National Autonomous University of Mexico

About: National Autonomous University of Mexico is a education organization based out in Mexico City, Distrito Federal, Mexico. It is known for research contribution in the topics: Population & Galaxy. The organization has 72868 authors who have published 127797 publications receiving 2285543 citations. The organization is also known as: UNAM & Universidad Nacional Autónoma de México.

Bacillus thuringiensis insecticidal three‐domain Cry toxins: mode of action, insect resistance and consequences for crop protection

Abstract: Bacillus thuringiensis bacteria are insect pathogens that produce different Cry and Cyt toxins to kill their hosts. Here we review the group of three-domain Cry (3d-Cry) toxins. Expression of these 3d-Cry toxins in transgenic crops has contributed to efficient control of insect pests and a reduction in the use of chemical insecticides. The mode of action of 3d-Cry toxins involves sequential interactions with several insect midgut proteins that facilitate the formation of an oligomeric structure and induce its insertion into the membrane, forming a pore that kills midgut cells. We review recent progress in our understanding of the mechanism of action of these Cry toxins and focus our attention on the different mechanisms of resistance that insects have evolved to counter their action, such as mutations in cadherin, APN and ABC transporter genes. Activity of Cry1AMod toxins, which are able to form toxin oligomers in the absence of receptors, against different resistant populations, including those affected in the ABC transporter and the role of dominant negative mutants as antitoxins, supports the hypothesis that toxin oligomerization is a limiting step in the Cry insecticidal activity. Knowledge of the action of 3d-Cry toxin and the resistance mechanisms to these toxins will set the basis for a rational design of novel toxins to overcome insect resistance, extending the useful lifespan of Cry toxins in insect control programs.

The genomes of four tapeworm species reveal adaptations to parasitism

Abstract: Tapeworms (Cestoda) cause neglected diseases that can be fatal and are difficult to treat, owing to inefficient drugs. Here we present an analysis of tapeworm genome sequences using the human-infective species Echinococcus multilocularis, E. granulosus, Taenia solium and the laboratory model Hymenolepis microstoma as examples. The 115- to 141-megabase genomes offer insights into the evolution of parasitism. Synteny is maintained with distantly related blood flukes but we find extreme losses of genes and pathways that are ubiquitous in other animals, including 34 homeobox families and several determinants of stem cell fate. Tapeworms have specialized detoxification pathways, metabolism that is finely tuned to rely on nutrients scavenged from their hosts, and species-specific expansions of non-canonical heat shock proteins and families of known antigens. We identify new potential drug targets, including some on which existing pharmaceuticals may act. The genomes provide a rich resource to underpin the development of urgently needed treatments and control.

A Bayesian approach to strong lensing modelling of galaxy clusters

Abstract: In this paper, we describe a procedure for modelling strong lensing galaxy clusters with parametric methods, and to rank models quantitatively using the Bayesian evidence We use a publicly available Markov chain Monte-Carlo (MCMC) sampler ('bayesys'), allowing us to avoid local minima in the likelihood functions To illustrate the power of the MCMC technique, we simulate three clusters of galaxies, each composed of a cluster-scale halo and a set of perturbing galaxy-scale subhalos We ray-trace three light beams through each model to produce a catalogue of multiple images, and then use the MCMC sampler to recover the model parameters in the three different lensing configurations We find that, for typical Hubble Space Telescope (HST)-quality imaging data, the total mass in the Einstein radius is recovered with ~1?5% error according to the considered lensing configuration However, we find that the mass of the galaxies is strongly degenerated with the cluster mass when no multiple images appear in the cluster centre The mass of the galaxies is generally recovered with a 20% error, largely due to the poorly constrained cut-off radius Finally, we describe how to rank models quantitatively using the Bayesian evidence We confirm the ability of strong lensing to constrain the mass profile in the central region of galaxy clusters in this way Ultimately, such a method applied to strong lensing clusters with a very large number of multiple images may provide unique geometrical constraints on cosmology The implementation of the MCMC sampler used in this paper has been done within the framework of the lenstool software package, which is publicly available

The Harvard Clean Energy Project: Large-Scale Computational Screening and Design of Organic Photovoltaics on the World Community Grid

Abstract: This Perspective introduces the Harvard Clean Energy Project (CEP), a theory-driven search for the next generation of organic solar cell materials. We give a broad overview of its setup and infrastructure, present first results, and outline upcoming developments. CEP has established an automated, high-throughput, in silico framework to study potential candidate structures for organic photovoltaics. The current project phase is concerned with the characterization of millions of molecular motifs using first-principles quantum chemistry. The scale of this study requires a correspondingly large computational resource, which is provided by distributed volunteer computing on IBM’s World Community Grid. The results are compiled and analyzed in a reference database and will be made available for public use. In addition to finding specific candidates with certain properties, it is the goal of CEP to illuminate and understand the structure–property relations in the domain of organic electronics. Such insights can o...

Isolation of Smaller Nanocrystal Au Molecules: Robust Quantum Effects in Optical Spectra

Abstract: Five massive gold-cluster molecules have been isolated in high yield and have undergone separate structural characterization, and their electronic structure has been deduced by optical absorption spectroscopy. These new molecules are distinguished by a crystalline (or quasicrystalline) core of densely packed Au atoms, ranging in size from ∼1.1 nm (∼40 atoms) to ∼1.9 nm (∼200 atoms), surrounded by a compact monolayer of various thio (RS) adsorbates. They are obtained as the thermally and environmentally stable products of the reductive decomposition of nonmetallic (−AuS(R)−) polymer in solution, are separated according to size by fractional crystallization or column chromatography, as monitored by high-mass spectrometry, and are characterized structurally by methods including X-ray diffraction (small and large angle), high-resolution electron microscopy, and scanning tunneling microscopy. The optical absorption spectra of dilute solutions of these molecules show size-dependent steplike structure with an on...