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71.
Cold-sensitive Mutations in Salmonella typhimurium Which Affect Ribosome Synthesis 总被引:31,自引:14,他引:17
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A number of mutations (45) expressed as cold-sensitive conditional lethal pheno-types were screened by transduction for their linkage to the streptomycin-resistance locus; 7 showed such linkage. Of these, two were studied in greater detail. The sedimentation profiles of ribosomes from cultures grown at low temperature differed from wild type and from one another. Both mutants lost ribonucleic acid control at low temperature. It is suggested that a high proportion of mutants expressing a cold-sensitive phenotype harbor mutations in genes affecting ribosome synthesis or regulation. 相似文献
72.
Tai Te Wu 《Bulletin of mathematical biology》1968,30(4):687-700
The conformation of a deoxyribonucleotide unit in a deoxyribonucleic acid molecule can be defined by six angles, each of which
specifies the relative orientations between two groups of atoms adjacent to a covalent bond. With the assumption that these
atoms are hard spheres with fixed van der Waal radii, conformations are sought to minimize their overlapping. The additional
requirement of the polymer having a periodic structure further reduces the allowable conformations. 相似文献
73.
Tai C. Chen Norman P. Curthoys Carl F. Lagenaur Jules B. Puschett 《In vitro cellular & developmental biology. Plant》1989,25(8):714-722
Summary Proximal tubules were prepared from rat kidney cortex by collagenase digestion and purified by percoll gradient centrifugation.
Their enrichment was estimated by comparing the specific activities of various cell-specific enzymes in homogenates of renal
cortex and of the isolated tubules. The tubules were cultured in a 50:50 mixture of Dulbecco’s modified Eagle’s and Ham’s
F12 media supplemented with insulin, transferrin, epidermal growth factor, hydrocortisone, and prostaglandin E1. After 2 to 3 d an extensive outgrowth of epithelial cells developed from the attached tubules. After 5 to 7 d near confluent
monolayers were obtained. Hormonal responsiveness, marker enzyme activities, and transport properties were determined to further
characterize the primary cultures. The cultured cells exhibited increased cyclic AMP production in response to parathyroid
hormone but not calcitonin or vasopressin, consistent with the absence of cells derived from distal and collecting tubules.
The cells also retained significant levels of 25-hydroxyvitamin D3-lα-hydroxylase, alkaline phosphatase, and ψ-glytamyltranspeptidase, three enzymes that are primarily associated with the
proximal tubule. The cultured epithelial cells also exhibit a Na+-dependent phosphate and glucose transport systems. Therefore, the cells retain many functional properties that are characteristic
of proximal tubules. Thus, the primary cultures should be suitable for the study of processes that occur specifically within
this segment of the rat nephron.
This work was supported in part by the Veterans Administration (JBP), Washington, DC, by grant DK-37124 (NPC) from the National
Institutes of Health, Bethesda, MD, and by grant BNS-86-17004 (CFL) from the National Science Foundation, Washington, DC. 相似文献
74.
Characterization of membrane antigens on human cytomegalovirus-infected fibroblasts recognized by human antibodies. 总被引:2,自引:1,他引:1
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The antigens on the surface of human cytomegalovirus (HCMV)-infected fibroblasts which are recognized by human HCMV antibody-positive sera were characterized. Three HCMV-induced polypeptides, with apparent molecular masses of 53 to 63, 94, and 94 to 120 kilodaltons, were precipitated from 125I-surface-labeled cell extracts with different sera obtained from healthy individuals. Renal transplant recipients who were suffering from active HCMV infections recognized the same set of antigens. By the use of monoclonal antibodies, these antigens were identified as polypeptides belonging to the gcI and gcIII families of HCMV glycoproteins. 相似文献
75.
Recent years have seen the convergence of both genetic and biochemical approaches in the study of protein translocation inE. coli. The powerful combination of these approaches is exemplified in the use of anin vitro protein synthesis-protein translocaltion system to analyze the role of genetically defined components of the protein translocation machinery. We describe in this review recent results focusing on the function of thesecA, secB, andsecY gene products and the demonstration of their requirement forin vitro protein translocation. The SecA protein was recently shown to possess ATPase activity and was proposed to be a component of the translocation ATPase. We present a speculative working model whereby the translocator complex is composed of the integral membrane proteins SecY, SecD, SecE, and SecF, forming an aqueous channel in the cytoplasmic membrane, and the tightly associated peripheral membrane protein SecA functioning as the catalytic subunit of the translocator or protein-ATPase. 相似文献
76.
