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941.
David A. Rouse Joseph A. DeVito Zhongming Li Heather Byer & Sheldon L. Morris 《Molecular microbiology》1996,22(3):583-592
Recent studies examining the molecular mechanisms of isoniazid (INH) resistance in Mycobacterium tuberculosis have demonstrated that a significant percentage of drug-resistant strains are mutated in the katG gene which encodes a catalase–peroxidase, and the majority of these alterations are missense mutations which result in the substitution of a single amino acid. In previous reports, residues which may be critical for enzymatic activity and the drug-resistant phenotype have been identified by evaluating INH-resistant clinical isolates and in vitro mutants. In this study, site-directed mutagenesis techniques were utilized to alter the wild-type katG gene from M. tuberculosis at 13 of these codons. The effects of these mutations were determined using complementation assays in katG -defective, INH-resistant strains of Mycobacterium smegmatis and Mycobacterium bovis BCG. This mutational analysis revealed that point mutations in the katG gene at nine of the 13 codons can cause drug resistance, and that enzymatic activity and resistance to INH are inversely related. In addition, mutations in the mycobacterial catalase–peroxidase which reduce catalase activity also decrease peroxidase activity. 相似文献
942.
943.
Further progress towards a catalogue of all Arabidopsis genes: analysis of a set of 5000 non-redundant ESTs 总被引:9,自引:1,他引:8
Richard Cooke Monique Raynal Michele Laudi Franoise Grellet Michel Delseny Peter-Christian Morris Danile Guerrier Jrme Giraudat Franoise Quigley Grard Clabault You-Fang Li Rgis Mache Micheline Krivitzky Isabelle Jean-Jacques Gy Martin Kreis Alain Lecharny Yves Parmentier Jacqueline Marbach Jacqueline Fleck Bernadette Clment Gabriel Philipps Christine Herv Claude Bardet Dominique Tremousaygue Bernard Lescure Christophe Lacomme Dominique Roby Marie-Franoise Jourjon Patrick Chabrier Jean-Louis Charpenteau Thierry Desprez Joelle Amselem Helen Chiapello Herman Hfte 《The Plant journal : for cell and molecular biology》1996,9(1):101-124
Nearly 7000 Arabidopsis thaliana -expressed sequence tags (ESTs) from 10 cDNA libraries have been sequenced, of which almost 5000 non-redundant tags have been submitted to the EMBL data bank. The quality of the cDNA libraries used is analysed. Similarity searches in international protein data banks have allowed the detection of significant similarities to a wide range of proteins from many organisms. Alignment with ESTs from the rice systematic sequencing project has allowed the detection of amino acid motifs which are conserved between the two organisms, thus identifying tags to genes encoding highly conserved proteins. These genes are candidates for a common framework in genome mapping projects in different plants. 相似文献
944.
Gejiao Wang Stefano Castiglione Ying Chen Ling Li Yifan Han Yingchuan Tian Dean W. Gabriel Yinong Han Kequiang Mang Francesco Sala 《Transgenic research》1996,5(5):289-301
Insect-resistant poplar (Populus nigra L.) plants have been produced by infecting leaves withAgrobacterium tumefaciens strains carrying a binary vector containing different truncated forms of aBacillus thuringiensis (B.t.) toxin gene under a duplicated CaMV 35S promoter. Putative transgenic plants were propagated by cuttings at two experimental farms (in Beijing and Xinjiang, China). At 2–3 years after transformation, 17 of them were selected on the bases of insect-tolerance and good silvicultural traits, and evaluated for insect resistance, for the presence of theB.t. toxin DNA fragment (Southern blots and PCR) and for the expression of the transgene (western and northern blots). Somaclonal variation, as suggested by the appearance of permanent changes in the shape of the leaves, was also investigated with molecular tools (RFLP (restriction fragment length polymorphism), RAPD (random amplified polymorphic DNA) and microsatellite DNA).Bioassays withApochemia cineraius andLymantria dispar on the leaves of the selected clones showed different and, in some cases, high levels of insecticidal activity. The molecular analysis demonstrated integration and expression of the foreign gene. Somatic changes were correlated to extensive genomic changes and were quantified in dendrograms, in terms of genomic similarity. The analysis of control plants suggested that genomic changes were correlated to thein vitro culture step necessary forA. tumefaciens-mediated gene transfer, rather than to the integration of the foreign genes.Three transgenic clones (12, 153 and 192), selected for insect resistance, reduced morphological changes and promising silvicultural traits, are now under large-scale field evaluation in six different provinces in China. 相似文献
945.
