Virus maturation involving large subunit rotations and local refolding

Large-scale conformational changes transform viral precursors into infectious virions. The structure of bacteriophage HK97 capsid, Head-II, was recently solved by crystallography, revealing a catenated cross-linked topology. We have visualized its precursor, Prohead-II, by cryoelectron microscopy and modeled the conformational change by appropriately adapting Head-II. Rigid-body rotations ( approximately 40 degrees) cause switching to an entirely different set of interactions; in addition, two motifs undergo refolding. These changes stabilize the capsid by increasing the surface area buried at interfaces and bringing the cross-link-forming residues, initially approximately 40 angstroms apart, close together. The inner surface of Prohead-II is negatively charged, suggesting that the transition is triggered electrostatically by DNA packaging.     

广东省林业人力资源的现状与结构调整

人力资源已经成为一个国家经济和社会发展最重要的战略资源.广东要加快林业发展,创建林业生态省,人力资源的开发和管理举足轻重,而且迫在眉睫.长期以来,广东省林业人力资源存在人才缺乏、结构不合理、管理不到位、开发利用工作滞后等问题.必须从广东省林业人力资源的现状入手,加强林业人力资源的合理配置和结构优化调整,更好地开发利用林业人力资源,为广东省林业生态建设提供可靠的人力资源保障和智力支撑.     

乙烯促进与抑制剂对旱后复水玉米生长、保护酶活性及膜脂过氧化的影响

 以玉米品种郑单958为材料,研究了不同程度干旱胁迫与复水条件下乙烯促进与抑制剂处理对春玉米生长、叶片保护酶系活性变化及其对膜脂过氧化作用的影响。结果表明：（1）乙烯利有利于控制玉米的株高,并提高轻度干旱条件下玉米的根重和生物量,而AgNO3（硝酸银）处理的玉米在轻度与重度干旱条件下,生物量明显降低。（2）乙烯利处理可明显抑制水分胁迫条件下玉米MDA（丙二醛）的合成,降低相对电导率,提高可溶性蛋白含量,而AgNO3处理的效果则与乙烯利刚好相反。（3）乙烯利处理可明显提高SOD（超氧化物酶）、CAT（过氧化氢酶）和POD（过氧化物酶）的活性,而AgNO3处理在一定程度上抑制SOD、CAT和POD的活性。     

奶牛MHC基因多态性及其与经济性状关系的研究进展

简述了奶牛MHC基因的结构、位置、分类、多态性的一般特性，并且介绍了MHC基因与生产性状、乳房炎等一些经济性状的关系。     

Teaching reasoning

Twentieth-century psychologists have been pessimistic about teaching reasoning, prevailing opinion suggesting that people may possess only domain-specific rules, rather than abstract rules; this would mean that training a rule in one domain would not produce generalization to other domains. Alternatively, it was thought that people might possess abstract rules (such as logical ones) but that these are induced developmentally through self-discovery methods and cannot be trained. Research suggests a much more optimistic view: even brief formal training in inferential rules may enhance their use for reasoning about everyday life events. Previous theorists may have been mistaken about trainability, in part because they misidentified the kind of rules that people use naturally.     

Increased insulin sensitivity and obesity resistance in mice lacking the protein tyrosine phosphatase-1B gene

Protein tyrosine phosphatase-1B (PTP-1B) has been implicated in the negative regulation of insulin signaling. Disruption of the mouse homolog of the gene encoding PTP-1B yielded healthy mice that, in the fed state, had blood glucose concentrations that were slightly lower and concentrations of circulating insulin that were one-half those of their PTP-1B+/+ littermates. The enhanced insulin sensitivity of the PTP-1B-/- mice was also evident in glucose and insulin tolerance tests. The PTP-1B-/- mice showed increased phosphorylation of the insulin receptor in liver and muscle tissue after insulin injection in comparison to PTP-1B+/+ mice. On a high-fat diet, the PTP-1B-/- and PTP-1B+/- mice were resistant to weight gain and remained insulin sensitive, whereas the PTP-1B+/+ mice rapidly gained weight and became insulin resistant. These results demonstrate that PTP-1B has a major role in modulating both insulin sensitivity and fuel metabolism, thereby establishing it as a potential therapeutic target in the treatment of type 2 diabetes and obesity.     

Epstein-Barr virus: inhibition of replication by three new drugs

Epstein-Barr virus (EBV) is the cause of infectious mononucleosis and is associated with three human malignancies. Acyclovir [9-(2-hydroxyethoxymethyl)guanine], the first clinically useful drug effective against replication of EBV, is without effect against latent or persistent EBV infection. Three nucleoside analogs, E-5-(2-bromovinyl)-2'-deoxyuridine, 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine, and 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-methyluracil are potent inhibitors of EBV replication in vitro. Moreover, in contrast to the reversibility of viral inhibition by Acyclovir, these three drugs have prolonged effects in suppressing viral replication even after the drugs are removed from persistently infected cell cultures.     

9个苹果新品种在榆林南部丘陵沟壑区的引种表现

为进一步筛选适宜榆林南部丘陵沟壑区栽植的优质苹果新品种,试验以长富2号为对照,通过对烟富系列、响富、瑞阳、瑞雪、维纳斯·黄金、秦脆、玉华早富等9个中晚熟苹果品种的主要性状进行观察记录,并对其进行分析研究。结果表明：烟富10、烟富6、响富、秦脆四个中晚熟红色品种和维纳斯·黄金、瑞雪两个晚熟黄色品种适宜于榆林南部丘陵沟壑区栽植。     

DCA、CCA和DCCA三种排序方法在中国草地植被群落中的应用现状

排序是用来分析植被与环境之间生态关系的重要手段。该文主要是对除趋势对应分析(DCA)、典范对应分析(CCA)和除趋势典范对应分析(DCCA)这三种排序方法进行总结,讨论它们在中国草地植被群落研究中的应用现状,并得出除趋势对应分析与聚类分析结合使用效果比较好,主要是用来揭示群落之间的关系,并且在实际的应用中也比较多,而典范对应分析和除趋势典范对应分析在揭示种与环境关系方面具有明显的优势,但是由于某些条件的限制,在实际研究中应用的比较少。可见这几种排序方法在实际应用中具有一定的优势,所以应该加强这方面的应用,更加深入的研究草地植被群落,以期对草地生态学及草地植被群落生态关系的研究工作发挥重要的借鉴作用。     

污染指示生物苔藓和蚂蚁中的重金属污染比较分析

采样测定并比较了城市不同区域两种指示生物苔藓和蚂蚁体内的Pb、Cu、Cr、Cd含量及分布特征，讨论了这两种指示生物的重金属累积率和土壤重金属浓度的关系。结果表明，苔藓对比有很强的富集能力，其体内的重金属浓度随土壤浓度的增大而增大，且比蚂蚁更易受到环境中重金属污染的影响；Pb和Cd是蚂蚁的环境敏感元素，但蚂蚁对重金属在体内的持续积累有一定的抑制机制，其体内Cu的浓度与土壤中浓度的相关性较Pb、Cd小，且Cd在较低浓度时和土壤浓度呈相关性，较高浓度时相关性受抑制。同时运用污染指数分析评估了城市环境的污染状况及重金属对指示生物的毒性。