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排序方式: 共有522条查询结果,搜索用时 15 毫秒
1.
The use of bromodeoxyuridine labeling in the human lymphocyte HGPRT somatic mutation assay 总被引:4,自引:0,他引:4
P Ostrosky-Wegman M R Montero C C de Nava R R Tice R Albertini 《Mutation research》1987,191(3-4):211-214
The autoradiographic assay developed by Strauss and Albertini (1979) to quantitate human in vivo somatic mutation at the hypoxanthine guanine phosphoribosyl-transferase locus uses tritiated thymidine to identify mutant cells by their ability to pass through 'S' phase in the presence of 6-thioguanine. An alternative method, based on the incorporation of bromodeoxyuridine (BrdUrd) into the DNA of proliferative cells, followed by differential staining with the fluorescence-plus-Giemsa method, was used to identify 3 classes of lymphocyte nuclei: (a) small darkly stained nuclei, (b) large, reddish-colored nuclei with an apparent nucleolus, and (c) large, bluish-colored nuclei. By double labeling with BrdUrd and tritiated thymidine, it was determined that only the nuclei of the third class had incorporated BrdUrd. These results demonstrate that the technique used for sister-chromatid differentiation can be used to detect putative HGPRT mutants and to determine variant frequencies at the HGPRT locus. 相似文献
2.
Isolation and characterization of the two major apoproteins in human lipoprotein [a] 总被引:4,自引:0,他引:4
Human Lp[a] was isolated in preparative amounts from two donors; the native lipoprotein and its constituent apoproteins, apo[a] and apoB, were characterized extensively. Based on differences in apparent molecular weight, four different isoforms of apo[a], a1-a4, were observed between the two donors. The number and relative distribution of these isoforms varied between donors but were constant for each donor. Each apo[a] isoform was shown to be derived from a discrete apo[a]-B100 disulfide-linked complex present before reduction. Complete delipidation of Lp[a] was followed by solubilization, reduction, and carboxamidomethylation of the constituent apoproteins. These apoproteins were then separated by immunoaffinity chromatography using anti-apo[a]- or anti-apoB-Sepharose; their purity and structural integrity were demonstrated by Western blot analysis. ApoB isolated by this procedure was essentially identical to apoB from autologous LDL with respect to molecular weight, secondary structure, amino acid composition, and sialic acid content. However, apo[a] differed from apoB in that it exhibited: a much less alpha-helical, less beta, but much more disordered structure; a lower proportion of aspartate, isoleucine, leucine, phenylalanine, and lysine, but a higher proportion of proline, glycine, and threonine; and a much higher content of sialic acid. These results indicate that apo[a] is not a superglycosylated form of apoB but is distinctly different in its composition and structure. 相似文献
3.
José Edmundo Nava Saucedo Jean-Noël Barbotin Daniel Thomas 《Applied microbiology and biotechnology》1989,30(3):226-233
Summary The continuous production of gibberellic acid with immobilized mycelia of Gibberella fujikuroi was maintained over a hundred days in a tubular fixed-bed reactor. Free mycelium at the beginning of the storage phase was harvested from G. fujikuroi shake-flask culture and was immobilized by ionotropic gelation in calcium alginate beads.The continuous recycle production system consisted of a fixed-bed reactor, a container in which the culture medium was heated, stirred and aerated, and valves for sample withdrawal or reactant addition during the first 1320 h (55 days). A two-phase continuous extractor was then added for the last 960 hours (40 days). Free and immobilized mycelium shake-flask cultures with the same strain used in the continuous culture system were also realized to compare growth, maintenance and production parameters. The results show about the same gibberellic acid productivity in both free and immobilized mycelium shakeflask cultures: 0.384 and 0.408 mgGA3·gBiomass-1 ·day-1, respectively, whereas in the continuous system the gibberellic acid production is about twice as large for a similar biomass: 0.768 mgGA3·gBiomass-1·day-1. Several factors affecting the overall productivity of the immobilized systems were found to be: the quality and the quantity of mycelia in the biocatalyst beads and the immobilization conditions. 相似文献
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We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
8.
