RESUMEN
Eley-Rideal (ER) reactions involving neutral atoms heavier than hydrogen reacting with adsorbed atoms of similar mass were first observed in recent molecular beam experiments by Zaharia et al. [Phys. Rev. Lett. 113, 053201 (2014)]. Through analysis of two types of measurements, they obtained different estimations for the N-O ER reaction cross section, one of which is unexpectedly high. This was qualitatively accounted for by invoking a secondary effect whereby the presence of N adatoms on the surface acted to "shield" O adatoms from prompt recombinative desorption. We apply a rate equation model that includes two ER processes involving different adsorbed species (N-Oad and N-Nad) and an N-adsorption process to the full-beam exposure subset of the experimental data in order to study the reaction kinetics. Values for the individual reaction cross sections are derived. The measured N2 response can be well described by the model, but it is insufficient to completely describe the NO response. Modeling of different exposures is used to evaluate the qualitative picture presented by Zaharia et al.
RESUMEN
We report on the mechanisms of hydrogen-induced blistering of multilayer coatings. Blister formation is a result of highly localized delamination occurring at the two outermost metal-on-silicon interfaces. The number, size, and type of blisters formed varied depending on the composition and ion energy of the incident flux. The results are explained in terms of the multilayer structure being simultaneously susceptible to blistering via two independent mechanisms. A high density of small blisters developed when relatively energetic (several 100 eV) ions were present. Independently, a hydrogenation process that was facilitated by the presence of a small flux of low energy ions (≤ 50 eV) induced a low density of large blisters.
Asunto(s)
Química Física/métodos , Hidrógeno , Metales/química , Silicio/química , Hidrógeno/química , Iones , Microscopía de Fuerza Atómica/métodos , Microscopía Electrónica de Transmisión/métodos , Molibdeno/química , Propiedades de Superficie , Factores de TiempoRESUMEN
We have simulated CF scattering from Si(100) using the molecular dynamics method. Translational energy loss spectra are presented. The shape of the energy loss distribution as a result of internal energy release is analyzed. At the classical turning point, the internal energy of the molecule is mainly in the form of rotational energy. The strong rotational excitation results in additional molecule-surfaces interactions during the latter half of the collision. These additional collisions permit some molecules that initially gain internal energy exceeding the bond strength to ultimately survive the collision process via rotational de-excitation. The rotational motion exhibited by surviving molecules is determined by the combination of the molecular axis orientation and the local surface structure during the collision process. The rotation planes of the surviving molecules are preferentially aligned with the surface normal (cartwheel-like and propeller-like motions). In this study, propeller-like motion of the surviving molecules is predicted. The majority of surviving molecules exhibit a cartwheel-like motion. However, molecules that gain a propeller-like rotation exhibit a much better alignment of their planes-of-rotation compared with molecules exhibiting cartwheel-like motion.
Asunto(s)
Modelos Teóricos , Silicio/química , Conformación Molecular , Rotación , Estereoisomerismo , Propiedades de SuperficieRESUMEN
To understand the RNA expression in response to acid stress of Helicobacter pylori in genomic scale, a microarray membrane containing 1,534 open reading frames (ORFs) from strain 26695 was used. Total RNAs of H. pylori under growth conditions of pH 7.2 and 5.5 were extracted, reverse transcribed into cDNA, and labeled with biotin. Each microarray membrane was hybridized with cDNA probe from the same strain under two different pH conditions and developed by a catalyzed reporter deposition method. Gene expression of all ORFs was measured by densitometry. Among the 1,534 ORFs, 53 ORFs were highly expressed (> or = 30% of rRNA control in densitometry ratios). There were 445 ORFs which were stably expressed (<30% of rRNA in densitometry) under both pH conditions without significant variation. A total of 80 ORFs had significantly increased expression levels at low pH, while expressions of 4 ORFs were suppressed under acidic condition. The remaining 952 ORFs were not detectable under either pH condition. These data were highly reproducible and comparable to those obtained by the RNA slot blot method. Our results suggest that microarray can be used in monitoring prokaryotic gene expression in genomic scale.
