DNA3′,5′-磷酸二酯键骨架结构稳定的热力学基础分析

为了解大自然选择3′,5′-磷酸二酯键作为DNA结构骨架的必然性,从热力学角度模拟和计算了磷酸、2′-脱氧核糖、胞嘧啶及它们在不同位置结合形成的磷酸-2′-脱氧核糖、胞嘧啶-2′-脱氧核糖、磷酸-2′-脱氧核糖-胞嘧啶的能量,发现3′-磷酸-2′-脱氧核糖、5′-磷酸-2′-脱氧核糖、1′(-4-胞嘧啶)-2′-脱氧核糖、3′-磷酸-1′(-4-胞嘧啶)-2′-脱氧核糖、5′-磷酸-1′(-4-胞嘧啶)-2′-脱氧核糖的能量比其他相应形式结合物的能量低.表明磷酸与2′-脱氧核糖形成的3′,5′-磷酸二酯键有作为DNA结构骨架的热力学依据.     

Taq酶体外合成DNA时模板错位机制的探讨

利用Taq DNA聚合酶体外合成DNA过程中,当反应体系中缺少与模板链互补配对的dNTP底物时,产物合成并不会在底物缺失位点处终止,聚合反应继续进行.为研究此复制缺陷现象,设计一系列模板用于DNA体外酶促合成.除了已知的碱基错配机制,笔者发现存在另一种"模板错位"机制,即模板中与底物非Watson-Crick互补配对的碱基位点首先进行收缩滑动,形成模板bulge结构后再继续进行酶促合成反应.这项研究有助于提高DNA样品合成保真度以及继续深入探索体外DNA合成的详细机制.     

黄曲霉素和N-亚硝基化合物借诱发DNA互补碱对交联而启动癌变

致癌机理的双区理论发现,绝大多数环境中的致癌剂,均通过引起DNA股间互补碱对的共价交联而启动细胞的癌变.DNA碱稀释过滤法证明:致癌物中的霉菌毒素即黄曲霉素G 1 ,N-亚硝基化合物中的亚硝基二乙胺,二丁胺,吗啉和四氢吡咯、偶氮染料中的4-二甲氨基偶氮苯和含氮杂环化合物中的喹啉,均剂量相关地引起DNA股间交联.而相应类型的非致癌剂黄曲霉素B 2 、亚硝基二苯胺、4'-溴-4-二甲氨基偶氮苯和异喹啉,均不能引起此种交联.用DNA交联24h修复实验,首次提出测定DNA股间交联中、互补碱对交联比率的方法.证明:DNA非互补碱对交联被完全修复,但互补碱对间的交联则难以修复,而互补碱对交联的比率与其致癌强度相关.致突变谱数据证明:突变即点突变和移码变异都是由交联的互补碱对所指导.因此,双区理论是化学、内源物和物理致癌作用的合理机理.     

“私人基因图”普及风暴悄然临近 “1000美元基因组”把你的基因图读给你

“1000美元基因组”把你的基因图读给你许多基因组解码技术利用DNA的碱基互补对规则。基因组语言的“字母表”只包含4个字母,即被称为碱基的基本单位一腺嘌呤[A],胞嘧啶[C],鸟嘌呤[G]和胸腺嘧啶[T]。它们彼此配对(A和T,C 和G),从而形成标准的DNA梯阶。活细胞使用这一规则复制和修复自身的DNA 分子;碱基配对规则也被人们来复制和感兴趣的DNA,直到如今,它仍是主流DNA 定序技术的基本原理。     

鱼类线粒体DNA控制区的结构和进化:以鳑鱼类为例

以鳑鱼类为例,研究了鱼类线粒体DNA控制区的结构和进化规律.识别了终止序列区、中央保守区和保守序列区3个区域.指出扩展终止相关序列(ETAS)的主体是TACAT和它的反向互补序列ATGTA形成的发夹结构.给出了鱼类中若干重要保守序列的普遍形式.研究结果表明,一般情况下,只有一个行使功能的ETAS,但可能会有多个复制的、不行使功能的ETAS存在.鱼类的保守序列CSB2最为保守.线粒体DNA控制区被认为是由各功能单位形成主体框架,主体框架复制产生重复序列,重复序列产生快速变异,这样造成不同类群间线粒体DNA控制区巨大差异.易突变点和二级结构的存在均可能与变异的发生相关.     

