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971.
Sayan Mukherjee Pablo Tamayo Simon Rogers Ryan Rifkin Anna Engle Colin Campbell Todd R Golub Jill P Mesirov 《Journal of computational biology》2003,10(2):119-142
A statistical methodology for estimating dataset size requirements for classifying microarray data using learning curves is introduced. The goal is to use existing classification results to estimate dataset size requirements for future classification experiments and to evaluate the gain in accuracy and significance of classifiers built with additional data. The method is based on fitting inverse power-law models to construct empirical learning curves. It also includes a permutation test procedure to assess the statistical significance of classification performance for a given dataset size. This procedure is applied to several molecular classification problems representing a broad spectrum of levels of complexity. 相似文献
972.
利用AP-PCR和RAPD技术对三个草菇菌株进行鉴别,其结果与用草菇菌株V34基因文库中的中等重复序列为探针进行限制性内切酶长度多态性分析(RFLP),及对编码核糖体5.8SrRNA的DNA(rDNA)进行PCR扩增后的产物进行限制性内切酶长度多态性分析(PCR-RFLP)的结果相一致。这一结果显示出用这四种方法对草菇菌株进行鉴别具有相似的效果。同时用这四种方法构建的分子生物学标记显示出这三个菌株中的两个菌株在遗传上有着较大程度的相似性。 相似文献
973.
本文对华北地区蓟属CirsiumAdans.16种植物的甲醇提取液紫外吸收光谱(UV)进行了比较研究。结果表明,蓟属植物的叶较其它部位的UV具有较好的稳定性和代表性,其光谱的特征可以作为属下分类的重要依据,其化学分类结果与形态分类基本一致。根据光谱特征,结合形态学及有关的细胞学和同工酶方面的资料,重新确立了Sect.Pseudo-Eriolepis(Nakai)Kitam.和C.segetumBge.的组级和种级地位,最后,作者进一步讨论了光谱特征在化学分类中的意义。 相似文献
974.
Genetic metabolic polymorphisms and the risk of cancer: a review of the literature 总被引:10,自引:0,他引:10
The purpose of this paper is to systematically analyse the design and results of epidemiological studies on the association between various types of cancer (lung, bladder, breast, colon, stomach) and four genetically-based metabolic polymorphisms, involved in the metabolism of several carcinogens (glutathione-S-transferase M1, debrisoquine hydroxylase, N acetyltransferase, aryl hydrocarbon hydroxylase). These inherited polymorphisms usually cause modifications in the quality or quantity of the relevant enzymes. Such enzymes are involved in the activation/inactivation of known carcinogens and seem to modify the extent to which carcinogens interact with DNA in target tissues. Two enzymes, debrisoquine hydroxylase and aryl hydrocarbon hydroxylase, activate procarcinogens to carcinogens (phase I enzymes). The other two, glutathione-S-transferase M1 and N-acetyltransferase, mainly detoxity carcinogenic substances (phase II enzymes). Because of their role as host factors (modulating the action of carcinogens), it has been hypothesized that subjects presenting a specific phenotype for such polymorphisms could be at a greater risk of developing various types of cancer. A number of epidemiological studies have investigated such associations, often with discordant results. We examine and discuss the design of the studies, and present a meta-analysis of the available data. 相似文献
975.
Dr J -H Huang C -J Chen Y -C Su 《Journal of industrial microbiology & biotechnology》1996,17(2):89-95
A bacterial strain secreting potent chitinolytic activity was isolated from shrimp-pond water by enrichment culture using colloidal crab-shell chitin as the major carbon source. The isolated bacterium, designated asAeromonas sp No. 16 exhibited a rod-like morphology with a polar flagellum. Under optimal culture conditions in 500-ml shaker flasks, it produced a chitinolytic activity of 1.4 U ml–1. A slightly higher enzymatic activity of 1.5 U ml–1 was obtained when cultivation was carried out in a 5-liter jar fermentor using a medium containing crystalline chitin as the carbon source. The secretion of the enzyme(s) was stimulated by several organic nitrogenous supplements. Most carbon sources tested (glucose, maltose, N-acetylglucosamine, etc) enhanced cell growth, but they slightly inhibited enzyme secretion. Glucosamine (0.5% w/v) severely inhibited cell growth (16% of the control), but it did not significantly affect enzyme secretion. The production of chitinolytic enzymes was pH sensitive and was enhanced by increasing the concentration of colloidal chitin to 1.5%. The observed chitinolytic activity could be attributed to the presence of -N-acetylglucosaminidase and chitinase. Chitinase was purified by ammonium sulfate fractionation and preparative gel electrophoresis to three major bands on SDS-PAGE. An in-gel enzymatic activity assay indicated that all three bands possessed chitinase activity. Analysis of the enzymatic products indicated that the purified enzyme(s) hydrolyzed colloidal chitin predominantly to N,N-diacetyl-chitobiose and, to a much lesser extent, the mono-, tri, and tetramer of N-acetylglucosamine, suggesting that they are mainly endochitinases. 相似文献
976.
