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1.
DNA-protein cross-links are formed when living cells or isolated chromatin is exposed to ionizing radiation. Little is known about the actual cross-linked products of DNA and proteins. In this work, a novel hydroxyl radical induced cross-link of thymine and tyrosine has been isolated along with a tyrosine dimer by high-performance liquid chromatography of aqueous mixtures of tyrosine and thymine that had been exposed to hydroxyl radicals generated by ionizing radiation. The isolated compounds have been examined by gas chromatography-mass spectrometry, high-resolution mass spectrometry, and 1H and 13C nuclear magnetic resonance spectroscopy. The structure of the thymine-tyrosine cross-link has been identified as the product from the formation of a covalent bond between the methyl group of the thymine and carbon 3 of the tyrosine ring. In addition, the 3,3' tyrosine dimer was isolated and characterized. The mechanism of the formation of these compounds is discussed. This work presents the first complete chemical characterization of a hydroxyl radical induced DNA base-amino acid cross-link. 相似文献
2.
3.
Phospholipase C-gamma, a substrate for PDGF receptor kinase, is not phosphorylated on tyrosine during the mitogenic response to CSF-1. 总被引:32,自引:10,他引:22 下载免费PDF全文
J R Downing B L Margolis A Zilberstein R A Ashmun A Ullrich C J Sherr J Schlessinger 《The EMBO journal》1989,8(11):3345-3350
Quiescent mouse NIH3T3 cells expressing a transduced human c-fms gene encoding the receptor for colony stimulating factor-1 (CSF-1) were stimulated with mitogenic concentrations of platelet-derived growth factor (PDGF) or CSF-1. Immunoprecipitated phospholipase C-gamma (PLC-gamma) was phosphorylated on tyrosine and calcium was mobilized following treatment of intact cells with PDGF. In contrast, only trace amounts of phosphotyrosine were incorporated into PLC-gamma and no intracellular calcium signal was detected after CSF-1 stimulation. Similarly, CSF-1 treatment did not stimulate phosphorylation of PLC-gamma on tyrosine in a CSF-1-dependent. SV40-immortalized mouse macrophage cell line that expresses high levels of the CSF-1 receptor. In fibroblasts, antiserum to PLC-gamma co-precipitated a fraction of the tyrosine phosphorylated form of the PDGF receptor (PDGF-R) after ligand stimulation, implying that phosphorylated PDGF-R and PLC-gamma were associated in a stable complex. Pre-treatment of cells with orthovanadate also led to tyrosine phosphorylation of PLC-gamma which was significantly enhanced by PDGF, but not by CSF-1. Thus, although the PDGF and CSF-1 receptors are structurally related and appear to be derived from a single ancestor gene, only PDGF-induced mitogenesis in fibroblasts correlated with tyrosine phosphorylation of PLC-gamma. 相似文献
4.
Relation of light and nitrogen source to growth, nitrate reductase and glutamine synthetase activity of jack pine seedlings 总被引:5,自引:0,他引:5
Two-month-old jack pine ( Pinus banksiana Lamb.) seedlings were placed in a greenhouse where both nitrogen source and light level were varied. After 4 months, whole seedling biomass, leaf biomass and relative growth rate were greatest in seedlings grown with NH+ 4 /NO/NO− 3 -N and full light (FL) and least in seedlings grown with NO − 3 -N and low light (LL). NO − 3 -seedlings grown under full light and NH+ 4 /NO− 3 -seedlings grown under low light were approximately equal. This indicates that the extra carbon costs of assimilating only NO− 3 -N were similar to the reduction of carbon fixation resulting from a 50% decrease in photon flux density. Percentage and total nitrogen content of needles were greater in seedlings grown under low light independent of nitrogen fertilization. Percentage and total nitrogen content of roots were higher under low light and lower when fertilized with NO− 3 .
