The molecular basis of the sparse fur mouse mutation

The ornithine transcarbamylase-deficient sparse fur mouse is an excellent model to study the most common human urea cycle disorder. The mutation has been well characterized by both biochemical and enzymological methods, but its exact nature has not been revealed. A single base substitution in the complementary DNA for ornithine transcarbamylase from the sparse fur mouse has been identified by means of a combination of two recently described techniques for rapid mutational analysis. This strategy is simpler than conventional complementary DNA library construction, screening, and sequencing, which has often been used to find a new mutation. The ornithine transcarbamylase gene in the sparse fur mouse contains a C to A transversion that alters a histidine residue to an asparagine residue at amino acid 117.     

p53 dynamics control cell fate

Cells transmit information through molecular signals that often show complex dynamical patterns. The dynamic behavior of the tumor suppressor p53 varies depending on the stimulus; in response to double-strand DNA breaks, it shows a series of repeated pulses. Using a computational model, we identified a sequence of precisely timed drug additions that alter p53 pulses to instead produce a sustained p53 response. This leads to the expression of a different set of downstream genes and also alters cell fate: Cells that experience p53 pulses recover from DNA damage, whereas cells exposed to sustained p53 signaling frequently undergo senescence. Our results show that protein dynamics can be an important part of a signal, directly influencing cellular fate decisions.     

Targets for dioxin: genes for plasminogen activator inhibitor-2 and interleukin-1 beta

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD), a widespread environmental contaminant, may elicit its effects by altering gene expression in susceptible cells. Five TCDD-responsive complementary DNA clones were isolated from a human keratinocyte cell line. One of these clones encodes plasminogen activator inhibitor-2, a factor that influences growth and differentiation by regulating proteolysis of the extracellular matrix. Another encodes the cytokine interleukin-1 beta. Thus, TCDD alters the expression of growth regulatory genes and has effects similar to those of other tumor-promoting agents that affect both inflammation and differentiation.     

不同花生品种B06基因的克隆与序列分析

Dof（DNA binding with one finger）转录因子是一类植物特有的、进化上高度保守的基因家族,对植物多方面的生理过程均发挥调控作用。根据Dof家族中的一个B06基因的cDNA保守序列设计引物,对8个品种花生的B06基因进行PCR扩增克隆相似基因,并测定序列。实验成功克隆出四粒红和073103的完整...     

Scanometric DNA array detection with nanoparticle probes

A method for analyzing combinatorial DNA arrays using oligonucleotide-modified gold nanoparticle probes and a conventional flatbed scanner is described here. Labeling oligonucleotide targets with nanoparticle rather than fluorophore probes substantially alters the melting profiles of the targets from an array substrate. This difference permits the discrimination of an oligonucleotide sequence from targets with single nucleotide mismatches with a selectivity that is over three times that observed for fluorophore-labeled targets. In addition, when coupled with a signal amplification method based on nanoparticle-promoted reduction of silver(I), the sensitivity of this scanometric array detection system exceeds that of the analogous fluorophore system by two orders of magnitude.     

表观遗传变异与作物遗传改良

植物天然群体中存在大量遗传变异,这些变异是随机突变和自然选择的结果,也是物种赖以生存和进化的原料.此外,不同植物种间乃至属间的天然远缘杂交是经常发生的事件,也是新种形成的重要方式,而远缘杂交为高度分歧的物种之间的基因交流提供了机会,因此也是产生新的遗传变异的重要途径.近年来的大量研究表明,植物天然群体中还存在一类不基于DNA序列差异的变异,被称为表观遗传变异(epigeneticvariation).植物发生远缘杂交以及此后的多倍体化过程可以产生大量的表观遗传变异,其遗传行为不能用经典遗传规律解释.表观遗传变异的另外一个重要来源是环境中的各种生物和非生物胁迫.研究较深入的表观遗传变异主要是编码基因和转座子DNA甲基化水平和模式的改变,但可以推测与之相关的组蛋白修饰和染色质结构也可能发生变化.目前对此类表观遗传变异的分子机理尚缺乏深入研究,但不难想像可能与各类non-coding RNA有关.这些表观遗传变异的后果是基因表达的大规模改变并由此产生新表型.作物远缘杂交育种实践表明,这些不能用经典遗传学理论解释的变异中蕴含许多在育种上有重要价值的变异并可能与杂种优势密切相关,对它们的产生机理和遗传规律的深入解析将有助于其在作物改良中的有效利用.     

Alteration of alpha 1 Na+,K(+)-ATPase 86Rb+ influx by a single amino acid substitution

The sodium- and potassium-dependent adenosine triphosphatase (Na+,K(+)-ATPase) maintains the transmembrane Na+ gradient to which is coupled all active cellular transport systems. The R and S alleles of the gene encoding the Na+,K(+)-ATPase alpha 1 subunit isoform were identified in Dahl salt-resistant (DR) and Dahl salt-sensitive (DS) rats, respectively. Characterization of the S allele-specific Na+,K(+)-ATPase alpha 1 complementary DNA identified a leucine substitution of glutamine at position 276. This mutation alters the hydropathy profile of a region in proximity to T3(Na), the trypsin-sensitive site that is only detected in the presence of Na+. This mutation causes a decrease in the rubidium-86 influx of S allele-specific sodium pumps, thus marking a domain in the Na+,K(+)-ATPase alpha subunit important for K+ transport, and supporting the hypothesis of a putative role of these pumps in hypertension.     

Grain boundary strengthening in alumina by rare earth impurities

Impurity doping often alters or improves the properties of materials. In alumina, grain boundaries play a key role in deformation mechanisms, particularly in the phenomenon of grain boundary sliding during creep at high temperatures. We elucidated the atomic-scale structure in alumina grain boundaries and its relationship to the suppression of creep upon doping with yttrium by using atomic resolution microscopy and high-precision calculations. We find that the yttrium segregates to very localized regions along the grain boundary and alters the local bonding environment, thereby strengthening the boundary against mechanical creep.     

