Structures of T7 bacteriophage portal and tail suggest a viral DNA retention and ejection mechanism

Double-stranded DNA bacteriophages package their genome at high pressure inside a procapsid through the portal, an oligomeric ring protein located at a unique capsid vertex. Once the DNA has been packaged, the tail components assemble on the portal to render the mature infective virion. The tail tightly seals the ejection conduit until infection, when its interaction with the host membrane triggers the opening of the channel and the viral genome is delivered to the host cell. Using high-resolution cryo-electron microscopy and X-ray crystallography, here we describe various structures of the T7 bacteriophage portal and fiber-less tail complex, which suggest a possible mechanism for DNA retention and ejection: a portal closed conformation temporarily retains the genome before the tail is assembled, whereas an open portal is found in the tail. Moreover, a fold including a seven-bladed β-propeller domain is described for the nozzle tail protein.This work was supported by the Ministry of Science, Innovation and Universities of Spain, grants BFU 2014-54181 (to J.L.C.), BFU 2014-53550-P and BFU2017-83720-P (to M.C.), and contracts SEV-2013-0347 (to A.C.) and RYC-2011-09071 (to C.M.). We acknowledge institutional funding through the Spanish Government Centres and Units of Excellence Severo Ochoa and Maria de Maeztu awards to IRB Barcelona (SEV-2015-0500) and IBMB Structural Biology Unit (MDM-2014-0435), respectively, and from the CERCA Programme of the Catalan Government to the IRB Barcelona. This work has also been supported by the European Commission, Horizon 2020 program through iNEXT project (grant number 653706)

Archaeomagnetic and rock magnetic study of six kilns from North Africa (Tunisia and Morocco)

International audienceNew full-vector archaeomagnetic data for North Africa recovered from the study of six kilns, five from Tunisia and one from Morocco, are presented. Archaeological and historical considerations, along with three radiocarbon dates, indicate that the age of the kilns ranges between the 9th and 15th centuries AD. Rock magnetic analyses showed that the principal magnetic carriers are magnetite and low Ti titanomagnetite, along with variable contributions of thermally stable maghemite and a high coercivity phase with low unblocking temperatures. The magnetic mineralogy of the studied material is thermally stable and behaves ideally during archaeointensity experiments. Stepwise alternating field demagnetization isolated a single, stable, characteristic remanence component with very well defined directions at both specimen and structure levels. Mean archaeointensities have been obtained from successful classical Thellier experiments conducted on between five and eight independent samples per kiln. Thermoremanent magnetization (TRM) anisotropy and cooling rate effects upon TRM intensity have been investigated. The results showed that these effects are low for four of the six studied kilns, with differences between the uncorrected and corrected means of less than 3 per cent. For the other two structures differences between the uncorrected and corrected mean site intensities are 4.4 per cent and 5.8 per cent. These results highlight the necessity for TRM anisotropy and cooling rate corrections in archaeomagnetic studies if accurate archaeointensities are to be obtained. The new results suggest that high intensities occurred in Northwest Africa during the 9th century. Although more data are clearly needed to define this period of high intensity, the results are in agreement with the available European archaeointensity data. Acomparison between the newdata, other available archaeomagnetic determinations in nearby locations, and palaeosecular variation (PSV) curves derived from the regional SCHA.DIF.3k and global ARCH3K.1 geomagnetic field models shows good agreement between the new data and directional results derived from the models. However, some differences are observed between geomagnetic field models intensity results and available archaeointensity data for the studied regions. This highlights the need for new data for unexplored regions such as North Africa. The new data presented here better constrains the evolution of the geomagnetic field during historical times in this region. They represent a new step towards the construction of a reference PSV curve for Northwest Africa. Once established, this curve will represent a new dating method for this region

White on blue: A study on underglaze-decorated ceramic tiles from 15th-16th-century Valencian and Sevillian productions

This study characterises and compares tin-opacified underglaze-decorated tiles from Valencian and Sevillian provenances. This technique, where the cobalt and manganese pigments are applied below an opaque white glaze, was used in the Iberian Peninsula between the 14th and early 16th centuries. The chemical and morphological characterisation of the glazes was performed by Optical Microscopy (OM), Scanning Electron Microscopy with Energy-Dispersive X-Ray Spectroscopy (SEM-EDS), μ-Raman Spectroscopy, and μ-Particle-Induced X-Ray Emission (μ-PIXE). Both the morphology of the glazes and their chemical composition allowed for the distinction between the two production centres. Sevillian glazes exhibit a thicker pigment layer, as well as higher SnO2 and lower K2O contents than the Valencian ones. Furthermore, the SEM analysis of cobalt pigment particles identified an interior nucleus rich in Co, Fe and Ni, and an exterior layer rich in Si, Ca, Mg and Na,suggesting that the pigment was used mixed with clay or sand

The effect of Sb-surfactant on GaInP CuPtB type ordering: Assessment through dark field TEM and aberration corrected HAADF imaging

We report on the effect of Sb on the microstructure of GaInP layers grown by metal organic vapor phase epitaxy (MOVPE). These layers exhibit a CuPtB single variant ordering due to the intentional misorientation of the substrate (Ge(001) substrates with 6°misorientation towards the nearest [111] axis). The use of Sb as a surfactant during the GaInP growth does not modify the type of ordering, but it is found that the order parameter (η) decreases with increasing Sb flux. Dark field microscopy reveals a variation of the angle of the antiphase boundaries (APBs) with Sb amount. The microstructure is assessed through high angle annular dark field (HAADF) experiments and image simulation revealing Z-contrast loss in APBs due to the superposition of ordered domains. © the Owner Societies 2017

Simulation of STEM-HAADF image contrast of Ruddlesden-Popper faulted LaNiO₃ thin films

LaNiO3 (LNO) thin films are widely used as electrode materials. Yet, their properties greatly depend on such parameters as strain state and defect density. In this work we present a detailed structural characterization of epitaxial LNO thin films grown on LaAlO3(001). Based on scanning transmission electron microscope - high-angle annular darkfield imaging (STEM-HAADF) contrast analysis and image simulations, Ruddlesden-Popper faulted configurations, with 1/2a relative displacement of defect free perovskite blocks, are atomically modeled and simulated to disentangle the variation of Z-contrast in the experimental image

Simulation of STEM-HAADF image contrast of Ruddlesden-Popper faulted LaNiO₃ thin films

LaNiO3 (LNO) thin films are widely used as electrode materials. Yet, their properties greatly depend on such parameters as strain state and defect density. In this work we present a detailed structural characterization of epitaxial LNO thin films grown on LaAlO3(001). Based on scanning transmission electron microscope - high-angle annular darkfield imaging (STEM-HAADF) contrast analysis and image simulations, Ruddlesden-Popper faulted configurations, with 1/2a relative displacement of defect free perovskite blocks, are atomically modeled and simulated to disentangle the variation of Z-contrast in the experimental image