Single strands, triple strands, and kinks in H-DNA

A naturally occurring (dT-dC)18:(dA-dG)18 repeat in the H conformation of DNA was shown to contain single-stranded nucleotides in the center of the TC18 repeat and on one half of the AG18 repeat. These results support the model that H-DNA is a structure containing both triple-stranded and single-stranded regions. The stability of this structure was affected by both pH and the degree of negative supercoiling: at pH 7.6 to 7.7, a high level of supercoiling was needed to keep about half of the molecules in the H conformation; at pH 6 and pH 5, normal levels of supercoiling supported H-DNA; and at pH 4, no supercoiling was required. At mildly alkaline pH, the TC/AG18 repeat assumed a novel conformation called J-DNA that differed from both the B and H forms. A three-dimensional model for the structure of H-DNA is proposed that accounts both for the single-strandedness of the nucleotides and for the influence of supercoiling on H-DNA formation. This model predicts and evidence is presented that H-DNA introduces a sharp kink in the DNA. Moreover, the angle of this kink appears not to be fixed, so that H-DNA is also a hinged-DNA.     

中国乌骨鸡品种BCDO2基因多态性和肤色鉴定

为分析β-胡萝卜素脱氧酶2(β-carotene dioxygenase2, BCDO2)基因在我国乌骨鸡中的变异情况，采用PCR方法分别扩增和测序了我国5个乌骨鸡品种(丝羽乌骨鸡、东乡绿壳蛋鸡、金湖乌凤鸡、余干乌骨鸡和新兴竹丝鸡3号)、白耳黄鸡(黄肤色)和崇仁麻鸡(白肤色)的BCDO2基因，并与GenBank数据库中的原鸡序列进行系统发育分析。结果显示：7个品种215条序列，总计发现6个多态位点，分别为6273091(G-A)、6273129(A-G)、6273229(C-T)、6273240(C-T)、6273307(A-G)和6273672(A-G)。基于6个多态点界定了3种单倍型，定义为Hap1、Hap2和Hap3。其中只有白耳黄鸡、崇仁麻鸡和丝羽乌骨鸡有1种单倍型，东乡绿壳蛋鸡、金湖乌凤鸡、余干乌骨鸡和新兴竹丝鸡3号均有2种单倍型。系统发育分析显示：Hap1和Hap2只与红色原鸡聚为一类，Hap3和多个原鸡聚为一类。BCDO2基因多态位点能够很好地区分黄白肤色的品种，但很难区分乌骨鸡品种。多个原鸡在我国乌骨鸡品种形成过程中都做出了贡献。该研究结果为我国乌骨鸡遗传资源的保护、选育和鉴定工作提供了遗传背景信息。     

Size-Specific Infrared Spectra of Benzene-(H2O)n Clusters (n = 1 through 7): Evidence for Noncyclic (H2O)n Structures

Resonant ion-dip infrared spectroscopy has been used to record size-specific infrared spectra of C(6)H(6)-(H(2)O)n clusters with n = 1 through 7 in the O-H stretch region. The O-H stretch spectra show a dramatic dependence on cluster size. For the n = 3 to 5 clusters, the transitions can be divided into three types-attributable to free, pi hydrogen-bonded, and single donor water-water O-H stretches-consistent with a C(6)H(6)-(H(2)O)n structure in which benzene is on the surface of a cyclic (H(2)O)n cluster. In n = 6 and 7 clusters, the spectra show distinct new transitions in the 3500 to 3600 wave number region. After comparison of these results with the predictions of ab initio calculations on (H(2)O)n clusters, these new transitions have been assigned to double donor O-H stretches associated with the formation of a more compact, noncyclic structure beginning with (H(2)O)(6). This is the same size cluster for which ab initio calculations predict that a changeover to noncyclic (H(2)O)n structures will occur.     

关于丢番图方程(13n)~x (84n)~y=(85n)~z

设ｎ 为任意正整数,本文证明了丢番图方程（１３ｎ）ｘ＋ （８４ｎ）ｙ＝ （８５ｎ）ｚ 仅有正整数解ｘ＝ ｙ＝ ｚ＝ ２。     

Synthesis and Characterization of Molybdenum Carbide Clusters MonC4n, (n = 1 to 4)

Laser radiation (XeCl laser, 308-nanometer wavelength) focused into a cell containing Mo(CO)(6) vapor produced ultrafine particles in the extended waist of the laser beam. Negative ion mass spectrometry revealed molybdenum carbide cluster ions with a stoichiometry MonC4n (n = 1 to 4). The MonC4n(-) (n = 2 to 4) ions are completely unreactive with NH(3), H(2)O, and O(2), suggesting structures in which the molybdenum atoms are unavailable for coordination to additional ligands. Collision-induced dissociation studies of these anions show the loss of MoC(4) units as the main fragmentation pathway. This observation, together with the lack of addition reactions, provides a basis for structures in which a planar cluster of two, three, or four molybdenum atoms is surrounded by, and bonded to, carbon dimers.     

