DNA binding and nuclease protection by the HMf histones from the hyperthermophilic archaeon Methanothermus fervidus

The DNA-binding and nuclease-protection properties of the HMf histones from the hyperthermophilic archaeon Methanothermus fervidus have been shown to be consistent with the formation of nucleosome-like structures (NLS). These proteins bind to DNA molecules as short as 20 bp and form complexes that protect DNA fragments from micrococcal nuclease (MNase) digestion that are 30 bp, ∼ 60 bp and multiples of ∼ 60 bp in length. The sequences of 49 of the ∼ 60-bp DNA fragments protected from MNase digestion by HMfA have been determined and their intrinsic curvatures calculated. A circular permutation gel mobility-shift assay was used to determine directly the curvatures for five of these sequences. HMfA bound to intrinsically curved and noncurved DNAs, but exhibited a slight preference for the model curved DNA in binding competitions with a model noncurved DNA. The results obtained are consistent with the concept that the archaeal NLS is analogous, and possibly homologous, to the central core of the eukaryal nucleosome formed by a histone (H3 + H4)2 tetramer. Received: August 11, 1996 / Accepted: November 12, 1996     

乙型肝炎病毒核心抗原基因序列的启动子活性

将核心抗原基因起始码下游的序列,构建两个ＣＡＴ报告基因表达质粒,即ｐＣＡＴＮ Ｉ和ｐＣＡＴＮⅡ,转染ＨｅｐＧ２与ＣＶ－１细胞后,均可使ＣＡＴ报告基因表达,表现出启动子活性。     

Secondary Bile Acid Induced DNA Damage in HT29 Cells: are Free Radicals Involved?

Increased bile acid secretion, as a consequence of a high fat diet, results in the increased production of bile acids that may escape the enterohepatic circulation, and be subsequently metabolised by the colonic micro-flora to form the co-mutagenic and cwarcinogenic secondary bile acids. The potential of the secondary bile acids lithocholate (LOC) and deoxycholate (DOC), to induce DNA damage, in the colonocyte cell line HT29, at physiological concentrations both individually and in a 2:l ratio was assessed. Results indicated significant levels of DNA damage induced by both bile acids, with LOC having the greater DNA damaging capacity. The potential role of vitamin A, and the antioxidant vitamin E, in reducing this damage was determined, over a range of vitamin concentrations. Both vitamins reduced the bile acid induced DNA damage. Vitamin A displayed a dose response relationship, whereas vitamin E reduced DNA damage close to negative control values at all concentrations above 50 μM. These results indicate a protective role for Vitamins A and E, against the DNA damaging capacity of LOC and DOC.     

Inhibition of protein synthesis sensitizes thermotolerant cells to heat shock induced apoptosis

Hyperthermia is a potent inducer of apoptosis in many cell lines. A brief exposure to mildly elevated temperatures elicits a transient state of augmented resistance to subsequent thermal stress. Here we show that a hyperthermic treatment of 43°C for 1 h is sufficient to induce apoptosis in the cell line HL-60. This observation is based on morphologic evaluation and on comet assay results (an extremely sensitive method of detecting and quantifying apoptotic DNA fragmentation in individual cells). The thermotolerance phenomenon was also verified in the same manner by giving the cells a brief 30 min sub-lethal heat conditioning treatment at 43°C followed by a 6 h incubation time prior to the administration of a lethal heat load (43°C for 1 h). We observed a dramatic decrease in resultant apoptoses in the thermotolerized cells in comparison to unconditioned cells. We assessed the necessity of de novo protein synthesis in the protective phenomenon. When the conditioned cells were given a cycloheximide treatment prior to heat conditioning we saw a sensitization of the conditioned cells to secondary thermal injury. This revised version was published online in June 2006 with corrections to the Cover Date.     

Quantitative bioreduction assays for calibrating spore content and viability of commercial Bacillus thuringiensis insecticides

The redox dyes MTT (3-{4,5-dimethylthiazol-2-yl}-2,5-diphenyl tetrazolium bromide, thiazolyl blue) and XTT (sodium 3′- {1-[(phenylamino)-carbonyl]-3,4-tetrazolium}-bis{4-methoxy-6-nitro} benzene sulphonic acid hydrate) were used as dosimetry reporters in liquid (multi-well) and solid support (membrane) assays to estimate spore viability and content of commercial BT products derived from fermentation of Bacillus thuringiensis subsp kurstaki (Btk) and subsp israelensis (Bti). QC tests on five BT products were done using spore, protein and gene contents, and morphology (scanning electron microscopy) as indicators. Spore levels (6–40 × 10⁹ colony forming units (CFU) ml⁻¹) were approximately equivalent when based on International Units (IU) of potency. Spore viability was highly stable over a broad range of temperatures and pHs but germination and growth were restricted (optima: pH ≈ 7.5 and 37°C). Quantitative bioreduction activity (QBA) of MTT and XTT correlated with vegetative cell production. Depending on manipulation of pre-assay conditions, both dyes could discriminate doses from ∼2 to 10⁹ spores (or 10⁻³ to 10⁶ IU). Non-toxic effects of XTT and its formazan product enabled automated collection of data on growth and dose. Solid support assays also reliably estimated product dosage by in situ detection of CFU. With appropriate reference dilutions of microbe-containing products the QBA assays can provide high throughput QC monitoring of product comparisons and field release in aerial spray or water injection applications. Received 18 December 1996/ Accepted in revised form 11 March 1997     

Expression of firefly luciferase gene in Erwinia amylovora

In this study we describe an ef?cient stable genetic transformation of the phytopathogenic bacterium Erwinia amylovora using a recombinant expression vector encoding the ?re?y luciferase gene of Photinus pyralis, which is further controlled by IPTG‐inducible promoter. Stably transformed E. amylovora cells maintain the same infectivity as the wild‐type strain and, after induction with IPTG, produce luciferase. Luminescence produced by the action of luciferase on an exogenous substrate was easily detectable by a simple and rapid bioluminescent assay (BL). The transformed E. amylovora strain maintains the same high emission level, even after passage in pears, until about 15 days post‐infection. Our ?ndings therefore show that the luciferase assay can be conveniently used to follow the bacterial movement in plant tissue and its dissemination in controlled environments.     

