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Autonomous replication sequences in an extrachromosomal element of a pathogenic Entamoeba histolytica. 总被引:2,自引:1,他引:1 下载免费PDF全文
Entamoeba histolytica possesses a 24.5 kilobase plasmid-like molecule which encodes for the organism's ribosomal RNAs. Sequence analysis of this extrachromosomal element revealed the presence of AT rich sequences which show homology to the origin of replication of other lower eucaryotes. An 802 bp fragment containing these sequences was cloned into a yeast shuttle vector lacking the origin of replication and the construct tested for its ability to replicate autonomously in yeast. Mitotic stability tests as well as evidence for plasmid maintenance indicate that the transformed cells contained self-replicating episomes and not stably integrated molecules. The nucleotide sequence of this ARS-containing fragment is presented. 相似文献
4.
A Halobacterium strain, isolated by Ginzburg et al. from the Dead Sea in the late 1960's, often referred to as "Halobacterium marismortui" or "Halobacterium of the Dead Sea" (deposited in the American Type Culture Collection as ATCC 43049) was compared with Halobacterium (Haloarcula) vallismortis ATCC 29715. The strains appeared to be very closely related, as shown by the near identity of their 5S and 16S ribosomal RNA's, and a large number of other common properties. Distinct differences exist, however, in cell morphology, and in their potency to utilize different sugars and other compounds. 相似文献
5.
Enhanced binding of a 95 kDa protein to p53 in cells undergoing p53-mediated growth arrest. 总被引:10,自引:1,他引:9
To explore the biochemical functions of p53, we have initiated a search for cellular p53-binding proteins. Coprecipitation of three polypeptides was observed when cell lines overexpressing a temperature-sensitive (ts) p53 mutant were maintained at 32.5 degrees C (wild-type p53 activity, leading to growth arrest) but not at 37.5 degrees C (mutant p53 activity). One of these three proteins, designated p95 on the basis of its apparent molecular mass, was highly abundant in p53 immune complexes. We demonstrate herein that p95 is a p53-binding protein, which exhibits poor p53-binding in cells overproducing several distinct mutant p53 proteins. Yet, p95 associates equally well with both the wild-type (wt) and the mutant conformations of the ts p53 in transformed cells growth-arrested at 32.5 degrees C. On the basis of our findings we suggest that wt p53 activity increases p53-p95 complex formation and that such interaction may play a central role in p53 mediated tumour suppression. 相似文献
6.
Identification of a minimal transforming domain of p53: negative dominance through abrogation of sequence-specific DNA binding. 总被引:21,自引:5,他引:16 下载免费PDF全文
Mutations in the p53 gene are most frequent in cancer. Many p53 mutants possess transforming activity in vitro. In cells transformed by such mutants, the mutant protein is oligomerized with endogenous cell p53. To determine the relevance of oligomerization for transformation, miniproteins containing C-terminal portions of p53 were generated. These miniproteins, although carrying no point mutation, transformed at least as efficiently as full-length mutant p53. Transforming activity was coupled with the ability to oligomerize with wild-type p53, as well as with the ability to abrogate sequence-specific DNA binding by coexpressed wild-type p53. These findings suggest that p53-mediated transformation may operate through a dominant negative mechanism, involving the generation of DNA binding-incompetent oligomers. 相似文献
7.
Simian virus 40 can overcome the antiproliferative effect of wild-type p53 in the absence of stable large T antigen-p53 binding. 总被引:4,自引:0,他引:4 下载免费PDF全文
In simian virus 40 (SV40)-transformed cells, a tight complex is formed between the viral large T antigen (large T) and p53. It has been proposed that this complex interferes with the antiproliferative activity of p53. This notion was tested in primary rat fibroblasts by assessing the ability of SV40-mediated transformation to be spared from the inhibitory effect of wild-type (wt) p53. The data indicate that relative to transformation induced by myc plus ras, SV40-plus-ras-mediated focus formation was indeed much less suppressed by p53 plasmids. A majority of the resultant cell lines made a p53 protein with properties characteristic of a wt conformation. Furthermore, cell lines expressing stably both SV40 large T and a temperature-sensitive p53 mutant continued to proliferate at a temperature at which this p53 assumes wt-like properties and normally causes a growth arrest. Surprisingly, at least partial resistance to the growth-inhibitory effect of wt p53 was also evident when transformation was mediated by an SV40 deletion mutant, encoding a large T which does not bind p53 detectably. In addition to supporting the idea that SV40 can overcome the growth-restrictive activity of wt p53, these findings strongly suggest that at least part of this effect does not require a stable association between p53 and large T. 相似文献
8.
p53 cellular tumor antigen: analysis of mRNA levels in normal adult tissues, embryos, and tumors. 总被引:39,自引:10,他引:29 下载免费PDF全文
The relative levels of mRNA specific for the mouse p53 cellular tumor antigen were determined in various normal adult tissues, embryos, and tumors. All tumors studied contained concentrations of p53 mRNA well above those present in most normal tissues. Normal spleen, however, had p53 mRNA levels comparable to those found in some tumors, despite the fact that they contained barely detectable p53 protein. This apparent discrepancy was found to be due to the extremely rapid turnover rate of p53 in the spleen (half-life, approximately equal to 6 min). In developing fetuses, a marked reduction of p53 mRNA levels was manifest from day 11 onwards, whereas the levels during organogenesis (days 9 to 11) were comparable to those found in undifferentiated embryonic stem cells and in some tumors. 相似文献
9.
Overproduction of protein p53 contributes to simian virus 40-mediated transformation. 总被引:13,自引:4,他引:9 下载免费PDF全文
The possible involvement of p53 overproduction in simian virus 40 (SV40)mediated transformation was studied by using the rat embryo fibroblast focus formation assay. Transformation by wild-type SV40 was enhanced two- to threefold by cotransfection of a plasmid overexpressing mouse p53. More significantly, such a plasmid could partially complement a transformation-defective deletion mutant of SV40. Hence, the ability of SV40 T antigen to induce high p53 levels may indeed be directly relevant to the viral transforming potential. 相似文献
10.
Aharon Oren 《FEMS microbiology ecology》1993,12(1):15-23
Abstract A sensitive assay for glycerol and other polyols was developed, based on periodate oxidation to formaldehyde, followed by a colorimetric assay with 3-methyl-2-benzothiazolone hydrazone. Apparent glycerol concentrations thus measured in saltern crystallizer ponds were around 20–36 μM, while in the Dead Sea, during a Dunaliella bloom, values were up to 27 μM. However, these values probably overestimate the glycerol concentrations present, as shown by labeled glycerol uptake experiments. Values of [K + Sn ] (natural concentration + affinity constant) in saltern ponds were as low as 0.76–1.4 μM, with Vmax values of 193–303 nmol 1−1 h−1 , and turnover times between 2.6–7.2 h at 35°C. Similar measurements in the Dead Sea were: [K + Sn ] 0.07–1.41 μM, Vmax values 160–426 nmol 1−1 h−1 , and turnover times in the range of 0.45–3.3 h. 相似文献