运用交流阻抗技术直接监测DNA杂交

介绍了基于交流阻抗技术构建非标记型脱氧核糖核酸（DNA）杂交传感器的方法.以24个碱基长度的寡聚DNA作为实验对象，将5′端巯基化的单链寡聚DNA（SH-ssDNA）探针与巯基乙酸（RSH）同时自组装到金电极表面，形成杂交识别层，利用交流阻抗技术测量出杂交前后金电极表面电子传递电阻R_et的增量作为杂交信号.实验中对DNA探针的自组装时间、杂交温度、杂交时间和阻抗测量液等实验条件进行了观察和优化；通过选择自组装液中SH-ssDNA探针和RSH的浓度，减少DNA在金电极表面的非特异性吸附，同时保证金电极表面自组装的SH-ssDNA探针有合适的疏密度，提高了杂交效率.在各优化条件下，无需扩增杂交信号，此非标记型DNA杂交传感器的检测下限为3.0×10^-14mol/L；和完全互补序列相比，一个和三个碱基错配序列分别产生55.6%和1.3%的杂交信号.     

酪氨酸过渡金属配合物的合成、结构及其与DNA相互作用的光谱学研究

选择具有生物活性的酪氨酸作配体,合成了两个Ni(Ⅱ)和Cu(Ⅱ)配合物.解析了它们的晶体结构,并采用电子吸收光谱、荧光光谱、黏度等方法研究了配合物与DNA的相互作用,结果表明,两种配合物均与DNA发生不同程度的键合作用.     

特性函数与配分函数

<正> 引言 特性函数和配分函数分别为热力学和统计物理中的二个重要函数,它们对热力学状态的描述有重要意义。本文通过讨论在闭系(粒子数不变的系统)中两者之间的内在联系将它们作统一描述,并由此强调了自由能的重要性。 马林(Massieu )在1869年证明,在独立变数适当选择之下,只要知道一个热力学函数,就可以通过求偏导数而求得均匀系统的基本热力学函数(即物态方程、内能和熵),从而将均匀系统的平衡性质完全确定。这个热力学函数称为特性函数,相     

基于语料库的多词单位抽取算法

分析了研究者们在多词单位抽取算法中的一些工作,包括多词单位的评分和选择.将评分算法根据它们的设计依据划分为3类,对它们进行总结分析,并用实验进行了验证.本文还分析了多种评分算法的组合方法,使用这些组合方法可以互补各种评分算法,达到更好的抽取效果.     

栖热菌(Thermus)的DNA转化研究

由栖热菌FDB8(Thermus sp.FDB8)提取的染色体DNA对栖热菌FD3009(Thermus sp.FD3009)进行了转化.用丝裂霉素C选择培养基对转化子进行选择,共获得3个转化子.它们的菌落色泽、对丝裂霉素C的抗性强度和耐热DNA聚合酶活性均介于供体菌和受体菌之间,而其菌体生长速度和破壁难易程度则优于供体菌和受体菌.结果表明,转化子是由供体菌FDB8的染色体DNA转化了受体菌FD3009所致,同时还可由转化子进一步选育出抗丝裂霉素C的耐热DNA聚合酶高产菌株.     