At all stages of male gametogenesis, generative and vegetative pollen nuclei of Nicotiana sylvestris can be distinguished without ambiguity after Feulgen or ethidium bromide staining. They differ by their morphology and their apparent DNA content, always lower in vegetative nuclei. These differences provide a basis for their separation by sedimentation and fluorometry. After elimination of the another somatic cells and after crushing the pollen, vegetative and generative nuclei are separated by two successive Percoll gradients (purity 80–90%). Analysis of the gradient fractions and final purification can be done with a cell sorter. DNAs of both types are isolated by a cetyltrimethylammonium method, followed by a RNase treatment. Yields are lower for vegetative than for generative nuclei, and decrease with the age of pollen. Molecular weights and digestibility by restriction enzymes are compatible with molecular analyses. 相似文献
77.
Thi Thanh Thuy Pham Abderrazzek Maaroufi Etienne Odier 《Applied microbiology and biotechnology》1990,33(1):99-104
Summary The progeny of Dichomitus squalens CBS-432-34 is heterogeneous with respect to specific growth rate on glucose, cellulolytic ([U14C]cellulose 14CO2) and ligninolytic ([14C]synthetic lignin 14CO2) activities with little correlation between these metric characters. Variations do not show clear-cut phenotypes but rather a continuous range between extreme values pointing to multigenic control of these characters. Most homocaryons showed decreased cellulolytic or ligninolytic activity compared to the parent dicaryon. However a few homocaryons were comparable or even superior to the parent dicaryon for ligninolytic or cellulolytic activity with no correlation between each factor. Strains with reduced cellulolytic activity and altered isozyme patterns of endoglucanases were isolated in the progeny of D. squalens CBS-432-34. While the parent strain produced three main endoglucanase multiple enzymes designated EnI, EnII and EnIII, several strains in the progeny produced a different multiple enzyme pattern. In contrast to the quantitative ability to degrade cellulose, multiple enzyme pattern variation in the progeny did not show continuous variations. characterization of heterocaryon phenotypes derived from Ien+ and Ien 1 homocaryons and first filial generation (f1) analysis showed that genetic control of the multiple enzyme pattern (Ien 1 phenotype) in D. squalens is complex.
Offprint requests to: E. Odier 相似文献
78.
Y.-H. Tai J. Flick S.A. Levine J.L. Madara G.W.G. Sharp M. Donowitz 《The Journal of membrane biology》1996,149(1):71-79
Elevation in intracellular Ca2+ acting via protein kinase C (PKC) is shown to regulate tight junction resistance in T84 cells, a human colon cancer line and a model Cl− secretory epithelial cell. The Ca2+ ionophore A23187, which was used to increase the intracellular Ca2+ concentration, caused a decrease in tight junction resistance in a concentration- and time-dependent manner. Dual Na+/mannitol serosal-to-mucosal flux analysis performed across the T84 monolayers treated with 2 μm A23187 revealed that A23187 increased both fluxes and that in the presence of ionophore there was a linear relationship between
the Na+ and mannitol fluxes with a slope of 56.4, indicating that the decrease in transepithelial resistance was due to a decrease
in tight junction resistance. Whereas there was no effect of 0.1 μm A23187, 1 or 2 μm produced a 55% decrease in baseline resistance in 1 hr and 10 μm decreased resistance more than 80%. The A23187-induced decrease in tight junction resistance was partially reversible by
washing 3 times with a Ringer's-HCO3 solution containing 1% BSA. The A23187 effect on resistance was dependent on intracellular Ca2+; loading the T84 cells with the intracellular Ca2+ chelator BAPTA significantly reduced the decrease in tight junction resistance caused by A23187. This intracellular Ca2+ effect was mediated by protein kinase C and not calmodulin. While the protein kinase C antagonist H-7 totally prevented the
action of A23187 on tight junction resistance, the Ca2+/calmodulin inhibitor W13 did not have any effect. Sphingosine, another inhibitor of PKC, partially reduced the A23187-induced
decline in tight junction resistance. The PKC agonist PMA mimicked the A23187 effect on resistance, although the effect was
delayed up to 1 hr after exposure. In addition, however, PMA also caused an earlier increase in resistance, indicating it
had an additional effect in addition to mimicking the effect of elevating Ca2+. The effects of a phospholipase inhibitor (mepacrine) and of inhibitors of arachidonic acid metabolism (indomethacin for
the cyclooxygenase pathway, NDGA for the lipoxygenase pathway, and SKF 525A for the epoxygenase pathway) on the A23187 action
were also examined. None of these agents altered the A23187-induced decrease in resistance. Monolayers exposed to 2 μm A23187 for 1 hr were stained with fluorescein conjugated phalloidin, revealing that neighboring cells did not part one from
another and that A23187 did not have a detectable effect on distribution of F-actin in the perijunctional actomyosin ring.
