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31.
Y Chu  M T Hsu 《Nucleic acids research》1992,20(15):4033-4038
We investigated the in vivo effect of ellipticine, a mammalian topoisomeraseII(topoII) inhibitor, on SV40 DNA topology. In contrast to epipodophyllotoxins, ellipticine did not cause significant double stranded cleavage of intracellular SV40 DNA. Furthermore, ellipticine reduced cleavage induced by epipodophyllotoxins, VP16 and VM26. Unexpectedly, ellipticine dramatically increased the superhelical density of a fraction of intracellular SV40 DNA. Several lines of evidence suggest that the formation of this highly supercoiled DNA species (Ih form DNA) is not due to the inhibition of topoII per se, but is the result of intercalation by ellipticine in a subfraction of the intracellular SV40 chromatin followed by the fixation of DNA linking number by a topoisomerase activity. Based on the linking number change and the known unwinding angle of ellipticine, the intercalation density was calculated as one ellipticine molecule per 10-20 bp in the Ih DNA. This result suggests the existence of different populations of intracellular SV40 chromatin with respect to the accessibility to ellipticine intercalation.  相似文献   
32.
马铃薯Y病毒外壳蛋白基因的克隆及序列分析   总被引:1,自引:0,他引:1  
本文报道应用聚合酶链式反应(PCR)技术,在体外扩增马铃薯 Y 病毒外壳蛋白基因及其克隆和序列分析的结果。病毒 RNA 从马铃薯 Y 病毒感染的烟草叶片中提取,用合成的PCR 3引物及 AMV 逆转录酶合成了单链的 cDNA。利用 PCR 技术,经30个循玎的扩增。得到了一特异的0.8kb 片段。克隆后对此片段进行了限制性内切酶物理图谱分析,并测定了其全序列。实验结果证明,我们克隆到的是完整的马铃薯 Y 病毒的外壳蛋白基因。与国外报道的马铃薯 Y 病毒 N 株相比,其核苷酸序列及推测的氨基酸序列的同源率分别为97.8%和97%。将该基因导入马铃薯以期获得抗 Y 病毒马铃薯的工作正在进行。本文还对 PCR 技术用于扩增植物 RNA 病毒的方法以及用基因工程方法培育抗病毒作物新品种的可行性等进行了讨论。  相似文献   
33.
A SEM study was performed on the surface of adult P. kobayashii Park, 1940, recovered from the snake, Elaphe rufodorsata. The anterior part of the worms was cup-shape and equipped with oral, ventral suckers, pseudosuckers, and tribocytic organ, and the posterior one was finger-like and round-ended. The tegument of the anterior body was covered with 3-4 pointed small spines on the mid-ventral surface and 1-2 pointed ones on the lateral surface. Sensory papillae such as type II, dome-shape ones, and papillae with an opening were distributed over the ventral surface of the anterior portion. The round tribocytic organ was bearing small stout spines laterally, whereas the surface which comes in contact with the host tissues consisted of numerous long fibrillar fibers. The lip of the oral sucker contained type II papillae. Lateral margin of the anterior body revealed type III papillae.  相似文献   
34.
F S Chu 《Mutation research》1991,259(3-4):291-306
Mycotoxins constitute a large number of naturally occurring fungal secondary metabolites with very diversified toxic effects in humans and animals. Among many mycotoxins discovered, aflatoxins, ochratoxin A, sterigmatocystin and several others are identified as carcinogens; several others were found to be mutagenic. Nevertheless, aflatoxin B1 has been found to be one of the most potent carcinogens and contamination of aflatoxins in the food supply is still a major concern. Whereas extensive studies have been made on aflatoxins, little is known about the mode of action of other carcinogenic and mutagenic mycotoxins. Recent progress on research for the carcinogenic and mutagenic mycotoxins is presented in this review with emphasis on their contamination in foods, their carcinogenic potential to humans, and the mode of action as well as possible preventive measures.  相似文献   
35.
36.
