Gene conversion between duplicated genetic elements in yeast

The mitotic recombination behaviour of a duplication of the his4 region on chromosome III in the yeast Saccharomyces cerevisiae was studied. The major recombination event between the duplicated segments is gene conversion unassociated with reciprocal recombination. The rad52-1 mutation preferentially decreases mitotic gene conversion. These results suggest that mitotic gene conversion may occur by a different pathway from that occurring in meiosis. This mitotic gene conversion may be important in yeast mating type interconversion and the maintenance of sequence homogeneity in families of repeated eukaryotic genes.     

Creation of human tumour cells with defined genetic elements.

During malignant transformation, cancer cells acquire genetic mutations that override the normal mechanisms controlling cellular proliferation. Primary rodent cells are efficiently converted into tumorigenic cells by the coexpression of cooperating oncogenes. However, similar experiments with human cells have consistently failed to yield tumorigenic transformants, indicating a fundamental difference in the biology of human and rodent cells. The few reported successes in the creation of human tumour cells have depended on the use of chemical or physical agents to achieve immortalization, the selection of rare, spontaneously arising immortalized cells, or the use of an entire viral genome. We show here that the ectopic expression of the telomerase catalytic subunit (hTERT) in combination with two oncogenes (the simian virus 40 large-T oncoprotein and an oncogenic allele of H-ras) results in direct tumorigenic conversion of normal human epithelial and fibroblast cells. These results demonstrate that disruption of the intracellular pathways regulated by large-T, oncogenic ras and telomerase suffices to create a human tumor cell.     

Sequence of retrovirus provirus resembles that of bacterial transposable elements

The nucleotide sequences of the terminal regions of an infectious integrated retrovirus cloned in the modified lambda phage cloning vector Charon 4A have been elucidated. There is a 569-base pair direct repeat at both ends of the viral DNA. The cell-virus junctions at each end consist of a 5-base pair direct repeat of cell DNA next to a 3-base pair inverted repeat of viral DNA. This structure resembles that of a transposable element and is consistent with the protovirus hypothesis that retroviruses evolved from the cell genome.     

腺病毒同源重组子的鉴定

携带入ＩＦＮ－γｃＤＮＡ序列的Ｅ１区缺失的腺病毒载体ｐＡｄｌ２／ＲＳＶ－ＩＦＮ－ｂｐＡ与ｐＪＭ１７质粒，通过磷酸钙沉淀法共转染２９３细胞，经同源重组，共获得６个病毒噬斑。病毒噬斑感染２９３细胞，至出现完全细胞病变效应（ＣＰＥ）后，抽提细胞内的病毒ＤＮＡ，经ＸｈｏⅠ酶切后走凝胶电泳，出现重组腺病毒圾的３．５ｋｂ大小的ＤＮＡ条带，＾３２Ｐ标记的探针ｐＡｄｌ２／ＲＳＶ－ＩＦＮ－ｂｐＡ与ＸｈｏⅠ酶切过的病     

Transposable genetic elements as agents of gene instability and chromosomal rearrangements.

Transposable genetic elements in prokaryotes and eukaryotes, when inserted at a given locus, can control expression of the locus and cause large scale rearrangements of adjacent DNA sequences. Striking similarities in genetic behaviour between the two groups of elements have led to the proposal of a molecular model of eukaryotic controlling elements, and to suggestions about the part such elements may play in evolution and differentiation.     

