Mitochondrial DNA in yeast and some mammalian species

Yeast DNA, in a cesium chloride density gradient, shows a minor or satellite band with a density lower than that of the main nuclear component. The DNA isolated from purified mitochondria of yeasts corresponds in density to this satellite band. In solution, this DNA more easily undergoes renaturation as compared to DNA from cell nuclei. The ease of this renaturation is presumably due to a homogeneity greater than that of nuclear DNA. Mitochondrial DNA isolated from several mammalian species has the same or higher density than nuclear DNA, but differs in its ready renaturability.     

Satellite deoxyribonucleic acid from Bacillus cereus strain T

DNA isolated from exponentially growing cultures of Bacillus cereus T has a single component (density 1.696 g cm(-3)) in a cesium chloride density gradient whereas DNA isolated from spores shortly after the initiation of germination has two components: a major one (density 1.696 g cm(-3)) and a satellite (density, 1.725 g cm(-3)). The DNA of both components is doublestranded. By the first cell division there is no satellite DNA.     

Carcinogen and microsomal membrane interactions: changes in membrane density and ability to bind nucleic acids

DNA and synthetic copolymer polyribocytidylic-polyriboguanylic acid bind to microsomal membrane. The nucleic acid-membrane complex may be detected by centrifugation in cesium chloride density gradients. The density of the nucleic acid-membrane complex and, in certain cases, the amount of nucleic acid associated with the membrane was changed in the presence of various carcinogenic chemicals.     

Cytoplasmic DNA from petite colonies of Saccharomyces cerevisiae: a hypothesis on the nature of the mutation

The density of the cytoplasmic DNA of two strains of "petite" mutants of yeast, obtained by treatment with acriflavin and with ultraviolet light, was examined in cesium chloride density-gradient centrifugation and in all cases appeared to be less than that of the wild type. A cytoplasmic respiratory-deficient strain, treated with additional acriflavin, can show a further shift of the position of the satellite band, always in the direction of reduction of density. Also, from the p(+) x p(-) cross, p(-) strains can be recovered in which the density of the satellite DNA is different from the density of the parent p(-) strain. This finding suggests the existence of recombination in cytoplasmic DNA moleciules.     

Mitochondrial-satellite and circular DNA filaments in yeast

Mitochondrial DNA of Saccharomyces cerevisiae contains a satellite DNA (density, 1.682) that appears to exist as open-ended filaments at least 5 microns long. DNA from intact cells contains circular filaments whose lengths vary from 0.5 to 7 microns, with a great majority at 1.95 microns. The circular DNA has a density similar to that of the major nuclear peak (1.697). When heat-denatured mitochondrial-satellite DNA is renatured, it cross-links to form a molecule that is larger than the native molecule. The formation of cross-links results in hypersharpening of the density profiles in cesium chloride and also leads to failure to pass Millipore filter paper.     

Satellite DNA in constitutive heterochromatin of the guinea pig

Total DNA and DNA from the heterochromatin and euchromatin fractions of male guinea pig liver nuclei were analyzed by cesium sulfate-silver density-gradient centrifugation. Total DNA is composed of three components: a heavy satellite DNA, a main DNA of intermediate density, and a light satellite DNA. Heterochromatin DNA shows a fourfold enrichment in the satellite components while euchromatin DNA is relatively devoid of them. The strands of both satellite DNA's are separable by centrifugation in alkaline cesium chloride. Base analyses on the separate strands demonstrate that the two satellite DNA's represent different species.     

Inserted sequences in bovine satellite DNA's

The nucleotide sequence of the 1413-base-pair repeat unit of bovine 1.711a satellite DNA (density in cesium chloride, 1.711 grams per cubic centimeter) has been determined. The repeat unit contains two segments consisting of variants of a basic 23-base-pair sequence that is closely related to sequences of bovine 1.706 satellite DNA. A third segment of the repeat unit contains an unrelated 611-base-pair sequence that is not internally repetitive. This segment is flanked by inverted repeats of 8 base pairs and, on one side, by a direct repeat of the terminal sequence. A related segment is present in bovine 1.711b satellite DNA and is inserted into sequences derived from the 1.715 satellite. These nucleotide sequences suggest the timing of some of the stages in the evolution of these complex, closely related satellite DNA's and indicate the mechanisms inherent in their divergence from a common ancestor.     

