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.     

Isolation of genetic elements that increase frequencies of plasmid recombinants

Some plasmid DNAs, when maintained in wild-type Escherichia coli strains, form high levels of oligomeric species while others remain primarily monomers. One explanation of this observation is that the plasmids that do not form circular oligomers lack a DNA sequence necessary for the formation or maintenance of circular oligomeric species. Here we describe the isolation of segments of DNA from the E. coli genome and other sources that through a recA+ -dependent process: (1) stimulate the conversion of monomeric plasmids to different oligomeric forms, (2) stimulate the conversion of an oligomeric plasmid to a mixture of monomeric and different oligomeric forms, and (3) increase the frequency of recovery of figure-8 molecules. Both cis-acting and trans-acting elements were found. These elements seen to act by stimulating either the frequency of the recombination events that lead to the interconversion of different oligomeric plasmid DNA molecules or some process involved in the maintenance of newly-formed recombinant molecules.     

An exonucleolytic activity of human apurinic/apyrimidinic endonuclease on 3' mispaired DNA

Human apurinic/apyrimidinic endonuclease (APE1) is an essential enzyme in DNA base excision repair that cuts the DNA backbone immediately adjacent to the 5' side of abasic sites to facilitate repair synthesis by DNA polymerase beta (ref. 1). Mice lacking the murine homologue of APE1 die at an early embryonic stage. Here we report that APE1 has a DNA exonuclease activity on mismatched deoxyribonucleotides at the 3' termini of nicked or gapped DNA molecules. The efficiency of this activity is inversely proportional to the gap size in DNA. In a base excision repair system reconstituted in vitro, the rejoining of nicked mismatched DNA depended on the presence of APE1, indicating that APE1 may increase the fidelity of base excision repair and may represent a new 3' mispaired DNA repair mechanism. The exonuclease activity of APE1 can remove the anti-HIV nucleoside analogues 3'-azido-3'-deoxythymidine and 2',3'-didehydro-2', 3'-dideoxythymidine from DNA, suggesting that APE1 might have an impact on the therapeutic index of antiviral compounds in this category.     

利用降落PCR扩增KMT-1基因

用试剂盒提取一株牦牛源多杀性巴氏杆菌(C47-8)基因组DNA,同时应用降落PCR和普通PCR扩增KMT-1基因片段。结果表明:降落PCR法扩增出KMT-1基因片段的特异性条带与目的片段长度一致,普通PCR法没有结果。相同的反应体系,降落PCR程序能明显提高PCR的特异性,可用于扩增普通PCR难以扩增的基因片段。     

射极跟随器的辅助放大作用

射极跟随器输入电阻很高、输出电阻很低，使得其用途非常广泛。本文就射极跟随器作输入级和输出级时，对主放大器的电压放大倍数的影响，作出简单的剖析。     

Virus-mediated killing of cells that lack p53 activity

A major goal of molecular oncology is to identify means to kill cells lacking p53 function. Most current cancer therapy is based on damaging cellular DNA by irradiation or chemicals. Recent reports support the notion that, in the event of DNA damage, the p53 tumour-suppressor protein is able to prevent cell death by sustaining an arrest of the cell cycle at the G2 phase. We report here that adeno-associated virus (AAV) selectively induces apoptosis in cells that lack active p53. Cells with intact p53 activity are not killed but undergo arrest in the G2 phase of the cell cycle. This arrest is characterized by an increase in p53 activity and p21 levels and by the targeted destruction of CDC25C. Neither cell killing nor arrest depends upon AAV-encoded proteins. Rather, AAV DNA, which is single-stranded with hairpin structures at both ends, elicits in cells a DNA damage response that, in the absence of active p53, leads to cell death. AAV inhibits tumour growth in mice. Thus viruses can be used to deliver DNA of unusual structure into cells to trigger a DNA damage response without damaging cellular DNA and to selectively eliminate those cells lacking p53 activity.     