The endonuclease activity of Mili fuels piRNA amplification that silences LINE1 elements

Piwi proteins and Piwi-interacting RNAs (piRNAs) have conserved functions in transposon silencing. The murine Piwi proteins Mili and Miwi2 (also called Piwil2 and Piwil4, respectively) direct epigenetic LINE1 and intracisternal A particle transposon silencing during genome reprogramming in the embryonic male germ line. Piwi proteins are proposed to be piRNA-guided endonucleases that initiate secondary piRNA biogenesis; however, the actual contribution of their endonuclease activities to piRNA biogenesis and transposon silencing remain unknown. To investigate the role of Piwi-catalysed endonucleolytic activity, we engineered point mutations in mice that substitute the second aspartic acid to an alanine in the DDH catalytic triad of Mili and Miwi2, generating the Mili(DAH) and Miwi2(DAH) alleles, respectively. Analysis of Mili-bound piRNAs from homozygous Mili(DAH) fetal gonadocytes revealed a failure of transposon piRNA amplification, resulting in the marked reduction of piRNA bound within Miwi2 ribonuclear particles. We find that Mili-mediated piRNA amplification is selectively required for LINE1, but not intracisternal A particle, silencing. The defective piRNA pathway in Mili(DAH) mice results in spermatogenic failure and sterility. Surprisingly, homozygous Miwi2(DAH) mice are fertile, transposon silencing is established normally and no defects in secondary piRNA biogenesis are observed. In addition, the hallmarks of piRNA amplification are observed in Miwi2-deficient gonadocytes. We conclude that cycles of intra-Mili secondary piRNA biogenesis fuel piRNA amplification that is absolutely required for LINE1 silencing.     

直接反污染控制下具有反污染产出的经济最优增长模型

在对列昂惕夫投入产出扩展表修订后,结合最优化理论,对具有直接反污染控制目标和具有反污染产出的动态多部门经济系统建立最优增长模型。     

Identification and comparison of two sequence elements that confer cell-type specific transcription in yeast

The MAT alpha 2 protein of budding yeast represses a set of genes; if the MATa1 protein is also present, a further set of genes is repressed. DNA sequence comparisons reveal a 20-base pair 'operator' sequence that is present in genes repressed by a1/alpha 2. A related, but distinct, sequence is found in genes repressed by alpha 2 alone.     

人类磷酸泛酰巯基乙胺结合蛋白新基因的分离和鉴定

在对AD293和HEK293进行差减杂交以探索两者在吸附和凋亡特性上的差异时,从AD293的高表达文库中分离得到一段新的cDNA片段.从人类胎脑文库克隆得到该基因,全长2 745 bp,编码的蛋白含518个氨基酸,被预测为磷酸泛酰巯基乙胺结合蛋白.该基因在染色体上定位于2p22.3,包含8个外显子.该cDNA编码的蛋白序列含有一个凋亡抑制蛋白5结构域,外皮蛋白重复片段和铜结合辛肽重复片段.RT-PCR分析显示该基因在人类正常组织和癌组织中广泛表达,但在癌组织中表达量相对较低,提示其可能对细胞凋亡有抑制作用.该基因在进化过程中高度保守.     

Human immunodeficiency virus genetic variation that can escape cytotoxic T cell recognition.

In a longitudinal study of HIV seropositive patients, there were fluctuations in the specificity of cytotoxic T cells for the virus. This was matched by variability in proviral gag DNA epitope sequences in the lymphocytes of these patients. Some of these viral variants are not recognized by autologous T cells. Accumulation of such mutations in T-cell antigenic targets would provide a mechanism for immune escape.     

重组质粒βhCG—pPIC9K的构建及嗜甲醇酵？…

目的：为用基因重组技术表达ｈＣＧ避孕疫苗抗原,构建在酵母细胞中表达的重组质粒βｈＣＧ－ｐＰＩＣ９Ｋ,转化嗜甲醇酵母,方法：根据βｈＣＧ的ｃＤＮＡ序列设计两条引物,使上游带ＥｃｏＲⅠ酶切位点,下游带ＮｏｔⅠ酶切位点,以质粒βｈＣＧ－ＰＢＳＫＳ为模板,进行ＰＣＲ扩增反应;将所得的ＤＮＡ片段经ＥｃｏＲⅠ和ＮｏｔⅠ双酶切后用Ｔ４连接酶与ｐＰＩＣ９Ｋ质粒进行连接,然后导入大肠杆菌ＤＨ５α,用ＰＣＲ筛选阳性克     

