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1.
G G Hillebrand A H McCluskey K A Abbott G G Revich K L Beattie 《Nucleic acids research》1984,12(7):3155-3171
A method has been developed for simultaneous comparison of the propensity of a DNA polymerase to misincorporate at different points on a natural template-primer. In this method elongation of a [5'-32P] primer, annealed to a bacteriophage template strand, is carried out in the presence of only three dNTPs (highly purified by HPLC). Under these conditions the rate of primer elongation (monitored by gel electrophoresis/autoradiography) is limited by the rate of misincorporation at template positions complementary to the missing dNTP. Variations in the rate of elongation (revealed by autoradiographic banding patterns) reflect variations in the propensity for misincorporation at different positions along the template. The effect on primer elongation produced by addition of a chemically modified dNTP to 'minus' reactions reveals the mispairing potential of the modified nucleotide during DNA synthesis. By use of this electrophoretic assay of misincorporation we have demonstrated that the fidelity of E. coli DNA polymerase I varies greatly at different positions along a natural template, and that BrdUTP and IodUTP can be incorporated in place of dCTP during chain elongation catalyzed by this enzyme. 相似文献
2.
Owing to the exceptional intracellular distribution and the heterogeneous expression pattern during transformation and metastasis
in various tumors, the EF-hand calcium-binding protein S100A2 attracts increasing attention. Unlike the majority of S100 proteins,
S100A2 expression is downregulated in many cancers and the loss in nuclear expression has been associated with poor prognosis.
On the other hand, S100A2 is upregulated in some cancers. This mini review highlights the general characteristics of S100A2
and discusses recent findings on its putative functional implication as a suppressor or promoter in cancerogenesis. 相似文献
3.
4.
Karin Lindström Albert E. G. Kr. Von Dem Borne Michael E. Breimer Bertil Cedergren Yasuto Okubo Lennart Rydberg Susann Teneberg Bo E. Samuelsson 《Glycoconjugate journal》1992,9(6):325-329
A 12-week-old fetus and one 17-week-old fetus + placenta were obtained after spontaneous abortions from two women of blood group p. The 17-week-old fetus was dissected into intestine, liver, brain and residual tissue. Nonacid glycosphingolipid fractions were prepared from the tissues. Glycolipid characterization was carried out using thin layer chromatography immunostained with monoclonal antibodies and bacteria and by1H NMR spectroscopy and mass spectrometry. In the placental fraction substantial amounts of globotetraosylceramide (P-antigen) and globotriaosylceramide (Pk-antigen) were identified. In contrast, the fetuses contained only trace amounts of these structures, as revealed by immunostaining. These results indicate that the primary target for the antibodies of the anti-Tja serum is the placenta tissue, resulting in termination of the pregnancy. 相似文献
5.
Influence of template primary and secondary structure on the rate and fidelity of DNA synthesis 总被引:5,自引:0,他引:5
High resolution gel electrophoresis was used to monitor the successive addition of dNMP residues onto the 3'-OH ends of discrete 5'-32P-primers, during DNA synthesis on natural templates. Resulting autoradiographic banding patterns revealed considerable variation in the relative rates of incorporation at different positions along the template. The pattern of "pause sites" along the template was unique for each of three different DNA polymerases (polymerase I (the "large fragment" form of Escherichia coli), T4 polymerase (encoded by bacteriophage T4), and AMV polymerase (DNA polymerase of avian myeloblastosis virus]. Most pause sites were not caused by attenuation of polymerization at regions of local secondary structure in the template. Assays of the accuracy of incorporation at different positions along the template (in which elongation was monitored in the presence of only 3 of the 4 2'-deoxynucleoside 5'-triphosphates) strongly suggested that the relative fidelity of DNA synthesis catalyzed by different polymerases depends on the position on the template at which the comparison is made. Primer-templates were constructed that permitted comparison of elongation during synthesis on a single-stranded template with that during polymerization through a double-stranded region (wherein elongation required concomitant displacement of a strand annealed adjacent to the 5'-32P-primer). Although strand displacement DNA synthesis catalyzed by polymerase I occurred approximately ten times more slowly than synthesis in the same region of a single-stranded viral template, most of the pause sites were the same in the presence or absence of "tandem" primer. Electrophoretic assays of the fidelity of DNA synthesis suggested that an increased tendency toward misincorporational "hotspots" occurred when elongation required concomitant strand displacement. 相似文献
6.
