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101.
Xiao B Jing C Wilson JR Walker PA Vasisht N Kelly G Howell S Taylor IA Blackburn GM Gamblin SJ 《Nature》2003,421(6923):652-656
Acetylation, phosphorylation and methylation of the amino-terminal tails of histones are thought to be involved in the regulation of chromatin structure and function. With just one exception, the enzymes identified in the methylation of specific lysine residues on histones (histone methyltransferases) belong to the SET family. The high-resolution crystal structure of a ternary complex of human SET7/9 with a histone peptide and cofactor reveals that the peptide substrate and cofactor bind on opposite surfaces of the enzyme. The target lysine accesses the active site of the enzyme and the S-adenosyl-l-methionine (AdoMet) cofactor by inserting its side chain into a narrow channel that runs through the enzyme, connecting the two surfaces. Here we show from the structure and from solution studies that SET7/9, unlike most other SET proteins, is exclusively a mono-methylase. The structure indicates the molecular basis of the specificity of the enzyme for the histone target, and allows us to propose a model for the methylation reaction that accounts for the role of many of the residues that are invariant across the SET family. 相似文献
102.
The secretion of lecithinase of Pseudomonas alcaligenes S2 was via type Ⅱ secretion pathway 总被引:1,自引:0,他引:1
LU Jing LI Fan CHEN Sanfeng LI Jilun 《科学通报(英文版)》2005,50(16):1731-1736
Strain S2 is a lecithin (or phosphatidylcholine)- solubilizing bacterium, which was isolated from the rice rhizosphere in rural areas of Beijing, China. On the basis of a polyphasic study involving phenotypic tests, physiological and biochemical tests, 16S rDNA sequence analysis, G+C content determination and DNA-DNA hybridizations analysis, strain S2 was identified as Pseudomonas alcaligenes. R alcaligenes S2 was mutagenized with Tn5 and four mutants showing decreased or increased solubilizing ability of lecithin were isolated based on the halo size around colonies on the solid plate supplemented with egg yolk. To characterize the genes of R alcaligenes S2 involved in solubilization of lecithin, the EcoR I fragments of the chromosomes from the four mutant strains carrying a single transposon were cloned, and the DNA sequences flanking the Tn5 were determined. The Tn5 insertion sites in the mutants M808, M1329 and M1400, showing decreased solubilizing ability of lecithin, were found to be located in the xcpS, xcpX and xcpW , respectively, whose products XcpS, XcpX and XcpW were the components of type Ⅱ secretion pathway. Complementation of xcpS, xcpX and xcpW could restore the corresponding mutants M808, M1329 and M1400 to solubilize lecithin. The data suggested that mutation in one of these xcp genes would lead to the absence of mature lecithinase secretion into the extracellular medium. The data also indicated that the secretion of lecithin-hydrolyzing enzyme of R alcaligenes was via type Ⅱ secretion pathway. In the mutant M20 showing increasing lecithin-hydrolyzing activity, the interrupted gene showed 86% identity with chpA of Pseudomonas aeruginosa PAO1, whose product plays an important role in controlling twitching motility of the bacterial ceils. 相似文献
103.
The chemical evolution of the Earth and the terrestrial planets is largely controlled by the density of silicate melts. If melt density is higher than that of the surrounding solid, incompatible elements dissolved in the melt will be sequestered in the deep mantle. Previous studies on dry (water-free) melts showed that the density of silicate melts can be higher than that of surrounding solids under deep mantle conditions. However, melts formed under deep mantle conditions are also likely to contain some water, which will reduce the melt density. Here we present data constraining the density of hydrous silicate melt at the conditions of approximately 410 km depth. We show that the water in the silicate melt is more compressible than the other components, and therefore the effect of water in reducing melt density is markedly diminished under high-pressure conditions. Our study indicates that there is a range of conditions under which a (hydrous) melt could be trapped at the 410-km boundary and hence incompatible elements could be sequestered in the deep mantle, although these conditions are sensitive to melt composition as well as the composition of the surrounding mantle. 相似文献
104.
