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1.
Plateau distributions of DNA fragment lengths produced by extended light exposure of extranuclear photosensitizers in human cells.
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We have exploited properties of photosensitizers to study an aspect of the packing of chromatin in the cell nucleus. The fluorescent photosensitizers mesotetra(3-hydroxyphenyl) porphyrin and Photofrin II were both localized in the nuclear membrane and other membrane structures, but could not be found inside the nuclei. Light exposure of cells at 1 degrees C in the presence of the sensitizers induced DNA double-strand breaks. The length distributions of DNA fragments were determined by pulsed field gel electrophoresis. Because DNA damage is produced mainly via singlet oxygen diffusing less than 0.1 microns from the sensitizer, DNA double-strand breaks were supposedly produced within this distance of the nuclear membrane. Consistent with this, with prolonged illumination and with increasing concentrations of sensitizer the distribution of DNA fragment lengths reached a plateau level. In contrast, with the hydrophilic, intranuclear sensitizer meso-tetra(4-sulphonatophenyl)porphyrin, no such plateau level was found. The plateau distributions of DNA fragment lengths of different cell types had the same general shape with average fragment lengths ranging from 174 to 194 kilobasepairs. Particular genes, c-myc, fos and p53, were found on broad distributions of photocleaved fragment lengths. The results indicate that on each side of the genes the locus of the chromatin fibre situated close to the nuclear membrane, varied randomly. 相似文献
2.
Kristian Bjro Torstein Hovig Kjell Torgeir Stokke Sverre Stray-Pedersen 《Prostaglandins & other lipid mediators》1986,31(4)
Four major prostanoids (6-keto-PGF1α, PGE2, PGF2α and TXB2) were measured by specific radioimmunoassays in the outputs from human umbilical vessels perfussed
. As evaluated by scanning electron microscopy (SEM) only few blood platelets were attached to the vessel wall. After an initial flush with decreasing concentrations of all four prostanoids, a stable stage was reached, lasting for 4–5 hours. During this stage the production could be inhibited by indomethacin and only slightly stimulated with arachidonic acid. The TXA2 synthetase inhibitor UK 38485 depressed the TXB2 production, while only slightly affecting the other three prostanoids at very high concentrations. The arteries produced relatively more 6-keto-PGF1α than did the vein. 相似文献
3.
Four major prostanoids (6-keto-PGF1 alpha, PGE2, PGF2 alpha and TXB2) were measured by specific radioimmunoassays in the outputs from human umbilical vessels perfused in vitro. As evaluated by scanning electron microscopy (SEM) only few blood platelets were attached to the vessel wall. After an initial flush with decreasing concentrations of all four prostanoids, a stable stage was reached, lasting for 4-5 hours. During this stage the production could be inhibited by indomethacin and only slightly stimulated with arachidonic acid. The TXA2 synthetase inhibitor UK 38485 depressed the TXB2 production, while only slightly affecting the other three prostanoids at very high concentrations. The arteries produced relatively more 6-keto-PGF1 alpha than did the vein. 相似文献
4.
Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state 总被引:6,自引:1,他引:5
The genes for cellobiose utilization are normally cryptic in Escherichia
coli. The cellobiose system was used as a model to understand the process
by which silent genes are maintained in microbial populations. Previously
reported was (1) the isolation of a mutant strain that expresses the
cellobiose-utilization (Cel) genes and (2) that expression of those genes
allows utilization of three beta- glucoside sugars: cellobiose, arbutin,
and salicin. The Cel gene cluster has now been cloned from that mutant
strain. In the course of locating the Cel genes within the cloned DNA
segment, it was discovered that inactivation of the Cel-encoded hydrolase
rendered the host strain sensitive to all three beta-glucosides as potent
inhibitors. This sensitivity arises from the accumulation of the
phosphorylated beta- glucosides. Because even the fully active genes
conferred some degree of beta-glucoside sensitivity, the effects of
cellobiose on a series of five Cel+ mutants of independent origin were
investigated. Although each of those strains utilizes cellobiose as a sole
carbon and energy source, cellobiose also acts as a potent inhibitor that
reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand,
wild-type strains that cannot utilize cellobiose are not inhibited. The
observation that the same compound can serve either as a nutrient or as an
inhibitor suggests that, under most conditions in which cellobiose will be
present together with other resources, there is a strong selective
advantage to having the cryptic (Cel0) allele. In those environments in
which cellobiose is the sole, or the best, resource, mutants that express
the genes (Cel+) will have a strong selective advantage. It is suggested
that temporal alternation between these two conditions is a major factor in
the maintenance of these genes in E. coli populations. This alternation of
environments and fitnesses was predicted by the model for cryptic-gene
maintenance that was previously published.
