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1.
GroE heat-shock proteins promote assembly of foreign prokaryotic ribulose bisphosphate carboxylase oligomers in Escherichia coli 总被引:66,自引:0,他引:66
Assembly of foreign prokaryotic ribulose bisphosphate carboxylases (Rubiscos) in Escherichia coli requires both heat-shock proteins groEL and groES. GroEL is related to a chloroplast protein implicated in Rubisco assembly. Bacteria and chloroplasts therefore have a conserved mechanism that uses auxiliary proteins to assist in the assembly of Rubisco. 相似文献
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Reconstitution of actin-based motility of Listeria and Shigella using pure proteins. 总被引:11,自引:0,他引:11
Actin polymerization is essential for cell locomotion and is thought to generate the force responsible for cellular protrusions. The Arp2/3 complex is required to stimulate actin assembly at the leading edge in response to signalling. The bacteria Listeria and Shigella bypass the signalling pathway and harness the Arp2/3 complex to induce actin assembly and to propel themselves in living cells. However, the Arp2/3 complex alone is insufficient to promote movement. Here we have used pure components of the actin cytoskeleton to reconstitute sustained movement in Listeria and Shigella in vitro. Actin-based propulsion is driven by the free energy released by ATP hydrolysis linked to actin polymerization, and does not require myosin. In addition to actin and activated Arp2/3 complex, actin depolymerizing factor (ADF, or cofilin) and capping protein are also required for motility as they maintain a high steady-state level of G-actin, which controls the rate of unidirectional growth of actin filaments at the surface of the bacterium. The movement is more effective when profilin, alpha-actinin and VASP (for Listeria) are also included. These results have implications for our understanding of the mechanism of actin-based motility in cells. 相似文献
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Competence for genetic transformation in pneumococcus depends on synthesis of a small set of proteins. 总被引:1,自引:0,他引:1
In bacterial genetic transformation the uptake of DNA and its integration into the resident chromosome is dependent on a special cellular state, termed competence. In those species where appearance of competence has been studied, specific (but often poorly defined) growth conditions lead to a simultaneous development of competence in a substantial fraction of the cells in a culture. In Bacillus subtilis, and in Haemophilus species, competence appears in the stationary phase of growth or in certain other growth-limiting conditions. Streptococcus pneumoniae (pneumococcus) is perhaps unusual in that virtually all cells of a culture become competent, for a short period at a specific cell density during logarithmic growth, without perturbing the growth rate. The synchronous appearance of competence in pneumococcal cultures results from an autocatalytic effect of a small protein released by the cells that induces competence. The response to competence factor has been shown to require protein synthesis. We report here additional information on the nature of competence in pneumococcus: pulse-labelling studies show that for the brief period of competence protein synthesis is restricted to a few specific polypeptides. 相似文献
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基于主动替代策略的单周期两种产品库存模型 总被引:1,自引:0,他引:1
基于零售商在产品出现缺货时,需采用被动产品替代行为的现象.该文提出一种主动替代策略.以零售商的整个周期内的期望总收益最大为目标建立了一个两阶段的数学模型,分别得到了最优促销成本和周期内的最优订货批量.并通过算例,说明了随着产品替代度的增加,周期内的期望总收益也随着增加;同时通过对该文模型与被动替代策略进行比较,显示主动替代策略对于产品替代度大的产品能进一步提高零售商整个周期的效益. 相似文献
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Assembly and function of the two ABC transporter proteins encoded in the human major histocompatibility complex. 总被引:30,自引:0,他引:30