After periodic signals pass through some nonlinear systems, they are usually transformed into noise-like and wide-band chaotic signals. The discrete spectrums of the original periodic signals are often covered by the chaotic spectrums. Recovering the periodic driving signals from the chaotic signals is important not only in theory but also in practical applications. Based on the modeling theory of nonlinear dynamic system, a "polynomial-simple harmonic drive" non-autonomous equation (P-S equation) to approximate the original system is proposed and the approximation error between P-S equation and the original system is obtained. By changing the drive frequency, we obtain the curve of the approximation error vs. drive frequency. Based on the relation between this curve and the spectrums of the original periodic signals, the spectrum of the original driving signal is extracted and the original signal is recovered. 相似文献
105.
JIANG Jing AN Guoyong WANG Pengcheng WANG Pengtao HAN Jinfeng JIA Yanbin & SONG Chunpeng . College of Life Sciences Henan University Kaifeng China . College of Agriculture Science Henan Agriculture University Zheng-zhou China Correspondence should be addressed to Song Chunpeng 《科学通报(英文版)》2003,48(18):1919-1926
The plant hormone abscisic acid (ABA) is involved in regulating adverse physiological processes, including stomatal closure, seed development and germination, and mediating many environmental stress responses, such as drought, salinity and extreme temperatures[1,2]. In re-sponse to various stress stimuli, ABA synthesis is in-creased in plant cells, which triggers a series of physio-logical responses to adapt the stress conditions[1—3]. For example, under water deficit, ABA acts directly on… 相似文献
106.
Neural network model for the constitutive relations of soil 总被引:1,自引:0,他引:1
Zeng Jing Wang J ing |tao School of Civil Engineering Mechanics Huazhong University of Science Technology Wuhan Hubei China 《武汉大学学报:自然科学英文版》2003,8(1):86-90
0 IntroductionAccordingtothedifferenttheoriesappliedintheestablishingconstitutivemodel,theconstitutivemodelisgenerallygroupedintotwocategories :elasticmodelandelasto plasticmodel.Asoneoftheelasticmodels,Duncan Chang’smodel[1] iswidelyappliedinengineeringpr… 相似文献
107.
108.
Jing Yang ? Jingjing Ma ? Shi Liu ? Cheng Zhang 《科学通报(英文版)》2014,59(11):1192-1198
With the progress of DNA computing, DNA- based cryptography becomes an emerging interdisciplinary research field. In this paper, we present a novel DNA cryptography that takes advantage of DNA self assembled structure. Making use of the toehold strands recognition and strand displacement, the bit-wise exclusive-or (XOR) operation is carried out to fulfill the information encryption and decryption in the form of a one-time-pad. The security of this system mainly comes from the physical isolation and specificity of DNA molecules. The system is con- structed by using complex DNA self-assembly, in which technique of fluorescent detection is utilized to implement the signal processing. In the proposed DNA cryptography, the XOR operation at each bit is carried out individually, thus the encryption and decryption process could be con- ducted in a massive, parallel way. This work may dem- onstrate that DNA cryptography has the great potential applications in the field of inRwmation security. 相似文献
109.
Lattice defects are unavoidable structural units in materials and play an important role in determining material properties. Compared with the periodic structure of crystals, the atomic configurations of the lattice defects are determined by the coordinates of a large number of atoms, making it difficult to experimentally investigate them. In computational materials science, multiparameter optimization is also a difficult problem and experimental verification is usually required to determine the possibility of obtaining the structure and properties predicted by cal- culations. Using our recent studies on oxide surfaces as examples, we introduce the method of integrated aberra- tion-corrected electron microscopy and the first-principles calculations to analyze the atomic structure of lattice defects. The atomic configurations of defects were mea- sured using quantitative high-resolution electron micros- copy at subangstrom resolution and picometer precision, and then the electronic structure and dynamic behavior of materials can be studied at the atomic scale using the first- principles calculations. The two methods complement each other and can be combined to increase the understanding of the atomic structure of materials in both the time and space dimensions, which will benefit materials design at the atomic scale. 相似文献
110.
Thermo-Calc and Dictra commercial calculation software programs have been used to simulate the formation of fine microstructure of 9%Ni cryogenic steel processed by quench–lamellarize–temper(QLT)heat treatment.The calculations show many compositional fluctuations in each single-martensite lath after QLT treatment;the peak concentrations of carbon and nickel reach about 0.40%and 18%,respectively.The width of the C or Ni element-enriched zone increases when the critical lamellarizing temperature decreases or the temper temperature increases.Extending the temper time has a similar effect on the element profiles.The simulation results are in accordance with the observed fine microstructures. 相似文献