Marjolijn J. A. Christianen Fee O. H. Smulders Jan Arie Vonk Leontine E. Becking Tjeerd J. Bouma Sabine M. Engel Rebecca K. James Mabel I. Nava Jaco C. de Smit Jurjan P. van der Zee Per J. Palsbøll Elisabeth S. Bakker 《Global Change Biology》2023,29(1):215-230
Large grazers (megaherbivores) have a profound impact on ecosystem functioning. However, how ecosystem multifunctionality is affected by changes in megaherbivore populations remains poorly understood. Understanding the total impact on ecosystem multifunctionality requires an integrative ecosystem approach, which is especially challenging to obtain in marine systems. We assessed the effects of experimentally simulated grazing intensity scenarios on ecosystem functions and multifunctionality in a tropical Caribbean seagrass ecosystem. As a model, we selected a key marine megaherbivore, the green turtle, whose ecological role is rapidly unfolding in numerous foraging areas where populations are recovering through conservation after centuries of decline, with an increase in recorded overgrazing episodes. To quantify the effects, we employed a novel integrated index of seagrass ecosystem multifunctionality based upon multiple, well-recognized measures of seagrass ecosystem functions that reflect ecosystem services. Experiments revealed that intermediate turtle grazing resulted in the highest rates of nutrient cycling and carbon storage, while sediment stabilization, decomposition rates, epifauna richness, and fish biomass are highest in the absence of turtle grazing. In contrast, intense grazing resulted in disproportionally large effects on ecosystem functions and a collapse of multifunctionality. These results imply that (i) the return of a megaherbivore can exert strong effects on coastal ecosystem functions and multifunctionality, (ii) conservation efforts that are skewed toward megaherbivores, but ignore their key drivers like predators or habitat, will likely result in overgrazing-induced loss of multifunctionality, and (iii) the multifunctionality index shows great potential as a quantitative tool to assess ecosystem performance. Considerable and rapid alterations in megaherbivore abundance (both through extinction and conservation) cause an imbalance in ecosystem functioning and substantially alter or even compromise ecosystem services that help to negate global change effects. An integrative ecosystem approach in environmental management is urgently required to protect and enhance ecosystem multifunctionality. 相似文献
9.
A Rhizobium tropici DNA region carrying the amino-terminal half of a nodD gene and a nod-box-like sequence confers host-range extension 总被引:1,自引:0,他引:1
Carolina Sousa Jorge Luis Folch Purificación Boloix Manuel Megías Noreide Nava Carmen Quinto 《Molecular microbiology》1993,9(6):1157-1168
Rhizobium tropici CIAT899 is a broad-host-range strain that, in addition to Phaseolus, nodulates other plant legumes such as Leucaena and Macroptilium. The narrow-host-range of Rhizobium leguminosarum biovars phaseoli (strain CE3) and trifolii (strain RS1051) can be extended to Leucaena esculents and Phaseolus vulgaris plants, respectively, by the introduction of a DNA fragment 521 bp long, which carries 128 amino acids of the amino-terminal region of a nodD gene from R. tropici, as well as a putative nod-box-like sequence, divergently oriented. The 521 bp fragment, in the presence of L. esculenta or P. vulgaris root exudates, induced a R. leguminosarum bv. viciae nodA-lacZ fusion in either a CE3 or RS1051 background, respectively. 相似文献
10.
Gracia Revello M Percivalle E Baldanti F Gerna G Kustermann A Nava S Nicolini U 《Clinical and diagnostic virology》1993,1(1):61-67
Ganciclovir was administered 'in utero' for 12 days in a 29-week-old fetus with ascertained congenital human cytomegalovirus (HCMV) infection, thrombocytopenia and elevated gamma-glutamyl transferase (gammaGT) value. Efficacy of therapy was shown by reduction in virus titer of amniotic fluid and fetal urine, disappearance of viral DNA in fetal blood, and normalization of platelet count and gammaGT value. However, stillbirth occurred at 32 weeks of gestation and HCMV inclusion bodies were detected in kidneys, lungs, heart and pancreas at autopsy. During therapy, side-effects,possibly related to ganciclovir administration, were observed. 相似文献