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1.
Mui Keng Tan 《Plant molecular biology》1991,17(2):221-227
A total of 864 bases from 5 regions interspersed in the 18S and 26S rRNA molecules from various clones of Pteridium covering the general geographical distribution of the genus was analysed using a rapid rRNA sequencing technique. No base difference has been detected amongst the three major lineages, two of which apparently separated before the breakup of the ancient supercontinent, Pangaea. These regions of the rRNA sequences have thus been conserved for at least 160 million years and are here compared with other eukaryotic, especially plant rRNAs. 相似文献
2.
H Siu E S Vitetta R D May J W Uhr 《Journal of immunology (Baltimore, Md. : 1950)》1986,137(4):1376-1382
The growth of the BCL1 tumor in murine H-2 chimeras was studied. Lethally x-irradiated BALB/c mice were reconstituted with C57BL/6 bone marrow that had been depleted of T cells. When chimerism was established 90 to 120 days later, large doses of BCL1 cells were injected. The tumor grew progressively, reaching a peak level of as many as 10(9) tumor cells per animal by 40 days after inoculation. After that time, the tumor regressed in all the chimeric animals, and by 100 days after inoculation, virtually all the animals appeared disease free as judged by an absence of BCL1-idiotype-positive cells in the spleen and peripheral blood, a normal spleen size, and absence of an elevated white blood cell count. Such animals were followed for as long as 8 mo after tumor inoculation and remained disease free. However, transfer of graded numbers of splenocytes from these animals into normal BALB/c recipients resulted in development of tumor in recipients receiving 100 or more spleen cells. These results indicate a large tumor burden in the spleen of each donor, namely, 10(6) to 10(7) BCL1 cells. The present model should facilitate characterization of the mechanisms underlying tumor dormancy. 相似文献
3.
Characterization of temperature-sensitive [3H]serotonin (5-HT) binding sites (1 and 4 nM Kd sites) revealed complex inhibition by neuroleptics and serotonin antagonists. There was no simple correlation with affinities for S1 and S2 receptors. pretreatment (48 h before) with mianserin did not alter Bmax or Kd for the 1 nM Kd [3H]5-HT site, although [3H]ketanserin (S2) densities were decreased by 50%. This suggested that possible S2 components of [3H]5-HT binding must be negligeable, even though ketanserin competed with high affinity (IC50 = 3 nM) for a portion of the 1 nM Kd [3H]5-HT site. Low concentrations of mianserin inhibited the 1 nM Kd [3H]5-HT site in a non-competitive manner, as shown by a decrease in Bmax with no change in Kd after incubation. The complex inhibition data may therefore represent indirect interactions through another site. 相似文献
4.
3β, 7α, 26-Triacetoxy-5α-cholestane was prepared from 25R-3β, 26-diacetoxy-5α-cholestan-7α-ol, and partially hydrolyzed with potassium carbonate in methanol-benzene. The three acetylated products thus obtained were characterized by thin layer and gas liquid chromatography, and mass spectrometry. By oxidation and alkaline hydrolysis, 3β, 7α-diacetoxy-5α-cholestan-26-ol was converted to 3β, 7α-dihydroxy-5α-cholestanoic acid. 7α, 26-Diacetoxy-5α-cholestan-3β-ol was characterized as indicated. The third product, 7α-acetoxy-5α-cholestane-3β, 26-diol was oxidized to 3-oxo-7α-acetoxy-5α-cholestanoic acid which was reduced catalytically and hydrolyzed to provide 3α, 7α-dihydroxy-5α-cholestanoic acids and its 3β-isomer. By comparison of the specific rotation of this sample of 3α, 7α-dihydroxy-5α-cholestanoic acid derived from 25R-kryptogenin with a similar product derived from arihydro-5α-cyprinol obtained from carp bile, the latter derivative appears to be primarily the 25S material. 相似文献
5.
Interleukin-3 stimulates the tyrosine phosphorylation of the 140-kilodalton interleukin-3 receptor 总被引:9,自引:0,他引:9
Murine interleukin-3 (mIL-3) stimulates the rapid and transient tyrosine phosphorylation of a number of proteins in mIL-3-dependent B6SUtA1 cells. Two of these proteins, p68 and p140, are maximally phosphorylated at tyrosine residues within 2 min of addition of mIL-3. Because 125I-mIL-3 can be cross-linked to both 70- and 140-kDa proteins on intact B6SUtA1 cells, we investigated whether the tyrosine phosphorylated p68 and p140 were these two mIL-3 receptor proteins. Addition of antiphosphotyrosine antibodies (alpha PTyr Abs) to cell lysates from B6SUtA1 cells, to which 125I-mIL-3 had been disuccinimidyl suberate-cross-linked, resulted in the immunoprecipitation of 125I-mIL-3 complexed to both 70- and 140-kDa proteins. To determine if the observed immunoprecipitation pattern was due to the direct interaction of alpha-PTyr Abs with these two mIL-3 receptor proteins or with tyrosine-phosphorylated proteins that were associated with the receptor proteins, cell lysates were treated with 2% sodium dodecyl sulfate, 5% 2-mercaptoethanol, and boiled for 1 min. After removal of sodium dodecyl sulfate and 2-mercaptoethanol, alpha PTyr Abs immunoprecipitated 125I-mIL-3 cross-linked to only the 140-kDa protein. To confirm this finding, 32P-labeled B6SUtA1 cells were treated with biotinylated or fluoresceinated mIL-3. Addition of immobilized streptavidin or antifluorescein antibodies, respectively, to cell lysates from these cells resulted in the enrichment of only a 140-kDa tyrosine phosphorylated protein. Taken together, these results strongly suggest that only the 140-kDa receptor protein is tyrosine phosphorylated upon mIL-3 binding. 相似文献
6.