Two distinct cDNAs for 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) were obtained from a glyphosate-tolerant tobacco cell line. The cDNAs were 89% identical and the predicted sequences of the mature proteins were greater than 83% identical with EPSPS proteins from other plants. Tobacco EPSPS proteins were more similar to those from tomato and petunia than Arabidopsis. One cDNA clone, EPSPS-1, represented a gene that was amplified in glyphosate-tolerant cells, while the gene for EPSPS-2 was unaltered in these cells. Consequently, EPSPS-1 mRNA was more abundant in tolerant than unselected cells, whereas EPSPS-2 mRNA was at relatively constant levels in these cell lines. Exposure of unselected cells and tobacco leaves to glyphosate produced a transient increase in EPSPS mRNA. However, glyphosate-tolerant cells containing amplified copies of EPSPS genes did not show a similar response following exposure to glyphosate. A significant proportion of the EPSPS gene amplification was maintained when tolerant cells were grown in the absence of glyphosate for eight months. Plants regenerated from these cells also contained amplified EPSPS genes.  相似文献   
37.
本研究观察了肾血管性高血压大鼠(RHR)肥大左室的等容峰压-容积关系(PIPVR)和左室压力最大上升速率-容积关系(PRPVR)的曲线特征,并用两曲线的升支斜率E_(max)和dE/dt_(max)及曲线的特征参数评价了RHR(8周)左室的收缩能力及其对异丙肾上腺素的反应性。结果显示,大鼠高血压8周后左室发生明显肥大;与同龄假手术对照大鼠(SOR)相似,RHR的PIPVR和PRPVR也呈指数曲线形式;与SOR比较,RHR左室的PIPVR和PRPVR左上移位,E_(max)、dE/dt_(max)显著增大(P均<0.01),分别增加78%和97%,曲线的特征参数K_1、K_2、B_1和B_2也明显高于SOR(P均<0.05),分别增加37%、32%、25%和57%;灌注异丙肾上腺素(0.94μg/min)后,上述指标的增加幅度均较SOR低(P均<0.05)。结果提示,压力超负荷心肌肥大并不影响PIPVR的非线性特征,基础状态下,RHR肥大左室的收缩能力增强,但对异丙肾上腺素的反应性降低。  相似文献   
38.
39.
A new, improved approach for the production of antibodies against T-2 toxin and diacetoxyscirpenol (DAS) was developed. The method involves the use of immunogens which were prepared by conjugating O-carboxymethoxyl oxime (CMO) derivatives of both toxins to bovine serum albumin (BSA). Isomers a and b of CMO-T-2 toxin and isomer b of CMO-DAS were tested. Antibodies against both toxins were demonstrated as early as 4 weeks after immunization. a-CMO-T-2-BSA conjugate was a better immunogen than the b isomer, and the highest titers (6,000) were reached 14 weeks after immunization and one booster injection. Antibody titers for rabbits immunized with the b isomer of CMO-T-2 never reached more than 2,000. The specificity of antibodies obtained from rabbits after immunization with CMO-T-2-BSA was similar to that of hemisuccinate-T-2-BSA. Anti-b-T-2 antibodies had slightly higher cross-reactivity with H-T-2 toxin than did the antibody obtained from rabbits immunized with the conjugate of the a isomer. The relative cross-reactivities of anti-a-CMO-T-2 antibody with T-2, acetyl-T-2, H-T-2, T-2-triol, 3'-OH-T-2, and T-2 tetraol were 1, 4.5, 5.7, 250, 500, and 3,000, respectively. The relative cross-reactivities of anti-b-T-2 antibody with T-2, acetyl-T-2, H-T-2, and T-2 triol were 1, 2, 3, and 488, respectively. Antibodies against b-CMO-DAS showed a high degree of cross-reactivity with monoacetoxyscirpenols (MAS). The relative cross-reactivities of anti-B-DAS antibody with DAS, 4-MAS, 15-MAS, acetyl-deoxynivalenol, T-2-toxin, acetyl-T-2, and neosolaniol were 1, 4, 5, 76, 107, 147, and 266, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
40.
A technique using C-14 isotope tracers to probe the branching of carbon flow in methylotrophic bacteria has been devised and applied to continuous steady-state cultures. Methylomonas L3, a strain which utilizes the KDPG/TA variant of the ribulose monophosphate cycle for carbon fixation, was employed in the experimental studies. The actual in vivo rates of substrate-carbon incorporation into biomass, both direct and via CO(2), and of the two carbon oxidation schemes were determined in three different steady-state cultures. The results show that the carbon substrate is oxidized predominantly via formate (the linear oxidation scheme), and that the cyclic scheme of oxidation is minimally, if at all, utilized. The carbon incorporation and oxidation patterns appear to vary considerably with the dilution rate and the inoculum history. The experimental accuracy of the new technique is discussed in detail.  相似文献   
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