Mise en évidence d'ADN extrachromosomique chez Rhizobium meliloti

1978 ◽  
Vol 24 (8) ◽  
pp. 960-966 ◽  
Author(s):  
M. Bechet ◽  
J. B. Guillaume
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Base Composition ◽  
Density Gradient Centrifugation ◽  
Rhizobium Meliloti ◽  
Gradient Centrifugation ◽  
Buoyant Density ◽  
Sedimentation Analysis ◽  
Extrachromosomal Dna ◽  
Very High

Seven effective (nitrogen-fixing) strains of Rhizobium meliloti have been studied. By sedimentation analysis of their alkaline lysates in alkaline sucrose gradients, a plasmid was found in four strains. In a strain (2011 str 3) which gave no result with this method, supercoiled DNA was detected by CsCl-dye buoyant density gradient centrifugation. That result was confirmed by analytical Cs2SO4–Ag+ density gradients, which showed a heterogeneity in the average base composition of the DNA extracted from three strains, including the 2011 str 3 strain. Two of those last strains seemed to contain an extrachromosomal DNA of very high molecular weight.

scholarly journals A study of nucleated erythrocytes by density-gradient centrifugation in a zonal rotor

1969 ◽  
Vol 111 (4) ◽  
pp. 583-591 ◽  
Author(s):  
A P Mathias ◽  
D. Ridge ◽  
N. St G. Trezona
Keyword(s):  
Molecular Weight ◽  
Ribosomal Rna ◽  
Base Composition ◽  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Density Gradients ◽  
Avian Erythrocytes ◽  
Nuclear Rna ◽  
Zonal Rotor

1. Several substances of high molecular weight were examined for their suitability as suspension media in the formation of density gradients for the zonal centrifugation of avian erythrocytes. None proved satisfactory. 2. The behaviour of pigeon erythrocytes in rate-sedimentation experiments in a type A zonal rotor with density gradients of sucrose was examined. The mature cells sediment more rapidly than the younger cells and have a lower RNA/DNA ratio. Maturation is accompanied by a greater loss of RNA from the nucleus than from the cytoplasm. 3. The base composition of the nuclear RNA and of the two species of cytoplasmic ribosomal RNA is reported. 4. The RNA of erythrocytes may be labelled in vivo by injection of inorganic [32P]phosphate. The cells most active in the synthesis of RNA sediment less rapidly than the bulk of the cells. 5. Reticulocyte nuclei sediment more slowly than those from erythrocytes. Reticulocyte nuclei have a mean volume of 35μ3 and are isopycnic with sucrose of density 1·2871 (measured at 20°). Maturation of the nuclei causes them to shrink to a volume of 25μ3 and the density to increase to 1·2944.

scholarly journals Appearance of a methylated ribonucleic acid on illumination of Euglena gracillis cells grown in the dark

1971 ◽  
Vol 125 (2) ◽  
pp. 401-405 ◽  
Author(s):  
M. Perl
Keyword(s):  
Molecular Weight ◽  
Nucleic Acid ◽  
High Molecular Weight ◽  
Ribonucleic Acid ◽  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Sucrose Density Gradient ◽  
Acid Fraction ◽  
Sucrose Density Gradient Centrifugation ◽  
Exclusion Chromatography

Investigation of the methylation of nucleic acids by [Me-3H]methionine after illumination of Euglena cells grown in the dark has shown that a high-molecular-weight nucleic acid fraction undergoes methylation after exposure to light for 60–120min. This methylated nucleic acid fraction was isolated both by sucrose-density-gradient centrifugation and exclusion chromatography on Sephadex G-200. The fraction was shown to consist of a preformed RNA that is present in cells grown in the dark and which on illumination is transmethylated by methionine.

A malate dehydrogenase of high molecular weight, from bean leaves

1968 ◽  
Vol 46 (5) ◽  
pp. 719-720 ◽  
Author(s):  
William Habig ◽  
David Racusen
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Malate Dehydrogenase ◽  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Sucrose Density Gradient ◽  
Sucrose Density Gradient Centrifugation ◽  
Molecular Weights ◽  
Young Leaves ◽  
Bean Leaves

Two forms of malate dehydrogenase (MDH) of widely differing molecular weight were found in primary leaves of Phaseolus vulgaris. Their molecular weights were estimated as 69 000 and 275 000 by sucrose density gradient centrifugation. The ratio of these two forms followed an orderly course in which the high molecular weight MDH increased from near zero in very young leaves to about 35% of the total MDH activity in leaves older than 2 weeks. Conditions which cause the high molecular weight MDH to dissociate to active normal molecular weight enzyme are discussed.

scholarly journals Covalently closed, circular DNA in kappa endosymbionts ofParamecium

1976 ◽  
Vol 27 (2) ◽  
pp. 161-170 ◽  
Author(s):  
Judith A. Dilts
Keyword(s):  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Buoyant Density ◽  
Bacterial Chromosome ◽  
Contour Length ◽  
Paramecium Tetraurelia ◽  
Extrachromosomal Dna ◽  
Circular Dna ◽  
Covalently Closed Circular Dna ◽  
Circular Molecule

SUMMARYCaedobacter taeniospiralis(kappa), a bacterial endosymbiont isolated fromParamecium tetraureliastock 51, contains, in addition to the bacterial chromosome, covalently closed circular DNA molecules as shown by isolation on dye-buoyant-density gradients. The closed circular molecule has a contour length of 13·75 ± 0·04 µm with a buoyant density of 1·698 g/cm3. The buoyant density of the bacterial chromosome is 1·700–1·701 g/cm3. Kappa of the 51 group isolated from stock 298 and stock 6g2,P. tetraurelia, also contain the closed circular DNA. Two forms of kappa coexist in paramecia: brights and nonbrights. Examination by density-gradient centrifugation of the DNA of brights and nonbrights shows the extrachromosomal DNA to be associated mainly with brights. It is suggested that the extrachromosomal DNA might be the determinant for the refractile bodies and the helical phage-like structures found in brights.

