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41.
DNA demethylation induced by 5-azacytidine does not affect fragile X expression. 总被引:1,自引:0,他引:1
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T W Glover J Coyle-Morris L Pearce-Birge C Berger R M Gemmill 《American journal of human genetics》1986,38(3):309-318
Experiments were performed to determine the role of DNA demethylation in fragile X expression. Fragile X positive lymphoblastoid cells were treated with 5-azacytidine and harvested for analysis of fragile X expression both directly following treatment and after a recovery period in the absence of the drug. The effectiveness of 5-azacytidine treatment in inducing DNA demethylation was concurrently monitored by analysis of methylation changes at random autosomal loci in isolated DNA from treated cells. Under conditions where 5-azacytidine was found to inhibit fragile X expression, no DNA demethylation was observed. At the time when demethylation did occur, fragile X expression was not affected. These results strongly indicate that DNA demethylation is not involved in fragile X expression. 相似文献
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43.
Polyomavirus small T antigen enhances replication of viral genomes in 3T6 mouse fibroblasts. 总被引:10,自引:8,他引:2
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Transfection of 3T6 cells with a cloned polyomavirus genome encoding only large T antigen resulted in DNA replication with only about 1/10 the efficiency of wild-type viral DNA coding for all three T antigens. This replication defect was at least in part overcome by the simultaneous transfections of polyomavirus genomes which allowed the expression of small T antigen. We conclude that polyomavirus small T antigen has a (probably indirect) role in replication. 相似文献
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R R Minor M Sippola-Thiele J McKeon J Berger D J Prockop 《The Journal of biological chemistry》1986,261(21):10006-10014
This is a study of the processing of procollagen to collagen in cultures of skin and tendon fibroblasts. Processing was markedly increased by growing cells for 2-4 days postconfluence and then adding ascorbate to the medium for 2 days prior to labeling with [3H] proline. With this system, more than two-thirds of the pro-alpha chains of type I procollagen in the culture medium, and more than 90% of those in the cell layer, were rapidly processed to pC-alpha, pN-alpha, or alpha chains. Purified, exogenous procollagen was also rapidly processed in cell-free culture medium. The results showed for the first time that exogenous procollagen can be processed in conditioned cell-free medium. The system was then used to compare the processing of procollagen in the medium of normal fibroblasts, cells from one bovine and four human variants of osteogenesis imperfecta, and those from eight human variants of the Ehlers-Danlos syndrome. The cells could be divided into three groups, based on their ability to process type I procollagen: normal, consistently slow, and very slow. The cause of the decreased processing was shown to be associated with either a mutation causing a shortening of an alpha chain or decreased activity of procollagen N-proteinase in cell-free culture medium. Decreased processing of procollagen to collagen occurred with cultured fibroblasts from patients with different forms of both osteogenesis imperfecta and Ehlers-Danlos syndrome. Both of these disease syndromes are associated with abnormalities in the structure or metabolism of procollagen in fibrous connective tissues, bones, and teeth. The results show that defects in the structure, synthesis, or processing of procollagen are readily demonstrated with cultured fibroblasts. 相似文献
46.
Four naked men, selected for their ability to sleep in the cold, were exposed to an ambient temperature (Ta) of 21 degrees C for five consecutive nights. Electrophysiological stages of sleep, O2 consumption (VO2), and skin (Tsk), rectal (Tre), and tympanic (Tty) temperatures were recorded. Compared with five nights at a thermoneutral Ta of 29 degrees C, cold induced increased wakefulness and decreased stage 2 sleep, without significantly affecting other stages. Tre and Tty declined during each condition. The decrease in Tre was greater at 21 degrees C than at 29 degrees C, whereas Tty did not differ significantly between conditions. Increases in Tty following REM sleep onset at 21 degrees C were negatively correlated with absolute Tty. VO2 and forehead Tsk also increased during REM sleep at both TaS, whereas Tsk of the limb extremities declined at 21 degrees C. Unsuppressed REM sleep in association with peripheral vasoconstriction and increased Tty and VO2 in cold-exposed humans, do not signify an inhibition of thermoregulation during this sleep stage as has been observed in other mammals. 相似文献
47.
