT? A PRAGMATIC APPROACH IS NEED OF THE HOUR

Electric power is a growing need in a developing...

This report outlines the customisation opportunities for IUCLID version 6. It also gives an overview of what IUCLID offers to regulatory bodies and industry as a key application to record, store, maintain and exchange data on chemicals. IUCLID is used in a variety of countries and regulatory contexts, therefore the report describes to which extent it is customisable to facilitate the management of chemical data across these contexts.

Lockdown in Tamil Nadu: 800 guest workers stage protest at Kudankulam Nuclear Power Plant, attack cops

A method is presented for the automatic building of nucleotide chains into electron density which is fast enough to be used in interactive model-building software. Likely nucleotides lying in the vicinity of the current view are located and then grown into connected chains in a fraction of a second. When this development is combined with existing tools, assisted manual model building is as simple as or simpler than for proteins.

Factor for inversion stimulation (Fis) is a versatile bacterial nucleoid-associated protein that can directly bind and bend DNA to influence DNA topology. It also plays crucial roles in regulating bacterial virulence factors and in optimizing bacterial adaptation to various environments. Fis from Pseudomonas aeruginosa (PA4853, referred to as PaFis) has recently been found to be required for virulence by regulating the expression of type III secretion system (T3SS) genes. PaFis can specifically bind to the promoter region of exsA, which functions as a T3SS master regulator, to regulate its expression and plays an essential role in transcription elongation from exsB to exsA. Here, the crystal structure of PaFis, which is composed of a four-helix bundle and forms a homodimer, is reported. PaFis shows remarkable structural similarities to the well studied Escherichia coli Fis (EcFis), including an N-terminal flexible loop and a C-terminal helix–turn–helix (HTH) motif. However, the critical residues for Hin-catalyzed DNA inversion in the N-terminal loop of EcFis are not conserved in PaFis and further studies are required to investigate its exact role. A gel-electrophoresis mobility-shift assay showed that PaFis can efficiently bind to the promoter region of exsA. Structure-based mutagenesis revealed that several conserved basic residues in the HTH motif play essential roles in DNA binding. These structural and biochemical studies may help in understanding the role of PaFis in the regulation of T3SS expression and in virulence.

The title tetra­nuclear stannoxane, [Sn4(C6H5)8(C6H4NO3)4O2]·1.5CHCl3·solvent, crystallized with two independent complex mol­ecules, A and B, in the asymmetric unit together with 1.5 mol­ecules of chloro­form. There is also a region of disordered electron density, which was corrected for using the SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9–18]. The oxo-tin core of each complex is in a planar `ladder' arrangement and each Sn atom is fivefold SnO3C2 coordinated, with one tin centre having an almost perfect square-pyramidal coordination geometry, while the other three Sn centres have distorted shapes. In the crystal, the complex mol­ecules are arranged in layers, composed of A or B complexes, lying parallel to the bc plane. The complex mol­ecules are linked by a number of C—H⋯O hydrogen bonds within the layers and between the layers, forming a supra­molecular three-dimensional structure.

Reaction of 2-(anthracen-9-yl)phenol (HOPhAn, 1) with divalent Yb[N(SiMe3)2]2·2THF in THF–toluene mixtures affords the mixed-valence YbII–YbIII dimer {[2-(anthracen-9-yl)phenolato-κO]bis­(tetra­hydro­furan)­ytterbium(III)}-tris­[μ-2-(anthracen-9-yl)phenolato]-κ4O:O;κO:1,2-η,κO-{[2-(anthracen-9-yl)phenolato-κO]ytterbium(II)} toluene tris­olvate, [Yb2(C20H13O)5(C4H8O)2]·3C7H7 or [YbIII(THF)2(OPhAn)](μ-OPhAn)3[YbII(OPhAn)]·3C7H7 (2), as the major product. It crystallized as a toluene tris­olvate. The Yb—O bond lengths in the crystal structure of this dimer clearly identify the YbII and YbIII centres. Inter­estingly, the formally four-coordinate YbII centre shows a close contact with one anthracene C—C bond of a bridging OPhAn ligand, bringing the formal coordination number to five.

