Poly(ADP-ribose) is required for spindle assembly and structure

The mitotic spindle is typically thought of as an array of microtubules, microtubule-associated proteins and motors that self-organizes to align and segregate chromosomes. The major spindle components consist of proteins and DNA, the primary structural elements of the spindle. Other macromolecules including RNA and lipids also associate with spindles, but their spindle function, if any, is unknown. Poly(ADP-ribose) (PAR) is a large, branched, negatively charged polymeric macromolecule whose polymerization onto acceptor proteins is catalysed by a family of poly(ADP-ribose) polymerases (PARPs). Several PARPs localize to the spindle in vertebrate cells, suggesting that PARPs and/or PAR have a role in spindle function. Here we show that PAR is enriched in the spindle and is required for spindle function--PAR hydrolysis or perturbation leads to rapid disruption of spindle structure, and hydrolysis during spindle assembly blocks the formation of bipolar spindles. PAR exhibits localization dynamics that differ from known spindle proteins and are consistent with a low rate of turnover in the spindle. Thus, PAR is a non-proteinaceous, non-chromosomal component of the spindle required for bipolar spindle assembly and function.     

Crystal structure of spinach major light-harvesting complex at 2.72 A resolution

The major light-harvesting complex of photosystem II (LHC-II) serves as the principal solar energy collector in the photosynthesis of green plants and presumably also functions in photoprotection under high-light conditions. Here we report the first X-ray structure of LHC-II in icosahedral proteoliposome assembly at atomic detail. One asymmetric unit of a large R32 unit cell contains ten LHC-II monomers. The 14 chlorophylls (Chl) in each monomer can be unambiguously distinguished as eight Chla and six Chlb molecules. Assignment of the orientation of the transition dipole moment of each chlorophyll has been achieved. All Chlb are located around the interface between adjacent monomers, and together with Chla they are the basis for efficient light harvesting. Four carotenoid-binding sites per monomer have been observed. The xanthophyll-cycle carotenoid at the monomer-monomer interface may be involved in the non-radiative dissipation of excessive energy, one of the photoprotective strategies that have evolved in plants.     

Actin dynamics in the contractile ring during cytokinesis in fission yeast

Cytokinesis in many eukaryotes requires a contractile ring of actin and myosin that cleaves the cell in two. Little is known about how actin filaments and other components assemble into this ring structure and generate force. Here we show that the contractile ring in the fission yeast Schizosaccharomyces pombe is an active site of actin assembly. This actin polymerization activity requires Arp3, the formin Cdc12, profilin and WASP, but not myosin II or IQGAP proteins. Both newly polymerized actin filaments and pre-existing actin cables can contribute to the initial assembly of the ring. Once formed, the ring remains a dynamic structure in which actin and other ring components continuously assemble and disassemble from the ring every minute. The rate of actin polymerization can influence the rate of cleavage. Thus, actin polymerization driven by the Arp2/3 complex and formins is a central process in cytokinesis. Our studies show that cytokinesis is a more dynamic process than previously thought and provide a perspective on the mechanism of cell division.     

Coulomb blockade and the Kondo effect in single-atom transistors

Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems. Experiments to date have examined a multitude of molecules conducting in parallel, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions or scanning probes as well as three-terminal single-molecule transistors made from carbon nanotubes, C(60) molecules, and conjugated molecules diluted in a less-conducting molecular layer. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect.     

一种新型多燃料油炉的开发

介绍了所设计的新型多燃料油炉的基本结构和主要性能 .在该多燃料油炉中 ,应用旋焰燃烧理论解决了油炉在低温环境和高海拔缺氧环境中点火困难的问题 ,并应用安全阀技术解决了油炉“回火”和“非正常熄火”等关键问题     

谐波对电能计量影响的分析及对策研究

本文介绍了谐波产生的原因及其对感应式电能表和电子式电能表的影响 ,从感应式电能表和电子式电能表频率响应曲线入手 ,分析了由于谐波的存在而引起的电能计量仪表误差的变化情况 ,并提出了减小电能计量误差的方法和对策     

Twisted gastrulation can function as a BMP antagonist

Bone morphogenetic proteins (BMPs), including the fly homologue Decapentaplegic (DPP), are important regulators of early vertebrate and invertebrate dorsal-ventral development. An evolutionarily conserved BMP regulatory mechanism operates from fly to fish, frog and mouse to control the dorsal-ventral axis determination. Several secreted factors, including the BMP antagonist chordin/Short gastrulation (SOG), modulate the activity of BMPs. In Drosophila, Twisted gastrulation (TSG) is also involved in dorsal-ventral patterning, yet the mechanism of its function is unclear. Here we report the characterization of the vertebrate Tsg homologues. We show that Tsg can block BMP function in Xenopus embryonic explants and inhibits several ventral markers in whole-frog embryos. Tsg binds directly to BMPs and forms a ternary complex with chordin and BMPs. Coexpression of Tsg with chordin leads to a more efficient inhibition of the BMP activity in ectodermal explants. Unlike other known BMP antagonists, however, Tsg also reduces several anterior markers at late developmental stages. Our data suggest that Tsg can function as a BMP inhibitor in Xenopus; furthermore, Tsg may have additional functions during frog embryogenesis.     

教育本质：知识论的困惑与存在论的彰显－兼论教育本质探讨思路的转向

教育本质的论争之所以陷入“疑无路”的境地,根本在于论争只是囿于探究知识论的“教育是什么”而遗忘了追寻存在论的“怎样教育”这一教育之“根”与“本”,以致教育之本质与语言遭际异化。缘此,本文拟在反思以往教育本质论争的基础上,试图走向“怎样教育”,以期扬弃异化,返朴归真。