首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   101篇
  国内免费   2篇
  完全免费   19篇
  2018年   2篇
  2017年   2篇
  2016年   3篇
  2015年   1篇
  2014年   2篇
  2013年   3篇
  2012年   4篇
  2011年   10篇
  2010年   2篇
  2009年   3篇
  2008年   1篇
  2007年   6篇
  2006年   2篇
  2005年   2篇
  2004年   5篇
  2003年   1篇
  2002年   1篇
  2001年   12篇
  2000年   6篇
  1999年   11篇
  1998年   3篇
  1997年   3篇
  1996年   4篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1992年   7篇
  1991年   4篇
  1990年   6篇
  1989年   2篇
  1988年   5篇
  1985年   1篇
  1983年   1篇
排序方式: 共有122条查询结果,搜索用时 46 毫秒
1.
2.
The mechanism of protein splicing and its modulation by mutation.   总被引:16,自引:2,他引:14       下载免费PDF全文
M Q Xu  F B Perler 《The EMBO journal》1996,15(19):5146-5153
Protein splicing results in the expression of two mature proteins from a single gene. After synthesis of a precursor protein, an internal segment (the intein) is excised and the external domains are joined together. A self-catalyzed mechanism for this cleavage-ligation reaction is presented, based on mutagenesis data and analysis of splicing intermediates. Mutations were used to block various steps in the protein splicing pathway, allowing each isolated step to be studied independently. A linear ester intermediate was identified and functional roles for the four conserved splice junction residues were determined. Understanding the mechanism of protein splicing provides a basis for protein engineering studies. For example, inteins can be constructed which fail to splice, but instead cleave the peptide bond at a chosen splice junction.  相似文献
3.
M Mayr  C Li  Y Zou  U Huemer  Y Hu  Q Xu 《The FASEB journal》2000,14(2):261-270
The present study was designed to investigate whether apoptosis occurs in early-stage vein grafts and to determine the mechanisms by which mechanical stress contributes to apoptosis in vascular smooth muscle cells (SMCs). Apoptosis in vessel walls of mouse vein grafts was confirmed by morphological changes and by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL). TUNEL(+) cells in vein grafts 1, 4, and 8 wk postoperatively was 13%, 29%, and 21%, respectively, and apoptosis occurred mainly in veins grafted to arteries, remaining unchanged in vein-to-vein grafts. When mouse, rat, and human arterial SMCs were cultured on a flexible membrane and subjected to cyclic strain stress, apoptosis was observed in a time- and strength-dependent manner. All three types of SMCs showed apoptotic death as confirmed by TUNEL, propidium iodide, and annexin V staining. To further study the signal pathways leading to apoptosis, activities of p38, a subfamily of mitogen-activated protein kinases (MAPKs), were determined. Mechanical stress resulted in p38 MAPK activation, reaching high levels within 8 min. SB 202190, a specific inhibitor for p38 MAPKs, prevented SMC apoptosis in response to mechanical stress. SMC lines stably transfected with a dominant negative rac, an upstream signal transducer, or overexpressing MAPK phosphatase-1, a negative regulator for MAPKs, completely inhibited mechanical stress stimulated p38 activation and abolished mechanical stress-induced apoptosis. Thus, we provide solid evidence that one of the earliest events in venous bypass grafts is apoptosis, in which mechanical stress-induced p38-MAPK activation is responsible for transducing signals leading to apoptosis.-Mayr, M., Li, C., Zou, Y., Huemer, U., Hu, Y., Xu, Q. Biomechanical stress-induced apoptosis in vein grafts involves p38 mitogen-activated protein kinases.  相似文献
4.
Delayed leaf-senescence, or stay-green, has been regarded as a desired characteristic for the production of a number of crops including rice. In this study, we analyzed the genetic basis of stay-green using a population of 190 doubled haploid lines from the cross between an indica parent Zhenshan 97 and a stay-green japonica parent Wuyujing 2. The population was tested in replicated field trials in 2 consecutive years, and six traits were defined to evaluate the stay-green characteristics. A genetic linkage map with 179 SSR (simple sequence repeat) marker loci was constructed. The software QTLMapper, based on a mixed linear model approach, was applied to detect QTLs, epistatic effects and their environmental interactions for these traits. A total of 46 main-effect QTLs was detected for the six traits that can be localized to 25 chromosomal regions. The individual effects of all the QTLs were small. Fifty digenic interactions were resolved that involved 66 loci distributed on all 12 chromosomes. Environmental interactions were detected for 18 of the main-effect QTLs and 14 of the epistatic interactions. Collectively, the epistatic effects and QTL by year interactions accounted for large proportions of the phenotypic variations. The results also showed that most of the stay-green traits were negatively correlated with yield and its component traits. The implications of the results in crop improvement were discussed.Communicated by C. Möllers  相似文献
5.
A conventional affinity protein purification system often requires a separate protease to separate the target protein from the affinity tag. This paper describes a unique protein purification system in which the target protein is fused to the C-terminus of a modified protein splicing element (intein). A small affinity tag is inserted in a loop region of the endonuclease domain of the intein to allow affinity purification. Specific mutations at the C-terminal splice junction of the intein allow controllable C-terminal peptide bond cleavage. The cleavage is triggered by addition of thiols such as dithiothreitol or free cysteine, resulting in elution of the target protein while the affinity-tagged intein remains immobilized on the affinity column. This system eliminates the need for a separate protease and allows purification of a target protein without the N-terminal methionine. We have constructed general cloning vectors and demonstrated single-column purification of several proteins. In addition, we discuss several factors that may affect the C-terminal peptide bond cleavage activity.  相似文献
6.