Encapsidation of free host DNA by simian virus 40: a simian virus 40 pseudovirus

Under specified growth conditions, simian virus 40 encapsidated host DNA in a noncircular form free of viral DNA. Two bands of virus particles were present in cesium chloride equilibrium density centrifugation. The host DNA species contained in the upper band was of a lower molecular weight than the DNA present in the mature virus in the lower band.     

Isopycnic separation of subcellular components from poliovirus-infected and normal HeLa cells

A rapid method for determining the density of ribonucleoprotein particles and complexes has been developed. The method involves glutaraldehyde fixation of sucrose gradient fractions and immediate centrifugation for 5 hours through preformed cesium chloride gradients. There is little or no aggregation of particles, so that components which co-sediment in sucrose gradients are resolved by the cesium chloride gradient. By this method the densities of HeLa cell ribosomes, polyribosomes, and subribosomal particles have been determined. Furthermore, the poliovirus replication complex has been separated from polyribosomes and its density has been found to be unaffected by treatment with ethylene-diaminetetraacetic acid.     

TRANSCRIPTION IN VIVO OF DNA FROM BACTERIOPHAGE SP8

The DNA of bacteriophage SP8, when denatured, yields two components differing in buoyant density in cesium chloride gradients and separable by chromatography on a column of methylated bovine serum albumin and kieselguhr. The denser of the two strands (H) contains more pyrimidines and fewer purines than the lighter (L) strand. Only the H strand forms hybrids with the RNA synthesized by the infected host. The L strand is capable of annealing with complementary RNA synthesized in vitro with it as primer in reactions catalyzed by RNA polymerase. During the vegetative development of phage, host-specific messenger RNA is also synthesized.     

Isopycnic centrifugation for the isolation of DNA strands coding for ribosomal RNA

Denatured DNA preparations from Escherichia coli were centrifuged to equilibrium in cesium chloride solutions. Hybridizing experiments with radioactively labeled ribosomal RNA showed that the DNA strands complementary to ribosomal RNA were distributed on the heavy side of the DNA band. By fractionating this band the DNA strands coding for ribosomal RNA may be enriched 5- to 20- fold.     

HETEROGENEITY OF DNA IN DENSITY AND BASE COMPOSITION

Chromatography, on methylated-albumin columns, of DNA from calf thymus, mouse testis, and Bacillus subtilis, yielded, on elution by a sodium chloride gradient, fractions differing in density. The fractions eluted by higher sodium chloride concentrations had lower densities in a CsCl density gradient. Since DNA with higher guaninecytosine content is eluted from the column with lower concentration of sodium chloride and has higher density, the density heterogeneity of DNA is best interpreted as a result of heterogeneity of base composition. An extra band observed in calf-thymus DNA had a higher density than that of the main DNA; it was eluted at a lower concentration of NaCl, indicating a higher content of guanine and cytosine. On the other hand, an additional DNA component in the mouse-testis DNA had a lower density and also it was eluted at a lower salt concentration, possibly an indication of an unusual base component in its structure.     

Calcium uptake by isolated sarcoplasmic reticulum treated with dithiothreitol

Isolated vesicles of the sarcoplasmic reticulum are known to take up calcium when provided with magnesium adenosine triphosphate as an energy source. Preparations of high activity are obtained by keeping the vesicles in 5 millimolar dithiothreitol (a reagent that reduces disulfide groups), and these preparations retain activity for a week or longer. The highly active preparations lend themselves to a spectrophotometric method for following calcium uptake, and continuous uptake kinetics are readily obtained. Calcium uptake appears to follow Michaelis-Menten kinetics (K(m) = 8x10(-6); V(mas), = 7x10(-7) mole per second per milligram of protein). These preparations are also useful for studying the effects of inhibitors of uptake, such as quinine. When extrapolated to the intact muscle, the results from these isolated vesicles should give a better estimate than has been available of the actual rates of calcium uptake and of the physiological effect of inhibitors of uptake.     

