Physical properties of the DNA of bacteriophage SP50

Summary The following properties of the DNA of B. subtilis phage SP50 were established: Molecular weight (in Daltons) 102×10⁶ (sedimentation velocity) 97×10⁶ (viscosity) 97×10⁶ (contour lengths of electron micrographs) Base Composition (in % GC) 41.7 (chemical analysis) 44 (melting point) 44 (buoyant density) No unusual bases were observed. The complementary strands of the DNA can be separated. The phage DNA has genuine single strand breaks. The number and distribution of such breaks appears to be determined by the host on which phages were grown.This investigation was supported in part by a Public Health Service research grant GM 13,666 from the National Institutes of General Medical Sciences, AI 01267 from the National Institutes of Allergy and Infectious Diseases, AM 04763 from the National Institutes of Arthritis and Metabolic Diseases; cancer research funds from the University of California; and a grant from the Hartford Foundation.     

Permeabilities of theChara cell wall to saccharides,albumin and ficoll

A method was developed to enable the determination of the permeability coefficient of theChara cell wall to various solutes from a measurement of the water flow occurring in the solution-cell wall-water system. For this method, the cell wall tube, closed at one end with the natural septum, was connected to a pipette, which serves as a volumeter, by using a glass capillary and a needle. Permeability coefficientsk _s of the cell wall to glucose (M.W.=180.2), mannitol (M.W.=182.2), sucrose (M.W.=342.3), lactose (M.W.=342.3), raffinose (M.W.=504.5) and melezitose (M.W.=504.4) were 2.27, 2.36, 1.43, 1.38, 1.11 and 1.09×10⁻⁴ cm sec⁻¹, respectively. The reciprocal ofk _s is expressed as a linear function of molecular weight,M, by the equation 1/k _s =16M+1.5×10³ (cm⁻¹ sec) Albumin (M.W.=68,000) passed through the cell wall fairly well. Ficoll (M.W.=400,000±100,000) for practical purposes could not permeate the cell wall.     

The comparative cell cycle and metabolic effects of chemical treatments on root tip meristems. III. Chlorsulfuron

Intact and excised cultured pea roots (Pisum sativum L. cv Alaska) were treated with chlorsulfuron at concentrations ranging from 2.8 ×10^–4 M to 2.8×10^–6 M. At all concentrations this chemical was demonstrated to inhibit the progression of cells from G₂ to mitosis (M) and secondarily from G₁ to DNA synthesis (S). The S and M phases were not directly affected, but the transition steps into those phases were inhibited. Total protein synthesis was unaffected by treatment of intact roots with 2.8×10^–6 M chlorsulfuron. RNA synthesis was inhibited by 43% over a 24-h treatment period. It is hypothesized that chlorsulfuron inhibits cell cycle progression by blocking the G₂ and G₁ transition points through inhibition of cell cycle specific RNA synthesis.     

Hybridization of Gossypium species through in ovulo embryo culture

An interspecific hybrid of the sexually incompatible species G. hirsutum cv. Laxmi and G. arboreum cv. Jyoti was obtained through in ovulo embryo culture. Eightto twelve-day-old ovules were excised and cultured on Beasley and Ting's medium supplemented with Indol-3 acetic acid (5×10^-6 to 7×10^-6 M), Kinetin (5×10^-6 to 5×10^-8 M), Gibberellic acid (5×10^-7 to 5×10^-9M), Ammonium chloride (5 to 15mM) and Casein hydrolysate (50 to 200mg/l) added individually and in various combinations along with sucrose. No single medium was adequate to ensure complete development of the fertilized ovules to plantlets, thus necessitating a sequential five step transfer to different media. Cytological studies confirmed the hybrid nature of the plants.Abbreviation IAA Indol-3 acetic acid - Kn Kinetin - GA₃ Gibberellic acid - CH Casein hydrolysate - NAA -Naphthalene-acetic acid - BT Beasley and Ting's basal medium - MS Murashige and Skoog's basal medium - W White's basal medium NCL Communication number 3823.     

