The structure of the CstF-77 homodimer provides insights into CstF assembly

The cleavage stimulation factor (CstF) is essential for the first step of poly(A) tail formation at the 3' ends of mRNAs. This heterotrimeric complex is built around the 77-kDa protein bridging both CstF-64 and CstF-50 subunits. We have solved the crystal structure of the 77-kDa protein from Encephalitozoon cuniculi at a resolution of 2 Å. The structure folds around 11 Half-a-TPR repeats defining two domains. The crystal structure reveals a tight homodimer exposing phylogenetically conserved areas for interaction with protein partners. Mapping experiments identify the C-terminal region of Rna14p, the yeast counterpart of CstF-77, as the docking domain for Rna15p, the yeast CstF-64 homologue

3D measurements of inclined vortex rings interacting with a density stratification

Vortex rings are coherent vortical structures that dominate the dynamics of numerous flows as they are generated each time an impulsive jet occurs in a homogeneous fluid. They are also considered as elementary bricks of turbulence. Their faculty to propagate along their revolution axis by self-induction confers to such structures interesting transport properties, namely, transport of momentum, mass and heat. They are therefore often qualified as good candidates for mixing. From this perspective, the present study addresses the interaction of a vortex ring with a density stratification in order to get a better understanding of the subsequent mixing mechanisms. A new 3D time-resolved technique is used and gives a highlight at short timescale on the 3D vorticity reorganization and at larger timescale on the 3D patterns of internal gravity waves forced by the impacting/penetrating vortex. The influence of the Reynolds number of the vortex ring and its angle of attack relative to isopycnals will be detailed

Dynamics of an inclined Vortex Ring interacting with a density stratification

Vortex Rings are coherent vortical structures that dominate the dynamics of numerous flows as they are generated each time an impulsive jet occurs in a homogeneous fluid (for instance, plumes can be considered as Vortex Rings). Such structures have the faculty to self-propagate along their revolution axis, conferring them capacities of transport and mixing that could be exploited. Among applications, one can mention nuclear safety and the need to mix fluids of different density to prevent explosion hazard. The scope of the present study is to identify and evaluate the mixing mechanisms associated with a Vortex Ring interacting with a density stratification, in particular, the reorganization of the flow and the generation of internal waves. The influence of the Vortex Ring propagation speed and propagation angle relative to the density gradient on its dynamics and mixing power are studied thanks to 2D and 3D time-resolved TOMO-PIV

Molecular basis of Diamond–Blackfan anemia: structure and function analysis of RPS19

Diamond–Blackfan anemia (DBA) is a rare congenital disease linked to mutations in the ribosomal protein genes rps19, rps24 and rps17. It belongs to the emerging class of ribosomal disorders. To understand the impact of DBA mutations on RPS19 function, we have solved the crystal structure of RPS19 from Pyrococcus abyssi. The protein forms a five α-helix bundle organized around a central amphipathic α-helix, which corresponds to the DBA mutation hot spot. From the structure, we classify DBA mutations relative to their respective impact on protein folding (class I) or on surface properties (class II). Class II mutations cluster into two conserved basic patches. In vivo analysis in yeast demonstrates an essential role for class II residues in the incorporation into pre-40S ribosomal particles. This data indicate that missense mutations in DBA primarily affect the capacity of the protein to be incorporated into pre-ribosomes, thus blocking maturation of the pre-40S particles

Detection of label-free cancer biomarkers using nickel nanoislands and quartz crystal microbalance

We present a technique for the label-free detection and recognition of cancer biomarkers using metal nanoislands intended to be integrated in a novel type of nanobiosensor. His-tagged (scFv)-F7N1N2 is the antibody fragment which is directly immobilized, by coordinative bonds, onto ~5 nm nickel islands, then deposited on the surface of a quartz crystal of a quartz crystal microbalance (QCM) to validate the technique. Biomarker GTPase RhoA was investigated because it has been found to be overexpressed in various tumors and because we have recently isolated and characterized a new conformational scFv which selectively recognizes the active form of RhoA. We implemented a surface chemistry involving an antibiofouling coating of polyethylene glycol silane (PEG-silane) (<2 nm thick) and Ni nanoislands to reach a label-free detection of the active antigen conformation of RhoA, at various concentrations. The methodology proposed here proves the viability of the concept by using Ni nanoislands as an anchoring surface layer enabling the detection of a specific conformation of a protein, identified as a potential cancer biomarker. Hence, this novel methodology can be transferred to a nanobiosensor to detect, at lower time consumption and with high sensitivity, specific biomolecules