Procollagen N-proteinase, the enzyme which cleaves the NH2-terminal propeptides from type I procollagen, was purified over 15,000-fold from extracts of chick embryos by chromatography on columns of DEAE-cellulose, concanavalin A-agarose, heparin-agarose, pN-collagen-agarose, and a filtration gel. The purified enzyme had an apparent molecular weight of 320,000 as estimated by gel filtration and a pH optimum for activity of 7.4 to 9.0. The enzyme was inhibited by metal chelators and the thiol reagent dithiothreitol. Addition of calcium was required for maximal activity under the standard assay conditions, and the presence of calcium decreased thermal inactivation at 37 degrees C. The purified enzyme cleaved a homotrimer of pro-alpha 1(I) chains, an observation which indicated that the presence of pro-alpha 2(I) chain is not essential for the enzymic cleavage of NH2-terminal propeptides. Previous observations suggesting that the enzyme requires a substrate with a native conformation were explored further by reacting the enzyme with type I procollagen at different temperatures. Type I procollagen from chick embryo fibroblasts became resistant to cleavage at about 43 degrees C. Type I procollagen from human skin fibroblasts, which was previously shown to have a slightly lower thermal stability than chick embryo type I procollagen, became resistant to cleavage at temperatures that were about 2 degrees C lower. The results suggested that the enzyme is a sensitive probe for the three-dimensional structure of the NH2-terminal region of the procollagen molecule and that it requires the protein substrate to be triple helical. 相似文献
48.
Summary In mammals, a number of liver-derived plasma proteins, termed acute phase reactants, are induced during an inflammation response. We have studied genetic variation in the structure and expression of several of these proteins in a variety of inbred and wild-derived mice. In a genetic cross, electrophoretic polymorphisms for the two 1-acid glycoproteins, AGP-1 and AGP-2, co-segregated in 58 backcross progeny, indicating that either a single gene or two tightly-linked genes on chromosome 4 encode the AGPs. In the same backcross, segregation of variation in haptoglobin structure showed that the gene encoding this acute phase reactant is on chromosome 8. Structural variation in serum amyloid A correlated with restriction fragment length polymorphisms in the Saa gene determined by Taylor and Rowe (1984). Analysis of a number of highly diverged species of mice indicated that AGP expression has undergone considerable modification during evolution of the Mus genus; this is associated with alterations in Agp gene organization, which may include species-specific amplification and/or deletion events. 相似文献
49.
Nitrogen Metabolism in Senescent Flag Leaves of Wheat (Triticum aestivum L.) in the Light 总被引:5,自引:2,他引:3
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Nitrogen metabolism was examined in senescent flag leaves of 90- to 93-day-old wheat (Triticum aestivum L. cv Yecora 70) plants. CO2 assimilation and the levels of protein, chlorophyll, and nitrogen in the leaves decreased with age. Glutamine synthetase activity decreased to one-eighth of the level in young flag leaves. Detached leaves were incubated (with the cut base) in 15N-labeled NH3, glutamate, or glycine in the light (1.8 millieinstein per square meter per second) at 25°C in an open gas exchange system under normal atmospheric conditions for up to 135 minutes. The 15N-enrichment of various amino acids derived from these 15N-substrates were examined. The amido-N of glutamine was the first 15N-labeled product in leaves incubated with 15NH4Cl whereas serine, closely followed by the amido- and amino-N of glutamine, were the most highly 15N-labeled products during incubation with [15N]glycine. In contrast, aspartate and alanine were the first 15N-labeled products when [15N] glutamate was used. These results indicate that NH3 was assimilated via glutamine synthetase and glutamate synthase activities and the photorespiratory nitrogen cycle remained functional in these senescent wheat flag leaves. In contrast, an involvement of glutamate dehydrogenase in the assimilation of ammonia could not be detected in these tissues. 相似文献
50.
The effect of light on the metabolism of ammonia was studied by subjecting detached maize leaves to 150 or 1350 mol m–2 s–1 PAR during incubation with the leaf base in 2 mM 15NH4Cl. After up to 60 min, leaves were extracted. Ammonia, glutamine, glycine, serine, alanine, and aspartate were separated by isothermal distillation and ion exchange chromatography. 15N enrichments were analyzed by emission spectroscopy. The uptake of ammonium chloride did not influence CO2 assimilation (8.3 and 17.4 mol m–1 s–1 at 150 and 1350 mol m–2 s–1 PAR, respectively). Leaves kept at high light intensity contained more serine and less alanine than leaves from low light treatments. Within 1 h of incubation the enrichment of ammonia extracted from leaves rose to approximately 20% 15N. In the high light regime the amino acids contained up to 15% 15N, whereas in low light 15N enrichments were small (up to 6%). The kinetics of 15N incorporation indicated that NH3 was firstly assimilated into glutamine and then into glutamate. After 15 min 15N was also found in glycine, serine and alanine. At high light intensity nearly half of the 15N was incorporated in glycine. On the other hand, at low light intensity alanine was the predominant 15N sink. It is concluded that light influences ammonia assimilation at the glutamine synthetase reaction. 相似文献