Nitrate reductase (NR) activity was higher in roots than in needles, while glutamine synthetase (GS) activity was higher in needles than in roots. Low light resulted in decreased NR activity (mg N)−1 in needles, but not in roots. However, no nitrate was detected in the needles in any treatment. GS activity, on the other hand, was greater under low light in both needles and roots. GS activity in needles is most likely involved with the reassimilation rather than the initial assimilation of ammonium. Some implications of these shifts in enzymatic activity for ecological phenomena in forests are discussed. 相似文献
Nitrate reductase (NR) activity was higher in roots than in needles, while glutamine synthetase (GS) activity was higher in needles than in roots. Low light resulted in decreased NR activity (mg N)
5.
Cloning of PI3 kinase-associated p85 utilizing a novel method for expression/cloning of target proteins for receptor tyrosine kinases. 总被引:101,自引:0,他引:101
E Y Skolnik B Margolis M Mohammadi E Lowenstein R Fischer A Drepps A Ullrich J Schlessinger 《Cell》1991,65(1):83-90
A novel method has been developed to allow cloning of protein targets for receptors with tyrosine kinase activity. By utilizing the carboxy-terminal tail of EGF receptor (EGFR) as a probe to screen lambda gt11 expression libraries, several EGFR-binding proteins have been cloned; two have been analyzed and contain unique SH2 and SH3 domains. One gene (GRB-1) has been fully sequenced, is expressed in various tissues and cell lines, and has a molecular mass of 85 kd. Interestingly, GRB-1 encodes the human counterpart of the PI3 kinase-associated protein p85. Advantages of this technique include the ease of cloning tyrosine kinase receptor targets present at low levels and the ability to identify proteins that are related in their capacity to bind activated receptors but contain no significant DNA sequence homology. This method, termed CORT (for cloning of receptor targets), offers a general approach for the identification and cloning of various receptor targets. 相似文献
6.
Yu. Yu. Sharovskaja L. M. Chailakhjan L. B. Margolis 《Experimental cell research》1988,175(2):404-408
A popular criterion of cell-cell communication in tissue cultures is dye coupling: the ability of the injected fluorescent dye of low molecular weight to be transferred from one cell to another. We report about a new factor which induces cell-to-cell dye coupling in previously uncoupled epithelial sheets. Paradoxically it is the standard fluorescent microscopy itself (that is, blue light of 320- to 480-nm wavelength) which induces rapid morphological alterations of cell culture followed by the transfer of fluorescent dye from one cell to another. Thus monitoring cell-cell dye coupling by fluorescent microscopy may itself induce the dye coupling in previously uncoupled epithelial cells. 相似文献
7.
Phosphatidylinositol-anchored glycoproteins of PC12 pheochromocytoma cells and brain 总被引:1,自引:0,他引:1
PC12 pheochromocytoma cells and cultures of early postnatal rat cerebellum were labeled with [3H]glucosamine, [3H]fucose, [3H]leucine, [3H]ethanolamine, or sodium [35S]sulfate and treated with a phosphatidylinositol-specific phospholipase C. Enzyme treatment of [3H]glucosamine- or [3H]fucose-labeled PC12 cells led to a 15-fold increase in released glycoproteins. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, most of the released material migrated as a broad band with an apparent molecular size of 32,000 daltons (Da), which was specifically immunoprecipitated by a monoclonal antibody to the Thy-1 glycoprotein. A second glycoprotein, with an apparent molecular size of 158,000 Da, was also released. After treatment with endo-beta-galactosidase, 40-45% of the [3H]glucosamine or [3H]fucose radioactivity in the phospholipase-released glycoproteins was converted to products of disaccharide size, and the molecular size of the 158-kDa glycoprotein decreased to 145 kDa, demonstrating that it contains fucosylated poly-(N-acetyllactosaminyl) oligosaccharides. The phospholipase also released labeled Thy-1 and the 158-kDa glycoprotein from PC12 cells cultured in the presence of [3H]ethanolamine, which specifically labels this component of the phosphatidylinositol membrane-anchoring sequence, while in the lipid-free protein residue of cells not treated with phospholipase, Thy-1 and a doublet at 46/48 kDa were the only labeled proteins. At least eight early postnatal rat brain glycoproteins also appear to be anchored to the membrane by phosphatidylinositol. Sulfated glycoproteins of 155, 132/134, 61, and 21 kDa are the predominant species released by phospholipase, which does not affect a major 44-kDa protein seen in [3H]ethanolamine-labeled brain cultures. The 44-48- and 155/158-kDa proteins may be common to both PC12 cells and brain. 相似文献
8.