A Kelly S H Powis L A Kerr I Mockridge T Elliott J Bastin B Uchanska-Ziegler A Ziegler J Trowsdale A Townsend 《Nature》1992,355(6361):641-644
Presentation of cytoplasmic antigens to class I-restricted cytotoxic T cells implied the existence of a specialized peptide transporter. For most class I heavy chains, association with peptides of the appropriate length is required for stable assembly with beta 2-microglobulin. Mutant cells RMA-S and .174/T2 neither assemble stable class I molecules nor present intracellular antigens, and we have suggested that they have lost a function required for the transport of short peptides from the cytosol to the endoplasmic reticulum. The genetic defect in .174 has been localized to a large deletion in the class II region of the major histocompatibility complex, within which two genes (RING4 and RING11) have been identified that code for 'ABC' (ATP-binding cassette) transporters. We report here that the protein products of these two genes assemble to form a complex. Defects in either protein result in the formation of unstable class I molecules and loss of presentation of intracellular antigens. The molecular defect in a new mutant, BM36.1, is shown to be in the ATP-binding domain of the RING11/PSF2 protein. This is in contrast to the mutant .134, which lacks the RING4/PSF1 protein. 相似文献
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RC有源滤波器设计希望获得多个设计目标,而这些设计目标又会相互竞争难以同时获得,针对这个特点,提出了一种基于对策论和遗传算法的解决RC有源滤波器设计中诸目标竞争问题的设计方法,并通过实例对其进行验证,证明了此种方法的可行性. 相似文献
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为了研究在10 m×0.5 m的玻璃水槽内的主动冲箱造波技术,设计了基于PLC运动控制器、伺服电机和驱动器、工控机以及浪高采集仪的造波系统。该系统根据水动力学参数在PLC运动控制程序中实现主动造波算法;采用交流伺服驱动器并搭配相应尺寸的电机,完成楔形板的上下造波运动;通过工控机上的人机界面对造波机系统的整体状态进行控制。为了提高控制精度,该系统在伺服驱动器内部闭环控制的基础上,还增加了基于PID算法的波高和频率闭环控制。实际应用表明,该造波系统可通过对波形的实时反馈,保证控制的准确性和稳定性,达到了主动造波的目的。 相似文献
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基于PLC和伺服电机的主动冲箱式造波系统的控制及实现 《山东科学》2010,33(3):40-44
为了研究在10 m×0.5 m的玻璃水槽内的主动冲箱造波技术,设计了基于PLC运动控制器、伺服电机和驱动器、工控机以及浪高采集仪的造波系统。该系统根据水动力学参数在PLC运动控制程序中实现主动造波算法;采用交流伺服驱动器并搭配相应尺寸的电机,完成楔形板的上下造波运动;通过工控机上的人机界面对造波机系统的整体状态进行控制。为了提高控制精度,该系统在伺服驱动器内部闭环控制的基础上,还增加了基于PID算法的波高和频率闭环控制。实际应用表明,该造波系统可通过对波形的实时反馈,保证控制的准确性和稳定性,达到了主动造波的目的。 相似文献
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Homology of 54K protein of signal-recognition particle, docking protein and two E. coli proteins with putative GTP-binding domains 总被引:60,自引:0,他引:60
Most proteins exported from mammalian cells contain a signal sequence which mediates targeting to and insertion into the membrane of the endoplasmic reticulum (ER). Involved in this process are the signal-recognition particle (SRP) and docking protein (DP), the receptor for SRP in the ER membrane. SRP interacts with the signal sequence on nascent polypeptide chains and retards their further elongation, which resumes only after interaction of the arrested ribosomal complex with the docking protein. SRP is a ribonucleoprotein particle comprising a 7S RNA and six polypeptides with relative molecular masses (Mr) of 9,000 (9K) 14K, 19K, 54K, 68K and 72K (ref. 1). The 9K and 14K proteins are essential for elongation arrest and the 68K-72K heterodimer is required for docking to the ER membrane. The 54K protein binds to the signal sequence when it emerges from the ribosome. Docking protein consists of two polypeptides, a 72K alpha-subunit (DP alpha) and a 30K beta-subunit (DP beta). No components structurally homologous to SRP and docking protein have yet been found in yeast or Escherichia coli. To understand the molecular nature of the interaction between the signal sequence and its receptor(s) we have characterized a complementary DNA coding for the 54K protein of SRP. Significant sequence homology was found to part of DP alpha and two E. coli proteins of unknown function. The homologous region includes a putative GTP-binding domain. 相似文献
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刘超 《淮北煤炭师范学院学报(自然科学版)》2010,31(2):93-96