Cell-cell adhesion and morphogenesis in Dictyostelium discoideum 总被引:1,自引:0,他引:1
During development of Dictyostelium discoideum, cells acquire EDTA-resistant cell-cell adhesion at the aggregation stage. The EDTA-resistant cell binding activity is associated with a cell surface glycoprotein of Mr 80,000 (gp80), which mediates cell-cell binding via homophilic interaction. Analysis of the structure of gp80 deduced from cDNA sequence reveals the presence of three internally homologous segments in the NH2-terminal domain, which also contains regions with homology to the neural cell adhesion molecule. Secondary structure predictions show an abundance of beta-structures and very few alpha-helices. This is confirmed by circular dichroism measurements. It is likely that the homologous segments are organized into globular structures, extended from the cell surface by a Pro-rich stalk domain. The cell binding activity of gp80 resides within the first globular repeat of the NH2-terminal domain and has been mapped to a 51 amino acid region between Val123 and Leu173. Synthetic oligopeptides corresponding to sequences within this region have been prepared and assayed for their ability to bind to cell surface gp80. Results lead to identification of the homophilic binding site to an octapeptide sequence within this region. Synthetic peptides containing this octapeptide sequence and univalent antibodies directed against this site block the formation of organized cell streams during aggregation. Although cell aggregates are eventually formed, most fail to undergo further development to give rise to slugs and fruiting bodies, indicating that cell-cell adhesion involving gp80 is an important step in normal morphogenesis. 相似文献
7.
Rapid accumulation and disappearance of plasma membrane proteins during development of wild-type and mutant strains of Dictyostelium discoideum 总被引:8,自引:0,他引:8
Plasma membranes were purified from the cellular slime mold Dictyostelium discoideum at different developmental stages and the protein compositions compared. The protein components of the plasma membrane of vegetative cells are largely conserved during development. Specific morphogenetic events are accompanied by synthesis and accumulation of several new proteins which are subsequently lost as development progresses. Proteins with apparent molecular weights of 38,000, 36,500 and 10,000 to 12,000 rapidly accumulate during the first six hours of development and then disappear from the plasma membrane after 12 hours. Later in development, several new high molecular weight proteins are synthesized and appear in the membrane. The pattern of accumulation of membrane proteins in wild-type and mutant strains suggests that appearance of membrane proteins is linked to a dependent sequence of events. 相似文献
8.
The effects of tunicamycin on protein glycosylation and cell differentiation were examined during early development of Dictyostelium discoideum. Tunicamycin inhibited cell growth reversibly in liquid medium. At a concentration of 3 μg/ml, tunicamycin completely inhibited morphogenesis and cell differentiation in developing cells. These cells remained as a smooth lawn and failed to undergo chemotactic migration. The expression of EDTA-resistant contact sites was also inhibited. The inhibition by tunicamycin was reversible if cells were washed free of the drug within the first 10 hr of incubation. After 12 hr of development, cells were protected from the drug by the sheath. When cells were treated with tunicamycin during the first 10 hr of development, incorporation of [3H]mannose and [3H] fucose was inhibited by approximately 75% within 45 min while no significant inhibition of [3H]leucine incorporation was observed during the initial 3 hr of drug treatment. The inhibition of protein glycosylation was further evidenced by the reduction in number of glycoproteins “stained” with 125I-labelled con A. A number of developmentally regulated high-molecular-weight glycoproteins, including the contact site A glycoprotein (gp80), were undetectable when cells were labelled with [3H]fucose in the presence of tunicamycin. It is therefore evident that glycoproteins with N-glycosidically linked carbohydrate moieties may play a crucial role in intercellular cohesiveness and early development of D. discoideum. 相似文献
9.
10.
Donald J. Brasch Hi Mui Chang Chaw T. Chuah Laurence D. Melton 《Carbohydrate research》1981,97(1):113-125
A galactan sulfate has been isolated from the seaweed Porphyra columbina, and its structure established by a combination of methylation, methanolysis, treatment with alkali followed by methylation, and 13C-n.m.r. spectroscopy. The polysaccharide belongs to the porphyran class, and consists of 3-linked β-d-galactosyl residues and 4-linked α-l-galactosyl residues. 3,6-Anhydro-l-galactose and l-galactose 6-sulfate residues total approximately half of the sugar units, the other half being made up of d-galactose and 6-O-methyl-d-galactose residues. Some evidence is presented that suggests that the galactan sulfate does not have a completely alternating structure. 相似文献