Probing the (H3-H4)(2) histone tetramer structure using pulsed EPR spectroscopy combined with site-directed spin labelling

The (H3-H4)2 histone tetramer forms the central core of nucleosomes and, as such, plays a prominent role in assembly, disassembly and positioning of nucleosomes. Despite its fundamental role in chromatin, the tetramer has received little structural investigation. Here, through the use of pulsed electron-electron double resonance spectroscopy coupled with site-directed spin labelling, we survey the structure of the tetramer in solution. We find that tetramer is structurally more heterogeneous on its own than when sequestered in the octamer or nucleosome. In particular, while the central region including the H3-H3′ interface retains a structure similar to that observed in nucleosomes, other regions such as the H3 αN helix display increased structural heterogeneity. Flexibility of the H3 αN helix in the free tetramer also illustrates the potential for post-translational modifications to alter the structure of this region and mediate interactions with histone chaperones. The approach described here promises to prove a powerful system for investigating the structure of additional assemblies of histones with other important factors in chromatin assembly/fluidity

Climate Quality Broadband and Narrowband Solar Reflected Radiance Calibration Between Sensors in Orbit

vAs the potential impacts of global climate change become more clear [1], the need to determine the accuracy of climate prediction over decade-to-century time scales has become an urgent and critical challenge. The most critical tests of climate model predictions will occur using observations of decadal changes in climate forcing, response, and feedback variables. Many of these key climate variables are observed by remotely sensing the global distribution of reflected solar spectral and broadband radiance. These "reflected solar" variables include aerosols, clouds, radiative fluxes, snow, ice, vegetation, ocean color, and land cover. Achieving sufficient satellite instrument accuracy, stability, and overlap to rigorously observe decadal change signals has proven very difficult in most cases and has not yet been achieved in others [2]. One of the earliest efforts to make climate quality observations was for Earth Radiation Budget: Nimbus 6/7 in the late 1970s, ERBE in the 1980s/90s, and CERES in 2000s are examples of the most complete global records. The recent CERES data products have carried out the most extensive intercomparisons because if the need to merge data from up to 11 instruments (CERES, MODIS, geostationary imagers) on 7 spacecraft (Terra, Aqua, and 5 geostationary) for any given month. In order to achieve climate calibration for cloud feedbacks, the radiative effect of clear-sky, all-sky, and cloud radiative effect must all be made with very high stability and accuracy. For shortwave solar reflected flux, even the 1% CERES broadband absolute accuracy (1-sigma confidence bound) is not sufficient to allow gaps in the radiation record for decadal climate change. Typical absolute accuracy for the best narrowband sensors like SeaWiFS, MISR, and MODIS range from 2 to 4% (1-sigma). IPCC greenhouse gas radiative forcing is approx. 0.6 W/sq m per decade or 0.6% of the global mean shortwave reflected flux, so that a 50% cloud feedback would change the global reflected flux by approx. 0.3 W/sq m or 0.3% per decade in broadband SW calibration change. Recent results comparing CERES reflected flux changes with MODIS, MISR, and SeaWiFS narrowband changes concluded that only SeaWiFS and CERES were approaching sufficient stability in calibration for decadal climate change [3]. Results using deep convective clouds in the optically thick limit as a stability target may prove very effective for improving past data sets like ISCCP. Results for intercalibration of geostationary imagers to CERES using an entire month of regional nearly coincident data demonstrates new approaches to constraining the calibration of current geostationary imagers. The new Decadal Survey Mission CLARREO is examining future approaches to a "NIST-in-Orbit" approach of very high absolute accuracy reference radiometers that cover the full solar and infrared spectrum at high spectral resolution but at low spatial resolution. Sampling studies have shown that a precessing CLARREO mission could calibrate other geo and leo reflected solar radiation and thermal infrared sensors

A novel hypothesis of dinosaur relationships and early dinosaur evolution

For nearly 130 years dinosaurs have been divided into two distinct clades Ornithischia and Saurischia. Here, we present a radical new hypothesis for the phylogenetic relationships of the major dinosaurian groups, one that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study recovers, for the first time, a sister-group relationship between Ornithischia and Theropoda (Ornithoscelida), with Sauropodomorpha + Herrerasauridae forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests the independent acquisition of hypercarnivory in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as striking convergences between theropods and early ornithischians

Vocational education and training and employment services in Malta

This country monograph is the result of a request from the European Commission (Directorate-General for Employment and Social Affairs) in the context of the Employment Policy Reviews launched by the latter in the future member states in 1999. According to this request, the key aim of the country monographs is to provide up-to-date, detailed information and analysis on the vocational education and training systems and structures as well as on the public and private employment services in order to support the monitoring of the Joint Assessment Papers of Employment Priorities (JAP). This analysis is considered to provide a useful input enabling the future member states and the European Commission to identify the most important needs and gaps. In particular, the analysis aims at providing: (1) an instrument to assess the progress made by the countries to increase the responsiveness of their education and training systems to labour market needs; this assessment is addresses particularly the challenges and priorities related to the development of lifelong learning; (2) a tool to assess the effectiveness of the public and private employment services to assist both young and adult unemployed people and those threatened by unemployment to enter the labour market; and (3) a basis for positioning the development trends of these systems in relation to those in EU member states. The work has been conducted by a team of national, EU and ETF experts, under the responsibility of the European Training Foundation (ETF) and with the support of the Employment Training Corporation (ETC). The method of work combined the use of desk research and field visits in the capital and also in some selected regions. The final document has been prepared by the European Training Foundation and therefore, reflects primarily an ETF viewpoint. The preparation of the monographs has also benefited from a close consultation process with representatives of the national authorities. The latter were informed about this work right from the beginning of the process and they were invited to provide their opinion on the final draft. In addition, a seminar was organised on 27 September 2002 in Brussels with the aim of presenting and discussing the documents with the national authorities of the future member states as well as with the European Commission. This monograph also reflects the outcomes of this seminar and further discussions and comments from the country. The document makes use of quantitative indicators from international institutions as well as national sources. As discussed during the 27 September meeting, it should be acknowledged that in relation to indicators used in the EU, some data are still missing, while others might refer to different realities. Therefore, figures must be interpreted with caution, taking into account that statistics should be complemented by more qualitative assessments. Further analytical work will be needed to improve the picture and in particular the positioning of developments in the country towards developments in the EU.peer-reviewe