Chromatographic resolution of nucleic acids extracted from Penicillium chrysogenum

Summary High molecular weight DNA extracted from Penicillium chrysogenum has been fractionated using RPC-5 Analog, into three distinct types designated 1, 2 and 3. Types 1 and 2 have the same buoyant density of 1.710 g/cm³ and together appear to comprise the nuclear DNA. Type 1 is enriched for repeated sequences which are normally observed in restriction digests of P. chrysogenum total DNA. Conversely, type 2 appears to be composed entirely of non-repetitive sequences. Type 3 has been identified as mitochondrial DNA, having a buoyant density of 1.695 g/cm³ and an estimated molecular weight of 31.6×10⁶ Daltons.     

2,6-Diisopropylphenol,a general anesthetic,inhibits glutamate action on rat synaptosomes

2,6-diisopropylphenol (propofol), a general intravenous anesthetic, inhibits the glutamate-dependent Ca²⁺ entry in rat synaptosomes with an approximate IC₅₀ of 3.0×10^–5 M.Propofol, at concentrations above 10^–6M, also inhibits the ATP-dependent uptake of glutamate in the presence of Ca²⁺, with an approximate IC₅₀ of 3.5×10^–5M, while it only has a slight inhibitory effect on the release of glutamate. The ouabain-insensitive synaptosomal ATPase is strongly inhibited by propofol, with an IC₅₀ of about 2.5×10^–6M, at concentrations which do not affect the luciferase system.     

Distribution of transcribable DNA sequences in mouse liver hepatoma chromatin

Summary Shearing in either a Virtis small or large volume capacity cup under defined conditions gave chromatin fragment size distribution upon agarose exclusion column chromatography (50 × 10⁶) that varied inversely with shear time. The large- and small-sized chromatin fragments possessed high template capacity while the intermediate fragments (the majority) had relatively low template capacity; the differences in template capacity of these size groups varying inversely with the shear time. The protein/DNA and RNA/DNA ratios remained relatively constant in all size groups.     

Study of interactions between DNA and aflatoxin B1 using electrochemical and fluorescence methods

In this study, a carbon paste electrode modified with N-butylpyridinium hexafluorophosphate (BPPF₆) ionic liquid and DNA was introduced as an electrochemical biosensor to study the interaction between DNA and aflatoxin B1 molecules. For this purpose, variations in oxidation peak current of guanine in various concentrations of aflatoxin B1 were measured by using the differential pulse voltammetry (DPV) method. According to this study, the binding constant of DNA–aflatoxin B1 was found to be 3.5 × 10⁶ M⁻¹. This modified electrode was also used for determination of low concentrations of aflatoxin B1 by using differential pulse voltammetry. A linear dynamic range from 8.00 × 10⁻⁸ to 5.91 × 10⁻⁷ M and a limit of detection of 2.00 × 10⁻⁸ M resulted from DPV measurements. To confirm our results, a fluorescence study was also performed. It resulted in a binding constant of 2.8 × 10⁶ M⁻¹, which is in good agreement with that obtained from electrochemical study.     

Inhibition of cell division and induction of chromosome aberrations in cultured Ehrlich ascites tumor cells by deoxyguanosine

Summary Exposure of exponentially growing cultures of Ehrlich ascites tumor cells to 1 or 2×10^-3 M deoxyguanosine resulted in an inhibition of DNA synthesis and cell multiplication. Continued increase in the RNA and protein content of these cultures suggests a state of unbalanced growth. Deoxyguanosine-inhibition is prevented by the presence of deoxycytidine (1×10^-4–2×10^-3 M).Treatment with deoxyguanosine (2×10^-3 M) for about one generation-time (18 hrs) and removal of deoxyguanosine thereafter resulted in chromosome aberrations (breaks and exchange figures) in 30–50% of those mitotic cells which were harvested 5 to 12 hrs after treatment. Chromosome defects were strongly reduced after incubation of cell-cultures in the presence of deoxyguanosine (2×10^-3 M) together with deoxycytidine (5×10^-4 M).The biochemical mechanisms by which deoxyguanosine and other inhibitors of DNA synthesis might produce chromosome damaging effects, are discussed.Supported by grants from Deutsche Forschungsgemeinschaft (Scha 176/1 and Scha 176/2).     