The complete mol­ecule of the binuclear title complex, bis­[μ-1H-1,2,4-triazole-5(4H)-thione-κ2S:S]bis­{(thio­cyanato-κS)[1H-1,2,4-triazole-5(4H)-thione-κS]silver(I)}, [Ag2(SCN)2(C2H3N3S)4], is generated by crystallographic inversion symmetry. The independent triazole-3-thione ligands employ the exocyclic-S atoms exclusively in coordination. One acts as a terminal S-ligand and the other in a bidentate (μ2) bridging mode to provide a link between two AgI centres. Each AgI atom is also coordinated by a terminal S-bound thio­cyanate ligand, resulting in a distorted AgS4 tetra­hedral coordination geometry. An intra­molecular N—H⋯S(thio­cyanate) hydrogen bond is noted. In the crystal, amine-N—H⋯S(thione), N—H⋯N(triazol­yl) and N—H⋯N(thio­cyanate) hydrogen bonds give rise to a three-dimensional architecture. The packing is consolidated by triazolyl-C—H⋯S(thio­cyanate), triazolyl-C—H⋯N(thiocyanate) and S⋯S [3.2463 (9) Å] inter­actions as well as face-to-face π–π stacking between the independent triazolyl rings [inter-centroid separation = 3.4444 (15) Å]. An analysis of the calculated Hirshfeld surfaces shows the three major contributors are due to N⋯H/H⋯N, S⋯H/H⋯S and C⋯H/H⋯C contacts, at 35.8, 19.4 and 12.7%, respectively; H⋯H contacts contribute only 7.6% to the overall surface.

A copper(II) dimer with the deprotonated anion of 2-bromo­nicotinic acid (2-BrnicH), namely, tetrakis(μ-2-bromonicotinato-κ2O:O')bis[aquacopper(­II)](Cu—Cu), [Cu2(H2O)2(C6H3BrNO2)4] or [Cu2(H2O)2(2-Brnic)4], (1), was prepared by the reaction of copper(II) chloride dihydrate and 2-bromo­nicotinic acid in water. The copper(II) ion in 1 has a distorted square-pyramidal coordination environment, achieved by four carboxyl­ate O atoms in the basal plane and the water mol­ecule in the apical position. The pair of symmetry-related copper(II) ions are connected into a centrosymmetric paddle-wheel dinuclear cluster [Cu⋯Cu = 2.6470 (11) Å] via four O,O'-bridging 2-bromo­nicotinate ligands in the syn-syn coordination mode. In the extended structure of 1, the cluster mol­ecules are assembled into an infinite two-dimensional hydrogen-bonded network lying parallel to the (001) plane via strong O—H⋯O and O—H⋯N hydrogen bonds, leading to the formation of various hydrogen-bond ring motifs: dimeric R22(8) and R22(16) loops and a tetra­meric R44(16) loop. The Hirshfeld surface analysis was also performed in order to better illustrate the nature and abundance of the inter­molecular contacts in the structure of 1.