采用文献资料、走访调查和逻辑分析等方法,从体育课程指导思想不够明确,学校体育的功能没有充分挖掘;体育课程的目标不明确;体育课程教学内容人文价值缺失,课程结构不合理,脱离学生实际需要;体育课程教学效果的评价不科学,过于注重甄别与选拔功能等4个方面对我国高师院校体育课程的现状进行分析.在此基础上,提出要树立"健康第一"的思想、根据社会发展的需要来设置体育课程、科学制定高师院校的体育课程目标、科学选择与组织体育课程教学内容、更新教学方法与教学手段、加强体育教师队伍建设、科学的评价"教"与"学"等8个方面的改革举措. 相似文献
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Drosophila genes Posterior Sex Combs and Suppressor two of zeste encode proteins with homology to the murine bmi-1 oncogene. 总被引:23,自引:0,他引:23
The Polycomb group (Pc-G) genes are needed to maintain expression patterns of the homeotic selector genes of the Antennapedia (Antp-C) and bithorax (bx-C) complexes, and hence for the maintenance of segmental determination. We report the predicted protein sequence of the Pc-G gene Posterior Sex Combs (Psc), and of the neighbouring and related gene Suppressor two of zeste (Su(z)2). Both genes encode large proteins that contain a 200 amino-acid domain identical over 37.4% that is also conserved in the murine oncogene bmi-1. At the amino terminus of this domain is a cysteine-rich sequence that has been proposed as a novel type of zinc finger. 相似文献
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茨威格的小说《一个陌生女人的来信》,已分别被中外两位导演改编为电影。本文旨在研究这两次改编的差别,同时对两位改编者借助小说展开的电影叙事和意图进行分析比较。 相似文献
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基于国家测绘局GPS连续运行参考站的定轨 总被引:4,自引:2,他引:2
为了解决采用地面GPS连续运行参考站进行高精度定轨问题,采用轨道积分方法,利用国家测绘局8个GPS连续运行参考站和9个中国周边IGS连续运行参考站,设计了多种天数的区域性定轨计算方案,研究了轨道确定的理论、步骤和参数设置规律.结果表明:3天轨道解的平均精度为0.19 m,5天轨道解的平均精度为O.21 m,7天轨道解的平均精度为O.28 m,3天解平均定轨精度最高,优于0.2 m,证明了并非随着地面数据天数的增加而精度随之增加,可以用最少的数据量获得最优的定轨结果.定轨试验计算的是区域性轨道,与全球轨道相比,存在一定的偏差.该成果对我国定轨研究特别是未来的广域增强系统轨道预测具有一定的指导意义和参考价值. 相似文献
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WANG ShanShan LI Qin Lü XueFei LIU Tong ZHANG WeiBo GENG LiNa & DENG YuLin School of Life Science Technology Beijing Institute of Technology Beijing China Analysis Test Center Sh ong Academy of Sciences Jinan 《科学通报(英文版)》2010,55(10):910-914
In the present study,a new enzymatic microreactor is developed by immobilizing trypsin on the matrix-HILIC (hydrophilic interaction chromatography).The influences of different types of buffer solutions (borate,Tris·HCl,and phosphate),their concentrations and pH values on the immobilizing rate and the activity of immobilized trypsin were investigated.The optimal condition for off-line immobilization of trypsin on matix-HILIC was Tris·HCl buffer (20 mmol/L,pH 8.0),and then,under the optimal condition,an enzym... 相似文献
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Insights into Wnt binding and signalling from the structures of two Frizzled cysteine-rich domains. 总被引:12,自引:0,他引:12
Members of the Frizzled family of seven-pass transmembrane proteins serve as receptors for Wnt signalling proteins. Wnt proteins have important roles in the differentiation and patterning of diverse tissues during animal development, and inappropriate activation of Wnt signalling pathways is a key feature of many cancers. An extracellular cysteine-rich domain (CRD) at the amino terminus of Frizzled proteins binds Wnt proteins, as do homologous domains in soluble proteins-termed secreted Frizzled-related proteins-that function as antagonists of Wnt signalling. Recently, an LDL-receptor-related protein has been shown to function as a co-receptor for Wnt proteins and to bind to a Frizzled CRD in a Wnt-dependent manner. To investigate the molecular nature of the Wnt signalling complex, we determined the crystal structures of the CRDs from mouse Frizzled 8 and secreted Frizzled-related protein 3. Here we show a previously unknown protein fold, and the design and interpretation of CRD mutations that identify a Wnt-binding site. CRDs exhibit a conserved dimer interface that may be a feature of Wnt signalling. This work provides a framework for studies of homologous CRDs in proteins including muscle-specific kinase and Smoothened, a component of the Hedgehog signalling pathway. 相似文献