Radioprotection by mitotic inhibitors and mercaptoethylamine

In the mouse, chemical interference with cellular proliferation alters the radiosensitivity of the bone marrow, and this results in protection from otherwise lethal x-irradiation. When intestinal damage is minimized by appropriate timing and dosage, many mitotic inhibitors increase radioresistance and enhance the protective effects of mercaptoethylamine.     

Streptonigrin: effect on the first meiotic metaphase of the mouse egg

Streptonigrin, an antibiotic and antitumor agent, alters the chromosomes of the mouse ovum during meiosis. Agglutination of bivalents or achromatic gaps and breaks occurred in the larger pairs both in vitro and in vivo. This newly detected cytogenetic effect suggests that such agents can gain access to developing mammalian ova and destroy the normal progress of meiosis.     

Coherin: a new peptide of the bovine neurohypophysis with activity on gastrointestinal motility

A factor with potent activity in the regulation of mammalian gastrointestinal motor function has been isolated from the bovine posterior pituitary gland by a process allowing minimal dissociation of neurophysin-bound complexes and the separation of free unbound peptides. This substance alters the frequency, amplitude, rhythm, and duration of peristaltic contraction.     

Hybridization experiments: evidence of dissociation equilibrium in hemerythrin

Partial succinylation of hemerythrin alters its electrophoretic mobility even though it remains an octameric macromolecule. Mixtures of this modified protein and unmodified hemerythrin generate species of intermediate electrophoretic mobility. Such behavior provides strong evidence that the octameric macromolecule is in mobile equilibrium with monomeric subunits.     

Desmosine biosynthesis: nature of inhibition by D-penicillamine

Administration of D-penicillamine and lathyrogens such as beta-amino-propionitrile to animals markedly alters connective tissue by preventing the normal cross-linkage of elastin and collagen. It had been shown that beta-aminopropionitrile blocks the cross-linkage of elastin and collagen by preventing the initial step in cross-linkage: the conversion of lysine in peptide linkage to alpha-amino adipic-delta-semialdehyde. We show that penicillamine acts after the initial step, causing the accumulation of an elastin rich in alpha-amino adipic-delta-semialdehyde.     

Aging, chromatin, and food restriction--connecting the dots

Model organisms such as yeast have proved exceptionally valuable for revealing new information about the molecular pathways involved in the aging of cells. In her Perspective, Campisi comments on new work showing that caloric restriction increases longevity in yeast by activating the SIR2 gene, which alters the compactness of chromatin and thus regulates gene expression (Lin et al.).     

多媒体技术在预科生汉语教学中的应用

在教学过程中运用计算机多媒体技术,已成为当今时代的潮流.多媒体技术应用到预科生汉语课堂教学中,改变了传统的课堂教学方法,大大提高了教学实效,对加快预科生汉语教学的改革有促进作用.本文主要从多媒体在预科生汉语教学中的作用及运用两个方面进行了探究.     

Zinc deficiency in murine milk underlies expression of the lethal milk (lm) mutation

The inability of nursing pups to survive on milk of mice homozygous for the recessive mutation, lethal milk (lm), is correlated with a reduction in zinc levels of both milk and pup carcass. Administration of zinc to pups nursing on lmlm dams reduces the observed mortality and morbidity. It is suggested that lm alters zinc transport from maternal blood to milk and that its study may provide useful information for understanding the rare human disease, acrodermatitis enteropathica.     

Interaction Between the Antibiotic Trichothecenes and the Higher Plant Baccharis megapotamica

The Brazilian shrub Baccharis megapotamica contains significant amounts of antibiotic trichothecenes. When these plants are grown in the United States, they are devoid of the mycotoxins. Feeding experiments with fungus-produced trichothecenes show that Baccharis megapotamica absorbs, translocates, and chemically alters these compounds to ones with structures analogous to those found in the plant in its native habitat. The mycotoxins, which have no apparent ill effect in Baccharis megapotamica, kill tomatoes, peppers, and artichokes.     

Amantadine: neuromuscular blockade by suppression of ionic conductance of the acetylcholine receptor

Amantadine hydrochloride decreases the sensitivity of denervated mammalian muscle to iontophoretically applied acetylcholine. The drug depresses the amplitude of the end-plate current and reverses the slope of the relation between half-decay time and membrane potential suggesting that it alters the ionic conductance that is mediated by the acetylcholine receptor. Binding studies confirm that amantadine acts on the ion conductance modulator rather than the acetylcholine receptor.     

Autoradiographic evidence for a calcitonin receptor on testicular Leydig cells

Previous studies have indicated that there is a relation between testicular function and adequate concentrations of zinc in testicular cells, and that calcitonin alters cellular zinc transfer in the testis. The present studies provide autoradiographic evidence that calcitonin binds in vivo to the cell membrane of testicular Leydig cells. The data thus confirm the presence of the testicular cell membrane calcitonin receptors that were previously demonstrated indirectly by Scatchard analysis of data collected from binding studies.     

Vasoactive intestinal polypeptide and muscarinic receptors: supersensitivity induced by long-term atropine treatment

Long-term treatment of rats with atropine induced large increases in the numbers of muscarinic receptors and receptors for vasoactive intestinal polypeptide in the salivary glands. Since receptors for vasoactive intestinal polypeptide coexist with muscarinic receptors on the same neurons in this preparation, the results suggest that a drug that alters the sensitivity of one receptor may also affect the sensitivity of the receptor for a costored transmitter and in this way contribute to the therapeutic or side effects of the drugs.