Carcinogenesis of asbestos switched on by inducing cross-linkage between DNA complementary pair bases

Since the beginning of the 1980s, Dai Qianhuan predicted based upon his di-region theory that the carcinogenesis switched on by the so-called physical carcinogenic factors including radiation, asbestos and foreign matter implantation, is just initiated through the cross-linking between DNA complementary pair bases induced by them. In this note, it was evidenced with the DNA filter elution method that the oxygenase activated by asbestos induces the cross-linking between DNA inter-strands and DNA-protein with dosage correlation, in which over 80% of DNA inter-strand cross-link ratio account for the total cross-link ratio. Obviously, both of the cross-linkages are just induced by hydroxyl free radical, HO ·, because the ferrous ion increased the cross-link ratios up to several times through Fenton reaction and vitamin C inhibited the cross-link ratios with factors of 8–9 by destroying the hydroxyl radical. Non-carcinogen but with lower free radical formation energy, pyrene, by culturing with asbestos gave 3–4 times cross-link ratios than the original ratios induced by asbestos only. Estradiol, an endogenous carcinogen, as a bio-electrophilic species but with higher free radical formation energy by culturing with asbestos, gave only 1.2 time cross-link ratios than expected ones. Ferrous ion which can increase HO · concentration through Fenton reaction, increased the ratios to 2–2.5 times in the former case but only 1.2 time in the latter case. Vitamin C, a free radical scavenger, gave a powerful inhibition to the cross-linking with a factor of 8–11 in the former case but a weak inhibition with a factor of 1.2 only in the latter case. So, it is evidenced further that the cross-linkages induced by asbestos are originated from hydroxyl radical. Reasonable structures of the cross-linking products induced by asbestos or hydroxyl radical have been depicted based upon AMI MO theory. These structures have been verified further by a reasonable explanation of the mutational spectrum induced by hydroxyl radical.     

塑性力学变形理论的相似非耦联变分原理和广义变分原理

引入了相似非耦联方程的概念，应用加权余量法建立了塑性力学变形理论的相似非耦联势能原理和余能原理．应用拉氏乘子法于该势能原理和余能原理，建立了广义相似非耦联势能原理和余能原理．并应用该余能原理于相似非耦联的三角形桁架的计算．     

乌江流域水光互补梯级蓄能调度图绘制

为适应大规模光伏出力接入乌江流域与梯级水电站联合调度、打捆送出的新要求,基于流域实际蓄能控制方式提出了水光互补模式下梯级水电站分期发电策略,确定了汛初、年末关键时间节点的蓄能合理范围,据此绘制了水光互补梯级蓄能调度图,以指导中长期水光互补调度。实例验证结果表明,与流域梯级水电站实际发电量相比,水光互补梯级蓄能调度图能够提高系统发电量0.7亿~2.1亿kW·h；水光互补梯级蓄能调度图编制过程简单、合理,优化调度结果符合实际,可用于乌江流域中长期水光互补优化调度。     

Primary structure and functional expression from complementary DNA of the rod photoreceptor cyclic GMP-gated channel

The complete amino-acid sequence of the cyclic GMP-gated channel from bovine retinal rod photoreceptors, deduced by cloning and sequencing its complementary DNA, shows that the protein contains several putative transmembrane segments, followed by a region that is similar to the cyclic GMP-binding domains of cyclic GMP-dependent protein kinase. Expression of the complementary DNA produces cyclic GMP-gated channel activity in Xenopus oocytes.     

模态分析的应力方法

基于弹性体固有振动问题的余能变分原理,导出了弹性体固有振动的应力模态方程,进而探讨了一种模态分析的应力方法。并以平面桁架和简支矩形板为例说明了以应力作为基本变量的模态分析方法的可行性。     

Carcinogenesis switched on by DNA cross-link between complementary bases aroused by aflatoxin and N-nitroso compounds