Capping of Concanavalin A (Con A) on the surface of epithelial cells near the cell-cell contacts has been compared with that in the regions of cell contacts with the edges of lipid films. If the lipids are in "fluid" state, Con A is capped likely as on the free edges of epithelial sheets, while contacts with the edge of solid lipid film inhibit capping of Con A as do cell-cell contacts. The same is true for capping of liposomes adsorbed on the surface of epithelial cells. We suppose that solid rather than fluid domains in plasma membranes may play a significant role in establishing cell-cell contacts. 相似文献
9.
Complex carbohydrates of cultured PC12 pheochromocytoma cells. Effects of nerve growth factor and comparison with neonatal and mature rat brain 总被引:7,自引:0,他引:7
The composition and biosynthesis of glycoproteins, proteoglycans, and gangliosides have been studied in a clonal line of rat pheochromocytoma (PC12) cells. Glycoproteins account for approximately 78% of the glucosamine-labeled complex carbohydrates found in the culture medium, together with 17% chondroitin sulfate and 5% heparan sulfate. 10% of the glycoproteins but less than 1% of the proteoglycans are released by trypsin treatment of the cells, whose complex carbohydrates are composed of 93% glycoproteins, 1.3% chondroitin sulfate, 3.4% heparan sulfate, and 2.6% of mono- and disialogangliosides. Sequential lectin affinity chromatography and alkali treatment of glycopeptides prepared from the medium, trypsin-releasable, membrane, and cell-soluble glycoproteins demonstrated that in all of the subfractions large tri- and tetraantennary complex oligosaccharides account for 82 to 97% of those present in PC12 cell glycoproteins. Biantennary oligosaccharides account for approximately 2-6% of those in medium and trypsinate, as compared to 10-13% in the membrane and cell soluble glycoproteins, and there were large differences (ranging from 7 to 60%) in the proportions of biantennary oligosaccharides which are substituted by fucose on the core N-acetylglucosamine which is linked to asparagine. High mannose oligosaccharides are present predominantly in the cell membrane and soluble glycoproteins, where they account for 4 to 5% of the total glycoprotein labeling. In response to nerve growth factor (NGF), the PC12 cells extend long processes and acquire other properties similar to those of differentiated sympathetic neurons. Significant alterations were also observed in the complex carbohydrates of NGF-treated cells, the most striking of which were an almost 3-fold increase in labeled gangliosides and a 75% increase in trypsin-releasable glycoproteins. Cellular heparan sulfate decreased by 70% in response to NGF and increased by an equivalent amount in the culture medium, whereas an NGF-induced increase in chondroitin sulfate labeling occurred specifically in the cell membranes. 相似文献
10.
B. A. Baibakov T. A. Chipisheva V. I. Guelstein V. D. Ermilova E. B. Polevaya J. M. Vasiliev L. B. Margolis 《In vitro cellular & developmental biology. Animal》1994,30(8):490-495
Summary Blocks of breast tissue obtained during radical mastectomies from 23 patients with mammary gland carcinomas were used for
cultivation in native-state, gel-supported histocultures. We show that the human mammary gland can be successfully maintained
in this system so that normal epithelial breast structures proliferate and undergo differentiation for several weeks and a
well-developed system of ducts and lobules is formed. Using antibodies to individual keratins 17 and 8 we have shown for the
first time that ducts and alveoles developing in vitro undergo differentiation into the lining epithelium and myoepithelium
in the same way as mammary gland epithelium in vivo. Growth of epithelial structures in vitro is also accompanied by the development
of continuous basal membrane. 相似文献