scholarly journals The multiple complexes formed by the interaction of platelet factor 4 with heparin

1980 ◽  
Vol 191 (3) ◽  
pp. 769-776 ◽  
Author(s):  
P E Bock ◽  
M Luscombe ◽  
S E Marshall ◽  
D S Pepper ◽  
J J Holbrook
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Chain Length ◽  
Salt Concentration ◽  
Human Platelet ◽  
Platelet Factor 4 ◽  
High Protein ◽  
Platelet Factor ◽  
The Stability ◽  
Very High

The anisotropy of the fluorescence of dansyl (5-dimethylaminonaphthalene-1- sulphonyl) groups covalently attached to human platelet factor 4 was used to detect the macromolecular compounds formed when the factor was mixed with heparin. At low heparin/protein ratios a very-high-molecular-weight compound (1) was formed that dissociated to give a smaller compound (2) when excess heparin was added. 2. A large complex was also detected as a precipitate that formed at high protein concentrations in chloride buffer. It contained 15.7% (w/w) polysaccharide, equivalent to four or five heparin tetrasaccharide units per protein tetramer. In this complex, more than one molecule of protein binds to each heparin molecule of molecular weight greater than about 6 × 10(3).3. The stability of these complexes varied with pH, salt concentration and the chain length of the heparin. The limit complexes found in excess of the larger heparins consisted of only one heparin molecule per protein tetramer, and the failure to observe complexes with four heparin molecules/protein tetramer is discussed.

scholarly journals SYNTHESIS OF CHLOROPLAST DNA IN ISOLATED CHLOROPLASTS

1968 ◽  
Vol 38 (1) ◽  
pp. 151-157 ◽  
Author(s):  
N. Steele Scott ◽  
Vinod C. Shah ◽  
Robert M. Smillie
Keyword(s):  
Molecular Weight ◽  
Chloroplast Dna ◽  
Euglena Gracilis ◽  
Bacterial Contamination ◽  
Actinomycin D ◽  
Density Gradient Centrifugation ◽  
Tritiated Thymidine ◽  
Gradient Centrifugation ◽  
Acid Stable ◽  
Isolated Chloroplasts

Chloroplasts isolated from Euglena gracilis incorporated both tritiated thymidine 5'-triphosphate and tritiated deoxyadenosine 5'-triphosphate into an acid-stable fraction. The incorporation was dependent on the presence of all four deoxynucleoside triphosphates and was sensitive to treatment with deoxyribonuclease and actinomycin D. It was demonstrated that bacterial contamination could not account for the incorporation of label. Extraction of DNA from the chloroplasts and subsequent density gradient centrifugation of the DNA in CsCl2 showed that the incorporation was into chloroplast DNA (ρ = 1.686) of high molecular weight.

Mixing of Carbon Black with Rubber. VI. Analysis of NR/SBR Blends

1988 ◽  
Vol 61 (4) ◽  
pp. 609-618 ◽  
Author(s):  
George R. Cotten ◽  
Lawrence J. Murphy
Keyword(s):  
Molecular Weight ◽  
Carbon Black ◽  
High Molecular Weight ◽  
Surface Area ◽  
Bound Rubber ◽  
Very High

Abstract The distribution of carbon black in NR/SBR blends was determined through the analysis of bound rubber. The NR/SBR blends were found to be very different from the previously studied SBR/BR compounds: these differences were assigned to mutual insolubility of the two polymers and a very high molecular weight of NR. In NR/SBR blends, it was found that changes in molecular weight of the polymer has no effect on the carbon black distribution in the blend. While the “activity” of carbon black did not affect the distribution, the loading of the black in NR decreased linearly with increasing surface area of the black. Approximately 35% of normal tread blacks (surface area 80–100 m2/g) was found in the NR phase. However, the bond between NR and carbon black is quite weak, and black continues to migrate into the SBR phase on prolonged mixing or during blending of NR and SBR masterbatches.

Chromosome age and segregation during sporulation of Bacillus megaterium

1978 ◽  
Vol 24 (10) ◽  
pp. 1227-1235 ◽  
Author(s):  
Anthony D. Hitchins
Keyword(s):  
Bacillus Megaterium ◽  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Buoyant Density ◽  
Growth Period ◽  
Circular Dna ◽  
Chromosomal Segregation ◽  
Seven Generations ◽  
Minor Correction

The effect of chromosome age on segregation during sporulation was investigated. Vegetative cells of Bacillus megaterium were labeled with [Me-3H]thymine and then were grown at 30 °C in nonradioactive medium for various times before being allowed to sporulate. The ratio of the amount of label in sporal DNA to that in sporangial DNA, obtained after minor correction for the sporulation frequency, remained essentially constant as the postlabeling growth period was increased from one to seven generations. The spores were preferentially located at the older poles of sporangia, i.e. the poles formed by divisions occurring prior to those forming the sporangia. Therefore, it seems that old (labeled) chromosomes segregate randomly with respect to both the morphological and genealogical polarities of sporangia. Examination of total cell lysates by dye–buoyant density gradient centrifugation revealed the presence of covalently closed circular DNA from cells grown at 37 °C, but none was obtained from cells grown at 30 °C. Thus, possible interference by large amounts of extrachromosomal DNA in the determination of the chromosomal segregation pattern is unlikely.

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