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D R Wolstenholme

Publications and source records attributed to D R Wolstenholme.

At least 73 records · Page 4Linked to original sources
PubMed1973

Single strand-containing replicating molecules of circular mitochondrial DNA.

Mitochondrial DNAs (mtDNAs) from Chang rat solid hepatomas and Novikoff rat ascites hepatomas were examined in the electron microscope after preparation by the aqueous and by the formamide protein monolayer techniques. MtDNAs from both tumors were found to include double-forked circular molecules with a form and size suggesting they were replicative intermediates. These molecules were of two classes. In molecules of one class, all three segments were apparently totally double stranded. Molecules of the second class were distinguished by the fact that one of the segments spanning the region between the forks in which replication had occurred (the daughter segments) was either totally single stranded, or contained a single-stranded region associated with one of the forks. Daughter segments of both totally double-stranded and single strand-containing replicating molecules varied in length from about 3 to about 80% of the circular contour length of the molecule. Similar classes of replicating molecules were found in mtDNA from regenerating rat liver and chick embryos, indicating them to be normal intermediates in the replication of mtDNA All of the mtDNAs examined included partially single-stranded simple (nonforked) circular molecules. A possible scheme for the replication of mtDNA is presented, based on the different molecular forms observed

Animals↗
PubMed1972

The form and structure of kinetoplast DNA of Crithidia.

Cesium chloride centrifugation of each of the DNAs extracted from eight strains of Crithidia revealed a main band at rho = 1.717 g/cm(3) and a satellite band varying from rho = 1.701 to 1.705 g/cm(3) for the different strains By electron microscopy each DNA was shown to include circular molecules, 0.69-0.80 micro in mean contour length, and large, topologically two-dimensional masses of DNA in which the molecules appeared in the form of rosettes. DNA isolated from kinetoplast fractions of Crithidia acanthocephali was shown to consist of light satellite DNA and to be mainly in the form of large masses, 0.8 micro (mol wt = 1.54 x 10(6) daltons) circular molecules, and a few long, linear molecules. The results of experiments involving ultracentrifugation, heating, and quenching, sonication, and endodeoxyribonuclease digestion, combined with electron microscopy, are consistent with the following hypothesis. The large DNA masses are associations of 0.8 micro circles which are mainly covalently closed. The circles are held together in groups (the rosettes) of up to 46 by the topological interlocking of each circle with many other circles in the group. A group of circles is attached to an adjacent group by one or more circles, each interlocking with many circles of both groups. Each of the associations comprises, on the average, about 27,000 circles (total mol wt approximately 41 x 10(9) daltons). A model is proposed for the in situ arrangement of the associations which takes into consideration their form and structure, and appearance in thin sections

Acridines↗
PubMed1971

Circular chloroplast DNA from Euglena gracilis.

Chloroplast DNA of the protozoan flagellate, Euglena gracilis, exists as circular molecules, 40 mum in contour length, as shown by electron microscopy and buoyant density analyses.

Cell Fractionation↗
PubMed1970

Kinetoplast deoxyribonucleic acid of the hemoflagellate Trypanosoma lewisi.

Cesium chloride centrifugation of DNA extracted from cells of blood strain Trypanosoma lewisi revealed a main band, rho = 1.707, a light satellite, rho = 1.699, and a heavy satellite, rho = 1.721. Culture strain T. lewisi DNA comprised only a main band, rho = 1.711, and a light satellite, rho = 1.699. DNA isolated from DNase-treated kinetoplast fractions of both the blood and culture strains consisted of only the light satellite DNA. Electron microscope examination of rotary shadowed preparations of lysates revealed that DNA from kinetoplast fractions was mainly in the form of single 0.4 micro circular molecules and large masses of 0.4 micro interlocked circles with which longer, often noncircular molecules were associated. The 0.4 micro circular molecules were mainly in the covalently closed form: they showed a high degree of resistance to thermal denaturation which was lost following sonication; and they banded at a greater density than linear DNA in cesium chloride-ethidium bromide gradients. Interpretation of the large masses of DNA as comprising interlocked covalently closed 0.4 micro circles was supported by the findings that they banded with single circular molecules in cesium chloride-ethidium bromide gradients, and following breakage of some circles by mild sonication, they disappeared and were replaced by molecules made up of low numbers of apparently interlocked 0.4 micro circles. When culture strain cells were grown in the presence of either ethidium bromide or acriflavin, there was a loss of stainable kinetoplast DNA in cytological preparations. There was a parallel loss of light satellite and of circular molecules from DNA extracted from these cells.

Acridines↗
PubMed1968

Renaturation and hybridization studies of mitochondrial DNA.

The products of the renaturation reaction of mitochondrial DNA from oocytes of Xenopus laevis have been studied by electron microscopy and CsCl equilibrium density gradient centrifugation. The reaction leads to the formation of intermediates containing single-stranded and double-stranded regions. Further reactions of these intermediates result in large complexes of interlinking double-stranded filaments. The formation of circular molecules of the same length as native circles of mitochondrial DNA was also observed. The formation of common high molecular weight complexes during joint reannealing of two DNA's with complementary sequences was used as a method to detect sequence homology in different DNA samples. Although this method does not produce quantitative data it offers several advantages in the present study. No homologies could be detected between the nuclear DNA and the mitochondrial DNA of X. laevis or of Rana pipiens. In interspecies comparisons homologies were found between the nuclear DNA's of X. laevis and the mouse and between the mitochondrial DNA's of X. laevis and the chick, but none between the mitochondrial DNA's of X. laevis and yeast. These results are interpreted as indicating the continuity of mitochondrial DNA during evolution.

Animals↗