茶叶清除羟自由基的能力与其高分子活性中心元素群子参数之间的关系

测定了小叶苦丁,普洱,大叶苦丁,云南大叶红茶等若干著名茶叶的羟自由基清除能力,并且利用电感耦合等离子体原子发射光谱仪测定了茶叶中V、Ti、Mo、Co、Cr、Cu、Fe、Mn、Ni、Sr和Zn这11种高分子活性中心元素的含量;用三参数群子统计方程分别确立了这些茶叶的群子参数,对这些茶叶的羟自由基清除率进行比较。研究发现,所有茶叶都有一定的羟自由基清除能力,清除率在50%~97%之间,其中铁观音,祁门红茶,白毫乌龙茶,黄山雀舌,洞庭碧螺春等的羟自由基清除能力较强,均在90%以上;茶叶中的羟自由基清除能力参数lnF与其高分子活性中心元素分布参数ln(k2r1/r2)之间有很好的线性关系,因此认为可以将高分子活性中心元素的分布参数作为近似判断抗氧化能力大小的依据之一,通过此参数可评价茶叶的抗氧化性。     

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.     

碱金属元素对山东蓝宝石结晶的促进作用研究

目的研究碱金属元素对山东蓝宝石结晶的促进作用。方法对山东蓝宝石寄主玄武岩的主量、微量、稀土元素以及蓝宝石包裹体中的主量元素进行分析,再对碱金属氧化物在岩浆网络中的化学行为进行研究。结果晶出山东蓝宝石的母岩浆源于富集地幔的低度熔融,并在蓝宝石结晶前或者结晶过程中与下地壳发生过强烈的壳—幔交互作用,这种交互作用为母源岩浆提供了充足的硅铝质和碱金属氧化物;其中的铝质为蓝宝石的结晶提供了物质基础,而碱金属氧化物则极大地促进了蓝宝石的结晶。结论碱金属元素对山东蓝宝石的结晶有积极的推动作用。     

谱V(1)同伦群中一些元素的存在性

利用May谱序列以及一些代数和数论的方法,证明了当p≥7时,b1h1,b1g0在Adams谱序列中是永久循环且不是dr边缘,从而分别收敛到同伦群π*V(1)中相应的非零元,其中V(1)是Toda-Smith谱.     

The structural basis of Holliday junction resolution by T7 endonuclease I

The four-way (Holliday) DNA junction is the central intermediate in homologous recombination, a ubiquitous process that is important in DNA repair and generation of genetic diversity. The penultimate stage of recombination requires resolution of the DNA junction into nicked-duplex species by the action of a junction-resolving enzyme, examples of which have been identified in a wide variety of organisms. These enzymes are nucleases that are highly selective for the structure of branched DNA. The mechanism of this selectivity has, however, been unclear in the absence of structural data. Here we present the crystal structure of the junction-resolving enzyme phage T7 endonuclease I in complex with a synthetic four-way DNA junction. Although the enzyme is structure-selective, significant induced fit occurs in the interaction, with changes in the structure of both the protein and the junction. The dimeric enzyme presents two binding channels that contact the backbones of the junction's helical arms over seven nucleotides. These interactions effectively measure the relative orientations and positions of the arms of the junction, thereby ensuring that binding is selective for branched DNA that can achieve this geometry.     

食用菌中高分子活性中心元素分布与其自由基清除能力之间的关系

测定了食用菌的含水量(w_水)、高分子活性中心元素含量以及羟自由基清除能力,计算了食用菌中高分子活性中心元素(Ti、V、Cr、Mn、Mo、Zn、Fe、Co、Ni、Cu和Sr)的分布。结果表明,由含水量校正过的高分子活性中心元素分布参数(1－w_水)^１／３ln(k^２r_１/r_２)与羟自由基清除能力参数ln[F(1－w_水)^３]之间有很好的线性关系。由此笔者认为可以把此高分子活性中心元素分布参数作为近似判断抗氧化能力大小的依据之一,通过此参数可评价食用菌的抗氧化性。     

几种碱金属元素对硫酸催化剂低温活性的影响

研究了用冶金废液制备的低温硫酸催化剂中铯、铷、锂等碱金属元素的助催化作用和熔盐用量对催化剂低温活性的影响．结果表明,铯的低温助催化效果最好,其用量宜控制在n(Cs)／n(V)=0．3～0．6．当n(Cs)／n(V)=0．6时,410℃的SO2转化率达42．5％,比无铯催化剂的SO2转化率高18．5％．铷的加入会降低催化剂的低温活性,宜采取措施降低废液中的铷含量．在多种碱金属元素混合使用的情况下,锂元素有较好的助催化作用,其最佳用量为n(Li)／n(V)=0．4,410℃时SO2转化率达46％．活性组分含量对催化剂低温活性和高温活性影响较大,n(M)／n(v)宜小于4．5．     

The fuzzy computation model of five elements

用自然科学定量方法实现对社会问题的描述,是计算机技术应用于社会分析与预测的关键.五元模糊计算模型源于五行学假设,摆脱用还原论方法对复杂系统建模的难度,是一种符合对立统一基本规律的、能引导计算向可持续方向发展的计算模型.以股市预测为证例,说明模型应用于实现社会宏观问题分析演化的可行性.     