相似文献
5.
Bwee Tien Poll-The Ola H. Skjeldal Oddvar Stokke Alf Poulos France Demaugre Jean-Marie Saudubray 《Human genetics》1989,81(2):175-181
Summary We have measured the production of 14CO2 from exogenous [1-14C] phytanic acid in fibroblast monolayers from patients with classical Refsum's disease and peroxisomal disorders. Activities in the different disorders were (percentage of control): classical Refsum's disease (5%), isolated peroxisomal acyl-CoA oxidase deficiency (75%), Zellweger syndrome (4%), neonatal adrenoleukodystrophy (5%), and rhizomelic chondrodysplasia punctate (3%). Absence of complementation was demonstrated between Zellweger syndrome and infantile Refsum's disease lines after polyethylene glycol fusion, with decreases of average activity of 11% relative to unfused cell mixtures. Classical Refsum's disease, rhizomelic chondrodysplasia punctata, and neonatal adrenoleukodystrophy lines all complemented one another, and Zellweger syndrome or infantile Refsum's disease lines, with average activity increases of 522%–772%. No intragenic complementation was observed within either group. Four complementation groups were detected suggesting that at least four genes are involved in phytanic acid -oxidation: one gene for the enzyme phytanic acid -hydroxylase (probably mitochondrial); one gene for a regulatory factor for the expression of phytanic acid -decarboxylation activity and two membrane-bound peroxisomal enzymes involved in the synthesis of plasmalogens; two genes for the assembly of functional peroxisomes and/or import of proteins into peroxisomes. 相似文献
6.
Quenching of the fluorescence of DNA-bound Hoechst 33258 in erythroid precursors was studied by flow cytometry and cytochemistry. This quenching artifact may affect the measurement of ploidy in specific cases. The bone marrow cells of two patients with hemolytic disease and active erythropoiesis contained subpopulations of cells with an apparent hypodiploid DNA content as measured by flow cytometry of paraformaldehyde-fixed cells stained with Hoechst 33258. No aneuploidy was detected in either of the two cases when cells were stained with mithramycin or 7-aminoactinomycin D. Cells exhibiting reduced Hoechst 33258 fluorescence expressed glycophorin A and low amounts of CD36, and were therefore erythroid precursors. In one case studied, the number of cells with reduced Hoechst 33258 fluorescence and glycophorin A expressed agreed well with the number of cells containing nuclear hemoglobin. In the other case, hemoglobin was present in a significant proportion of nucleated cells. Calculated values for the efficiency of resonance energy transfer from Hoechst 33258 to hemoglobin were in accordance with the observed levels of quenching (approximately 10%). However, the results could also be explained by hemoglobin reabsorption of Hoechst 33258 fluorescence. Nuclei stained with Hoechst 33258 showed uniform fluorescence, probably due to extraction of hemoglobin during the isolation procedure. 相似文献
7.
Shinichi Kitamura Takashi Hirano Kenichi Takeo Mitsuru Mimura Kanji Kajiwara Bjrn T. Stokke Tsutomu Harada 《International journal of biological macromolecules》1994,16(6)
The conformation and dilute solution properties of (2→1)-β-d-fructan in aqueous solution were studied by gel permeation chromatography, low-angle laser light-scattering photometry, viscometry, small-angle X-ray scattering and electron microscopy. Fractions covering a broad range of weight-average molecular weights (Mw) from 1.49 × 104 to 5.29 × 106 were obtained from a native sample by ultrasonic degradation and fractional precipitation. For Mw < 4 × 104, the intrinsic viscosity [η] varies with Mw0.71, indicating that the fructan chain behaves as a random coil expanded by an excluded-volume effect in this molecular weight region. For Mw > 105, [η] exhibits an unusually weak dependence on Mw and finally becomes almost independent of molecular weight. This behaviour is interpreted in terms of a globular conformation of the high-molecular-weight fructan molecules. Small-angle X-ray-scattering measurements and electron microscopic observations support this interpretation of the values of [η] observed. 相似文献
8.
