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Biomedical subjects

M Mandel

Publications and source records attributed to M Mandel.

At least 181 records · Page 10Linked to original sources
PubMed1970

Correlation of melting temperature and cesium chloride buoyant density of bacterial deoxyribonucleic acid.

Samples of bacterial deoxyribonucleic acid from bacteria having guanine plus cytosine (GC) contents in the range of 27 to 72 moles per cent GC were analyzed by optical melting (T(m)) and equilibrium buoyant density methods. The relation between these properties is shown to be linear. The relative value of 1.99 moles per cent GC per degree C change in T(m) is calculated, and a reference method for the calculation of GC contents relative to a standard is derived.

Cesium↗
PubMed1970

Nature of the ethylenediaminetetraacetic acid requirement for transformation of Bacillus subtilis with single-stranded deoxyribonucleic acid.

The ethylenediaminetetraacetate (EDTA) requirement for transformation of Bacillus subtilis with single-stranded deoxyribonucleic acid (DNA) was examined. The results indicate that a chelating agent such as EDTA is a stringent requirement for transformation with single DNA strands only at nonsaturating DNA concentrations, and that EDTA, when required, must be present during several steps in the transformation process and appears to insure the survival of single-stranded DNA by rendering a nuclease in competent populations inactive.

Bacillus subtilis↗
PubMed1970

Effect of miracil D on marker frequency ratio and cytotoxicity in Bacillus subtilis.

When Miracil D was added to mid-log phase Bacillus subtilis cells, the rate of growth decreased immediately, and the turbidity of the culture began to decrease within 15 to 20 min after addition of the drug. At this stage, ghostlike cells were observed under phase-contrast microscopy. The viable count also began to decrease rapidly after 15 min in the presence of the drug, and within 60 min there was a 10,000-fold reduction in viability. Incorporation of (3)H-thymidine into deoxyribonucleic acid (DNA) proceeded normally up to 20 min of exposure to the drug, after which incorporation ceased. Cells which were prelabeled with (3)H-thymidine and exposed to the drug released labeled DNA into the medium after 15 to 20 min. Results of transformation analyses with donor DNA from cells grown in the presence of Miracil show a decrease with time in the ratio of origin markers to terminus markers. Electron micrographs of sectioned cells grown for 5, 10, and 15 min in the presence of Miracil D show profound cytotoxic effects. The most striking aspect of such cells is the very condensed appearance of the nucleoid. In those cells about to divide, the nucleoid appears not to be properly separating, being strung out in the region of the developing septum. Finally, the mesosome is very poorly defined or entirely absent in Miracil-treated cells.

Adenine↗
PubMed1970

Properties of the deoxyribonucleic acid contained in the defective particle coliphage 15.

Escherichia coli strain 15 TAU, which requires thymine, arginine, and uracil for growth and harbors an apparently defective prophage, was induced by exposure to ultraviolet light (580 ergs/mm(2)) or to mitomycin C (5 mug/ml). Phage particles (coliphage 15) were recovered from the resulting lysate by treatment with deoxyribonuclease, filtration, and several cycles of differential centrifugation. Analysis of the phage particles obtained by using cesium chloride density gradient centrifugation in a preparative ultracentrifuge resulted in the resolution of three components. The major component had a peak density of 1.52 to 1.53 g/cm(3) followed by components with densities of 1.5 and 1.49 g/cm(3). The guanine plus cytosine content of coliphage 15 deoxyribonucleic acid (DNA) was determined by both analytical ultracentrifugation in cesium chloride and by thermal denaturation in standard saline citrate buffer. Respective values of 46.4 +/- 1% and 46.6 +/- 1% guanine plus cytosine content were obtained. Coliphage 15 DNA formed molecular hybrids with messenger ribonucleic acid (RNA) from both uninduced and ultraviolet-induced cultures of E. coli 15 TAU, but did not hybridize with E. coli ribosomal RNA. The molecular weight of coliphage 15 DNA was determined by constant velocity sucrose density gradient centrifugation to be about 33 x 10(6) daltons.

Arginine↗
PubMed1969

Plus and minus single-stranded DNA separately encapsidated in adeno-associated satellite virions.

Based on physical and chemical determinations, the mnolecular weight of the type 4 adeno-satellite virus is 5.4 X 10(6) daltons, and the virion contains 1.4 X 10(6) daltons of DNA. Denaturation and renaturation studies indicate that the viral genome is a single-stranded DNA molecule and that each virion contains either a minus or a plus strand. Upon extraction, the minus and plus strands unite to form double-stranded DNA molecules with no obvious excess of unpaired strands.

Adenoviridae↗
PubMed1969

Deoxyribonucleic acid characterization of Bdellovibrios.

The guanine plus cytosine (GC) content of the deoxyribonucleic acid (DNA) of 11 isolates of host-dependent (H-D) bdellovibrios and 18 host-independent (H-I) derivatives was determined from thermal denaturation curves and buoyant densities in CsCl. The H-D and respective H-I cultures have GC contents which are identical within the limits of experimental error. Most cultures of Bdellovibrio bacteriovorus, including the holotype culture, have 50.4 +/- 0.9 moles% GC in their DNA; two bdellovibrio isolates of presently uncertain nomenclatural status contain DNA of about 43% GC. Optical melting profiles of all the DNA from all of these organisms are particularly steep, indicating little compositional heterogeneity. Chromatography of acid hydrolysates of Bdellovibrio nucleic acids reveal no unusual components. The DNA content per cell of one H-I derivative is about one-third the amount per Escherichia coli cell growing at a comparable rate.

Bacteria↗
PubMed1969

Zone electrophoresis of enzymes in bacterial taxonomy.

The electrophoretic mobilities in starch gels have been determined for eight enzymes in extracts of representative cultures of members of the family Enterobacteriaceae. These values were compared with each other and with those obtained from certain bacteria not in this family. The migrations of the eight enzymes were virtually identical for each of eight strains of Escherichia coli and for two species of Shigella. A number of these enzymes appeared to be identical in other organisms believed to be closely related to E. coli (Salmonella), and the number of differences increased in organisms which appeared to have lesser degrees of relatedness by other criteria (deoxyribonucleic acid base compositions, overall similarity).

Alcaligenes↗