Leukocyte chemotactic activity of cyclophilin.   总被引:14,自引:0,他引:14  
During the purification of eosinophil chemotactic factors synthesized by the uterus in response to estrogen we isolated a protein having an N-terminal (15 amino acids) sequence identical to that of rat cyclophilin. Our data demonstrate that cyclophilin, a cytosolic protein isolated from bovine thymocytes, which specifically binds the immunosuppressive drug cyclosporin A, as well as recombinant human cyclophilin, displays eosinophil chemotactic activity. In addition to its chemotactic activity, cyclophilin stimulated the release of peroxidase activity from eosinophils. Maximal chemotactic activity of cyclophilin was achieved at a concentration of approximately 10 nM. At similar concentrations cyclophilin was also able to stimulate the migration of neutrophils. This chemotactic activity could be prevented by the addition of cyclosporin A, but not by a nonimmunosuppressive analog (1-fur-furyl-cyclosporin A) at similar concentrations. This chemotactic activity may represent an additional mechanism by which immunosuppressive drugs function to prevent tissue rejection.  相似文献
7.
We report a self-splicing intron in bacteriophage SPO1, whose host is the gram-positive Bacillus subtilis. The intron contains all the conserved features of primary sequence and secondary structure previously described for the group IA introns of eukaryotic organelles and the gram-negative bacteriophage T4. The SPO1 intron contains an open reading frame of 522 nucleotides. As in the T4 introns, this open reading frame begins in a region that is looped out of the secondary structure, but ends in a highly conserved region of the intron core. The exons encode SPO1 DNA polymerase, which is highly similar to E. coli DNA polymerase I. The demonstration of self-splicing introns in viruses of both gram-positive and gram-negative eubacteria lends further evidence for their early origin in evolution.  相似文献
8.
Domain structure in yeast tRNA ligase   总被引:12,自引:0,他引:12  
Q Xu  D Teplow  T D Lee  J Abelson 《Biochemistry》1990,29(26):6132-6138
Yeast tRNA ligase is one of two proteins required for the splicing of precursor tRNA molecules containing introns. The 95-kDa tRNA ligase has been purified to homogeneity from a strain of Escherichia coli which overexpresses the protein. The ligation reaction requires three enzymatic activities: phosphodiesterase, polynucleotide kinase, and ligase. By partial proteolytic digestion, we have produced fragments of tRNA ligase which contain the constituent activities. These results provide evidence for a model in which the three constituent activities of ligase are located in three distinct domains separated by protease-sensitive regions. We have also located the active adenylylated site in the ligase domains. It is lysine-114. The tRNA ligase sequence in this region has limited homology to the active-site region of T4 RNA ligase.  相似文献
9.
T. C. Evans  Jr  J. Benner    M. Q. Xu 《Protein science》1998,7(11):2256-2264
Two cytotoxic proteins, bovine pancreatic ribonuclease A (RNase A), and a restriction endonuclease from Haemophilus parainfluenzae (HpaI), were produced using a novel semisynthetic approach that utilizes a protein splicing element, an intein, to generate a reactive thioester at the C-terminus of a recombinant protein. Nucleophilic attack on this thioester by the N-terminal cysteine of a synthetic peptide ultimately leads to the ligation of the two reactants through a native peptide bond. This strategy was used to produce RNase A and HpaI by isolating inactive truncated forms of these proteins, the first 109 and 223 amino acids of RNase A and HpaI, respectively, as fusion proteins consisting of the target protein, an intein, and a chitin binding domain. Thiol-induced cleavage of the precursor led to the liberation of the target protein with a C-terminal thioester-tag. Addition of synthetic peptides representing the amino acids missing from the truncated forms led to the generation of full-length products that displayed catalytic activity indicative of the wild-type enzymes. The turnover numbers and Km for ligated and renatured RNase A were 8.2 s(-1) and 1.5 mM, in good agreement with reported values of 8.3 s(-1) and 1.2 mM (Hodges & Merrifield, 1975). Ligated HpaI had a specific activity of 0.5-1.5 x 10(6) U/mg, which compared favorably with the expected value of 1-2 x 10(6) U/mg (J. Benner, unpubl. obs.). Besides assisting in the production of cytotoxic proteins, this technique could allow the easy insertion of unnatural amino acids into a protein sequence.  相似文献
10.
M Q Xu  D G Comb  H Paulus  C J Noren  Y Shao    F B Perler 《The EMBO journal》1994,13(23):5517-5522
Protein splicing involves the excision of an internal domain from a precursor protein and the ligation of the external domains so as to generate two new proteins. Study of this process has recently been facilitated by the isolation of a precursor and a branched intermediate from a thermophilic protein splicing element expressed in a foreign protein context. Two aspects of protein splicing are examined in this paper. We demonstrate a succinimide at the C-terminus of the spliced internal protein, implicating cyclization of asparagine in resolution of the branched intermediate, and we identify an alkali-labile bond in the branched intermediate. A revised protein splicing model based on these experimental results is presented.  相似文献
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号