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21.
Cell-surface expression of a membrane-anchored form of the human chorionic gonadotropin alpha subunit 总被引:15,自引:0,他引:15
We carried out experiments designed to generate a novel cell-surface protein from a small glycosylated secretory protein. DNA encoding the entire precursor of human chorionic gonadotropin (hCG, alpha subunit) was fused precisely to DNA encoding the transmembrane and cytoplasmic domains of the vesicular stomatitis virus glycoprotein. When expressed in animal cells this DNA encoded the 92-amino acid hCG-alpha subunit anchored in cellular membranes by an extension composed of the 49 carboxyl-terminal amino acids of vesicular stomatitis virus glycoprotein. This hybrid protein was transported efficiently to the plasma membrane of animal cells. The two asparagine-linked glycans on the anchored form of hCG-alpha were large and heterogeneous when compared to those on the secretory form. Experiments employing in vitro mutagenesis and the glycosylation inhibitor tunicamycin established that the presence of at least one of the two asparagine-linked glycans was required for expression of the anchored molecule on the cell surface. However, as reported previously, secretion of hCG-alpha occurred in the absence of glycosylation. Also, mutations eliminating the second glycosylation site (at amino acid 78) in both the anchored or secreted forms apparently led to partial denaturation or a conformational change interfering with transport of the protein. 相似文献
22.
Litterfall Production Along Successional and Altitudinal Gradients of Subtropical Monsoon Evergreen Broadleaved Forests in Guangdong, China 总被引:3,自引:0,他引:3
Guoyi Zhou Lili Guan Xiaohua Wei Deqiang Zhang Qianmei Zhang Junhua Yan Dazhi Wen Juxiu Liu Shuguang Liu Zhongliang Huang Guohui Kong Jiangming Mo Qingfa Yu 《Plant Ecology》2007,188(1):77-89
Evaluation of litterfall production is important for understanding nutrient cycling, forest growth, successional pathways, and interactions with environmental variables in forest ecosystems. Litterfall was intensively studied during the period of 1982–2001 in two subtropical monsoon vegetation gradients in the Dinghushan Biosphere Reserve, Guangdong Province, China. The two gradients include: (1) a successional gradient composed of pine forest (PF), mixed pine and broadleaved forest (MF) and monsoon evergreen broadleaved forest (BF), and (2) an altitudinal gradient composed of Baiyunci ravine rain forest (BRF), Qingyunci ravine rain forest (QRF), BF and mountainous evergreen broadleaved forest (MMF). Mean annual litterfall production was 356, 861 and 849 g m−2 for PF, MF and BF of the successional gradient, and 1016, 1061, 849 and 489 g m−2 for BRF, QRF, BF and MMF of the altitudinal gradient, respectively. As expected, mean annual litterfall of the pioneer forest PF was the lowest, but rapidly increased over the observation period while those in other forests were relatively stable, confirming that forest litterfall production is closely related to successional stages and growth patterns. Leaf proportions of total litterfall in PF, MF, BF, BRF, QRF and MMF were 76.4%, 68.4%, 56.8%, 55.7%, 57.6% and 69.2%, respectively, which were consistent with the results from studies in other evergreen broadleaved forests. Our analysis on litterfall monthly distributions indicated that litterfall production was much higher during the period of April to September compared to other months for all studied forest types. Although there were significant impacts of some climate variables (maximum and effective temperatures) on litterfall production in some of the studied forests, the mechanisms of how climate factors (temperature and rainfall) interactively affect litterfall await further study. 相似文献
23.
药用植物北五味子的组织培养 总被引:12,自引:0,他引:12
取北五味子带腋物嫩茎作为植体,培养于附加同种类和浓度激素的MS培养基上,在附国加6-BA2.0+ZT0.1mg/L时,诱导芽的效果最佳;在附加6~BA2.0+NAA0.2+ZT0.1mg/L时,芽的增殖率最好,在附加NAA0.2mg/L时,生根效果最佳,当苗高2.0~2.5cm根数达3-5条时,开瓶锻炼2天,移栽于消过毒的土壤中,10天后,成活率达100%。 相似文献
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25.
Mitochondrial tRNA mutations are one of the important causes of both syndromic and non-syndromic deafness. Of those, syndromic deafness-associated tRNA mutations such as tRNA(Leu(UUR)) 3243A>G are often present in heteroplasmy, while non-syndromic deafness-associated tRNA mutations including tRNA(Ser(UCN)) 7445A>G often occur in homplasmy or in high levels of heteroplasmy. These tRNA mutations are the primary mutations leading to hearing loss. However, other tRNA mutations such as tRNA(Thr) 15927G>A and tRNA(Ser(UCN)) 7444G>A may act in synergy with the primary mitochondrial DNA mutations, modulating the phenotypic manifestation of the primary mitochondrial DNA mutations. Theses tRNA mutations cause structural and functional alteration. A failure in tRNA metabolism caused by these tRNA mutations impaired mitochondrial translation and respiration, thereby causing mitochondrial dysfunctions responsible for deafness. These data offer valuable information for the early diagnosis, management and treatment of maternally inherited deafness. 相似文献
26.
