Thymocyte expression of RAG-1 and RAG-2: termination by T cell receptor cross-linking.

The expression of the V(D)J [variable (diversity) joining elements] recombination activating genes, RAG-1 and RAG-2, has been examined during T cell development in the thymus. In situ hybridization to intact thymus and RNA blot analysis of isolated thymic subpopulations separated on the basis of T cell receptor (TCR) expression demonstrated that both TCR- and TCR+ cortical thymocytes express RAG-1 and RAG-2 messenger RNA's. Within the TCR+ population, RAG expression was observed in immature CD4+CD8+ (double positive) cells, but not in the more mature CD4+CD8- or CD4-CD8+ (single positive) subpopulations. Thus, although cortical thymocytes that bear TCR on their surface continue to express RAG-1 and RAG-2, it appears that the expression of both genes is normally terminated during subsequent thymic maturation. Since thymocyte maturation in vivo is thought to be regulated through the interaction of the TCR complex with self major histocompatibility complex (MHC) antigens, these data suggest that signals transduced by the TCR complex might result in the termination of RAG expression. Consistent with this hypothesis, thymocyte TCR cross-linking in vitro led to rapid termination of RAG-1 and RAG-2 expression, whereas cross-linking of other T cell surface antigens such as CD4, CD8, or HLA class I had no effect.     

Dangling bond dynamics on the silicon (100)-2x1 surface: dissociation, diffusion, and recombination

The dynamics of dangling bond (DB) diffusion was studied after deuterium desorption from the silicon (100)-2x1 surface. At elevated temperatures, paired DB sites produced after desorption unpaired as deuterium atoms hopped from adjacent dimers. Below 620 kelvin, the unpaired configuration most commonly observed corresponded to two DBs on adjacent silicon dimers. At higher temperatures, unpaired DBs executed one-dimensional walks along the dimer rows, and recombination was observed with the same partner after walks lasting many minutes. The frequency and extent of these excursions increased with temperature. Above 660 kelvin, complete dissociation was observed and was sometimes followed by recombination by means of partner exchange. The implications for low-temperature materials growth are discussed.     

A Quantum State-Resolved Insertion Reaction: O((1)D) + H(2)(J = 0) --> OH((2) product operator product operator product operator, v, N) + H((2)S)

The O((1)D) + H(2) --> OH + H reaction, which proceeds mainly as an insertion reaction at a collisional energy of 1.3 kilocalories per mole, has been investigated with the high-resolution H atom Rydberg "tagging" time-of-flight technique and the quasiclassical trajectory (QCT) method. Quantum state-resolved differential cross sections were measured for this prototype reaction. Different rotationally-vibrationally excited OH products have markedly different angular distributions, whereas the total reaction products are roughly forward and backward symmetric. Theoretical results obtained from QCT calculations indicate that this reaction is dominated by the insertion mechanism, with a small contribution from the collinear abstraction mechanism through quantum tunneling.     

CAD／CAM集成数控自动编程系统的研制

SAAPT-2(1/2)D NC自动编程系统能高效、准确地实现零件源程序到NC程序、NC穿空纸带的转换。该系统由几何处理模块、工艺处理模块、后置处理模块和子程序库组成。几何处理模块对零件源程序几何定义语句进行词法、语法检查和参数标准化计算;工艺处理模块根据标准化参数对运动语句及其它非几何定义语句进行处理,生成中间代码文件;后置处理模块将中间代码文件变成NC加工程序。     

State-to-State Rates for the D + H2(v = 1, j = 1) rarr HD(v', j') + H Reaction: Predictions and Measurements

A fully quantal wavepacket approach to reactive scattering in which the best available H(3) potential energy surface was used enabled a comparison with experimentally determined rates for the D + H(2)(v = 1, j = 1) --> HD(v' = 0, 1, 2; j') + H reaction at significantly higher total energies (1.4 to 2.25 electron volts) than previously possible. The theoretical results are obtained over a sufficient range of conditions that a detailed simulation of the experiment was possible, thus making this a definitive comparison of experiment and theory. Good to excellent agreement is found for the vibrational branching ratios and for the rotational distributions within each product vibrational level. However, the calculated rotational distributions are slightly hotter than the experimentally measured ones. This small discrepancy is more marked for products for which a larger fraction of the total energy appears in translation. The most likely explanation for this behavior is that refinements are needed in the potential energy surface.     