Physicochemical basis for the rapid time-action of LysB28ProB29-insulin: dissociation of a protein-ligand complex. 总被引:2,自引:0,他引:2 下载免费PDF全文
D. L. Bakaysa J. Radziuk H. A. Havel M. L. Brader S. Li S. W. Dodd J. M. Beals A. H. Pekar D. N. Brems 《Protein science : a publication of the Protein Society》1996,5(12):2521-2531
The rate-limiting step for the absorption of insulin solutions after subcutaneous injection is considered to be the dissociation of self-associated hexamers to monomers. To accelerate this absorption process, insulin analogues have been designed that possess full biological activity and yet have greatly diminished tendencies to self-associate. Sedimentation velocity and static light scattering results show that the presence of zinc and phenolic ligands (m-cresol and/or phenol) cause one such insulin analogue, LysB28ProB29-human insulin (LysPro), to associate into a hexameric complex. Most importantly, this ligand-bound hexamer retains its rapid-acting pharmacokinetics and pharmacodynamics. The dissociation of the stabilized hexameric analogue has been studied in vitro using static light scattering as well as in vivo using a female pig pharmacodynamic model. Retention of rapid time-action is hypothesized to be due to altered subunit packing within the hexamer. Evidence for modified monomer-monomer interactions has been observed in the X-ray crystal structure of a zinc LysPro hexamer (Ciszak E et al., 1995, Structure 3:615-622). The solution state behavior of LysPro, reported here, has been interpreted with respect to the crystal structure results. In addition, the phenolic ligand binding differences between LysPro and insulin have been compared using isothermal titrating calorimetry and visible absorption spectroscopy of cobalt-containing hexamers. These studies establish that rapid-acting insulin analogues of this type can be stabilized in solution via the formation of hexamer complexes with altered dissociation properties. 相似文献
946.
铜锌超氧化物歧化酶(Cu, Zn-SOD)表面的赖氨酸经化学修饰后, 酶的稳定性显著提高. 赖氨酸被修饰后, 酶的电荷结构遂发生变化, 从而影响到酶分子电场. 使用FDPB方法(有限差分法求解Poission-Boltzman方程)计算了酶修饰前后的静电场变化, 以及对维持酶的结构稳定起重要作用的Cu, Zn配位结构的影响.结果表明, Cu, Zn配位体的两级离解常数在酶修饰后分别约下降103, 106. 相似文献
947.
改进了一种分析磷酸酶活性的终止酶反应方法.该方法通过在酶反应进行到一定程度时,在反应混合物中加入酶反应终止液(1mol/L NaOH-0.2mol/L EDTA),从而使测定更简捷、精确. 相似文献
948.
通过发育解剖学研究表明,秦艽根的初生结构正常,初生木质部四原型。次生生长早期阶段也是正常的,但天以后的次生生长过程中,由于木质部内部分薄壁细胞的分裂,且迅速 化成异常形成层细胞,并与原维管形成层相连,从而形成多个新的形成层环,将木质部柱分为几个子木质部。 相似文献
949.
950.
促进檀香种子发芽技术的研究 总被引:6,自引:0,他引:6
本文讨论了破除檀香种子休眠,提高发芽率和整齐度,缩短发芽期的方法,采用多因子试验,发现用1000mg/LGA处理檀香种子,播后一个月发芽率可高达80%左右,有效地解决了檀香种子发芽期长,发芽不整齐和发芽率低的问题。 相似文献