The results indicate that elevation in intracellular Ca2+ decreases tight junction resistance in the T84 monolayer, acting through protein kinase C by a mechanism which does not involve visible changes in the perijunctional actomyosin
ring.
Received: 14 July 1995/Revised: 25 September 1995 相似文献
79.
The Epstein-Barr virus-encoded nuclear antigen EBNA-5 accumulates in PML-containing bodies. 总被引:8,自引:6,他引:2
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L Szekely K Pokrovskaja W Q Jiang H de The N Ringertz G Klein 《Journal of virology》1996,70(4):2562-2568
EBNA-5 is one of the Epstein-Barr virus (EBV)-encoded nuclear proteins required for immortalization of human B lymphocytes. In the nuclei of EBV-transformed lymphoblastoid cell lines EBNA-5 is preferentially targetted to distinct nuclear foci. Previously we have shown (W.Q. Jiang, L. Szekely, V. Wendel-Hansen, N. Ringertz, G. Klein, and A. Rosen, Exp. Cell Res. 197:314-318, 1991) that the same foci also contained the retinoblastoma (Rb) protein. Using a similar double immunofluorescence technique, we now show that these foci colocalize with nuclear bodies positive for PML, the promyelocytic leukemia-associated protein. Artificial spreading of the chromatin by exposure to the forces of fluid surface tension disrupts this colocalization gradually, suggesting that the bodies consist of at least two subcomponents. Heat shock or metabolic stress induced by high cell density leads to the release of EBNA-5 from the PML-positive nuclear bodies and induces it to translocate to the nucleoli. In addition to their presence in nuclear bodies, both proteins are occasionally present in nuclear aggregates and doughnut-like structures in which PML is concentrated in an outer shell. Nuclear bodies with prominent PML staining are seen in resting B lymphocytes. This staining pattern does not change upon EBV infection. In freshly infected cells EBNA-5 antigens are first distributed throughout the nucleoplasm. After a few days intensely staining foci develop. These foci coincide with PML-positive nuclear bodies. At a later stage and in established lymphoblastoid cell lines EBNA-5 is almost exclusively present in the PML-positive nuclear foci. The colocalization is restricted to EBV-infected human lymphoblasts. The data presented indicate that the distinct EBNA-5 foci are not newly formed structures but the result of translocation of the viral protein to a specialized domain present already in the nuclei of uninfected cells. 相似文献
80.
Toshio Ariga Shama Bhat Takashi Kanda Masanaga Yamawaki Tadashi Tai Yasunori Kushi Takeshi Kasama Shizuo Handa Robert K. Yu 《Glycoconjugate journal》1996,13(2):135-145
We analysed the glycolipid composition of glioma cells (N-370 FG cells), which are derived from a culture of transformed human fetal glial cells. The neutral and acidic glycolipid fractions were isolated by column chromatography on DEAE-Sephadex and analysed by high-performance thin-layer chromatography (HPTLC). The neutral glycolipid fraction contained 1.6 µg of lipid-bound glucose/galactose per mg protein and consisted of GlcCer (11.4% of total neutral glycolipids), GalCer (21.5%), LacCer (21.4%), Gb4 (21.1%), and three unknown neutral glycolipids (23%). These unknown glycolipids were characterized as Lewisx (fucosylneolactonorpentaosyl ceramide; Lex), difucosylneolactonorhexaosyl ceramide (dimeric Lex), and neolactonorhexaosyl ceramide (nLc6) by an HPTLC-overlay method for glycolipids using specific mouse anti-glycolipid antibodies against glycolipid and/or liquid-secondary ion (LSI) mass spectrometry. The ganglioside fraction contained 0.6 µg of lipid-bound sialic acid per mg protein with GD1a as the predominant ganglioside species (83% of the total gangliosides) and GM3, GM2, and GM1 as minor components. Trace amounts of sialyl-Lex and the complex type of sialyl-Lex derivatives were also present. Immunocytochemical studies revealed that GD1a and GalCer were primarily localized on the surface of cell bodies. Interestingly, Lex glycolipids and sialyl-Lex were localized not only on the cell bodies but also on short cell processes. Especially, sialyl-Lex glycolipid was located on the tip of fine cellular processes. The unique localization of the Lex glycolipids suggests that they may be involved in cellular differentiation and initiation of cellular growth in this cell line. 相似文献