Susann Teneberg Timothy R. Hirst Jonas Ångström Karl-Anders Karlsson 《Glycoconjugate journal》1994,11(6):533-540
The binding specificities of cholera toxin andEscherichia coli heat-labile enterotoxin were investigated by binding of125I-labelled toxins to reference glycosphingolipids separated on thin-layer chromatograms and coated in microtitre wells. The binding of cholera toxin was restricted to the GM1 ganglioside. The heat-labile toxin showed the highest affinity for GM1 but also bound, though less strongly, to the GM2, GD2 and GD1b gangliosides and to the non-acid glycosphingolipids gangliotetraosylceramide and lactoneotetraosylceramide. The infant rabbit small intestine, a model system for diarrhoea induced by the toxins, was shown to contain two receptor-active glycosphingolipids for the heat-labile toxin, GM1 ganglioside and lactoneotetraosylceramide, whereas only the GM1 ganglioside was receptor-active for cholera toxin. Preliminary evidence was obtained, indicating that epithelial cells of human small intestine also contain lactoneotetraosylceramide and similar sequences. By computer-based molecular modelling, lactoneotetraosylceramide was docked into the active site of the heat-labile toxin, using the known crystal structure of the toxin in complex with lactose. Interactions which may explain the relatively high toxin affinity for this receptor were found.Abbreviations CT
cholera toxin
- CT-B
B-subunits of cholera toxin
- LT
Escherichia coli heat-labile enterotoxin
- hLT
humanEscherichia coli heat-labile enterotoxin
- pLT
porcineEscherichia coli heat-labile enterotoxin
- EI
electron ionization 相似文献
7.
Malin Bäckström Vafa Shahabi Susanne Johansson Susann Teneberg ers Kjellberg Halina Miller-Podraza Jan Holmgren & Michael Lebens 《Molecular microbiology》1997,24(3):489-497
The closely related B-subunits of cholera toxin (CTB) and Escherichia coli heat-labile enterotoxin (LTB) both bind strongly to GM1 ganglioside receptors but LTB can also bind to additional glycolipids and glycoproteins. A number of mutant CT B-subunits were generated by substituting CTB amino acids with those at the corresponding positions in LTB. These were used to investigate the influence of specific residues on receptor-binding specificity. A mutated CTB protein containing the first 25 residues of LTB in combination with LTB residues at positions 94 and 95, bound to the same extent as native LTB to both delipidized rabbit intestinal cell membranes, complex glycosphingolipids (polyglycosylceramides) and neolactotetraosylceramide, but not to non-GM1 intestinal glycosphingolipids. In contrast, when LTB amino acid substitutions in the 1–25 region were combined with those in the 75–83 region, a binding as strong as that of LTB to intestinal glycosphingolipids was observed. In addition, a mutant LTB with a single Gly-33→Asp substitution that completely lacked affinity for both GM1 and non-GM1 glycosphingolipids could still bind to receptors in the intestinal cell membranes and to polyglycosylceramides. We conclude that the extra, non-GM1 receptors for LTB consist of both sialylated and non-sialylated glycoconjugates, and that the binding to either class of receptors is influenced by different amino acid residues within the protein. 相似文献
8.
Template-dependent variation in the relative fidelity of DNA polymerase I of Escherichia coli in the presence of Mg2+ versus Mn2+ 总被引:2,自引:0,他引:2
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The fidelity of E. coli DNA polymerase I in the presence of Mg2+ vs Mn2+ was examined at many positions along natural DNA templates, by use of an electrophoretic assay of misincorporation. Although there was an overall greater tendency for misincorporation to occur in Mn2+-activated chain elongation, some specific sites on the template were more prone to misincorporation with Mg2+ and others with Mn2+. This sequence-dependent effect was seen in spite of the finding that the relative rate of incorporation of the correct nucleotide at different positions on the template was essentially the same with Mg2+ and Mn2+. In agreement with previous studies, the fidelity of E. coli pol I was higher at activating, than at inhibiting, concentrations of Mg2+. The results reveal new complexities regarding the role of divalent cation in the control of fidelity in DNA synthesis and attest to the dynamic nature of interactions between DNA polymerase, its substrates and divalent metal activator during the course of polymerization on natural templates. 相似文献
9.
10.
Susann Eichenberger-Glinz 《Development genes and evolution》1979,186(4):333-349
Summary The present investigation analyzes intercellular junctions in tissues with different developmental capacities. The distribution of junctions was studied inDrosophila embryos, in imaginal disks, and in cultures of disk cells that were no longer able to differentiate any specific pattern of the adult epidermis.The first junctions —primitive desmosomes andclose membrane appositions — already appear in blastoderm.Gap junctions are first detected in early gastrulae and later become more and more frequent.Zonulae adhaerentes are formed around 6 h after fertilization, whileseptate junctions appear in the ectoderm of 10-h-old embryos.Inwing disks of all stages studied (22–120 h), three types of junctions are found: zonulae adhaereentes, gap junctions, and septate junctions. Gap junctions, which are rare and small at 22 h, increase in number and size during larval development. The other types of junctions are found between all cells of a wing disk throughout development.All types of junctions that are found in normal wing disks are also present in theimaginal disk tissues cultured in vivo for some 15 years and in thevesicles of imaginal disk cells grown in embryonic primary cultures in vitro. However, gap junctions are smaller and in the vesicles less frequent than in wing disks of mature larvae.Thus gap junctions, which allow small molecules to pass between the cells they connect, are present in the early embryo, when the first developmental decisions take place, and in all imaginal disk tissues studied, irrespective of whether or not these are capable of forming normal patterns. 相似文献