PCR检测鸭疫里默氏菌的研究

对本研究室分离、鉴定并保存的42株鸭疫里默氏菌(包括8个血清型)、9株鸭源大肠杆菌和4株鸭源禽多杀性巴氏杆菌进行PCR扩增,结果所有的鸭疫里默氏菌均能扩增出809bp的特异性DNA片段,而鸭源大肠杆菌和鸭源禽多杀性巴氏杆菌均为阴性。试验证明以细菌DNA和全菌体分别作模板,对PCR的扩增结果无影响。经过优化的该PCR方法能检测出的最低DNA量为1pg。     

Introduction of human DNA into mouse eggs by injection of dissected chromosome fragments

A procedure has been developed for introducing exogenous DNA into mouse eggs by injection of chromosome fragments. Chromosome fragments were dissected from human metaphase spreads and microinjected into the pronuclei of fertilized mouse eggs. Many of the injected eggs subsequently exhibited normal pre- and postimplantation development. Embryos obtained from eggs injected with centromeric fragments retained human centromeric DNA as demonstrated by in situ hybridization analysis. From eggs injected with noncentromeric fragments, a mouse was obtained whose tail tissue exhibited the presence of human DNA. This procedure should facilitate incorporation of very large (more than 10 megabases) DNA fragments into cells and embryos without the need for cloned sequences.     

锈色粒肩天牛卵在国槐上垂直分布规律的研究

锈色粒肩天牛的卵在被害国槐上的分布研究表明:锈色粒肩天牛产卵数量随胸径的增大而减小;产卵株率随胸径的增大而增大;卵块在树干上的分布数量下段＞中段＞梢段;树干2 m以下产卵的数量占整株的72.72,树干在1 m以下的产卵数量占整株产卵总量的38.18.因此,在虫情调查时可以调查2 m以下的树干来估测全树的产卵密度.适时进行树干基部涂白的方法,可以有效地减轻虫口密度.     

Quantal secretion from adrenal medulla: all-or-none release of storage vesicle content

Neurogenic secretion of catecholamines from the adrenal medulla in rabbits, induced by administration of insulin, caused decreases in both the dopamine-beta-hydroxylase activity and the catecholamine content of the storage vesicle fraction. After sedimentation through a sucrose density gradient, the storage vesicles obtained from insulin-treated animals had the same density and the same ratio of dopamine-beta-hydroxylase to catecholamine as did vesicles from untreated animals. These and other data indicate that neurogenic secretion from the adrenal medulla occurs by an all-or-none release from the storage vesicles.     

Phase transition of FeO and stratification in Earth's outer core

Light elements such as oxygen in Earth's core influence the physical properties of the iron alloys that exist in this region. Describing the high-pressure behavior of these materials at core conditions constrains models of core structure and dynamics. From x-ray diffraction measurements of iron monoxide (FeO) at high pressure and temperature, we show that sodium chloride (NaCl)-type (B1) FeO transforms to a cesium chloride (CsCl)-type (B2) phase above 240 gigapascals at 4000 kelvin with 2% density increase. The oxygen-bearing liquid in the middle of the outer core therefore has a modified Fe-O bonding environment that, according to our numerical simulations, suppresses convection. The phase-induced stratification is seismologically invisible but strongly affects the geodynamo.     

DOUBLE-STRANDED RIBONUCLEIC ACID FORMATION IN VITRO BY MS 2 PHAGE-INDUCED RNA SYNTHETASE

Part of the RNA synthesized from nucleoside triphosphate precursors by partially purified RNA synthetase, an enzyme induced in Escherichia coli by the RNA-containing phage MS 2, is resistant to hydrolysis by ribonuclease. Upon heating in 0.15M sodium chloride, 0.015M sodium citrate followed by fast cooling the material becomes ribonuclease-sensitive with a sharp transition at 102 degrees to 104 degrees C. The suggestion that the ribonuclease-resistant product is double-stranded RNA is reinforced by restoration of the ribonuclease resistance of the heat-denatured material by reannealing at temperatures just below the transition point and by its buoyant density in cesium sulfate. It is suggested that double-stranded RNA is the replicative form of MS 2 phage RNA.