Functional replacement of a protein-induced bend in a DNA recombination site

In recent years the capacity of proteins to bend DNA by binding to specific sites has become a widely appreciated phenomenon. In many cases, the protein-DNA interaction is known to be functionally significant because destruction of the DNA site or the protein itself results in an altered phenotype. An important question to be answered in these cases is whether bending of DNA is important per se or is merely a consequence of the way a particular protein binds to DNA. Here we report direct evidence from the bacteriophage lambda integration system that a bend introduced by a protein is intrinsically important. We find that a binding site for a specific recombination protein known to bend DNA can be successfully replaced by two other modules that also bend DNA; related modules that fail to bend DNA are ineffective.     

DNA bending induced by cruciform formation

Cruciform structures in DNA are of considerable interest, both as extreme examples of sequence-dependent structural heterogeneity and as models for four-way junctions such as the Holliday junction of homologous genetic recombination. Cruciforms are of lower thermodynamic stability than regular duplex DNA, and have been observed only in negatively supercoiled molecules, where the unfavourable free energy of formation is offset by the topological relaxation of the torsionally stressed molecule. From an experimental viewpoint this can be a disadvantage, as cruciform structures can be studied only in relatively large supercoiled DNA circles, and are destabilized when a break is introduced at any point. We therefore set out to construct a pseudo-cruciform junction--by generating hereroduplex formation between two inverted repeat sequences. Stereochemically, this should closely resemble a true cruciform but remain stable in a linear DNA fragment. We have now created such a junction and find that it has the expected sensitivities to endonucleases. These DNA fragments exhibit extremely anomalous gel electrophoretic mobility, the extent of which depends on the relative position of the pseudo-cruciform along the length of the molecule. Our results are very similar to those obtained by Wu and Crothers using kinetoplast DNA, and we conclude that the pseudo-cruciform junction introduces a bend in the linear DNA molecule.     

DNA bending at adenine . thymine tracts

Intrinsic bending of DNA molecules results from local structural polymorphism in regions of homopolymeric dA . dT which are at least 4 base pairs long; the A . T tracts must be repeated in phase with the helix screw. Bending, in the direction of base-pair tilt rather than roll, occurs at the junctions between the A . T tract and adjacent B-DNA, with a larger angle at the 3' than at the 5' end of the A tract.     

DNA sequence determinants of CAP-induced bending and protein binding affinity

The sites of DNA bending induced by binding catabolite activator protein are identified and shown to coincide with positions where DNA grooves face the protein. The bendability of DNA with different sequences at these bend centres parallels the bending preference of the sequences in nucleosomal DNA. Anisotropic DNA bendability significantly affects the structure and strength of regulatory protein-DNA complexes.     

The role of CopG mediated DNA bending on the regulation of the σ^54-dependent promoters in E. coli

In prokaryotic cells, although the σ54 RNA poly- merase can stably bind to the σ54-dependent promoter without the enhancer-binding proteins (EBPs), it re- mains as a closed complex which is silent for transcrip- tion[1]. When binding to the enhancer-lik…     

大型U形件弯曲成形工艺和模具设计

介绍了大型U形件内侧中间板的特点,分析了大型U形件弯曲成形的工艺方法,阐述了单角两次弯曲成形模具设计和结构特点.     

Insertion of DNA sequences into the human chromosomal beta-globin locus by homologous recombination

A 'rescuable' plasmid containing globin gene sequences allowing recombination with homologous chromosomal sequences has enabled us to produce, score and clone mammalian cells with the plasmid integrated into the human beta-globin locus. The planned modification was achieved in about one per thousand transformed cells whether or not the target gene was expressed.     

箱型梁弯扭强度分析计算思路探讨

箱型梁具有非常好的力学性能和结构性能,被广泛应用到桥梁设计和施工中.通过对箱型梁弯扭强度分析计算思路进行研究,得出箱形梁在弯曲、扭转以及弯扭组合变形时的强度计算方法,为设计和施工提供有效的技术支持.     

接线片冲孔、弯曲、切断级进模设计

介绍了单工序模、级进模和复合模的生产特点 ,说明级进模适合于生产尺寸较小、形状复杂、内外形尺寸相差很小且具有较高精度要求的冲压件的生产 通过对接线片的形状、尺寸及精度的分析 ,说明对接线片使用级进模 ,在提高生产率、降低产品成本、提高产品质量和实现冲压自动化等方面的现实意义 同时介绍了接线片的排样 ,接线片级进模的结构与工作原理     

弯矩分配传递极限公式在薄板弯曲问题中的应用

用传统的弯矩分配法求解任意荷载作用下的薄板弯曲问题，将杆端弯矩表示为多次分配弯矩和传递弯矩之和，得到了当分配传递次数无穷大时其表达式为公比小于1的无究等比级数的和的形式，并求得了该和的表达式即极限公式。该极限公式便于编程电算，可方便地应用于任意荷载作用下的薄板弯曲问题。     

钣金件弯曲工序优化

工序编排问题可用解答树来描述，解答树的搜索空间通过采用复合弯曲、保存和重用前面的计算结果、从三维工件到二维展开图等多种方法进行优化。以干涉作为回溯条件得蓟可行的弯曲方案，再利用估算公式得到优化的弯曲工序。该优化结果优于其他已知的优化方法。     

