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32.
We have investigated chromatin structure in the beta-globin gene region of the K562 human erythroleukemic cell line by using S1 and DNase I nuclease sensitivity assays. Despite the lack of beta-globin gene expression in these cells, we find nuclease-hypersensitive sites to these enzymes in its 5' and 3' flanking regions in K562 chromatin. This result is in contrast to previous reports in which no hypersensitive sites were found in the immediate vicinity of this gene. In the 3' region, one major hypersensitive site at 0.9 kpb 3' and three minor hypersensitive sites at 0.7 kbp, 0.5 kbp 3' and 0.2 kbp 5' of the polyadenylation site were observed; these sites are very similar to those found in fetal liver and adult bone marrow cells in which the beta-globin gene is expressed. We find hypersensitive sites to both enzymes in the 5' region of the beta-globin gene: a major site 0.8 kbp 5' to the cap site, and two minor sites 1.2 and 1.5 kbp 5' to the cap site. The -0.8 kbp site is also present in plasmids containing the beta-globin gene. Our results suggest that the lack of beta-globin gene expression may be related to the lack of hypersensitivity sites in the immediate (150 bp) 5' flanking region of the beta-globin gene, as occurs in other active globin genes. 相似文献
33.
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
34.
Actively cycling human lymphocytes were treated with mitomycin C for 1 h (1.4 μg/ml) and then grown in medium containing 10 μg/ml bromodeoxyuridine. Serial 5-h colcemid accumulation samples were taken up to 35 h and the air-dried methaphase spreads stained for replication banding. A complete cell-cycle subphasing analysis was made, and classified cells scored for all categories of chromatid-type aberrations and their location.
Inspite of the high dose which produced massive delay and cycle perturbation, there was no evidence for selectively lethality of early-S cells, in fact such cells were in excess. Extreme localization of aberrations to late-replicating (mostly centromeric) regions was found at all subphases and in pre-S cells. This rules out ‘localization by default’ as an explanation for the observed preferential occurence of ‘break points’ in these regions.
The frequency of incomplete intrachanges, low in late S, rises dramaticallyin early S to become maximal in pre-S cells. 相似文献
35.
Ren-Huan Tang Min-Min Su Tong-Geng Cao Yuan-Fang Liu 《Biological trace element research》1985,7(2):95-102
Using two Chinese strains ofTetrahymena pyriformis, S1 and BJ4, as the biological models, the effects of lighter rare earths (lanthanum, cerium, praseodymium, neodymium, samarium, and europium), representatives of heavier rare earths (yttrium and thulium), and mixed rare earths were studied. The stimulation of population growth ofTetrahymena in peptone-glucose media containing trace amounts of these elements have been observed. The mechanisms for the beneficial effects of rare earth elements in low concentrations remains to be discovered. 相似文献
36.
本文对比研究了溴化氰活化及高碘酸活化肝素修饰的两种修饰尿激酶的性质。结果表明尿激酶在溴化氰活化肝素(肝素CN),高碘酸钠活化肝素(肝素I_4)的共价修饰后,其残余自由氨基分别是64%和52%;酶活性分别保留94%和90%;抗胃蛋白酶水解以及抗冻融变性的能力均高于天然酶;在离体血浆中的失活速变低于天然酶。本文还对修饰酶进行了萤光及紫外差光谱的分析,讨论了修饰过程对构象的影响。 相似文献
37.
[AlaB5]Insulin as well as a hybrid analogue of insulin and "insulin-like growth factor" (IGF-I), in which the N-terminal amino-acid sequence H-Phe-Val-Asn-Gln- of the B-chain has been replaced by the tripeptide H-Gly-Pro-Glu-of IGF-I, have been prepared by the partial-synthetic route. Their biological activity in vivo has been compared with that of other analogues in rabbits, mice and rats as far as data are available. These rodents respond differently, rats being less sensitive to modifications than rabbits and mice. The results explain unexpected discrepancies discussed in previous papers. 相似文献
38.
对8只成体树鼩的睾丸进行了精子发生的细胞学和动力学观察。精原细胞可区分为A型和已分化定向的B型。生精上皮周期可分为12个连续阶段,不同阶段典型的细胞组合可被辨认。各阶段的相对持续时间以阶段Ⅴ、Ⅵ、Ⅶ的比率最高,分别为11.43,18.88、15.44;阶段Ⅸ、Ⅹ最低,为3.78和3.87。A型精原细胞在各阶段的数量分布并不保持恒定,阶段Ⅵ—Ⅷ和阶段Ⅸ时,分别出现两次成倍增长。B型精原细胞和前细线期精母细胞与每100个足细胞之比的平均值,在阶段Ⅰ、Ⅴ、Ⅶ分别为28.89、76.98、196.91。精细胞经14步变态为成熟精子。精子形成过程中顶体发育的形态学变化及成熟精子的形态,与灵长类动物相比具有较多的类似之处;而同啮齿类动物相比,存在明显的形态差异。 相似文献
39.
40.
Hung Cao Danh Margherita Strolin Benedetti Philippe Dostert 《Journal of neurochemistry》1983,41(3):618-622
Abstract: Aldehyde dehydrogenase (ALDH) activity was measured in brains, livers, and hearts of 23–26-month-old and 3-month-old rats. A significant increase of ALDH activity was found in whole brain of old rats with both acetaldehyde (39%) and propionylaldehyde (15%) used as substrates. In different brain areas of old rats, with acetaldehyde used as substrate, a significant increase of ALDH activity was found in striatum (30–50%) and cerebral cortex (37%). However, no significant difference in ALDH activity was found in livers and hearts of young and old rats. Preliminary experiments showed a significant increase of aldehyde reductase activity (52%) with p -nitrobenzaldehyde used as substrate in whole brain of old rats compared with young rats. The present work indicates that an increase of ALDH activity in brain of old rats may be an adaptive phenomenon. 相似文献