The whole mol­ecule of the cadmium(II) complex, di­iodido­{N,N',N'',N'''-[pyrazine-2,3,5,6-tetra­yltetra­kis­(methyl­ene)]tetra­kis­(N-methyl­aniline)-κ3N2,N1,N6}cadmium(II), [CdI2(C36H40N6)], (I), of the ligand N,N',N'',N'''-[pyrazine-2,3,5,6-tetra­yltetra­kis­(methyl­ene)]tetra­kis­(N-methyl­aniline) (L), is generated by a twofold rotation symmetry; the twofold axis bis­ects the cadmium atom and the nitro­gen atoms of the pyrazine ring. The ligand coordinates in a mono-tridentate manner and the cadmium atom has a fivefold CdN3I2 coordination environment with a distorted shape. In the zinc(II) complex, dichlorido{N,N',N'',N'''-[pyrazine-2,3,5,6-tetra­yltetra­kis­(methyl­ene)]tetra­kis­(N-methyl­aniline)-κ3N2,N1,N6}zinc(II) di­chloro­methane 0.6-solvate, [ZnCl2(C36H40N6)]·0.6CH2Cl2, (II), ligand L also coordinates in a mono-tridentate manner and the zinc atom has a fivefold ZnN3Cl2 coordination environment with a distorted shape. It crystallized as a partial di­chloro­methane solvate. In the crystal of I, the complex mol­ecules are linked by weak C—H⋯I contacts, forming ribbons propagating along [100]. In the crystal of II, the complex mol­ecules are linked by a series of C—H⋯π inter­actions, forming layers lying parallel to the (1overline{1}1) plane. In the crystals of both compounds there are metal–halide⋯π(pyrazine) contacts present. The Hirshfeld analyses confirm the importance of the C—H⋯halide contacts in the crystal packing of both compounds.

The title pyrazine dicarboxamide ligand, N2,N3-bis­(quinolin-8-yl)pyrazine-2,3-dicarboxamide (H2L1), C24H16N6O2, has a twisted conformation with the outer quinoline groups being inclined to the central pyrazine ring by 9.00 (6) and 78.67 (5)°, and by 79.94 (4)° to each other. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming layers parallel to the (10overline{1}) plane, which are in turn linked by offset π–π inter­actions [inter­centroid distances 3.4779 (9) and 3.6526 (8) Å], forming a supra­molecular three-dimensional structure. Reaction of the ligand H2L1 with Cu(ClO4)2 in aceto­nitrile leads to the formation of the binuclear complex, [μ-(3-{hy­droxy[(quinolin-8-yl)imino]­meth­yl}pyrazin-2-yl)[(quinolin-8-yl)imino]­methano­lato]bis­[diaceto­nitrile­copper(II)] tris­(per­chlor­ate) aceto­nitrile disolvate, [Cu2(C24H15N6O2)(CH3CN)4](ClO4)3·2CH3CN or [Cu2(HL1−)(CH3CN)4](ClO4)3·2CH3CN (I). In the cation of complex I, the ligand coordinates to the copper(II) atoms in a bis-tridentate fashion. A resonance-assisted O—H⋯O hydrogen bond is present in the ligand; the position of this H atom was located in a difference-Fourier map. Both copper(II) atoms are fivefold coordinate, being ligated by three N atoms of the ligand and by the N atoms of two aceto­nitrile mol­ecules. The first copper atom has a perfect square-pyramidal geometry while the second copper atom has a distorted shape. In the crystal, the cation and perchlorate anions are linked by a number of C—H⋯O hydrogen bonds, forming a supra­molecular three-dimensional structure.

The new heterometallic complex, aqua-1κO-bis­(μ2-2-imino­methyl-6-meth­oxy­phenolato-1κ2O1,O6:2κ2O1,N)bis­(thio­cyanato-1κN)calcium(II)copper(II), [CaCu(C8H8NO2)2(NCS)2(H2O)], has been synthesized using a one-pot reaction of copper powder, calcium oxide, o-vanillin and ammonium thio­cyanate in methanol under ambient conditions. The Schiff base ligand (C8H9NO2) is generated in situ from the condensation of o-vanillin and ammonia, which is released from the initial NH4SCN. The title compound consists of a discrete binuclear mol­ecule with a {Cu(μ-O)2Ca} core, in which the Cu⋯Ca distance is 3.4275 (6) Å. The coordination geometries of the four-coordinate copper atom in the [CuN2O2] chromophore and the seven-coordinate calcium atom in the [CaO5N2] chromophore can be described as distorted square planar and penta­gonal bipyramidal, respectively. In the crystal, O—H⋯S hydrogen bonds between the coordinating water mol­ecules and thio­cyanate groups form a supra­molecular chain with a zigzag-shaped calcium skeleton.