Asunto(s)
Ácidos/farmacología , Adaptación Biológica/genética , Perfilación de la Expresión Génica/métodos , Helicobacter pylori/genética , Análisis de Secuencia por Matrices de Oligonucleótidos/métodos , Regulación hacia Abajo , Genoma Bacteriano , Concentración de Iones de Hidrógeno , Sistemas de Lectura Abierta , ARN Bacteriano/aislamiento & purificación , ARN Mensajero/aislamiento & purificación , Sensibilidad y Especificidad , Regulación hacia ArribaRESUMEN
We describe the isolation and characterization of three new biosynthetic genes-ARG4, ADE1, and URA3-from the methylotrophic yeast Pichia pastoris. The predicted products of the genes share significant sequence similarity to their Saccharomyces cerevisiae counterparts, namely argininosuccinate lyase, PR-aminoimidazolesuccinocarboxamide synthase, and orotidine-5'-phosphate decarboxylase, respectively. Along with the previously described HIS4 gene, each gene was incorporated as the yeast selectable marker into a set of shuttle vectors designed to express foreign genes in P. pastoris. In addition, we have constructed a series of host strains containing all possible combinations of ade1, arg4, his4, and ura3 auxotrophies to be used with these new vectors.
Asunto(s)
Proteínas Fúngicas/genética , Pichia/genética , Secuencia de Aminoácidos , Argininosuccinatoliasa/genética , Clonación Molecular , ADN de Hongos/química , ADN de Hongos/genética , Proteínas Fúngicas/metabolismo , Genes Fúngicos/genética , Prueba de Complementación Genética , Marcadores Genéticos , Metanol/metabolismo , Datos de Secuencia Molecular , Mutación , Orotidina-5'-Fosfato Descarboxilasa/genética , Péptido Sintasas/genética , Pichia/enzimología , Plásmidos/genética , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Saccharomyces cerevisiae/enzimología , Saccharomyces cerevisiae/genética , Análisis de Secuencia de ADN , Homología de Secuencia de AminoácidoRESUMEN
Testing for gene mutations that confer susceptibility to adult-onset disorders has potential benefits, but these must be balanced against the psychological harms, if any. We review published findings on the psychological effects of such testing, focusing on Huntington's disease, which has the most available data, and the hereditary cancer syndromes. Most of the evidence suggests that non-carriers and carriers differ significantly in terms of short-term, but not long-term, psychological adjustment to test results. The psychological impact of genetic testing depends more on pretest psychological distress than the test result itself.
Asunto(s)
Predisposición Genética a la Enfermedad/genética , Pruebas Genéticas/psicología , Adaptación Psicológica , Adulto , Heterocigoto , Humanos , Enfermedad de Huntington/genética , Mutación/genética , Síndromes Neoplásicos Hereditarios/genética , Estrés Psicológico/psicologíaRESUMEN
Women with a family history consistent with a hereditary breast/ovarian cancer syndrome are at significantly increased risk for ovarian cancer. Prophylactic oophorectomy is an option for high-risk women. This study explores the psychosexual impact of prophylactic oophorectomy. A qualitative methodology was selected as most appropriate as no previous research has examined this issue. In-depth interviews were conducted with fourteen women, between 4 months and 7 years after prophylactic oophorectomy. Of these, six were pre- and eight were postmenopausal at the time of oophorectomy. Even though individual differences were observed, a majority view was expressed on several issues. All but one participant reported being satisfied with their decision to undergo oophorectomy. Women emphasised that the procedure had decreased their anxiety about developing ovarian cancer. Postmenopausal women reported no negative impact on their libido. Amongst premenopausal women all but one commenced hormone replacement therapy (HRT) following surgery and, in these women, HRT appeared to mitigate the sexual impact of the procedure. Premenopausal women reported unmet information needs both before and after the procedure, including the effects of surgical menopause and the link between HRT and breast cancer. This exploratory study suggests that prophylactic oophorectomy is a psychologically acceptable risk reduction strategy in high-risk women.
