Molecular cloning of a new transforming gene from a chemically transformed human cell line

Molecular cloning of the transforming gene from a chemically transformed human osteosarcoma-derived cell line enables the gene to be mapped to chromosome 7 (7p11.4-7qter) and by this criterion and by direct hybridization to be shown to be unrelated to known oncogenes.     

The neuronal repellent Slit inhibits leukocyte chemotaxis induced by chemotactic factors

Migration is a basic feature of many cell types in a wide range of species. Since the 1800s, cell migration has been proposed to occur in the nervous and immune systems, and distinct molecular cues for mammalian neurons and leukocytes have been identified. Here we report that Slit, a secreted protein previously known for its role of repulsion in axon guidance and neuronal migration, can also inhibit leukocyte chemotaxis induced by chemotactic factors. Slit inhibition of the chemokine-induced chemotaxis can be reconstituted by the co-expression of a chemokine receptor containing seven transmembrane domains and Roundabout (Robo), a Slit receptor containing a single transmembrane domain. Thus, there is a functional interaction between single and seven transmembrane receptors. Our results reveal the activity of a neuronal guidance cue in regulating leukocyte migration and indicate that there may be a general conservation of guidance mechanisms underlying metazoan cell migration. In addition, we have uncovered an inhibitor of leukocyte chemotaxis, and propose a new therapeutic approach to treat diseases involving leukocyte migration and chemotactic factors.     

Cloning, sequence and expression of human interleukin-2 receptor

T lymphocytes, essential for the generation of a normal immune response, require the presence of the lymphokine interleukin-2 (IL-2) in order to proliferate. Cells that respond to IL-2 possess a surface receptor glycoprotein specific for this lymphokine. We have recently purified and chemically characterized the IL-2 receptor from both phytohaemagglutinin-activated human T cells and the human T-cell lymphoma HUT-102 (ref. 5). From the NH2-terminal protein sequence obtained in that study, we have now used synthetic oligonucleotides to probe a complementary DNA library, prepared from HUT-102 messenger RNA, for the presence of cDNA clones that might code for the IL-2 receptor. Two cDNA clones were isolated which had closely related DNA sequences. Interestingly, only one coded for an active receptor when transfected into COS-7 cells. This clone contained a 216-base pair (bp) insert that was not present in the other clone. The insert was flanked by an 8-bp direct repeat reminiscent of a transposable element, and appeared to code for a region of marked structural homology to the NH2-terminal region of the receptor molecule.     

Tree-ring precipitation records from Baiyinaobao,Inner Mongolia since A.D. 1838

Tree rings have attracted the wide attention of geo- environmental and climatic scientists due to its high resolution and accuracy. Lots of important results about climatic change have been obtained for the last 100 to 2000 years when it has no instrumental observation and people are very concerning about it nowadays. For example, by using tree-ring data, temperature, precipitation and drought history have been reconstructed back to hundreds of or thousands of years for different regions in th…     

Genetic retrieval of viral genome sequences from herpes simplex virus transformed cells

Oncogenic transformation of cultured cells by inactivated herpes simplex virus (HSV) types 1 and 2 has been demonstrated. Expression of HSV information in these transformed cells has been shown by immunofluorescence studies, detection of HSV neutralizing antibody in sera from tumour-bearing animals and by hybridization of HSV-specific RNA. Molecular hybridization studies of DNA from HSV-2 transformed hamster cells have detected up to 40% of the HSV genome present in several copies. Complementation of three HSV-2 temperature-sensitive mutants when superinfecting the RE1 rat embryo cell line (transformed by the HSV-2 temperature-sensitive mutant ts1) suggests that resident viral genes can be expressed. Brown et al. used a similar approach to detect HSV information latent in human ganglia. We report here retrieval of intertypic HSV recombinants from HSV transformed cells after superinfection with ts mutants of the alternative serotype of HSV. Restriction enzyme analysis which clearly differentiates between HSV-1 and HSV-2 DNA has demonstrated the isolation of recombinants spanning the genome and of virus indistinguishable from the original transforming virus.     

Nanomechanical oscillations in a single-C60 transistor

The motion of electrons through quantum dots is strongly modified by single-electron charging and the quantization of energy levels. Much effort has been directed towards extending studies of electron transport to chemical nanostructures, including molecules, nanocrystals and nanotubes. Here we report the fabrication of single-molecule transistors based on individual C60 molecules connected to gold electrodes. We perform transport measurements that provide evidence for a coupling between the centre-of-mass motion of the C60 molecules and single-electron hopping--a conduction mechanism that has not been observed previously in quantum dot studies. The coupling is manifest as quantized nano-mechanical oscillations of the C60 molecule against the gold surface, with a frequency of about 1.2 THz. This value is in good agreement with a simple theoretical estimate based on van der Waals and electrostatic interactions between C60 molecules and gold electrodes.     