本文用PCR方法获得大肠杆菌热休克蛋白转录因子σ32的编码基因rpoH,并克隆在含有tac启动子的表达载体pUHE中,经IPTG诱导,在大肠杆菌中表达了C端融合有6个寡聚组氨酸的σ32。表达产物经金属螯合层析一步纯化,达到SDS-PAGE银染一条带纯度,氨基酸组成分析及N端序列分析结果与文献报道一致。35S细胞内参入实验表明:即使在较低的温度下,表达产物σ32(His)6也能导致热休克蛋白如GroEl、DnaK、Htp的大量合成. 相似文献
977.
Introduction and expression of foreign DNA in isolated spinach chloroplasts by electroporation 总被引:3,自引:1,他引:2
Kin-Ying To Ming-Chih Cheng Long-Fang Oliver Chen Shu-Chen Grace Chen 《The Plant journal : for cell and molecular biology》1996,10(4):737-743
An electroporation-mediated method for the study of foreign gene expression within chloroplasts has been developed. The chloroplast expression vector pHD203-GUS, which consists of coding regions for β-glucuronidase (GUS) and chloramphenicol acetyltransferase (CAT) separated by a double psbA promoter fragment from pea (in opposite orientation) was electroporated into spinach chloroplasts and the transient gene expression was examined. Conditions for the expression of the reporter genes have been optimized. Both CAT and GUS activities were detected in chloroplasts electroporated with pHD203-GUS, but not with nuclear expression vector pBI221 or negative control pUC18. No GUS activity was detected when pHD203-GUS was electroporated into spinach protoplasts. Dot immunoblot analysis using anti-GUS antibody confirmed the existence of GUS protein in chloroplasts electroporated with chloroplast-specific vector but not the negative controls, excluding the possibilities of endogenous GUS or bacterial contamination. The expression of GUS protein in treated chloroplasts was further confirmed by Western blot analysis. 相似文献
978.
Overexpression of bacterio-opsin in Escherichia coli as a water-soluble fusion to maltose binding protein: efficient regeneration of the fusion protein and selective cleavage with trypsin. 总被引:2,自引:2,他引:0
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Bacteriorhodopsin (bR) is a light-driven proton pump from Halobacterium salinarium and is a model system for studying membrane protein folding, stability, function, and structure. bR is composed of bacterio-opsin (bO), the 248-amino acid apo protein, and all-trans retinal, which is linked to lysine 216 via a protonated Schiff base. A bO gene (sbOd) possessing 29 unique restriction sites and a carboxyl-terminal purification epitope (1D4, nine amino acids) has been designed and synthesized. Overexpression of bO was achieved by fusion to the carboxyl terminus of maltose binding protein (MBP). The expressed fusion protein (MBP-sbO-1D4) formed inclusion bodies in Escherichia coli and, following solubilization with urea and removal of the urea by dialysis, approximately 170 mg of approximately 75% pure MBP-sbO-1D4 was obtained from 1 L of culture. MBP-sbO-1D4 formed high molecular weight (> or = 2,000 kDa) oligomers that were water-soluble. The synthetic bO with the 1D4 tag (sbO-1D4) was separated from MBP by trypsin cleavage at the factor Xa site between the MBP and sbO-1D4 domains. Selective trypsin cleavage at the factor Xa site, instead of at the 14 other potential trypsin sites within bO, was accomplished by optimization of the digestion conditions. Both MBP-sbO-1D4 and sbO-1D4 were regenerated with all-trans retinal and purified to homogeneity. In general, 6-10 mg of sbR-1D4 and 52 mg of MBP-sbR-1D4 were obtained from 1 L of cell culture. No significant differences in terms of UV/vis light absorbance, light/dark adaptation, and photocycle properties were observed among sbR-1D4, MBP-sbR-1D4, and bR from H. salinarium. 相似文献
979.
980.
Nicolas Bouquin Mao X. Chen Sunghoon Kim Françoise Vannier Sylvie Bernard I. Barry Holland Simone J. Séror 《Molecular microbiology》1996,20(4):853-865
We previously described a mutation feeB1 conferring a temperature-sensitive filamentation phenotype and resistance to the calmodulin inhibitor 48/80 in Escherichia coli, which constitutes a single base change in the acceptor stem of the rare tRNA3Leu recognizing CUA codons. We now describe a second mutant, feeA1, unlinked to feeB, but displaying a similar phenotype, 48/80 resistance and a reduced growth rate at the permissive temperature, 30°C, and temperature-sensitive, forming short filaments at 42°C. In the feeA mutant, tRNA3Leu expression (but not that of tRNA1Leu) was reduced approximately fivefold relative to the wild type. We previously showed that the synthesis of β-galactosidase, which unusually requires the translation of 6-CUA codons, was substantially reduced, particularly at 42°C, in feeB mutants. The feeA mutant also shows drastically reduced synthesis of β-galactosidase at the non-permissive temperature and reduced levels even at the permissive temperature. We also show that increased copy numbers of the abundant tRNA1Leu, which can also read CUA codons at low efficiency, suppressed the effects of feeA1 under some conditions, providing further evidence that the mutant was deficient in CUA translation. This, and the previous study, demonstrates that mutations which either reduce the activity of tRNA3Leu or the cellular amount of tRNA3Leu confer resistance to the drug 48/80, with concomitant inhibition of cell division at 42°C. 相似文献