Herein the nucleation pathway of conformational polymorphs was revealed by studying the relationships and distinctions among a series of α,ω-alkanedicarboxylic acids [HOOC–(CH2)n−2–COOH, named DAn, where n = 5, 7, 9, 11, 13, 15] in the solid state and in solution. Their polymorphic outcomes, with the exception of DA5, show solvent dependence: form I with conformation I crystallizes from solvents with hydrogen-bond donating (HBD) ability, whereas form II with conformation II crystallizes preferentially from solvents with no HBD ability. In contrast, form II of DA5 does not crystallize in any of the solvents used. Quantum mechanical computation showed that there is no direct conformational link between the solvents and the resultant polymorphic outcomes. Surprisingly, solute aggregates were found in no-HBD solvents by Fourier transform infrared spectroscopy, and only monomers could be detected in HBD solvents, suggesting stronger solvation. Furthermore, it was found that all six compounds including DA5 followed the same pattern in solution. Moreover, crystal-packing efficiency calculations and stability tests stated that dimorphs of DA5 bear a greater stability difference than others. These suggest that the rearrangement from conformation II to I could not be limited by hard desolvation in HBD solvents, where form I was also obtained. In other systems, metastable II was produced in the same solvents, probably as a result of the rearrangement being limited by hard desolvation. In this work, a comparative study uncovers the proposed nucleation pathway: difficulty in desolvation has a remarkable effect on the result of rearrangement and nucleation outcome.

TatD has been thoroughly investigated as a DNA-repair enzyme and an apoptotic nuclease, and still-unknown TatD-related DNases are considered to play crucial cellular roles. However, studies of TatD from Gram-positive bacteria have been hindered by an absence of atomic detail and the resulting inability to determine function from structure. In this study, an X-ray crystal structure of SAV0491, which is the TatD enzyme from the Gram-positive bacterium Staphylococcus aureus (SaTatD), is reported at a high resolution of 1.85 Å with a detailed atomic description. Although SaTatD has the common TIM-barrel fold shared by most TatD-related homologs, and PDB entry 2gzx shares 100% sequence identity with SAV0491, the crystal structure of SaTatD revealed a unique binding mode of two phosphates interacting with two Ni2+ ions. Through a functional study, it was verified that SaTatD has Mg2+-dependent nuclease activity as a DNase and an RNase. In addition, structural comparison with TatD homologs and the identification of key residues contributing to the binding mode of Ni2+ ions and phosphates allowed mutational studies to be performed that revealed the catalytic mechanism of SaTatD. Among the key residues composing the active site, the acidic residues Glu92 and Glu202 had a critical impact on catalysis by SaTatD. Furthermore, based on the binding mode of the two phosphates and structural insights, a putative DNA-binding mode of SaTatD was proposed using in silico docking. Overall, these findings may serve as a good basis for understanding the relationship between the structure and function of TatD proteins from Gram-positive bacteria and may provide critical insights into the DNA-binding mode of SaTatD.

Nucleation of crystals from solution is fundamental to many natural and industrial processes. In this work, the molecular mechanism of conformational polymorphism nucleation and the links between the molecular conformation in solutions and in crystals were investigated in detail by using 5-nitro­furazone as the model compound. Different polymorphs were prepared, and the conformations in solutions obtained by dissolving different polymorphs were analysed and compared. The solutions of 5-nitro­furazone were proven to contain multiple conformers through quantum chemical computation, Raman spectra analysis, 2D nuclear Overhauser effect spectroscopy spectra analysis and molecular dynamics simulation. The conformational evolution and desolvation path was illustrated according to the 1H NMR spectra of solutions with different concentrations. Finally, based on all the above analysis, the molecular conformational evolution path during nucleation of 5-nitro­furazone was illustrated. The results presented in this work shed a new light on the molecular mechanism of conformational polymorphism nucleation in solution.