The di-region theory put forward by Dai Qianhuan, a molecular mechanism of chemical carcinogenesis, concluded that the carcinogenesis induced by most of the environmental carcinogens is switched on by the cross-linking between DNA complementary bases aroused by the bifunctional alkylation of their metabolic intermediates. It was evidenced in this paper with DNA filter elution method that one carcinogenic mycotoxin, aflatoxin G1, four carcinogenic N-nitroso compounds, N-nitrosodiethyl-amine, N-nitrosodibutyl-amine, N-nitrosomorpholine and N-nitrosopyrrolidine, one carcinogenic diazo color, 4-dimethylaminodiazobenzene and one carcinogenic nitrogen-containing heterocyclic compound, quinoline, all induced DNA interstrands cross-linking with dosage correlation after metabolic activation. However, the non-carcinogens in corresponding series for control, aflatoxin B2, N-nitroso-diphenylamine, 4′-bromo-4-dimethylaminodiazobenzene and isoquinoline, cannot induce DNA interstrands cross-linking at all in the same condition. A method for the determination of cross-linking ratio between DNA complementary bases in total DNA interstrands cross-linking, which has no monitoring measure as yet, has been established for the first time based upon a 24 hour repairing experiment. The DNA complementary pair cross-linking ratio induced by a metabolized carcinogen is correlated with its carcinogenic potential. It may be concluded that the mutations including point and frameshift mutagenesis induced by aflatoxin and other carcinogens are switched on by their corresponding cross-linking base pair between complementary bases. Therefore, the di-region theory is a reasonable molecular mechanism for chemical, endogenous and physical carcinogenesis.     

The DNA concentration effect on DNA radiation damage induced by <Superscript>7</Superscript>Li ions and γ rays

To evaluate the influence of the DNA concentration in the aqueous solution on DNA radiation damage, the plasmid DNA in the presence or absence of Mannitol （scavenger of free radical OH.） was irradiated by ^7Li ions and γ rays at various DNA concentrations. Gel electrophoresis analysis revealed that the DNA damage of single and double strand breaks induced by irradiation became more severe at lower DNA concentration. In the condition of γ-ray irradiation, most of double strand breaks （DSB） damage was neutralized and less associated with DNA concentration in the presence of mannitol. However, under ^7Li irradiation, DSB damage could not be cleared by mannitol but was gradually aggravated with decreasing DNA concentrations. These findings imply that under low-LET irradiation, most of the DSB damage is generated by free radical OH·diffusion, and thus may be counteracted by scavengers, while at higher-LET irradiation, quite a fraction of DSB induction is caused by direct ionizing energy deposition of heavy ions, which cannot be eliminated. This work also indicates that the proportion between free radical damage and direct ionizing damage is s constant which is independent of DNA concentration when the DNA concentration is under a certain value （50ng/μL）. Our study sheds light on the un- derlying mechanisms in the DNA radiation damage process.     

Mechanism of homologous recombination from the RecA-ssDNA/dsDNA structures

The RecA family of ATPases mediates homologous recombination, a reaction essential for maintaining genomic integrity and for generating genetic diversity. RecA, ATP and single-stranded DNA (ssDNA) form a helical filament that binds to double-stranded DNA (dsDNA), searches for homology, and then catalyses the exchange of the complementary strand, producing a new heteroduplex. Here we have solved the crystal structures of the Escherichia coli RecA-ssDNA and RecA-heteroduplex filaments. They show that ssDNA and ATP bind to RecA-RecA interfaces cooperatively, explaining the ATP dependency of DNA binding. The ATP gamma-phosphate is sensed across the RecA-RecA interface by two lysine residues that also stimulate ATP hydrolysis, providing a mechanism for DNA release. The DNA is underwound and stretched globally, but locally it adopts a B-DNA-like conformation that restricts the homology search to Watson-Crick-type base pairing. The complementary strand interacts primarily through base pairing, making heteroduplex formation strictly dependent on complementarity. The underwound, stretched filament conformation probably evolved to destabilize the donor duplex, freeing the complementary strand for homology sampling.     

拉氏乘子法和耦联变分原理

本文利用拉氏乘子法系统地导出了耦联势能和余能原理,二类变量和三类变量的耦联广义势能原理和广义余能原理