An electrochemical sensor based on single-stranded DNA-poly(sulfosalicylic acid) composite film for simultaneous determination of adenine, guanine, and thymine

Poly(sulfosalicylic acid) and single-stranded DNA composite (PSSA–ssDNA)-modified glassy carbon electrode (GCE) was prepared by electropolymerization and then successfully used to simultaneously determine adenine (A), guanine (G), and thymine (T). The characterization of electrochemically synthesized PSSA–ssDNA film was investigated by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The modified electrode exhibited enhanced electrocatalytic behavior and good stability for the simultaneous determination of A, G, and T in 0.1 M phosphate buffer solution (PBS, pH 7.0). Well-separated voltammetric peaks were obtained among A, G, and T presented in the analyte mixture. Under the optimal conditions, the peak currents for A, G, and T increased linearly with the increase of analyte mixture concentration in the ranges of 6.5 × 10⁻⁸ to 1.1 × 10⁻⁶, 6.5 × 10⁻⁸ to 1.1 × 10⁻⁶, and 4.1 × 10⁻⁶ to 2.7 × 10⁻⁵ M, respectively. The detection limits (signal/noise = 3) for A, G, and T were 2.2 × 10^–8, 2.2 × 10^–8, and 1.4 × 10^–6 M, respectively.     

Regeneration of multiple shoots and plants from Mesembryanthemum crystallinum

Mesembryanthemum crystallinum plants have been regenerated via organogenesis from hypocotyl, cotyledonary node, and leaf expiants with varying frequencies. The highest regeneration frequencies were obtained from either hypocotyls (23–34%) or cotyledonary nodes (21–41%). Leaf expiants yielded very poor regeneration frequencies (0–11%). Expiants were placed on Murashige and Skoog (MS) media supplemented with 3% sucrose, 0.8% bacto-agar and either, 10.8×10^–6M NAA and 8.8×10^–6M BA (MSmsh), 1×10^–5M BA and 1×10^–6M IAA, (MS4) or 1×10^–6M BA and 1×10^–6M IAA (MS5). Shoot formation frequencies were greater on MS4 and MS5 and lower on MSmsh, however, overall differences of regeneration frequency among media tested were not statistically significant. Regenerated plantlets were rooted on MS medium without growth regulators. Mature, regenerated plants were fertile and exhibited DNA content and ploidy profiles that were identical to wild type plants.Abbreviations MS Murashige and Skoog media - CAM Crassulacean acid metabolism - kbp kilobase pairs - NAA 1-naphthaleneacetic acid - BA 6-benzyladenine - IAA indole-3-acetic acid     

Fabrication of chronocoulometric DNA sensor based on gold nanoparticles/poly(l-lysine) modified glassy carbon electrode

In this work, we fabricated a sensitivity chronocoulometric DNA sensor (CDS) based on gold nanoparticles (AuNPs)/poly(l-lysine) complex film modified glassy carbon electrode. Hexaammineruthenium(III) chloride ([Ru(NH₃)₆]³⁺) was used as the electroactive indicator. The assembled process was investigated by cyclic voltammetry (CV) and chronocoulometry (CC). CC is used to monitor the DNA hybridization event by measurement of electrostatic binding [Ru(NH₃)₆]³⁺. Under the optimal conditions, the signal of [Ru(NH₃)₆]³⁺ was linear with the logarithm of the concentration of the complementary oligonucleotides from 1.0 × 10⁻¹³ to 1.0 × 10⁻¹¹ M, and the detection limit is 3.5 × 10⁻¹⁴ M.     

DNA immobilization on a polypyrrole nanofiber modified electrode and its interaction with salicylic acid/aspirin

A double-stranded calf thymus DNA (dsDNA) was physisorbed onto a polypyrrole (PPy) nanofiber film that had been electrochemically deposited onto a Pt electrode. The surface morphology of the polymeric film was characterized using scanning electron microscopy (SEM). The electrochemical characteristics of the PPy film and the DNA deposited onto the PPy modified electrode were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Then the interaction of DNA with salicylic acid (SA) and acetylsalicylic acid (ASA), or aspirin, was studied on the electrode surface with DPV. An increase in the DPV current was observed due to the oxidation of guanine, which decreased with the increasing concentrations of the ligands. The interactions of SA and ASA with the DNA follow the saturation isotherm behavior. The binding constants of these interactions were 1.15 × 10⁴ M for SA and 7.46 × 10⁵ M for ASA. The numbers of binding sites of SA and ASA on DNA were approximately 0.8 and 0.6, respectively. The linear dynamic ranges of the sensors were 0.1–2 μM (r² = 0.996) and 0.05–1 mM (r² = 0.996) with limits of detection of 8.62 × 10⁻¹ and 5.24 × 10⁻⁶ μM for SA and ASA, respectively.     

