The Structure of Ordinary Water: New data and interpretations are yielding new insights into this fascinating substance

The train of thought pursued in this article has led to the conclusion that the structure of cold water seems likely to consist, for the most part, of hydrogen-bonded, four-coordinated, framework regions, with interstitial monomers occupying some fraction of the cavities the framework encloses. The precise geometry of the framework has not been specified, but some evidence suggests that it is rather regular at low temperatures and becomes more random as the water gets warmer. These conclusions, meager as they are in comparison with what we shall eventually need to know about water, are still "subject to change without notice." Such a change would, for instance, be made necessary by the discrediting either of the data or of the interpretations on which the model is based. The discovery of new facts, or of new meanings in old facts, which were clearly in conflict with the model, would also make it necessary to modify, if not to abandon, it. Even this would be progress, however, for it would be another product of the method of drawing upon data from diverse sources and would be a further step toward the progressively more comprehensive model to which this method will lead and the progressively greater confidence we will be able to place in our conclusions.     

农业科技传播新思维

根据当前我国农业科技传播体系与机制现状及存在问题,提出了体系与机制创新的思路,强调将农民职业教育作为农业科技传播体系的重要组成部分。     

Protein kinase inhibitors: insights into drug design from structure

Protein kinases are targets for treatment of a number of diseases. This review focuses on kinase inhibitors that are in the clinic or in clinical trials and for which structural information is available. Structures have informed drug design and have illuminated the mechanism of inhibition. We review progress with the receptor tyrosine kinases (growth factor receptors EGFR, VEGFR, and FGFR) and nonreceptor tyrosine kinases (Bcr-Abl), where advances have been made with cancer therapeutic agents such as Herceptin and Gleevec. Among the serine-threonine kinases, p38, Rho-kinase, cyclin-dependent kinases, and Chk1 have been targeted with productive results for inflammation and cancer. Structures have provided insights into targeting the inactive or active form of the kinase, for targeting the global constellation of residues at the ATP site or less conserved additional pockets or single residues, and into targeting noncatalytic domains.     

Genomic insights into the immune system of the sea urchin

Comparative analysis of the sea urchin genome has broad implications for the primitive state of deuterostome host defense and the genetic underpinnings of immunity in vertebrates. The sea urchin has an unprecedented complexity of innate immune recognition receptors relative to other animal species yet characterized. These receptor genes include a vast repertoire of 222 Toll-like receptors, a superfamily of more than 200 NACHT domain-leucine-rich repeat proteins (similar to nucleotide-binding and oligomerization domain (NOD) and NALP proteins of vertebrates), and a large family of scavenger receptor cysteine-rich proteins. More typical numbers of genes encode other immune recognition factors. Homologs of important immune and hematopoietic regulators, many of which have previously been identified only from chordates, as well as genes that are critical in adaptive immunity of jawed vertebrates, also are present. The findings serve to underscore the dynamic utilization of receptors and the complexity of immune recognition that may be basal for deuterostomes and predicts features of the ancestral bilaterian form.     

Structure-based mechanistic insights into DNMT1-mediated maintenance DNA methylation

DNMT1, the major maintenance DNA methyltransferase in animals, helps to regulate gene expression, genome imprinting, and X-chromosome inactivation. We report on the crystal structure of a productive covalent mouse DNMT1(731-1602)-DNA complex containing a central hemimethylated CpG site. The methyl group of methylcytosine is positioned within a shallow hydrophobic concave surface, whereas the cytosine on the target strand is looped out and covalently anchored within the catalytic pocket. The DNA is distorted at the hemimethylated CpG step, with side chains from catalytic and recognition loops inserting through both grooves to fill an intercalation-type cavity associated with a dual base flip-out on partner strands. Structural and biochemical data establish how a combination of active and autoinhibitory mechanisms ensures the high fidelity of DNMT1-mediated maintenance DNA methylation.     

Genome sequence of a polydnavirus: insights into symbiotic virus evolution

Little is known of the fate of viruses involved in long-term obligatory associations with eukaryotes. For example, many species of parasitoid wasps have symbiotic viruses to manipulate host defenses and to allow development of parasitoid larvae. The complete nucleotide sequence of the DNA enclosed in the virus particles injected by a parasitoid wasp revealed a complex organization, resembling a eukaryote genomic region more than a viral genome. Although endocellular symbiont genomes have undergone a dramatic loss of genes, the evolution of symbiotic viruses appears to be characterized by extensive duplication of virulence genes coding for truncated versions of cellular proteins.     