Biochemical characterization of the mitochondrial tRNASer(UCN) T7511C mutation associated with nonsyndromic deafness 总被引:6,自引:0,他引:6
Li X Fischel-Ghodsian N Schwartz F Yan Q Friedman RA Guan MX 《Nucleic acids research》2004,32(3):867-877
We report here the biochemical characterization of the deafness-associated mitochondrial tRNASer(UCN) T7511C mutation, in conjunction with homoplasmic ND1 T3308C and tRNAAla T5655C mutations using cybrids constructed by transferring mitochondria from lymphoblastoid cell lines derived from an African family into human mtDNA-less (ρ°) cells. Three cybrids derived from an affected matrilineal relative carrying the homoplasmic T7511C mutation, exhibited ~75% decrease in the tRNASer(UCN) level, compared with three control cybrids. This amount of reduction in the tRNASer(UCN) level is below a proposed threshold to support a normal rate of mitochondrial protein synthesis in lymphoblastoid cell lines. This defect is likely a primary contributor to ~52% reduction in the rate of mitochondrial protein synthesis and marked defects in respiration and growth properties in galactose-containing medium. Interestingly, the T5655C mutation produces ~50% reduction in the tRNAAla level in mutant cells. Strikingly, the T3308C mutation causes a significant decrease both in the amount of ND1 mRNA and co-transcribed tRNALeu(UUR) in mutant cells. Thus, mitochondrial dysfunctions caused by the T5655C and T3308C mutations may modulate the phenotypic manifestation of the T7511C mutation. These observations imply that a combination of the T7511C mutation with two mtDNA mutations accounts for the high penetrance of deafness in this family. 相似文献
27.
28.
Electron microscopic examination of the orexin immunoreactivity in the dorsal raphe nucleus 总被引:1,自引:0,他引:1
The ultrastructure and the synaptic relationships of the orexin-A-like immunoreactive fibers in the dorsal raphe nucleus were examined with an immunoelectron microscopic method. At the electron microscopic level, most of the immunoreactive fibers, a varicosity appearance at the light microscopic level, were found as axon terminals. The large dense-cored vesicles contained in the immunoreactive axon terminals were the most intensely immunostained organellae. These axon terminals were often found to make synapses. While the axo-dendritic synapses were usually asymmetric in appearance, the axo-somatic synapses were symmetric. Orexin-A-like immunoreactive processes with no synaptic vesicles were also found. These processes often received asymmetric synapses. With less frequency, the synapses were found between the orexin-like immunoreactive processes. The results suggest that the orexin peptides are stored in the large dense-cored vesicles; the orexin-containing fibers may have influences on the physiological activities of the dorsal raphe nucleus through direct synaptic relationships. 相似文献
29.
L-阿拉伯糖异构酶(L-arabinose isomerase,L-AI)是一种可以催化D-半乳糖为D-塔格糖的胞内异构化酶。随着塔格糖在食品工业中越来越广泛的应用,能够将半乳糖转化为塔格糖的食品级微生物以及食品级来源的L-AI受到更大的关注。文中从各种酸奶制品、泡菜及其他一些食品中采集不同的样品,筛选出1株具有L-AI酶活的食品级菌株,经过生理生化鉴定以及16S rDNA序列测定,确定该菌株为戊糖片球菌,命名为Pediococcus pentosaceus PC-5。以该菌基因组为模板,克隆L-AI基因,并在大肠杆菌BL21成功地异源表达。表达产物经粗提取后,在40℃下加入Mn2+,使D-半乳糖转化为D-塔格糖的转化率为33%。 相似文献
30.
Guan S Ma S Zhu Y Ge R Wang Q Wang JH 《Biochemical and biophysical research communications》2006,345(1):175-180
Cerebellum is involved in the motion coordination and working memory, to which the programming of sequential spikes at Purkinje cells is essential. It is not clear about the intrinsic mechanisms underlying spike capacity and timing precision as well as their postnatal maturation. We investigated the programming and intrinsic property of sequential spikes at Purkinje neurons during postnatal development by whole-cell recording in cerebellar slices. Cerebellar Purkinje neurons demonstrate the increasing of spike capacity and timing precision, as well as the lowering of refractory periods and threshold potentials during the postnatal maturation. In addition, the correlation between spike parameters and intrinsic properties converts to be more linear. This postnatal plasticity of neuronal intrinsic properties improves the timing precision and capacity of spike programming at cerebellar Purkinje neurons. 相似文献