Inhibition of gibberellin biosynthesis by paclobutrazol in cell-free homogenates ofCucurbita maxima endosperm andMalus pumila embryos

The plant growth retardant paclobutrazol, (PP333) (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol, inhibits specifically the three steps in the oxidation of the gibberellin-precursorent-kaurene toent-kaurenoic acid in a cell-free system fromCucurbita maxima endosperm. The KI₅₀ for this inhibition is 2×10^–8 M. The KI₅₀ values for the separated2S, 3S, and2R, 3R enantiomers of paclobutrazol in this system are 2×10^–8 M and 7×10^–7 M, respectively. A cell-free preparation from immatureMalus pumila embryos convertsent-kaurene to gibberellin A₉, whereas no conversion occurs in a similar preparation fromMalus endosperm. The conversion ofent-kaurene by the embryo preparation is inhibited by paclobutrazol with KI₅₀ values for the2S,3S and2R,3R enantiomers of 2×10^–8 M and 6×10^–8 M, respectively.     

Development of DNA electrochemical biosensor based on immobilization of ssDNA on the surface of nickel oxide nanoparticles modified glassy carbon electrode

A sensitive electrochemical method for DNA hybridization based on immobilization of DNA probe and [Ru(NH₃)₅Cl]PF₆ complex onto nickel oxide nanomaterials (NiOx_np) modified glassy carbon electrode was developed. Due to strong affinity of NiOx_np for phosphate groups, oligonucleotides probe with a terminal 5′-phosphate group was attached to the surface of the modified electrode. DNA immobilization and hybridization were characterized by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry using K₃Fe(CN)₆/K₄Fe(CN)₆ and [Ru(NH₃)₅Cl]PF₆ as probe and indicator, respectively. The Ru-complex current response indicates only the complementary sequence showing an obvious current signal in comparison to non-complementary and three or single point mismatched sequences. The fabricated biosensor possessed good selectivity and sensitivity for complementary probe, taxon: 32630 tumor necrosis factor (TNF). The linear dynamic range, sensitivity and detection limit of the proposed biosensor were 4 × 10⁻¹⁰ M to 1 × 10⁻⁸ M, 34.32 nA nM⁻¹ and 6.8 × 10⁻¹¹ M, respectively. Excellent reproducibility and stability, quite simple and inexpensive preparation are the other advantages of proposed biosensor.     

Estrogenic activities of Psoralea corylifolia L. seed extracts and main constituents

Estrogenic activities of ethanol extract and its active components from Psoralea corylifolia L. were studied using various in vitro assays. The main components from ethanol extract were analyzed to be bakuchiol, psoralen, isobavachalcone, isobavachromene, and bavachinin. In a fractionation procedure, hexane and chloroform fractions showed estrogenic activity in yeast transactivation assay and E-screen assay. In yeast transactivation assay, ethanol extract, hexane, and chloroform fractions showed significantly higher activities at a concentration of 1.0 ng/ml, and bakuchiol at the concentration of 10⁻⁶ M was showed the highest activity, especially, which was higher than genistein at the same concentration. In E-screen assay, cell proliferation of bakuchiol (10⁻⁶ M) showed similar estrogenic activity with genistein (10⁻⁶ M). In ER binding assay, bakuchiol displayed the strongest ER-binding affinity (IC₅₀ for ERα = 1.01 × 10⁻⁶ M, IC₅₀ for ERβ = 1.20 × 10⁻⁶ M) and bakuchiol showed five times higher affinity for ERα than for ERβ.     

The repair of double-strand breaks in the nuclear DNA of Saccharomyces cerevisiae and its genetic control

Summary With the use of neutral sucrose sedimentation techniques, the size of unirradiated nuclear DNA and the repair of double-strand breaks induced in it by ionizing radiation have been determined in both wild-type and homozygous rad52 diploids of the yeast Saccharomyces cerevisiae. The number average molecular weight of unirradiated DNA in these experiments is 3.0×10⁸±0.3 Daltons. Double-strand breaks are induced with a frequency of 0.58×10^-10 per Daltonkrad in the range of 25 to 100 krad. Since repair at low doses is observed in wild-type but not homozygous rad52 strains, the corresponding rad52 gene product is concluded to have a role in the repair process. Cycloheximide was also observed to inhibit repair to a limited extent indicating a requirement for protein synthesis. Based on the sensitivity of various mutants and the induction frequency of double-strand breaks, it is concluded that there are 1 to 2 double-strand breaks per lethal event in diploid cells incapable of repairing these breaks.     