CBS domains form energy-sensing modules whose binding of adenosine ligands is disrupted by disease mutations

CBS domains are defined as sequence motifs that occur in several different proteins in all kingdoms of life. Although thought to be regulatory, their exact functions have been unknown. However, their importance was underlined by findings that mutations in conserved residues within them cause a variety of human hereditary diseases, including (with the gene mutated in parentheses): Wolff-Parkinson-White syndrome (γ2 subunit of AMP-activated protein kinase); retinitis pigmentosa (IMP dehydrogenase-1); congenital myotonia, idiopathic generalized epilepsy, hypercalciuric nephrolithiasis, and classic Bartter syndrome (CLC chloride channel family members); and homocystinuria (cystathionine β-synthase). AMP-activated protein kinase is a sensor of cellular energy status that is activated by AMP and inhibited by ATP, but the location of the regulatory nucleotide-binding sites (which are prime targets for drugs to treat obesity and diabetes) was not characterized. We now show that tandem pairs of CBS domains from AMP-activated protein kinase, IMP dehydrogenase-2, the chloride channel CLC2, and cystathionine β-synthase bind AMP, ATP, or S-adenosyl methionine,while mutations that cause hereditary diseases impair this binding. This shows that tandem pairs of CBS domains act, in most cases, as sensors of cellular energy status and, as such, represent a newly identified class of binding domain for adenosine derivatives

Open problems in artificial life

This article lists fourteen open problems in artificial life, each of which is a grand challenge requiring a major advance on a fundamental issue for its solution. Each problem is briefly explained, and, where deemed helpful, some promising paths to its solution are indicated

A general model to optimise CuII labelling efficiency of double-histidine motifs for pulse dipolar EPR applications

JLW is supported by the BBSRC DTP Eastbio. We thank the Leverhulme Trust for support (RPG-2018-397). This work was supported by equipment funding through the Wellcome Trust (099149/Z/12/Z) and BBSRC (BB/R013780/1). We gratefully acknowledge ISSF support to the University of St Andrews from the Wellcome Trust.Electron paramagnetic resonance (EPR) distance measurements are making increasingly important contributions to studies of biomolecules underpinning health and disease by providing highly accurate and precise geometric constraints. Combining double-histidine (dH) motifs with CuII spin labels shows promise for further increasing the precision of distance measurements, and for investigating subtle conformational changes. However, non-covalent coordination-based spin labelling is vulnerable to low binding affinity. Dissociation constants of dH motifs for CuII-nitrilotriacetic acid were previously investigated via relaxation induced dipolar modulation enhancement (RIDME), and demonstrated the feasibility of exploiting the double histidine motif for EPR applications at sub-μM protein concentrations. Herein, the feasibility of using modulation depth quantitation in CuII-CuII RIDME to simultaneously estimate a pair of non-identical independent KD values in such a tetra-histidine model protein is addressed. Furthermore, we develop a general speciation model to optimise CuII labelling efficiency, in dependence of pairs of identical or disparate KD values and total CuII label concentration. We find the dissociation constant estimates are in excellent agreement with previously determined values, and empirical modulation depths support the proposed model.Publisher PDFPeer reviewe

Variability in Global Top-of-Atmosphere Shortwave Radiation Between 2000 and 2005

Measurements from various instruments and analysis techniques are used to directly compare changes in Earth-atmosphere shortwave (SW) top-of-atmosphere (TOA) radiation between 2000 and 2005. Included in the comparison are estimates of TOA reflectance variability from published ground-based Earthshine observations and from new satellite-based CERES, MODIS and ISCCP results. The ground-based Earthshine data show an order-of-magnitude more variability in annual mean SW TOA flux than either CERES or ISCCP, while ISCCP and CERES SW TOA flux variability is consistent to 40%. Most of the variability in CERES TOA flux is shown to be dominated by variations global cloud fraction, as observed using coincident CERES and MODIS data. Idealized Earthshine simulations of TOA SW radiation variability for a lunar-based observer show far less variability than the ground-based Earthshine observations, but are still a factor of 4-5 times more variable than global CERES SW TOA flux results. Furthermore, while CERES global albedos exhibit a well-defined seasonal cycle each year, the seasonal cycle in the lunar Earthshine reflectance simulations is highly variable and out-of-phase from one year to the next. Radiative transfer model (RTM) approaches that use imager cloud and aerosol retrievals reproduce most of the change in SW TOA radiation observed in broadband CERES data. However, assumptions used to represent the spectral properties of the atmosphere, clouds, aerosols and surface in the RTM calculations can introduce significant uncertainties in annual mean changes in regional and global SW TOA flux