Asunto(s)
Salud Mental , Neoplasias Ováricas/prevención & control , Ovariectomía/psicología , Sexualidad , Adulto , Anciano , Toma de Decisiones , Femenino , Predisposición Genética a la Enfermedad , Terapia de Reemplazo de Hormonas , Humanos , Menopausia , Persona de Mediana Edad , Neoplasias Ováricas/genética , Neoplasias Ováricas/cirugía , Satisfacción del Paciente , Factores de RiesgoRESUMEN
The conserved nature of the transcriptional machinery between yeast and higher eukaryotes makes the yeast system suitable to genetically dissect the signal transduction pathway of steroid hormone receptors. This report describes the yeast protein, SPT6, which modulates the transcriptional activity of the human estrogen receptor (hER) by affecting the C-terminal activation domain. It is demonstrated that SPT6 is able to potentiate hER activity in yeast and also in mammalian cells in vivo. SPT6 interacts specifically with the hormone-binding domain of hER in vivo. The in vivo studies are substantiated by specific protein-protein interactions between SPT6 and the hormone-binding domain of hER in vitro. Therefore, the data suggest that the SPT6 protein may be involved in signal transmission of ER by acting as a coactivator.
Asunto(s)
Proteínas Fúngicas/farmacología , Proteínas Nucleares/farmacología , Receptores de Estrógenos/efectos de los fármacos , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/genética , Transducción de Señal/efectos de los fármacos , Transcripción Genética/efectos de los fármacos , Animales , Secuencia de Bases , Sitios de Unión , Línea Celular , Chlorocebus aethiops , Estrógenos/metabolismo , Chaperonas de Histonas , Datos de Secuencia Molecular , Unión Proteica , Receptores de Estrógenos/química , Transducción de Señal/fisiología , Especificidad de la Especie , Estimulación Química , Factores de Transcripción/metabolismo , Factores de Elongación TranscripcionalRESUMEN
Steroid hormones, vitamins, and thyroid hormone are potent chemical messengers that exert dramatic effects on cell differentiation, homeostasis, and morphogenesis. These molecules, though diverse in structure, share a mechanistically similar mode of action. The effector molecules diffuse across cellular membranes and bind to specific high affinity receptors in the target cell nuclei. This interaction results in the conversion of an inactive receptor to one that can interact with the regulatory regions of target genes and modulate the rate of transcription of specific gene sets. The recent cloning and characterization of the functional receptors for these hormones has been enlightening as to the individual steps involved in steroid signal transduction. In addition, emerging evidence suggests that receptor function can be influenced by cell and promoter context indicating that it may be possible to develop tissue specific or tissue-restricted drugs. The concept that a single receptor can modulate gene transcription in a cell-specific manner is of great medical and pharmaceutical importance. The focus of this review is to highlight the recent developments in the steroid receptor field and to illustrate the novel approaches been undertaken to identify novel pharmaceuticals.
Asunto(s)
Esteroides/farmacología , Animales , Humanos , Receptores de Superficie Celular/química , Receptores de Superficie Celular/efectos de los fármacos , Receptores Citoplasmáticos y Nucleares/química , Receptores Citoplasmáticos y Nucleares/efectos de los fármacos , Esteroides/químicaRESUMEN
There are two basic types of receptor transducing systems: those which utilize membrane bound receptors and are activated at the cell surface by the appropriate hormone and transmit their signal to the internae of the cell via a second messenger (i.e. cAMP), and those that utilize internal, cytoplasmic or nuclear receptors (intracellular receptors) which upon activation by hormones interact directly with DNA and alter the genetic program of a cell. This review focuses on the mechanism of action of these intracellular receptors and discusses how such an understanding is expected to facilitate the discovery of new therapeutic agents.