葡萄醛脱氢酶（ALDH2）基因进化、表达及启动子功能的生物信息学分析

【目的】研究葡萄醛脱氢酶ALDH2基因家族中ALDH2B4、ALDH2B8和ALDH2B9 3个成员的进化关系,对其在病原菌侵染、非生物胁迫及激素处理下的表达进行分析,为揭示ALDH2基因在植物逆境胁迫下的作用机理提供理论依据。【方法】运用生物信息学方法,鉴定葡萄ALDH蛋白序列;通过葡萄和拟南芥ALDH2基因的系统发育树、基因结构及同线性分析探讨其进化关系;利用葡萄Affymetrix芯片数据,分析葡萄ALDH2（ALDH2B4、ALDH2B8和ALDH2B9）基因在病原菌侵染、非生物胁迫和激素处理下的表达谱;采用在线软件PlantCARE分析3个葡萄ALDH2基因的启动子元件组成差异。【结果】在葡萄基因组中共鉴定出23个ALDH基因,并发现了ALDH2基因的可变剪接现象。基因结构分析结果表明,3个葡萄ALDH2基因的内含子/外显子组成高度相似,且均是通过大规模基因倍增产生的;仅有ALDH2B4具有剪接变体。葡萄与拟南芥的ALDH2基因位于同线区域,表明葡萄与拟南芥的ALDH2基因具有共同的祖先,ALDH2基因先于植物分化而存在。表达分析结果表明,VvALDH2B8是一个多病原菌和非生物胁迫响应基因,VvALDH2B4是一个渗透胁迫响应基因。葡萄的3个ALDH2基因的启动子区域均含有逆境胁迫响应元件,在VvALDH2B8上还发现了病原菌侵染响应元件Box-W1。【结论】葡萄的3个ALDH2基因虽然具有共同的祖先,但其在逆境条件下的表达差异很大,VvALDH2B8和VvALDH2B4可能在植物抵抗逆境胁迫中起重要作用。     

大麦转玉米淀粉分支酶基因的初步研究

以5个大麦品种的由成熟胚再生体系产生的胚性愈伤组织为受体材料，以构建好的Bar基因为选择基因的玉米淀粉分支酶基因表达载体为目的基因，用基因枪法对其进行了转化。在转化的大麦中，5个不同基因型品种的抗性愈伤获得率为10．32％～17．13％，将抗性愈伤组织转移到分化培养基中进行分化，绿苗分化率为0％～14．29％，移栽到小花盆中的再生植株有28株。其中87.3175有11株，87．0053有9株，97．4010有3株，97．6004未分化出苗，208813．509有5株；移栽成活的87．3175有4株，87．0053有5株，208813-509有3株。对10株再生植株进行了PCR检测，其中有7株扩增出0．5kb的Bar基因特异条带，2株扩增出2．4kb的sbe2b基因特异条带，3株扩增出2．5kb的sbel基因特异条带。对PCR扩增的条带回收测序，测序结果与各自的基因序列相符合，说明外源基因已经整合到大麦基因组中。     

Two pairs of recombination signals are sufficient to cause immunoglobulin V-(D)-J joining

The minimum sequence requirements for antigen receptor V-(D)-J joining were studied by constructing recombination-substrates containing synthetic recombination signals and introducing them into a recombination-competent pre-B cell line. Two sets of heptamer (CACTGTG) and nonamer (GGTTTTTGT) sequences were shown to be sufficient to cause the V-(D)-J joining, if the 12- and 23-base pair spacer rule is satisfied. A point mutation in the heptamer sequence, or a change in the combination of the two spacer lengths, drastically reduced the recombination.     