The t(14;18) chromosome translocations involved in B-cell neoplasms result from mistakes in VDJ joining

In this study, the joining sequences between chromosomes 14 and 18 on the 14q+ chromosomes of a patient with pre-B-cell leukemia and four patients with follicular lymphoma carrying a t(14;18) chromosome translocation were analyzed. In each case, the involved segment of chromosome 18 has recombined with the immunoglobulin heavy-chain joining segment (JH) on chromosome 14. The sites of the recombination on chromosome 14 are located close to the 5' end of the involved JH segment, where the diversity (D) regions are rearranged with the JH segments in the production of active heavy-chain genes. As extraneous nucleotides (N regions) were observed at joining sites and specific signal-like sequences were detected on chromosome 18 in close proximity to the breakpoints, it is concluded that the t(14;18) chromosome translocation is the result of a mistake during the process of VDJ joining at the pre-B-cell stage of differentiation. The putative recombinase joins separated DNA segments on two different chromosomes instead of joining separated segments on the same chromosome, causing a t(14;18) chromosome translocation in the involved B cells.     

柑橘属2n花粉自然发生与沙田柚2n花粉诱导研究

果树2n配子育种较其他植物起步晚,尤其是利用2n花粉进行育种的研究在柑橘上还无先例。试验中初步观察了柑橘属部分品种的2n花粉自然发生情况,证实了柑橘属内未减数花粉的存在。同时通过秋水仙碱不同浓度与作用时间处理促进了柑橘2n花粉的发生,将长寿沙田柚2n花粉发生比例由当年的自然发生率0.87%提高到9.76%。初步观察了2n花粉离体萌发状况,其萌发率与花粉管伸长速度较为正常,但萌发启动比单倍性花粉慢。     

添加不同物料对蟹味菇菌渣堆肥的影响

[目的]研究堆肥过程中温度、pH、有机碳、全量养分(全氮、全磷、全钾)和C/N的动态变化。[方法]以蟹味菇菌渣作为主要堆肥原料进行高温堆肥试验,设置:纯菌渣(T_1)、菌渣∶猪粪=8∶2(T_2)、菌渣∶猪粪=6∶4(T_3)、菌渣∶猪粪=5∶5(T_4)、菌渣∶羊粪=6∶4(T_5)、菌渣∶猪粪∶水稻秸秆粉碎物=6∶2∶2(T_5),研究堆肥过程中温度、pH、有机碳、全氮、全磷、全钾和C/N的动态变化。[结果]堆体温度在4 d后均达到50℃以上,保持高温30~40 d后开始下降,其中50℃以上持续时间T1处理高达40 d,而T_2、T_3处理仅为27 d;堆肥pH呈先快速上升后缓慢下降的趋势,由开始的偏酸性(pH 5.5~6.7)到堆制结束时呈弱碱性(pH 7.5~8.3);堆制过程中有机碳持续缓慢下降,至堆肥结束时不同处理平均下降了53.9%;堆肥全氮含量在9 d前均先快速上升,在9~45 d缓慢下降;菌渣的比例越高,堆制前后全氮增加幅度越高(T6除外),而全磷和全钾随着堆肥进程而逐渐被浓缩,至堆肥结束均表现为T_3和T_4处理较高,而T_1和T_5处理较低。[结论]综合考虑堆肥质量和堆期等因素,利用蟹味菇菌渣为主要原料大规模化生产有机肥,T2和T6处理的配方较适宜。     

Observation of d(x2-y2)-like superconducting gap in an electron-doped high-temperature superconductor

High-resolution angle-resolved photoemission spectroscopy of the electron-doped high-temperature superconductor Nd(2-x)Ce(x)CuO4 (x = 0.15, transition temperature T(c) = 22 K) has found the quasiparticle signature as well as the anisotropic d(x2-y2)-like superconducting gap. The spectral line shape at the superconducting state shows a strong anisotropic nature of the many-body interaction. The result suggests that the electron-hole symmetry is present in the high-temperature superconductors.     