一种用遗传算法求解装箱问题的新编码方法

装箱问题在实际生产中应用非常广泛,然而在传统装箱问题中箱子的容量是固定的,并没有考虑多种容量箱子的问题;文章提出一种用遗传算法求解装箱问题的新编码方法,并用单亲遗传算法实现;这种算法和混合遗传算法相比,有编码简单、收敛快及实现容易等优点。     

Isolation and characterization of rl（t）, a gene that controls leaf rolling in rice

Moderate leaf rolling is one of the most important morphological traits in rice breeding for plant ideotype. Previous studies have shown that the rl（t） gene has a high breeding potential for developing hybrid-rice varieties with an ideal ideotype, because it leads to an appropriate leaf rolling index （LRI） of about 30 % in the heterozygous state, and had a positive effect on grain yield. In this study, we isolated rl（t） and performed a preliminary investigation of its function in regulating leaf rolling in rice. DNA sequencing identified a single base change （G to T） in the finely mapped region （11 kb） containing rl（t）, and this is located in 3′-untranslated region （3′-UTR） of the only predicted gene, Roc5 （Rice outermost cell-specific）. The expression level of Roc5 is significantly higher in the rl（t） mutant than in the wild-type. Using RNAi and overexpression analysis, we found that the expression level of Roc5 correlated with LRI and leaf bulliform area, and wasalso associated with leaf abaxial or adaxial rolling. These results confirmed that Roc5 controls leaf rolling in a dosagedependent manner. Bioinformatics analysis revealed a conserved 17-nt sequence （called the GU-rich element） in the 3′-UTR of HD-GL2 （Homeodomain-Glabra2） family genes including Roc5. Based on the model of this element in regulating mRNA stability in mammals, we speculate that the single nucleotide change in this element accounts for the higher expression level of Roc5 in the rl（t） mutant compared to the wild-type, which ultimately leads to adaxial rolling of the leaf. This discovery further enhances our knowledge of the molecular mechanisms underlying leaf rolling in rice.     

分支系统固有频率分布规律的探讨

为了快速、简捷地确定固有频率、主振型与结构参数的关系,采用理论分析方法,对分支扭转系统的固有频率分布规律进行了研究.结果表明,固有频率、主振型与结构参数具有简明的关系,可根据结构参数快速、简捷、直观地确定固有频率、主振型.给出了固有频率、主振型计算式和系统具有相同固有频率的条件.算例表明了该计算式的正确性和简捷性.     

机械谐振式热声制冷机模态频率研究

研究了一种机械谐振式热声制冷机结构,建立了装置机械谐振系统的二维模型,从振动方程中分析获得了系统的模态频率关系,同时研究了振动质量、机械和气体弹簧、腔体尺寸以及工作压力等参数对模态频率的影响.研究结果显示系统存在两个模态频率,且频率随谐振参数的变化出现分岔.通过对谐振参数的设计和调节,装置可以获得所需的特性和谐振频率.     

Isolation of a human gene that inhibits HIV-1 infection and is suppressed by the viral Vif protein

Viruses have developed diverse non-immune strategies to counteract host-mediated mechanisms that confer resistance to infection. The Vif (virion infectivity factor) proteins are encoded by primate immunodeficiency viruses, most notably human immunodeficiency virus-1 (HIV-1). These proteins are potent regulators of virus infection and replication and are consequently essential for pathogenic infections in vivo. HIV-1 Vif seems to be required during the late stages of virus production for the suppression of an innate antiviral phenotype that resides in human T lymphocytes. Thus, in the absence of Vif, expression of this phenotype renders progeny virions non-infectious. Here, we describe a unique cellular gene, CEM15, whose transient or stable expression in cells that do not normally express CEM15 recreates this phenotype, but whose antiviral action is overcome by the presence of Vif. Because the Vif:CEM15 regulatory circuit is critical for HIV-1 replication, perturbing the circuit may be a promising target for future HIV/AIDS therapies.