Asunto(s)
Biotecnología , Núcleo Celular/metabolismo , Receptores de Superficie Celular/metabolismo , Animales , Diseño de Fármacos , Humanos , Modelos Biológicos , Receptores de Superficie Celular/antagonistas & inhibidores , Transducción de SeñalRESUMEN
Yeasts are attractive hosts for the production of heterologous proteins. Unlike prokaryotic systems, their eukaryotic subcellular organization enables them to carry out many of the post-translational folding, processing and modification events required to produce "authentic" and bioactive mammalian proteins. In addition, they retain the advantages of a unicellular microorganism, with respect to rapid growth and ease of genetic manipulation. The vast majority of yeast expression work has focused on the well-characterized baker's yeast Saccharomyces cerevisiae. However, with the development of DNA transformation technologies, a growing number of non-Saccharomyces yeasts are becoming available as hosts for recombinant polypeptide production. These include Hansenula polymorpha, Kluyveromyces lactis, Pichia pastoris, Schizosaccharomyces pombe, Schwanniomyces occidentalis and Yarrowia lipolytica. The performance of these alternative yeast expression systems is reviewed here relative to S. cerevisiae, and the advantages and limitations of these systems are discussed.
Asunto(s)
Clonación Molecular , Proteínas/genética , Saccharomyces cerevisiae/genética , Levaduras/genética , Animales , Humanos , Plásmidos , Regiones Promotoras Genéticas , Biosíntesis de Proteínas , Proteínas/aislamiento & purificación , Proteínas Recombinantes/biosíntesis , Proteínas Recombinantes/aislamiento & purificaciónRESUMEN
An enrichment scheme using nystatin was designed for the isolation of auxotrophic mutants from the diploid-alkane-utilizing yeast Candida tropicalis. A collection of 194 auxotrophs representing 7 phenotypes was isolated. One class of mutants was identified as having a defect in histidinol dehydrogenase activity and a second class of mutants was identified as having a defect in orotidine monophosphate decarboxylase activity. These strains are good candidates to be carrying mutations corresponding to the HIS4 and URA3 genes of Saccharomyces cerevisiae.
Asunto(s)
Candida/genética , Oxidorreductasas de Alcohol/genética , Candida/enzimología , Candida/aislamiento & purificación , Marcadores Genéticos , Mutación , Micología/métodos , Nistatina , Orotidina-5'-Fosfato Descarboxilasa/genética , Saccharomyces cerevisiae/genética , Especificidad de la EspecieRESUMEN
We developed the alkane and fatty-acid utilizing yeast Candida tropicalis as a host for DNA transformations. The system is based on an auxotrophic mutant host of C. tropicalis which is defective in orotidine monophosphate decarboxylase (ura3). The ura3 host was isolated by mutagenesis and a double-selection procedure that combined nystatin enrichment selection and 5-fluoro-orotic acid resistance selection. As a selectable marker, we isolated and characterized the C. tropicalis URA3 gene. Plasmid vectors that contained the C. tropicalis URA3 gene transformed the C. tropicalis mutant host at a frequency of 10(3) to 10(4) transformants per micrograms of plasmid DNA. Vectors that contained the Saccharomyces cerevisiae URA3 gene could not transform C. tropicalis. DNA transfer was accomplished by modified versions of either spheroplast generation (CaCl2-polyethylene glycol)-fusion or cation (LiCl) procedures developed for S. cerevisiae. Plasmid vectors that had been cut within the C. tropicalis URA3 fragment integrated by homologous recombination at the URA3 locus.
Asunto(s)
Candida/genética , Carboxiliasas/genética , Genes Fúngicos , Orotidina-5'-Fosfato Descarboxilasa/genética , Saccharomyces cerevisiae/genética , Transformación Genética , ADN de Hongos/genética , ADN de Hongos/aislamiento & purificación , Vectores Genéticos , Mutación , Plásmidos , Mapeo Restrictivo , Saccharomyces cerevisiae/enzimologíaRESUMEN
The advantages of Hansenula polymorpha as a new yeast expression system are discussed in terms of the powerful and regulatable methanol oxidase promoter and the organism's ability to grow on cheap carbon sources. The development of techniques for conventional genetic analysis is described. A total of 218 mutants have been assigned to 62 complementation groups, three genes have been found to be linked forming the first linkage group in this organism. Methods for molecular transformation have been developed allowing the expression of heterologous genes. The disruptive integration and expression of the neomycin phosphotransferase is described.