0～56日龄舍饲羔羊盲肠解剖特点和微生物菌群的变化

选择甘肃肉用绵羊新品种选育群公羔(单羔)45只,分别于0、7、14、21、28、35、42、49、56d屠宰测定盲肠的相对质量(消化道质量、肠道质量、大肠质量)、相对容积(消化道容积、肠道容积、大肠容积)、相对长度(肠道长度、大肠长度),盲肠内容物pH和粘膜pH,乳酸杆菌和大肠杆菌的数量.结果表明:盲肠相对质量(消化道质量、肠道质量、大肠质量)和盲肠相对容积(肠道容积、大肠容积)的增降趋势基本保持一致,随日龄增长均呈"降低-升高-降低"的变化趋势.0～56日龄羔羊盲肠内容物pH和粘膜pH分别在5.77～7.06和6.03～7.22之间,均呈弱酸性;粘膜pH略高于内容物pH.随着pH的升高,单位质量内容物中大肠杆菌的数量有所上升,而乳酸杆菌的数量则有所下降.0d羔羊盲肠中即有大肠杆菌和乳酸杆菌的存在,并且单位内容物中所含数量最高;盲肠内容物pH从21d开始趋于稳定;随着日龄的增大,单位内容物中大肠杆菌和乳酸杆菌的数量均处于下降趋势,乳酸杆菌数量从28d后趋于稳定,大肠杆菌数量35d后趋于稳定;试验期内乳酸杆菌数量始终高于大肠杆菌数量.在舍饲并始于7d补饲条件下,绵羊肉用羔羊于28d或35d断奶不会对其盲肠形态及内容物pH、单位内容物乳酸杆菌数量和大肠杆菌数量等指标的发育造成严重影响.     

DNA mismatch correction in a defined system

DNA mismatch correction is a strand-specific process involving recognition of noncomplementary Watson-Crick nucleotide pairs and participation of widely separated DNA sites. The Escherichia coli methyl-directed reaction has been reconstituted in a purified system consisting of MutH, MutL, and MutS proteins, DNA helicase II, single-strand DNA binding protein, DNA polymerase III holoenzyme, exonuclease I, DNA ligase, along with ATP (adenosine triphosphate), and the four deoxynucleoside triphosphates. This set of proteins can process seven of the eight base-base mismatches in a strand-specific reaction that is directed by the state of methylation of a single d(GATC) sequence located 1 kilobase from the mispair.     

HrpN_(Ea)蛋白的结构与功能分析

Harpins是由革兰氏阴性植物病原细菌产生的一类蛋白激发子,对蛋白酶敏感,在非寄主植物叶片上可以诱导hypersensitive response（HR）或hypersensitive cell death（HCD）。HrpNEa是Harpins蛋白的一种,是从梨火疫病菌（Erwinia amylovora）中分离得到的。大量试验证明,HrpNEa蛋白在引起植物过敏反应的同时,能诱导植物获得性系统抗性及刺激植物生长发育。从分子生物学角度,利用国际互联网上的相关生物信息学分析软件NPSA、Swiss-Model、SAPS、InterPro Scan等对HrpNEa蛋白进行了结构和功能的预测分析。HrpNEa蛋白由403个氨基酸组成,有较多的β折叠和无规卷曲结构;HrpNEa蛋白无N端信号肽,不形成跨膜结构,定位于细胞质中。     

Dynamics of Carbonium Ions Solvated by Molecular Hydrogen: CH5+(H2)n (n = 1, 2, 3)

The dynamics of the carbonium ion (CH(5)(+)), a highly reactive intermediate with no equilibrium structure, was studied by measuring the infrared spectra for internally cold CH(5)(+)(H(2))n(n = 1, 2, 3) stored in an ion trap. First-principle molecular dynamics methods were used to directly simulate the internal motion for these ionic complexes. The combined experimental and theoretical efforts substantiated the anticipated scrambling motion in the CH(5)(+) core and revealed the effect of the solvent molecular hydrogen in slowing down the scrambling. The results indicate the feasibility of using solvent molecules to stabilize the floppy CH(5)(+) ion in order to make it amenable to spectroscopic study.     