考虑弯剪相关性的钢筋混凝土受弯构件承载力计算

钢筋混凝土受弯构件中,弯剪承载力存在相关性。中国规范GBJ10—89,GB50010,JTJ023—85和JTG D62—2004,以及美国规范ACI318基本沿用了相同的思路,未充分考虑弯剪相关性,受弯构件纵筋和箍筋用量分别按正截面承载力和斜截面承载力单独计算确定,仅通过剪跨比分析了在集中荷载作用下的独立梁的弯矩对抗剪承载力的影响。在分析GB50010和ACI318的强度准则中隐含应力层次的弯剪相关性和承载力公式中剪跨比影响的基础上,提出了考虑弯剪相关性的弯剪承载力修正公式。通过典型算例,分析了不同参数下修正公式与规范公式的设计配筋量,比较了抗弯和抗剪可靠指标的变化,并基于GB50068—2001的目标可靠指标要求,探讨了考虑弯剪相关性的必要性。     

Detection of deletions spanning the Duchenne muscular dystrophy locus using a tightly linked DNA segment

The Duchenne muscular dystrophy (DMD) locus has been localized to the short arm of the human X chromosome (Xp21) by detection of structural abnormalities and by genetic linkage studies. A library highly enriched for human DNA from Xp21 was constructed using DNA isolated from a male patient who had a visible deletion and three X-linked disorders (DMD, retinitis pigmentosa and chronic granulomatous disease). Seven cloned DNA probes from this library and the probe 754 (refs 5, 8) are used in the present study to screen for deletions in the DNA isolated from 57 unrelated males with DMD. Five of these DMD males are shown to exhibit deletions for one of the cloned DNA segments and at least 38 kb of surrounding DNA. In addition, two subclones from the same region detect four restriction fragment length polymorphisms which exhibit no obligate recombination with DMD in 34 meiotic events. These new DNA segments will complement the existing Xp21 probes for use in carrier detection and prenatal diagnosis of DMD. Elucidation of the end points of the five deletions will help delineate the extent of the DMD locus and ultimately lead to an understanding of the specific sequences involved in DMD.     

泌水对水泥混凝土抗折强度的影响

抗折强度是水泥混凝土路面板承载力的决定性指标．通过对水泥混凝土弯拉破坏机理的分析，阐述了泌水引起混凝土抗折强度下降的原因，以及能引起泌水现象的主要因素．结合工程实践，介绍了减小泌水，有效提高混凝土抗折强度的主要措施。     

薄板中弯曲波的特性阻抗

对薄板波动方程的一般解应用边界条件得到无限大薄板中弯曲波的解。进一步得到弯矩特性阻抗和剪切力特性阻抗的表达式,并给出了阻抗的曲线图。     

lnc1343对小鼠胚胎干细胞多能性的影响及其基因座潜在作用机制

哺乳动物基因组可以转录数以千计的长非编码RNA(longnon-coding RNA, lncRNA),lncRNA能够在多种层次以灵活的方式对基因表达进行调控.尽管lncRNA在基因表达调控过程中的作用已经毋庸置疑,但目前只有少数lncRNA的功能和作用机制得到了研究.lnc1343是一条由小核仁RNA宿主基因3所转录的lncRNA,其表达失调与许多人类疾病有密切关联.研究结果表明lnc1343能够通过自身转录本来调控小鼠胚胎干细胞(mouse embryonic stem cells, mESCs)的多能性维持, CRISPR-cas9 介导的lnc1343的转录起始位点和基因座的敲除显著降低了多能性基因(Nanog, Sox2, Oct4)的表达,同时也能通过邻近调控相邻基因Rcc1的表达.此外,通过对Chip-seq数据库的分析,发现lnc1343基因座位存在大量的H3K27ac以及H3K4mel的表观遗传修饰,通过Capture C实验捕获与lnc1343基因座位相互作用的DNA区域,发现大部分相互作用区域位于基因的启动子区,表明lnc1343基因座位可能发挥增强子功能,通过长距离染色质相互作用调控基因表达,进而调控mESCs多能性.总之,lnc1343不仅可以通过自身的转录剪切形成的lncRNA来调控mESCs的多能性,同时也能通过其基因座位调控染色质的长远距离相互作用.     

抑制汽车纵梁弯曲回弹的弯曲模改进设计

汽车纵梁是一种形状和尺寸都比较大的冲压件,弯曲成形难度大且回弹不易控制.通过对U形件工艺和模具加工的分析,提出了解决回弹的工艺方法及可控制回弹的弯曲模改进设计,使汽车纵梁弯曲成形后的质量有了较大的提高,从而消除了由于产生回弹使零件侧壁的孔位与底部尺寸超差而影响纵梁装配等问题.     

排距对双排桩位移及弯矩的影响

双排桩作为一种新型支护形式,在工程中使用越来越广泛。本文通过使用理正深基坑软件,分析了双排桩位移及弯矩受排距的影响情况,得出的结果对工程具有一定的指导意义。同时,通过对数据的分析,指出了理正深基坑软件在计算双排桩时,也存在着一些需要改进的问题。