The Y128F single mutant of p-hydroxymandelate oxidase (Hmo) is capable of oxidizing mandelate to benzoate via a four-electron oxidative decarboxylation reaction. When benzoylformate (the product of the first two-electron oxidation) and hydrogen peroxide (an oxidant) were used as substrates the reaction did not proceed, suggesting that free hydrogen peroxide is not the committed oxidant in the second two-electron oxidation. How the flavin mononucleotide (FMN)-dependent four-electron oxidation reaction takes place remains elusive. Structural and biochemical explorations have shed new light on this issue. 15 high-resolution crystal structures of Hmo and its mutants liganded with or without a substrate reveal that oxidized FMN (FMNox) possesses a previously unknown electrophilic/nucleophilic duality. In the Y128F mutant the active-site perturbation ensemble facilitates the polarization of FMNox to a nucleophilic ylide, which is in a position to act on an α-ketoacid, forming an N5-acyl-FMNred dead-end adduct. In four-electron oxidation, an intramolecular disproportion­ation reaction via an N5-alkanol-FMNred C'α carbanion intermediate may account for the ThDP/PLP/NADPH-independent oxidative decarboxylation reaction. A synthetic 5-deaza-FMNox cofactor in combination with an α-hydroxyamide or α-ketoamide biochemically and structurally supports the proposed mechanism.

As one of the most important phenomena in crystallization, the crystal nucleation process has always been the focus of research. In this work, influences of pre-assembly species and the desolvation process on the crystal nucleation process were studied. p-Nitro­benzoic acid (PNBA) was taken as a model compound to investigate the relationship between solution chemistry and nucleation kinetics in seven different solvents. One unsolvated form and four solvates of PNBA were obtained and one of the solvates was newly discovered. The nucleation behaviours and nucleation kinetics of PNBA in the seven solvents were studied and analyzed. Density functional theory (DFT) and solvation energy calculation were adopted to evaluate the strength of solute–solvent interactions. Vibrational spectroscopy combined with molecular simulation was applied to reveal the pre-assembly species in the solution. Based on these results, a comprehensive understanding of the relationship between molecular structure, crystal structure, solution chemistry and nucleation dynamics was proposed and discussed. It was found that the structural similarity between solution chemistry and crystal structure, the interaction between specific sites and the overall strength of solvation will jointly affect the nucleation process.

Obtaining crystals and solving the phase problem remain major hurdles encountered by bio-crystallographers in their race to obtain new high-quality structures. Both issues can be overcome by the crystallophore, Tb-Xo4, a lanthanide-based molecular complex with unique nucleating and phasing properties. This article presents examples of new crystallization conditions induced by the presence of Tb-Xo4. These new crystalline forms bypass crystal defects often encountered by crystallographers, such as low-resolution diffracting samples or crystals with twinning. Thanks to Tb-Xo4's high phasing power, the structure determination process is greatly facilitated and can be extended to serial crystallography approaches.

The unique nucleating and phasing capabilities of the crystallophore, Tb-Xo4, are illustrated through challenging cases.

This paper reports on the two-scale fractal structure of chromatin organization in the nucleus of the HeLa cell.

The crystal structure of Pseudomonas aeruginosa Fis is composed of an N-terminal flexible loop and a C-terminal helix–turn–helix motif.

One problem in unraveling the mystery of quasars is that many (perhaps most) quasar nuclei seem to be surrounded by a torus of obscuring dust that makes them difficult to study.

The post The origins of a torus in a galactic nucleus appeared first on Smithsonian Insider.

Osiris Martinez-Guzman, Mathilda M. Willoughby, Arushi Saini, Jonathan V. Dietz, Iryna Bohovych, Amy E. Medlock, Oleh Khalimonchuk, and Amit R. Reddi