Hu-ets-1 and Hu-ets-2 genes are transposed in acute leukemias with (4;11) and (8;21) translocations

Human probes identifying the cellular homologs of the v-ets gene, Hu-ets-1 and Hu-ets-2, and two panels of rodent-human cell hybrids were used to study specific translocations occurring in acute leukemias. The human ets-1 gene was found to translocate from chromosome 11 to 4 in the t(4;11)(q21;23), a translocation characteristic of a subtype of leukemia that represents the expansion of a myeloid/lymphoid precursor cell. Similarly, the human ets-2 gene was found to translocate from chromosome 21 to chromosome 8 in the t(8;21)(q22;q22), a nonrandom translocation commonly found in patients with acute myeloid leukemia with morphology M2 (AML-M2). Both translocations are associated with expression different from the expression in normal lymphoid cells of ets genes, raising the possibility that these genes play a role in the pathogenesis of these leukemias.     

Synthesis, structure, and reactivity of an iron(V) nitride

Despite being implicated as important intermediates, iron(V) compounds have proven very challenging to isolate and characterize. Here, we report the preparation of the iron(V) nitrido complex, [PhB((t)BuIm)(3)Fe(V)≡N]BAr(F24) (PhB((t)BuIm)(3)(-) = phenyltris(3-tert-butylimidazol-2-ylidene)borato, BAr(F24) = B(3,5-(CF(3))(2)C(6)H(3))(4)(-)), by one electron oxidation of the iron(IV) nitrido precursor. Single-crystal x-ray diffraction of the iron(V) complex reveals a four-coordinate metal ion with a terminal nitrido ligand. M??bauer and electron paramagnetic resonance spectroscopic characterization, supported by electronic structure calculations, provide evidence for a d(3) iron(V) metal center in a low spin (S = 1/2) electron configuration. Low-temperature reaction of the iron(V) nitrido complex with water under reducing conditions leads to high yields of ammonia with concomitant formation of an iron(II) species.     

Coordination of meiotic recombination, pairing, and synapsis by PHS1

Pairing, synapsis, and recombination are prerequisites for accurate chromosome segregation in meiosis. The phs1 gene in maize is required for pairing to occur between homologous chromosomes. In the phs1 mutant, homologous chromosome synapsis is completely replaced by synapsis between nonhomologous partners. The phs1 gene is also required for installation of the meiotic recombination machinery on chromosomes, as the mutant almost completely lacks chromosomal foci of the recombination protein RAD51. Thus, in the phs1 mutant, synapsis is uncoupled from recombination and pairing. The protein encoded by the phs1 gene likely acts in a multistep process to coordinate pairing, recombination, and synapsis.     

非连通图C2h＋1（r1，r2，…，r2h＋1）∪Gm的优美性

证明了：当h≥2时，非连通图C2h＋1（r1，r2，…，r2h＋1）∪Gm是优美图，其中C2h＋1（r1，r2，…，r2h＋1）是圈C2h＋1的（r1，r2，…，r2h＋1）冠，Gm是任意一个有m条边的优美图，m＝h-1＋∑hk＝1r2k．     

二重(r_1·r_2)-循环Toeplitz矩阵求逆的简便算法

利用解一个方程组的方法，给出了（n1，n2）型二重（γ1，γ2）-循环Toeplitz矩阵逆阵的一种简便算法．该算法整个运算不超过矩阵本身元素及参数γ1，γ2所属的数域范围．     

斑马鱼Tph1a蛋白表达、纯化及对脂代谢基因的影响

对斑马鱼色氨酸羟化酶1a(Tph1a)进行原核表达、纯化,探究其在斑马鱼脂代谢中的作用.根据大肠埃希菌的偏爱密码序列,优化斑马鱼tph1a编码区,插入原核表达载体pET-28a,构建融合蛋白表达质粒,并诱导表达、纯化和复性后,腹腔注射斑马鱼,检测其对脂代谢基因表达的影响.结果表明:重组蛋白Tph1a表达形式为包涵体;纯...     

Rho(D) genotype and red cell Rho(D) antigen content

The Rh(o)(D) content of red cells obtained from different individuals as determined with I(181) anti-Rh(o)(D) showed a bimodal distribution. Family studies indicate that the cells with the lower antigen content represent the heterozygous Rh(o)(D) state and that the cells with 1.6 times more Rh(o)(D) correspond to the homozygous state.     