Selection-induced mutations are nonrandom mutations that occur as specific
and direct responses to environmental challenge. Examples of
selection-induced mutations have been reported both in bacteria and in
yeast. I previously showed (Hall 1988) that excisions of the mobile genetic
element IS150 from within bglF are selection induced and argued that they
occurred because they were potentially advantageous under the selective
conditions employed. Mittler and Lenski (Mittler and Lenski 1992) have
argued that such excisions are not selection induced but that they occur
randomly in nondividing cells. Here I provide further evidence that IS150
excisions are induced by selection and that the excisions are immediately,
rather than only potentially, advantageous to the cell. I also provide
evidence that excisions, which Mittler and Lenski claim occur randomly in
saturated broth cultures, actually occur after samples from those cultures
are plated onto selective medium.
相似文献
9.
In-situ gelation of semidilute xanthan solutions with trivalent chromium, aluminum or iron ions was studied by rheology and UV-spectroscopy. Measurements of the elastic modulus of xanthan gel cylinders prepared by dialysis against the complexing ion at pH values from 2 to 6 indicate that monomeric species of the ion are ineffective, whereas dimeric or higher oligomeric species are effective in crosslinking the polysaccharide. When chromium was used as the crosslinking species, the dependence of the gelation rate on the ionic concentration followed a power law with a coefficient of 1·7. The gelation time and the gelation rate were found to extrapolate to zero at 1 m
Cr for 2·5 mg/ml xanthan. The limiting concentration of xanthan needed for gelation with 5 m
Cr(III) at 20°C was estimated as 0·35 mg/ml. This critical xanthan concentration is close to the overlap concentration c* estimated from the experimentally determined intrinsic viscosity [η] using c* = 1·4/[η]. An apparent activation energy for crosslinking of xanthan was calculated as Ea = 42 kJ/mol and Ea = 108 kJ/mol for Cr and Al ions, respectively. The fractal dimensionality of xanthan-Cr at the sol-gel transition was estimated as 1·3 applying the Chambon-Winter criterion for gelation, thus indicating that this gelation criterion is applicable also to stiff-chain polysaccharides such as xanthan. 相似文献
10.
Lysine acetylome profiling uncovers novel histone deacetylase substrate proteins in Arabidopsis
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Paul J Boersema Jan‐Oliver Jost Katharina Kramer Ahmet Bakirbas Julia Sindlinger Magdalena Plöchinger Dario Leister Glen Uhrig Greg BG Moorhead Jürgen Cox Michael E Salvucci Dirk Schwarzer Matthias Mann Iris Finkemeier 《Molecular systems biology》2017,13(10)
Histone deacetylases have central functions in regulating stress defenses and development in plants. However, the knowledge about the deacetylase functions is largely limited to histones, although these enzymes were found in diverse subcellular compartments. In this study, we determined the proteome‐wide signatures of the RPD3/HDA1 class of histone deacetylases in Arabidopsis. Relative quantification of the changes in the lysine acetylation levels was determined on a proteome‐wide scale after treatment of Arabidopsis leaves with deacetylase inhibitors apicidin and trichostatin A. We identified 91 new acetylated candidate proteins other than histones, which are potential substrates of the RPD3/HDA1‐like histone deacetylases in Arabidopsis, of which at least 30 of these proteins function in nucleic acid binding. Furthermore, our analysis revealed that histone deacetylase 14 (HDA14) is the first organellar‐localized RPD3/HDA1 class protein found to reside in the chloroplasts and that the majority of its protein targets have functions in photosynthesis. Finally, the analysis of HDA14 loss‐of‐function mutants revealed that the activation state of RuBisCO is controlled by lysine acetylation of RuBisCO activase under low‐light conditions. 相似文献