Search

Precipitation of DNA is performed frequently in molecular biology laboratories for the purpose of purification and concentration of samples and also for transfer of DNA into cells. Metal ions are used to facilitate these processes, though their precise functions are not well characterized. In the current study we have investigated the precipitation of double-stranded DNA by group 1 and group 2 metal ions. Double-stranded DNAs were not sedimented efficiently by metals alone, even at high concentrations. Increasing the pH to 11 or higher caused strong DNA precipitation in the presence of the divalent group 2 metals magnesium, calcium, strontium and barium, but not group 1 metals. Group 2 sedimentation profiles were distinctly different from that of the transition metal zinc, which caused precipitation at pH 8. Analysis of DNAs recovered from precipitates formed with calcium revealed that structural integrity was retained and that sedimentation efficiency was largely size-independent above 400 bp. Several tests supported a model whereby single-stranded DNA regions formed by denaturation at high pH became bound by the divalent metal cations. Neutralization of negative surface charges reduced the repulsive forces between molecules, leading to formation of insoluble aggregates that could be further stabilized by cation bridging (ionic crosslinking)., (Copyright © 2020 Elsevier Inc. All rights reserved.)

We present an unusual cause of lung cavitation and a neck mass in an HIV positive child, initially thought to be tuberculosis. This case report illustrates that the cause for cavitatory lung disease in immunosuppressed children has a large number of possibilities and careful investigation to determine the etiological agent is warranted., (Copyright © 2012 Wiley Periodicals, Inc.)

We reviewed 42 cases of pediatric and adolescent imported malaria in Cape Town. Patients were predominantly new and returned immigrants from other African countries. Rapid diagnosis occurred in most cases. Eleven of 42 (26%) had severe malaria. Management issues included delay to and inappropriate treatment, inadequate monitoring for hypoglycemia, and under notification to health authorities.

Harold King was an analytical chemist of distinction, who worked with Sir Henry Dale and his colleagues in the Medical Research Institute, later the Medical Research Council. He helped to quash the theory that the anaesthetic action of ether was attributable to its impurities. Interest in alkaloids led to the elucidation of the structure of hyoscine, the synthesis of muscarine and the first isolation of crystalline tubocurarine for which he proposed a structural formula, work which influenced Bovet in the synthesis of gallamine. He proposed the synthesis of the homologous series of methonium compounds which included relaxant and hypotensive drugs. His collaboration with Rosenheim was outstanding and opened the way for synthesis of cholesterol and the steroids. He was always encouraging clinicians, and gave a sample of tubocurarine to Ranyard West who was the first to inject d-tubocurarine into a human patient.

Of 18 sick cows in a 100-cow dairy herd in Oregon, 14 died despite treatment. The cows were being fed high-moisture whole corn and alfalfa and rye haylage from pit silos. Signs of illness were anorexia, severe depression, and reduced milk production. Necropsy revealed only hyperemia of the abomasal mucosa and dilated, gas filled large intestine. On the basis of response to treatment, laboratory findings, necropsy findings, and herd history, a tentative diagnosis of botulism was made. This diagnosis was confirmed by results of mouse inoculation tests. Injections of extract from the corn killed mice that were not protected by botulinum antitoxin.

The results of genetic fine structure experiments, performed on the amiA locus of Pneumococcus are summarized. The peculiar feature of transformation genetics is that a given donor marker mutation transforms with an efficiency characteristic of the mutated site. In spite of this difficulty, mapping procedures have been devised and quantitative recombination studies performed. It is concluded from these studies that transformation, in this locus, is the consequence of frequent, and essentially random exchanges occurring between donor DNA and the chromosomal DNA of the recipient cell. The average length of uninterrupted donor DNA polynucleotide strand which could be inserted into the chromosome of a transformed cell is estimated, from genetic data, to be probably not greater than 3.10(5) daltons (for a double-stranded insertion). It is proposed, on the basis of genetic evidence, that following essentially random exchanges between donor DNA and recipient chromosome, a revision process, specific for certain types of mutated sites, occurs. The revision process appears to remove preferentially donor DNA sequences from the primary recombinant structure, and allow repair along the chromosomal template, leading to low efficiency in the genetic integration of these sites. A mechanism for this "destruction-choice" process is presented, and evidence in support of this mechanism discussed.