Exploring TAR–RNA aptamer loop–loop interaction by X-ray crystallography, UV spectroscopy and surface plasmon resonance

In HIV-1, trans-activation of transcription of the viral genome is regulated by an imperfect hairpin, the trans-activating responsive (TAR) RNA element, located at the 5′ untranslated end of all viral transcripts. TAR acts as a binding site for viral and cellular proteins. In an attempt to identify RNA ligands that would interfere with the virus life-cycle by interacting with TAR, an in vitro selection was previously carried out. RNA hairpins that formed kissing-loop dimers with TAR were selected [Ducongé F. and Toulmé JJ (1999) RNA, 5:1605–1614]. We describe here the crystal structure of TAR bound to a high-affinity RNA aptamer. The two hairpins form a kissing complex and interact through six Watson–Crick base pairs. The complex adopts an overall conformation with an inter-helix angle of 28.1°, thus contrasting with previously reported solution and modelling studies. Structural analysis reveals that inter-backbone hydrogen bonds between ribose 2′ hydroxyl and phosphate oxygens at the stem-loop junctions can be formed. Thermal denaturation and surface plasmon resonance experiments with chemically modified 2′-O-methyl incorporated into both hairpins at key positions, clearly demonstrate the involvement of this intermolecular network of hydrogen bonds in complex stability

A split horseradish peroxidase for detection of intercellular protein-protein interactions and sensitive visualization of synapses

Intercellular protein-protein interactions (PPIs) enable communication between cells in diverse biological processes, including cell proliferation, immune responses, infection and synaptic transmission, but they are challenging to visualize because existing techniques1,2,3 have insufficient sensitivity and/or specificity. Here we report split horseradish peroxidase (sHRP) as a sensitive and specific tool for detection of intercellular PPIs. The two sHRP fragments, engineered through screening of 17 cut sites in HRP followed by directed evolution, reconstitute into an active form when driven together by an intercellular PPI, producing bright fluorescence or contrast for electron microscopy. Fusing the sHRP fragments to the proteins neurexin (NRX) and neuroligin (NLG), which bind each other across the synaptic cleft4, enabled sensitive visualization of synapses between specific sets of neurons, including two classes of synapses in the mouse visual system. sHRP should be widely applicable for studying mechanisms of communication between a variety of cell types

Photoinduced ring-opening polymerizations

International audienc

Migration, wintering distribution and habitat use of an endangered tropical seabird, Barau's petrel Pterodroma baraui

Gadfly petrels are strictly oceanic seabirds that range very far from their breeding grounds. Foraging movements outside the breeding season are poorly described. We used global location sensing (GLS) to describe the migration pathways and wintering habitats of Barau’s petrels Pterodroma baraui, an endemic, endangered seabird of Réunion Island (western Indian Ocean). In 2 consecutive years, petrels migrated far eastward, up to 5000 km from their breeding colony, to the central and eastern Indian Ocean. Migration pathways, timing, and wintering areas varied little among individuals, and non-breeding areas were remarkably consistent between years. There was no sexual variation in migration patterns. Barau’s petrels did not occur in the most productive areas of the Indian Ocean (Arabian Gulf and Somalia upwelling region) but instead foraged over warm oligotrophic and mesotrophic waters. Tracked birds consistently occurred in areas with relatively strong and consistent easterly winds, and avoided northern regions with weaker westerly winds. Our results indicate that Barau’s petrels use an expansive wintering area between the western South Equatorial Current and the eastern Equatorial Counter Current, characterised by warm sea surface temperatures (SST) and low productivity. However, wind regimes in the Indian Ocean are strongly influenced by the Asian Monsoon; in this particular area, wind and currents may create a frontal system where prey are aggregated, increasing their accessibility for Barau’s petrels. These results provide important baseline information for conservation, and are useful for the selection of potential marine reserves and the evaluation of effects of pollution or climate change on this highly threatened species