瘤胃微生物基因组文库中BAC末端序列分析

基于前期从瘤胃微生物基因组文库中筛选的功能酶克隆菌,利用T7和pIBRP引物,测定功能酶克隆菌的BAC末端序列,并利用NCBI Blast系统对BAC末端序列进行分析.结果表明:共得到26条BAC末端序列,经Blast比对分析,与已知编码基因的匹配度低,而大部分BAC末端序列与阪崎肠杆菌和环境中的微生物匹配度高,说明瘤胃中的微生物与其它环境中的微生物具有一定的相似性,进一步丰富了对瘤胃微生物的认识.     

Topology and formation of triple-stranded H-DNA

Repeating copolymers of (dT-dC)n.(dA-dG)n sequences (TC.AGn) can assume a hinged DNA structure (H-DNA) which is composed of triple-stranded and single-stranded regions. A model for the formation of H-DNA is proposed, based on two-dimensional gel electrophoretic analysis of DNA's with different lengths of (TC.AG)n copolymers. In this model, H-DNA formation is initiated at a small denaturation bubble in the interior of the copolymer, which allows the duplexes on either side to rotate slightly and to fold back, in order to make the first base triplet. This nucleation establishes which of several nonequivalent H-DNA conformations is to be assumed by any DNA molecule, thereby trapping each molecule in one of several metastable conformers that are not freely interconvertible. Subsequently, the acceptor region spools up single-stranded polypyrimidines as they are released by progressive denaturation of the donor region; both the spooling and the denaturation result in relaxation of negative supercoils in the rest of the DNA molecule. From the model, it can be predicted that the levels of supercoiling of the DNA determine which half of the (dT-dC)n repeat is to become the donated third strand.     

Detection of minimal residual cells carrying the t(14;18) by DNA sequence amplification

By means of the polymerase chain reaction (PCR) technique, DNA sequences were amplified that flank the crossover sites of a characteristic chromosomal translocation for follicular lymphomas, t(14;18)(q32;q21). This technique permitted the detection of cells carrying the t(14;18) hybrid DNA sequences at a dilution of 1:100,000. The remission marrow and blood samples of a patient with follicular lymphoma and the t(14;18) failed to show any abnormality by morphological examination and conventional Southern blot analysis. However, the t(14;18) hybrid DNA sequences were detected by the PCR technique. Thus, this technique is a highly sensitive tool to detect minimal residual cells carrying the t(14;18) and has the potential to identify a subpopulation of patients with subclinical disease.     

Chromatin structure and de novo methylation of sperm DNA: implications for activation of the paternal genome

The chromatin structure characteristic of constitutively expressed genes, tissue-specific genes, and inactive genes is absent in chicken sperm chromatin. However, point sites of undermethylation in sperm DNA within constitutively expressed genes, but not within globin genes or an inactive gene, correspond to the location of regions of altered chromatin structure (hypersensitive sites) in somatic tissue and spermatogonial cells. A de novo methylation process whereby regions within and flanking these genes become methylated, but which excludes the methylation of sequences within hypersensitive sites, occurs between the spermatogonial stage and the first meiotic prophase. These undermethylated regions may play a role in the activation of the paternal genome during embryogenesis.     

兴义维蚋蚋卵(胚胎)原代细胞培养及鉴定

【目的】筛选出最适宜兴义维蚋蚋卵(胚胎)原代细胞的培养条件和最佳培养基组合,并对其原代细胞进行鉴定,为蚋类细胞系的建立打下基础。【方法】采用组织块和单细胞法对兴义维蚋蚋卵(胚胎)进行原代细胞培养,分析培养基、温度、pH、CO2和培养器皿对细胞培养的影响;并测定蚋卵(胚胎)及原代细胞的rDNA-ITS区序列,通过构建基于ITS区序列的蚋类系统发育进化树鉴定其种属来源。【结果】兴义维蚋蚋卵(胚胎)原代细胞最适宜的培养方法为组织块法,培养基为改良型Shields and Sang M3,pH 6.0~6.5,培养温度28℃,恒温生化培养箱和5% CO2培养箱对原代细胞培养无明显差异,培养器皿为经多聚赖氨酸(PLL)处理的一次性塑料培养皿/板。由基于ITS区序列构建的蚋类系统发育进化树可知,蚋卵(胚胎)及其原代培养细胞均来源于兴义维蚋。【结论】成功建立的兴义维蚋蚋卵(胚胎)原代细胞培养方法可在科研生产中进一步推广应用。