Heme is a cofactor and signaling molecule that is essential for much of aerobic life. All heme-dependent processes in eukaryotes require that heme is trafficked from its site of synthesis in the mitochondria to hemoproteins located throughout the cell. However, the mechanisms governing the mobilization of heme out of the mitochondria, and the spatio-temporal dynamics of these processes, are poorly understood. Herein, using genetically encoded fluorescent heme sensors, we developed a live cell assay to monitor heme distribution dynamics between the mitochondrial inner-membrane, where heme is synthesized, and the mitochondrial matrix, cytosol, and nucleus. Surprisingly, heme trafficking to the nucleus is ~25% faster than to the cytosol or mitochondrial matrix, which are nearly identical, potentially supporting a role for heme as a mitochondrial-nuclear retrograde signal. Moreover, we discovered that the heme synthetic enzyme, 5-aminolevulinic acid synthase (ALAS), and GTPases in control of the mitochondrial dynamics machinery, Mgm1 and Dnm1, and ER contact sites, Gem1, regulate the flow of heme between the mitochondria and nucleus. Overall, our results indicate that there are parallel pathways for the distribution of bioavailable heme.

Kasun Buddika, Ishara S. Ariyapala, Mary A. Hazuga, Derek Riffert, and Nicholas S. Sokol

Stressed cells downregulate translation initiation and assemble membrane-less foci termed stress granules (SGs). Extensively characterized in cultured cells, the existence of such structures in stressed adult stem cell pools remain poorly characterized. Here we report that Drosophila orthologs of mammalian SG components AGO1, ATX2, CAPRIN, eIF4E, FMRP, G3BP, LIN-28, PABP, and TIAR are enriched in adult intestinal progenitor cells where they accumulate in small cytoplasmic messenger ribonucleoprotein complexes (mRNPs). Treatment with sodium arsenite or rapamycin reorganized these mRNPs into large cytoplasmic granules. Formation of these intestinal progenitor stress granules (IPSGs) depended on polysome disassembly, led to translational downregulation, and was reversible. While canonical SG nucleators ATX2 and G3BP were sufficient for IPSG formation in the absence of stress, neither of them, nor TIAR, either individually or collectively, were required for stress-induced IPSG formation. This work therefore finds that IPSGs do not assemble via a canonical mechanism, raising the possibility that other stem cell populations employ a similar stress-response mechanism.

Kelly L. Dunlevy, Valentina Medvedeva, Jade E. Wilson, Mohammed Hoque, Trinity Pellegrin, Adam Maynard, Madison M. Kremp, Jason S. Wasserman, Andrey Poleshko, and Richard A. Katz

A large fraction of epigenetically silent heterochromatin is anchored to the nuclear periphery via "tethering proteins" that function to bridge heterochromatin and the nuclear membrane or nuclear lamina. We identified previously a human tethering protein, PRR14, that binds heterochromatin through an N-terminal domain, but the mechanism and regulation of nuclear lamina association remained to be investigated. Here we identify an evolutionarily conserved PRR14 nuclear lamina binding domain (LBD) that is both necessary and sufficient for positioning of PRR14 at the nuclear lamina. We also show that PRR14 associates dynamically with the nuclear lamina, and provide evidence that such dynamics are regulated through phosphorylation-dephosphorylation of the LBD. Furthermore, we identified a PP2A phosphatase recognition motif within the evolutionarily conserved PRR14 C-terminal Tantalus domain. Disruption of this motif affected PRR14 localization to the nuclear lamina. The overall findings demonstrate a heterochromatin anchoring mechanism whereby the PRR14 tether simultaneously binds heterochromatin and the nuclear lamina through two separable, modular domains. The findings also describe an optimal PRR14 LBD fragment that could be used for efficient targeting of fusion proteins to the nuclear lamina.

Isabella Guardamagna, Elisabetta Bassi, Monica Savio, Paola Perucca, Ornella Cazzalini, Ennio Prosperi, and Lucia A. Stivala