Assay of molybdenum cofactor of barley

Conditions for assay of molybdenum cofactor in barley shoot extracts in the presence of molybdate (25 mM N₂MoO₄) and the sulphydryl-group protector, reduced glutathione (5 mM) were optimized. Both total Mo-cofactor (assayed after heat-treatment of cell-free extracts) and ‘free’ Mo-cofactor (assayed in untreated cell-free extracts) were assayed. Compared to control plants grown in the absence of an exogenous nitrogen source total Mo-cofactor levels increased around 70 % when plants were grown for 4 days in the presence of either 15 mM KNO₃ or 15 mM NH₄NO₃. Growth in the presence of 15 mM (NH₄)₂SO₄ did not affect the Mo-cofactor level. Very similar results were seen when plants were transferred to these nitrogen sources for 24 hr after previous growth in the absence of an exogenous nitrogen source. In contrast ‘free’ Mo-cofactor levels of both KNO₃ and NH₄NO₃-treated plants were increased 2-3-fold over untreated controls. Growth in the presence of (NH₄)₂SO₄ did not affect the ‘free’ Mo-cofactor level.     

Comparison of bioassay and enzyme-linked immunosorbent assay for quantification of Spodoptera frugiperda nuclear polyhedrosis virus in soil

Standard curves with known amounts of Spodoptera frugiperda nuclear polyhedrosis virus (NPV) in soil were established with a bioassay and with an enzyme-linked immunosorbent assay (ELISA). The bioassay detected as few as 4 × 10⁴ polyhedral inclusion bodies (PIB)/g sandy soil and <10 PIB/g soils with large amounts of silt or clay. The ELISA detected as few as 360 PIB/g in all three soil types, and absorbance values were inversely related to the amount of clay. Results of the bioassay and ELISA were significantly (P < 0.01) correlated for natural NPV from field samples of silt (R = 0.961) and sandy soil (R = 0.723). Soil samples from Louisiana pastures and corn fields contain up to 7.6 × 10⁴ PIB/g, and 2× 10⁴ PIB/g are commonly present.     

An Improved Antiserum for Sensitive Serologic Detection of Chickpea chlorotic dwarf virus

A Syrian chickpea isolate of Chickpea chlorotic dwarf virus (CpCDV; genus Mastrevirus, family Geminiviridae) was purified and yielded 0.6–0.8 mg of purified virus per kg of infected chickpea tissue. The purified preparations were injected into a rabbit and an antiserum of good quality was obtained and used to evaluate different serological tests for the detection of CpCDV in infected chickpea leaf tissue and extracts. CpCDV was detected in sap dilutions of 1/640 by double‐antibody sandwich enzyme‐linked immunosorbent assay (DAS‐ELISA) and dot‐blot ELISA, and in sap dilutions of 1/1280 by direct antigen‐coating (DAC)‐ELISA using CpCDV immunoglobulin G (IgG) at 0.5 μg/ml. The antiserum was also able to detect the capsid protein of CpCDV by Western blot using raw antiserum at a dilution of 1/2000. The CpCDV raw antiserum (third bleeding) produced had a titre of 1/320 000 when determined by tissue‐blot immunoassay (TBIA); whereas, coating ELISA plates with CpCDV IgG at a concentration of 0.004 μg/ml was enough to detect the virus by DAS‐ELISA in a sap dilution of 1/20 using an enzyme conjugate at a dilution of 1/2000.     

Potential host plants of Corythucha arcuata (Het., Tingidae) in Europe: a laboratory study

Abstract:  The oak lace bug Corythucha arcuata (Say) (Het., Tingidae), native to North America, was found in Europe on Quercus robur L. and other oaks in the spring of 2000. The potential host plant range of this species in Europe and its development time were investigated in a laboratory study. An assay was performed on leaf cuts of different plant species. On the deciduous European oaks ( Q. robur , Quercus pubescens Willd, Quercus petraea (Mattuschka) Liebl., Quercus cerris L.), as well as Rubus ulmifolius Schott. and Rubus idaeus L., most of the lace bugs (>50%) reached the adult stage; on Castanea sativa Mill., Rubus caesius L. and Rosa canina L., a reduced number of individuals (<25%) reached the adult stage. No nymphs survived on Quercus rubra L. (mentioned in literature as a host plant), on the evergreen oaks Quercus suber L. and Quercus ilex L., on Malus domestica Borkh. and four tested maple species. On plant species where the lace bug reached the adult stage, the development time varied from 13 to 27 days. On European deciduous oak species, the development time was longer on leaves taken in late summer (September) than on those of late spring (June); on the contrary, such differences were not observed on Rubus species, and Castanea sativa .