角色分配格中的特异元

Agent组织是合作求解的Agent集合,它描述了Agent与其承担的角色之间的关系.本文主要讨论Agent组织中的角色分配问题,提出了一种考虑了Role与Agent的偏好因素的扩充的角色分配二部图的概念,并指出Agent的角色分配问题就是在扩充的角色分配二部图上构造一个二部图的完美匹配.在Agent组织中,由于Agent及其组织的管理者都具有智能性,虽然Agent及其角色都可以得到匹配,但有些匹配不具有稳定性,因此自利的组织管理者和Agent都会在利益的驱动下背叛对方,从而导致组织破坏.紧接着本文讨论了稳定的扩充角色分配二部图的完美匹配集合,并在其上构造一个强稳定关系,从而将稳定匹配集和强稳定关系构造成一个代数结构--角色分配格,并在该格上构造了两个运算,并分析了两个运算之间的关系,由此得出角色分配格是一个分配格.最后分析了角色分配格中的几类特殊元--最大元、最小元、补元及交不可约元,并指出任何一个角色分配格都存在最大元和最小元,从而角色分配格是一个有界格,但并不是任何元都存在补元,从而角色分配格不一定是布尔代数,但是在给定特定的偏好下,即在特定的扩充角色分配二部图上,角色分配格可以构成布尔代数.对于交不可约元来说,它的重要意义就在于角色分配格中的任何元都可以表示成一些交不可约元的交,从而所有的交不可约元构成的集合是稳定匹配集的一个完备集.本文的结论是:扩充的角色分配二部图是Agent组织中的角色分配模型,其上所有的稳定匹配在强稳定关系下构成一个角色分配格,该格是一个有界分配格,但不一定是布尔代数,该格中的所有元都可以用其中的交不可约元来构造,从而为快速求解角色分配格做好了理论上的准备.     

Molecular mechanism of the inhibitory effect of methylation outside the recognition sequence of restriction endonuclease Pvu II on its cleavage activity

In 1991, we found that methylation outside the Pvu II recognition sequence could partially inhibit its cleavage activity. To clarify the molecular mechanism, three plasmids with different methylation states were constructed. Then, together with the original one, four plasmids were digested with different amounts of Pvu II. Results show that methylation on both sites results in 90 % inhibition; moving the methylated site one base further away decreases the inhibitory effect to about 30 %; with the adjacent dam methylation site eliminated, the inhibitory effect disappears. The data suggest that the inhibition of cleavage activity caused by outside methylation is not “all or none”, and the degree of inhibition is dependent on the position and the number of methylated bases.     

人肿瘤细胞株中细小病毒H—1的DNA扩增与非结构蛋白NS—1基因的表达

研究三株人癌细胞和两株对照细胞对细小病毒Ｈ－１杀伤作用敏感性的分子机制．表明了在感染复数ｍｏｉ（ｍｕｌｔｉｐｉｃｉｔｙｏｆｉｎｆｅｃｔｉｏｎ）为５ｐｆｕ（ｐｌａｑｕｅｆｏｒｍｉｎｇｕｎｉｔ）／细胞的情况下，作为Ｈ—１病毒复制受纳细胞的人肝癌细胞株ＯＧＹ－７７０３和人胃癌细胞株ＳＧＣ—７９０１，能够支持病毒ＤＮＡ扩增和非结构蛋白ＮＳ—１基因的表达，这和作为阳性对照的由ＳＶ４０转化的新生儿肾细胞株ＮＢ—Ｋ一样，但对Ｈ—１病毒感染有抗性的人肾癌细胞株ＯＵＲ—１０和它的对照人胎肾细胞株ＨｕＫ—１，并不支持病毒ＤＮＡ扩增和ＮＳ—１蛋白的表达．本文结果指出，细小病毒Ｈ—１的杀伤作用与细胞中的病毒ＤＮＡ扩增及ＮＳ—１基因表达的程度相关．