Assessing DNA repair is an important endpoint to study the DNA damage response for investigating the biochemical mechanisms of this process and the efficacy of chemotherapy, which often uses DNA damaging compounds. Numerous in vitro methods to biochemically characterize DNA repair mechanisms have been developed so far. However, they show some limitations mainly due to the lack of chromatin organization. Here we describe a functional cell-free system to study DNA repair synthesis in vitro, using G1-phase nuclei isolated from human cells treated with different genotoxic agents. Upon incubation in the correspondent damage-activated cytosolic extracts, containing biotin-16-dUTP, nuclei are able to initiate DNA repair synthesis. The use of specific DNA synthesis inhibitors markedly decreased biotinylated dUTP incorporation, indicating the specificity of the repair response. Exogenously added human recombinant PCNA protein, but not the sensors of UV-DNA damage DDB2 or DDB1, stimulated UVC induced dUTP incorporation. In contrast, a DDB2^PCNA- mutant protein, unable to associate with PCNA, interfered with DNA repair synthesis. Given its responsiveness to different type of DNA lesions, this system offers an additional tool to study DNA repair mechanisms.

The positional change of nitro­gen-7 of the RNA constituent guanosine to the bridgehead position-5 leads to the base-modified nucleoside 5-aza-7-de­aza­guanosine. Contrary to guanosine, this mol­ecule cannot form Hoogsteen base pairs and the Watson–Crick proton donor site N3—H becomes a proton-acceptor site. This causes changes in nucleobase recognition in nucleic acids and has been used to construct stable `all-purine' DNA and DNA with silver-mediated base pairs. The present work reports the single-crystal X-ray structure of 7-iodo-5-aza-7-de­aza­guanosine, C10H12IN5O5 (1). The iodinated nucleoside shows an anti conformation at the glycosylic bond and an N conformation (O4'-endo) for the ribose moiety, with an anti­periplanar orientation of the 5'-hy­droxy group. Crystal packing is controlled by inter­actions between nucleobase and sugar moieties. The 7-iodo substituent forms a contact to oxygen-2' of the ribose moiety. Self-pairing of the nucleobases does not take place. A Hirshfeld surface analysis of 1 highlights the contacts of the nucleobase and sugar moiety (O—H⋯O and N—H⋯O). The concept of pK-value differences to evaluate base-pair stability was applied to purine–purine base pairing and stable base pairs were predicted for the construction of `all-purine' RNA. Furthermore, the 7-iodo substituent of 1 was functionalized with benzo­furan to detect motional constraints by fluorescence spectroscopy.

Simon L. Bullock
Apr 6, 2020; 133:jcs245134-jcs245134
Meeting Report

Focused attention by world leaders is needed to address the substantial challenges posed by disposal of spent nuclear fuel from reactors and high-level radioactive waste from processing such fuel for military or energy purposes.

The 2011 Fukushima Daiichi nuclear accident should serve as a wake-up call to nuclear plant operators and regulators on the critical importance of measuring, maintaining, and restoring cooling in spent fuel pools during severe accidents and terrorist attacks, says a new report from the National Academies of Sciences, Engineering, and Medicine.

The science questions that could be answered by an electron ion collider (EIC) – a very large-scale particle accelerator – are significant to advancing our understanding of the atomic nuclei that make up all visible matter in the universe, says a new report by the National Academies of Sciences, Engineering, and Medicine.

A new report from the National Academies of Sciences, Engineering, and Medicine recommends changes in the way that the U.S. Department of Energy manages science and technology (S&T) development in order to accelerate the cleanup of radioactive waste and contaminated soil, groundwater, and facilities at U.S. nuclear weapons sites.

A new report from the National Academies of Sciences, Engineering, and Medicine – which reviews a separate report by a federally funded laboratory that examines options for treating low-activity radioactive waste at the Hanford Nuclear Reservation -- is available for public comment until Oct. 31.

In 1943, the town of Hanford in Washington State was selected by the Manhattan Project to be home to the first full-scale plutonium production reactor in the world.

A recent study has assessed the sustainability of different nuclear cycle scenarios in Europe, and suggests trade-offs are required between reducing the amount of uranium fuel needed, costs and proliferation risks.

The Fukushima accident in Japan has sparked international debate on nuclear energy. A new study has identified five factors which may have influenced the contrasting energy policy responses to the incident in the UK and Germany. Following the disaster, the UK is continuing to back nuclear power generation, whilst Germany is withdrawing support.