Cooper instability of composite fermions

When confined to two dimensions and exposed to a strong magnetic field, electrons screen the Coulomb interaction in a topological fashion; they capture an even number of quantum vortices and transform into particles called 'composite fermions' (refs 1-3). The fractional quantum Hall effect occurs in such a system when the ratio (or 'filling factor, nu) of the number of electrons and the degeneracy of their spin-split energy states (the Landau levels) takes on particular values. The Landau level filling nu = 1/2 corresponds to a metallic state in which the composite fermions form a gapless Fermi sea. But for nu = 5/2, a fractional quantum Hall effect is observed instead; this unexpected result is the subject of considerable debate and controversy. Here we investigate the difference between these states by considering the theoretical problem of two composite fermions on top of a fully polarized Fermi sea of composite fermions. We find that they undergo Cooper pairing to form a p-wave bound state at nu = 5/2, but not at nu = 1/2. In effect, the repulsive Coulomb interaction between electrons is overscreened in the nu = 5/2 state by the formation of composite fermions, resulting in a weak, attractive interaction.     

Effects of elevation on spring phenological sensitivity to temperature in Tibetan Plateau grasslands

Vegetation phenology is an important indicator of climate change impacts on the seasonal dynamics of the biosphere. However, little is known about the influence of elevation on spring phenological sensitivity to temperature in an alpine ecosystem. Based on remotely sensed land surface phenology and temperature data from 2001 to 2010, this study investigated the rate of spring phenological change of the Tibetan Plateau （TP） grasslands in response to interannual temperature variations at different elevations. Results suggest that spring phenology in the TP grasslands exhibits a stronger response to changes in temperature at higher elevations than at lower ones. In particular, spring phenology advanced by 1-2 days in response to a 1 ℃ increase in May average temperature at elevations from 3,000 to 3,500 m, while the rate was up to 8-9 days/℃ at 5,000-5,500 m. Analysis using accumulated growing degree days （AGDD） from January 1 through May 31 showed the same general trend with increased elevation associated with increased sensitivity （as measured by phenological change per unit of AGDD change）. Such temperature sensitivity gradients in the TP grasslands could be partly explained by the growth efficiency hypothesis which suggests that vegetation adapted to colder climates likely requires less heat energy for the onset of growing season and vice versa in warmer climates. Furthermore, accumulated growing degree days from January 1 to the greenup date were found to decrease with increasing elevations, which provided evidence to support the applicability of the growth efficiency hypothesis in an alpine grassland ecosystem.     

不同沙尘天气微气象和沙尘演变规律的对比研究

利用内蒙古浑善达克沙地沙尘暴实验探测资料,给出2004年春季多次沙尘天气过程近地面微气象学要素、湍流通量及沙尘浓度的极值对比,重点分析了3月27-28日强沙尘暴过境时近地面微气象学要素和辐射分量的变化特征。结果表明： 沙尘天气过程中,白天近地层温差均有不同程度的降低,夜间逆温强度减弱;净辐射与感热通量较晴空值均有不同程度的削弱。沙尘天气过境时,动量通量显著增加,动力湍流与热力湍流配合,有利于加强沙尘源区的局地起沙和沙尘的垂直输送过程。3月27-28日强沙尘暴过境时,伴随地面水平风向的转变,沙尘浓度迅速增加,风速及其垂直梯度增大;在沙尘暴增强阶段,近地层降温达7℃,比湿出现极大值,净辐射和感热通量降为负值。当沙尘浓度达到最大值后,净辐射上升至零,反映了夜间沙尘气溶胶对低层大气和地表的保温作用。     

A metal complex that binds alpha-amino acids with high and predictable stereospecificity.

Molecular recognition is the key step in a wide range of controlled separation and chemical transformation processes, with enzymes performing this task with an unsurpassed degree of selectivity. Enzymes contain only 20 simple amino acids, yet it remains difficult to rationalize or even predict these stereospecific recognition events. Nonetheless, the rational design of receptors able to recognize amino acids stereospecifically is attracting considerable interest because therapeutic drugs, that may be developed from chiral amino acid intermediates, are increasingly required in enantiomerically pure form. Early work has stimulated the development of efficient receptors based on small molecules, but binding of amino acids with high and predictable stereospecificity remains difficult to achieve. Directed molecular evolution, on the other hand, does select for RNA sequences or antibodies that bind amino acids with high specificity, but typically without providing insights into the molecular recognition mechanisms involved. Here we show that a rationally designed metal complex formed from a trivalent cobalt ion and a tetradentate ligand binds natural amino acids, including the simple yet challenging amino acid alanine, with high and predictable regio- and stereospecificity. We expect that our approach will allow the binding as well as separation and stereospecific catalytic formation of its target amino acids.