传播学视角下选择性理论对高校思想政治教育工作的启示

高校思想政治教育工作可以视为一种传播活动,即思想政治教育信息在教育者和大学生之间的传递和接受。将传播学选择性理论研究同高校思想政治教育实践联系起来,探索高校思想政治教育工作新思路和新方法。通过大量的理论研究和实证分析,认为深入有效的了解和沟通、尊重个性差异的因材施教、易得易懂易记的信息传播、妥帖有效的方法技巧,是提高思...     

Structural insights into the assembly of the type III secretion needle complex

Type III secretion systems (TTSSs) mediate translocation of virulence factors into host cells. We report the 17-angstrom resolution structures of a central component of Salmonella typhimurium TTSS, the needle complex, and its assembly precursor, the bacterial envelope-anchored base. Both the base and the fully assembled needle complex adopted multiple oligomeric states in vivo, and needle assembly was accompanied by recruitment of the protein PrgJ as a structural component of the base. Moreover, conformational changes during needle assembly created scaffolds for anchoring both PrgJ and the needle substructure and may provide the basis for substrate-specificity switching during type III secretion.     

The Physcomitrella genome reveals evolutionary insights into the conquest of land by plants

We report the draft genome sequence of the model moss Physcomitrella patens and compare its features with those of flowering plants, from which it is separated by more than 400 million years, and unicellular aquatic algae. This comparison reveals genomic changes concomitant with the evolutionary movement to land, including a general increase in gene family complexity; loss of genes associated with aquatic environments (e.g., flagellar arms); acquisition of genes for tolerating terrestrial stresses (e.g., variation in temperature and water availability); and the development of the auxin and abscisic acid signaling pathways for coordinating multicellular growth and dehydration response. The Physcomitrella genome provides a resource for phylogenetic inferences about gene function and for experimental analysis of plant processes through this plant's unique facility for reverse genetics.     

Peptides enhance magnesium signature in calcite: insights into origins of vital effects

Studies relating the magnesium (Mg) content of calcified skeletons to temperature often report unexplained deviations from the signature expected for inorganically grown calcite. These "vital effects" are believed to have biological origins, but mechanistic bases for measured offsets remain unclear. We show that a simple hydrophilic peptide, with the same carboxyl-rich character as that of macromolecules isolated from sites of calcification, increases calcite Mg content by up to 3 mole percent. Comparisons to previous studies correlating Mg content of carbonate minerals with temperature show that the Mg enhancement due to peptides results in offsets equivalent to 7 degrees to 14 degrees C. The insights also provide a physical basis for anecdotal evidence that organic chemistry modulates the mineralization of inorganic carbonates and suggest an approach to tuning impurity levels in controlled materials synthesis.     

Probe into the chief modes of agricultural communication in new countryside

[目的]分析新农村背景下农业传播的主要模式及其应用,为农业传播学中相关理论的探讨和发展提供参考.[方法]以传播学研究中的传播过程模式为理论支点,通过对比传统农业传播模式,采取归纳分析的方法,提出当前新农村背景下农业传播的主要模式.[结果]目前,我国农业传播主要存在行政干预的上行下效模式、农业意见领袖的两级传播模式、社会互动的远程教育模式、大众传播的自发效仿模式等4种.[建议]应根据实际情况,扬长避短,综合考虑传播者、受众、信息内容、传播媒介以及反馈等传播过程的各要素,对传播各环节进行重新组合和整体把握,形成一个符合特定需求的动态发展的农业信息传播系统.     

New tools provide new insights in NMR studies of protein dynamics

There is growing evidence that structural flexibility plays a central role in the function of protein molecules. Many of the experimental data come from nuclear magnetic resonance (NMR) spectroscopy, a technique that allows internal motions to be probed with exquisite time and spatial resolution. Recent methodological advancements in NMR have extended our ability to characterize protein dynamics and promise to shed new light on the mechanisms by which these molecules function. Here, we present a brief overview of some of the new methods, together with applications that illustrate the level of detail at which protein motions can now be observed.     

The intrinsic electrophysiological properties of mammalian neurons: insights into central nervous system function

This article reviews the electroresponsive properties of single neurons in the mammalian central nervous system (CNS). In some of these cells the ionic conductances responsible for their excitability also endow them with autorhythmic electrical oscillatory properties. Chemical or electrical synaptic contacts between these neurons often result in network oscillations. In such networks, autorhythmic neurons may act as true oscillators (as pacemakers) or as resonators (responding preferentially to certain firing frequencies). Oscillations and resonance in the CNS are proposed to have diverse functional roles, such as (i) determining global functional states (for example, sleep-wakefulness or attention), (ii) timing in motor coordination, and (iii) specifying connectivity during development. Also, oscillation, especially in the thalamo-cortical circuits, may be related to certain neurological and psychiatric disorders. This review proposes that the autorhythmic electrical properties of central neurons and their connectivity form the basis for an intrinsic functional coordinate system that provides internal context to sensory input.