Sequence and analysis of chromosome 2 of the plant Arabidopsis thaliana

Arabidopsis thaliana (Arabidopsis) is unique among plant model organisms in having a small genome (130-140 Mb), excellent physical and genetic maps, and little repetitive DNA. Here we report the sequence of chromosome 2 from the Columbia ecotype in two gap-free assemblies (contigs) of 3.6 and 16 megabases (Mb). The latter represents the longest published stretch of uninterrupted DNA sequence assembled from any organism to date. Chromosome 2 represents 15% of the genome and encodes 4,037 genes, 49% of which have no predicted function. Roughly 250 tandem gene duplications were found in addition to large-scale duplications of about 0.5 and 4.5 Mb between chromosomes 2 and 1 and between chromosomes 2 and 4, respectively. Sequencing of nearly 2 Mb within the genetically defined centromere revealed a low density of recognizable genes, and a high density and diverse range of vestigial and presumably inactive mobile elements. More unexpected is what appears to be a recent insertion of a continuous stretch of 75% of the mitochondrial genome into chromosome 2.     

工科线性代数的教学策略研究

线性代数相对与其他课程具有体系感、较强的逻辑性和抽象性、应用非常广和计算量非常大的特点。而当前线性代数教学面临的形势是:任课老师教学工作量大和学生自觉性不高,工科学生学习数学的兴趣比学专业课的兴趣低,工科学生的数学基础普遍降低,课时非常紧张,现在大学生做作业的主动积极性不高。因此,要调动学生的学习积极性,关键在于让学生对这门课感兴趣,要善于启发和引导学生的思维,充分利用多媒体课件,培养或是引导学生的兴趣,要善于引导学生对内容归纳和总结,学会融会贯通。     

中学生物教师继续教育相关问题的调查研究

职后继续教育的课程设置对教师素质有一定的影响,采用问卷调查、文献分析和访谈等方法,对中学生物教师继续教育所应开设的课程、教学形式等继续教育方面的问题进行研究,并提出相应建议。     

A new class of synthetic antibacterials acting on lipopolysaccharide biosynthesis

Although there is a need for antibacterial agents that act only on Gram-negative bacteria, there are at present few such compounds. The 2-deoxy analogue of beta-KDO (3-deoxy-beta-D-manno-2-octulopyranosonic acid) is a potent inhibitor of a key enzyme (CMP-KDO synthetase) in lipopolysaccharide biosynthesis of Gram-negative bacteria, but it fails to penetrate intact bacteria. Coupling an L-L-dipeptide to the 8-amino-2,8-dideoxy analogue of beta-KDO enabled it to be recognized and actively accumulated by certain peptide permeases of the cytoplasmic membrane. The dipeptide was hydrolysed in the cell and the inhibitor released. Subsequent inhibition of CMP-KDO synthetase led to the accumulation of large amounts of lipid A precursor and bacterial death. These compounds represent a new class of synthetic antimicrobials with a novel mechanism of action and considerable potential as chemotherapeutic agents.     

Interchromosomal associations between alternatively expressed loci

The T-helper-cell 1 and 2 (T(H)1 and T(H)2) pathways, defined by cytokines interferon-gamma (IFN-gamma) and interleukin-4 (IL-4), respectively, comprise two alternative CD4+ T-cell fates, with functional consequences for the host immune system. These cytokine genes are encoded on different chromosomes. The recently described T(H)2 locus control region (LCR) coordinately regulates the T(H)2 cytokine genes by participating in a complex between the LCR and promoters of the cytokine genes Il4, Il5 and Il13. Although they are spread over 120 kilobases, these elements are closely juxtaposed in the nucleus in a poised chromatin conformation. In addition to these intrachromosomal interactions, we now describe interchromosomal interactions between the promoter region of the IFN-gamma gene on chromosome 10 and the regulatory regions of the T(H)2 cytokine locus on chromosome 11. DNase I hypersensitive sites that comprise the T(H)2 LCR developmentally regulate these interchromosomal interactions. Furthermore, there seems to be a cell-type-specific dynamic interaction between interacting chromatin partners whereby interchromosomal interactions are apparently lost in favour of intrachromosomal ones upon gene activation. Thus, we provide an example of eukaryotic genes located on separate chromosomes associating physically in the nucleus via interactions that may have a function in coordinating gene expression.     

小城镇规划的规模预测与发展时序——锡山市杨市镇规划试点研究

现行的小城镇规划规模预测如何补充完善？规模确定后如何分步实施？这些问题是我们当今小城镇能否良性发展的关键问题．本文从理论与实践两方面对其进行了探索研究     

Risk of severe asthma episodes predicted from fluctuation analysis of airway function

Asthma is an increasing health problem worldwide, but the long-term temporal pattern of clinical symptoms is not understood and predicting asthma episodes is not generally possible. We analyse the time series of peak expiratory flows, a standard measurement of airway function that has been assessed twice daily in a large asthmatic population during a long-term crossover clinical trial. Here we introduce an approach to predict the risk of worsening airflow obstruction by calculating the conditional probability that, given the current airway condition, a severe obstruction will occur within 30 days. We find that, compared with a placebo, a regular long-acting bronchodilator (salmeterol) that is widely used to improve asthma control decreases the risk of airway obstruction. Unexpectedly, however, a regular short-acting beta2-agonist bronchodilator (albuterol) increases this risk. Furthermore, we find that the time series of peak expiratory flows show long-range correlations that change significantly with disease severity, approaching a random process with increased variability in the most severe cases. Using a nonlinear stochastic model, we show that both the increased variability and the loss of correlations augment the risk of unstable airway function. The characterization of fluctuations in airway function provides a quantitative basis for objective risk prediction of asthma episodes and for evaluating the effectiveness of therapy.