贵州小麦品种(系)粒重相关基因TaCwi-A1、TaSus2-2B和TaGW2-6A等位变异类型鉴定

[目的]鉴定贵州小麦品种(系)中粒重相关基因TaCwi-A1、TaSus2-2B和TaGW2-6A的等位变异类型,筛选含高粒重基因型的小麦品种(系),为贵州小麦粒重的遗传改良和高粒重品种选育提供参考.[方法]以252份小麦品种(系)为材料,分别利用TaCwi-A1、TaSus2-2B和TaGW2-6A基因的分子标记(CWI22/CWI21、TaSus2-1/TaSus2-2和Hap-6A-P1/Hap-6A-P2)引物进行PCR扩增,利用毛细管电泳检测扩增产物,鉴定分析这3个基因的等位变异类型及分布频率,并结合籽粒性状测定结果,筛选含高粒重基因变异类型的小麦种质.[结果]252份小麦种质材料的粒重平均值为39.87 g,其中,有56份材料属于大粒种质(>45.00 g),仅有13份检测到等位变异;173份材料属于中粒种质(30.00~45.00 g),有24份检测到等位变异;23份材料属于小粒种质(<30.00 g),均未检测到等位变异.252份小麦材料中,含有TaCwi-A1、TaSus2-2B和TaGW2-6A基因等位变异的材料37份,占供试材料总数的14.7%,其中TaCwi-A1基因等位变异类型材料12份(包括TaCwi-A1a变异类型8份,TaCwi-A1b变异类型4份),占供试材料总数的4.8%;TaSus2-2B基因等位变异类型材料16份(包括TaSus2-2BH变异类型材料2份,TaSus2-2BL变异类型材料14份),占供试材料总数的6.4%;TaGW2-6A基因等位变异类型材料10份(包括Hap-6A-A变异类型4份,Hap-6A-G变异类型6份),占供试材料总数的4.0%;等位变异组合类型仅有1份材料(惠光2-2-2),为TaCwi-A1b/HAP-6A-A,占供试材料总数的0.4%.平均粒重最高的变异类型为TaCwi-A1b,其次是HAP-6A-G变异类型.对于平均粒重,TaCwi-A1b变异类型显著高于TaCwi-A1a变异类型(P<0.05,下同),Hap-6A-G变异类型显著高于Hap-6A-A变异类型,TaSus2-2BH变异类型也高于TaSus2-2BL变异类型,但差异不显著(P>0.05).[结论]从贵州小麦品种(系)检测到的粒重基因等位变异整体较少,表明贵州小麦种质遗传多样性较低,高粒重品种的选育工作开展不够,今后应重视小麦粒重基因等位变异综合效应研究.鉴定出含有TaCwi-A1、TaSus2-2B和TaGW2-6A基因等位变异类型、粒重>45.00 g的品种(系)13份,可应用于贵州小麦粒重的遗传改良和高粒重品种选育.     

BRCA2 function in DNA binding and recombination from a BRCA2-DSS1-ssDNA structure

Mutations in the BRCA2 (breast cancer susceptibility gene 2) tumor suppressor lead to chromosomal instability due to defects in the repair of double-strand DNA breaks (DSBs) by homologous recombination, but BRCA2's role in this process has been unclear. Here, we present the 3.1 angstrom crystal structure of a approximately 90-kilodalton BRCA2 domain bound to DSS1, which reveals three oligonucleotide-binding (OB) folds and a helix-turn-helix (HTH) motif. We also (i) demonstrate that this BRCA2 domain binds single-stranded DNA, (ii) present its 3.5 angstrom structure bound to oligo(dT)9, (iii) provide data that implicate the HTH motif in dsDNA binding, and (iv) show that BRCA2 stimulates RAD51-mediated recombination in vitro. These findings establish that BRCA2 functions directly in homologous recombination and provide a structural and biochemical basis for understanding the loss of recombination-mediated DSB repair in BRCA2-associated cancers.