Metabolism of benzene and phenol in macrophages in vitro and the inhibition of RNA synthesis by benzene metabolites

Benzene may affect hemopoiesis by damaging the bone marrow stroma that provides the microenvironment for hemopoiesis. A possible target of benzene toxicity in the stroma is the macrophage, which is a major source of protein factors required for the proliferation and differentiation of progenitor cells. As an initial approach towards understanding whether benzene inhibits hemopoietic factor production in bone marrow stroma, the metabolism of benzene and phenol has been studied and the effect of benzene and its metabolites on macrophage RNA synthesis has been examined. Benzene is not metabolized in macrophages but phenol, the major metabolite of benzene in bone marrow, is converted by peroxidase in the macrophage to both free metabolites and species which covalently bind to cellular macromolecules. Benzene and its metabolites inhibited RNA synthesis in a dose-dependent manner, with 50% inhibitory concentrations of 5 × 10^–3M for benzene, 2.5 × 10^–3 M for phenol, 2.5 × 10^–5 M for hydroquinone, and 6 × 10^–6 M for p-benzoquinone; this inhibition was not attributable to loss of cell viability. Benzene, possibly by an inhibition of uridine transport into macrophages, and phenol, by its conversion to covalently binding species, inhibit RNA synthesis in macrophages and thus may inhibit the synthesis of colony stimulating factors required for hemopoiesis.Abbreviations CFU-G / M colony forming unit-granulocyte / macrophage - FCS fetal calf serum - IC₅₀ molar concentration causing 50% inhibition - PBS phosphate buffered saline     

Inhibitory effects of GABA on synaptic excitation in isolated rat hippocampal slices

In research on -aminobutyric acid (GABA) used at different concentrations on the amplitude of EPSP within populations (PEPSP), as recorded from dentrites in isolated hippocampal slices, GABA induced a dose-dependent reversible reduction in PEPSP amplitude with no noticeable signs of desensitization. Highest sensitivity to GABA was shown by PEPSP in hippocampal zone CA1 (threshold concentration: 3×10^–5–2×10^–4 M; (concentration at which the effect equal to 1/2 of maximum occurs) IC₅₀: 5×10^–4–1×10^–3 M). The effects of GABA on PEPSP were not blocked by bicuculline, picrotoxin, or penicillin. Action of GABA on dendritic antidromic population spike (DAPS — postynaptic effects) were slightly diminished by these blockers. Baclofen inhibited PEPSP more powerfully than GABA (threshold concentration: 1×10^–6 M: IC₅₀: 3×10^–6 M), although it only produced a minor reduction in DAPS amplitude even at high concentrations. It is concluded that the inhibitory effect of GABA on PEPSP in hippocampal zone CA1 may be put down mainly to its presynaptic action mediated by GABA_B receptors on axonal terminals of Schaffer collaterals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 5, pp. 627–633, September–October, 1990.     

CL−-Fluxe,Akkumulation und Transport in abgeschnittenen Mais-Wurzeln

Summary Fluxes, accumulation and transport rates of Cl^- in excised corn roots were investigated.Flux equilibrium in 5×10^-4M KCl was not reached within an experimental period of 28 hr.Transport of Cl^- (5×10^-4M KCl) through the xylem of 4–6 cm long excised corn roots had a lag of 1–2 hr. From 6 to 28 hr rates of accumulation and transport were nearly constant (5×10^-4M KCl). The velocity of volume-flow within the xylem was 1.5–2 cm hr^-1 (5×10^-4M KCl). ³⁶Cl^--efflux through the cut end of roots preloaded in K³⁶Cl of low concentration exhibits a discontinuity which is explained by addition of two fluxes: efflux of ions concentrated in the xylem (and symplasm) plus efflux from the vacuoles through the xylem.Accumulation of Cl^- by excised roots approaches a maximum level (Jackson and Edwards, 1966). Influx rates remain constant while efflux rates increase with time. It is shown in this paper that the flux of Cl^- through the xylem becomes a large proportion of the influx across the plasmalemma. Flux rates suggest that more than 50% of the Cl^- ions transported to the xylem passed through a vacuole (5×10^-4M KCl; 20–28 hr).