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41.
Th. F. Spande J. W. Daly D. J. Hart Y-M. Tsai T. L. Macdonald 《Cellular and molecular life sciences : CMLS》1981,37(12):1242-1245
Summary The structure 3-butyl-5-propylindolizidine (2), tentatively assigned to a minor alkaloid in skin extracts from a number of poison frogs of the Neotropical genusDendrobates, has been confirmed and its stereochemistry determined as 5E, 9E (2d) by comparison on GC and GC-MS with the four synthetic diastereomers2a-2d. 相似文献
42.
DNA replication sites within nuclei of mammalian cells 总被引:12,自引:0,他引:12
43.
Mutations in a member of the ADAMTS gene family cause thrombotic thrombocytopenic purpura 总被引:114,自引:0,他引:114
44.
The SNRPN promoter is not required for genomic imprinting of the Prader-Willi/Angelman domain in mice. 总被引:2,自引:0,他引:2
J Bressler T F Tsai M Y Wu S F Tsai M A Ramirez D Armstrong A L Beaudet 《Nature genetics》2001,28(3):232-240
In mice and humans, the locus encoding the gene for small nuclear ribonucleoprotein N (SNRPN/Snrpn), as well as other loci in the region are subject to genomic imprinting. The SNRPN promoter is embedded in a maternally methylated CpG island, is expressed only from the paternal chromosome and lies within an imprinting center that is required for switching to and/or maintenance of the paternal epigenotype. We show here that a 0.9-kb deletion of exon 1 of mouse Snrpn did not disrupt imprinting or elicit any obvious phenotype, although it did allow the detection of previously unknown upstream exons. In contrast, a larger, overlapping 4.8-kb deletion caused a partial or mosaic imprinting defect and perinatal lethality when paternally inherited. 相似文献
45.
介绍东经 12 0°低纬电离层CT实验及CT重建结果 .提出一种改进的电离层CT算法 .该算法通过联合使用差分Doppler相位和差分Doppler频率数据 ,把相位积分常数估算融入重建过程之中 .CT重建结果发现 ,赤道异常峰电子密度等值线沿磁力线倾斜 ;峰位置逐日变化时 ,倾斜程度也随之改变 ,使峰电子密度等值线仍沿磁力线 ;峰朝赤道的运动通常伴随峰区展宽 .此外 ,对一次中等强度磁暴期间电离层响应的分析发现 ,在赤道异常峰区 ,磁暴急始之后 2 0min出现电子密度的深度耗空 ,这种耗空遍及从底到顶的整个F区 .结果表明 ,电离层CT技术在研究电离层赤道异常的动力过程、电离层行扰和不规则结构的时空演变以及暴时电离层响应等方面具有重要的应用价值与前景 . 相似文献
46.
Cloning of cDNA for the major DNA-binding protein of the erythroid lineage through expression in mammalian cells 总被引:154,自引:0,他引:154
Genes expressed in erythroid cells contain binding sites for a cell-specific factor believed to be an important regulator for this haematopoietic lineage. Using high-level transient expression in mammalian cells, we have identified complementary DNA encoding the murine protein. The factor, a new member of the zinc-finger family of DNA-binding proteins, is restricted to erythroid cells at the level of RNA expression and is closely homologous between mouse and man. 相似文献
47.
Increased gamma-globin expression in a nondeletion HPFH mediated by an erythroid-specific DNA-binding factor 总被引:63,自引:0,他引:63
In man, a shift from gamma- to beta-globin gene expression in erythroblasts underlies a switch from fetal to adult haemoglobin during development. In hereditary persistence of fetal haemoglobin (HPFH), inappropriately high gamma-globin expression in adult life is associated with deletions in the beta-globin cluster or with single-base changes upstream of the gamma-globin genes. To account for enhanced gamma-gene expression in HPFH of the non-deletion type, we tested the nuclear proteins of human erythroleukaemia cells that bind gamma-promoter sequences in vitro by correlating specific mutations in their binding sites with promoter activity. An erythroid-specific factor (GF-1) binds as a single molecule to the -195 to -170 region and contacts two TATCT(AGATA) motifs, but not the conserved octamer (ATGCAAAT) that separates them. We observe that a single change (at -175, T----C) found in HPFH leads to increased promoter activity only in erythroid cells. This effect is mediated by GF-1, the human counterpart of the chicken erythroid factor Eryf 1. The form of HPFH we studied here is an inherited disorder which can be ascribed to the action of a cell-specific DNA-binding factor on a mutant promoter. 相似文献
48.
甲烷氧化偶联金属氧化物催化剂组份分子设计程序 总被引:5,自引:1,他引:4
甲烷氧化偶联金属氧化物催化剂组份分子设计程序廖代伟,黄遵楠,林银钟,龚文华,万惠霖,张鸿斌,蔡启瑞(化学系 物理化学研究所 固体表面物理化学国家重点实验室)近几十年来所取得的显著成就提供了有可能在分子水平上进行催化剂分子设计的相当多的科学基础.国内外... 相似文献
49.
The dynamic linear model (DLM) with additive Gaussian errors provides a useful statistical tool that is easily implemented because of the simplicity of updating a normal model that has a natural conjugate prior. If the model is not linear or if it does not have additive Gaussian errors, then numerical methods are usually required to update the distributions of the unknown parameters. If the dimension of the parameter space is small, numerical methods are feasible. However, as the number of unknown parameters increases, the numerial methods rapidly grow in complexity and cost. This article addresses the situation where a state dependent transformation of the observations follows the DLM, but a priori the appropriate transformation is not known. The Box-Cox family, which is indexed by a single parameter, illustrates the methodology. A prior distribution is constructed over a grid of points for the transformation parameter. For each value of the grid the relevant parameter esitmates and forecasts are obtained for the transformed series. These quantities are then integrated by the current distribution of the transformation parameter. When a new observation becomes available, parallel Kalman filters are used to update the distributions of the unknown parameters and to compute the likelihood of the transformation parameter at each grid point. The distribution of the transformation parameter is then updated. 相似文献
50.