956 resultados para CODON USAGE


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In a number of species, individuals showing lateralized hand/paw usage (i.e. the preferential use of either the right or left paw) compared to ambilateral individuals have been shown to be more proactive in novel situations. In the current study we used an established test to assess preferential paw usage in dogs (the Kong test) and then compared the performance of ambilateral and lateralized dogs as well as left- vs. right-pawed dogs in a novel manipulative problem solving task. Results showed an equal proportion of ambilateral and lateralized dogs but contrary to predictions non-lateralized dogs were faster at accessing the apparatus in test trials. No differences emerged between right- and left-pawed dogs. Results are discussed in relation to previous studies on lateralization. © 2013 Elsevier B.V.

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Although the genetic code is generally viewed as immutable, alterations to its standard form occur in the three domains of life. A remarkable alteration to the standard genetic code occurs in many fungi of the Saccharomycotina CTG clade where the Leucine CUG codon has been reassigned to Serine by a novel transfer RNA (Ser-tRNACAG). The host laboratory made a major breakthrough by reversing this atypical genetic code alteration in the human pathogen Candida albicans using a combination of tRNA engineering, gene recombination and forced evolution. These results raised the hypothesis that synthetic codon ambiguities combined with experimental evolution may release codons from their frozen state. In this thesis we tested this hypothesis using S. cerevisiae as a model system. We generated ambiguity at specific codons in a two-step approach, involving deletion of tRNA genes followed by expression of non-cognate tRNAs that are able to compensate the deleted tRNA. Driven by the notion that rare codons are more susceptible to reassignment than those that are frequently used, we used two deletion strains where there is no cognate tRNA to decode the rare CUC-Leu codon and AGG-Arg codon. We exploited the vulnerability of the latter by engineering mutant tRNAs that misincorporate Ser at these sites. These recombinant strains were evolved over time using experimental evolution. Although there was a strong negative impact on the growth rate of strains expressing mutant tRNAs at high level, such expression at low level had little effect on cell fitness. We found that not only codon ambiguity, but also destabilization of the endogenous tRNA pool has a strong negative impact in growth rate. After evolution, strains expressing the mutant tRNA at high level recovered significantly in several growth parameters, showing that these strains adapt and exhibit higher tolerance to codon ambiguity. A fluorescent reporter system allowing the monitoring of Ser misincorporation showed that serine was indeed incorporated and possibly codon reassignment was achieved. Beside the overall negative consequences of codon ambiguity, we demonstrated that codons that tolerate the loss of their cognate tRNA can also tolerate high Ser misincorporation. This raises the hypothesis that these codons can be reassigned to standard and eventually to new amino acids for the production of proteins with novel properties, contributing to the field of synthetic biology and biotechnology.

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Ce travail consiste à décrire l’usage des pronoms relatifs dans le français de trois scripteurs de l’époque de la Nouvelle-France afin de vérifier si la variation existante en français moderne y était également présente. Pour ce faire, une description de la norme des pronoms relatifs en français moderne et historique a été élaborée, et une étude de corpus (corpus MCVF annoté syntaxiquement, Martineau et coll., 2005-2010) comprenant des textes de scripteurs français et canadiens (François Gendron, Marie-Andrée Regnard Duplessis et Marie Morin) a été réalisée. L’analyse de 2521 occurrences a révélé que la variation présente en français moderne existait déjà à l’époque et y était même un peu plus importante, que l’usage des scripteurs est conforme aux attestations et descriptions présentes dans les documents historiques et de l’époque, et que les systèmes moderne et historique (XVIIe et XVIIIe siècles) des pronoms relatifs sont similaires.

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The potential of online learning has long afforded the hope of providing quality education to anyone, anywhere in the world. The recent development of Massive Open Online Courses (MOOCs) heralded an exciting new breakthrough by providing free academic instruction and professional skills development from the world’s leading universities to anyone with the sufficient resources to access the internet. The research in Advancing MOOCs for Development Initiative study was designed to analyze the MOOC landscape in developing countries and to better understand the motivations of MOOC users and afford insights on the advantages and limitations of MOOCs for workforce development outcomes. The key findings of this study challenge commonly held beliefs about MOOC usage in developing countries, defying typical characterizations of how people in resource constrained settings use technology for learning and employment. In fact, some of the findings are so contrary to what has been reported in the U.S. and other developed environments that they raise new questions for further investigation.

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The usage of information and communication technologies has been growing among students and teachers. In order to improve the use of the Internet as a tool to support teaching and learning it is necessary to understand the Internet usage habits of students. Thus, a study was conducted with 1397 students from five schools of the Polytechnic of Porto. The data was collected through an online questionnaire abd was analized by age range, gender and scientific field. In this paper,gender differences are analyzed and presented in 3 dimensions: type of Internet usage, communication tools and the role of the Internet tools in education.

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When assessing investment options, investors focus on the graphs of annual reports, despite lack of auditing. If poorly constructed, graphs distort perceptions and lead to inaccurate decisions. This study examines graph usage in all the companies listed on Euronext Lisbon in 2013. The findings suggest that graphs are common in the annual reports of Portuguese companies and that, while there is no evidence of Selectivity Distortion, both Measurement and Orientation Distortions are pervasive. The study recommends the auditing of financial graphs, and urges preparers and users of annual reports to be wary of the possibility of graph distortion.

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As investors and other users of annual reports often focus their attention on graphs, it is important that they portray accurate and reliable information. However, previous studies show that graphs often distort information and mislead users. This study analyses graph usage in annual reports from the 52 most traded Norwegian companies. The findings suggest that Norwegian companies commonly use graphs, and that the graph distortions, presentational enhancement and measurement distortion, are present. No evidence of selectivity was found. This study recommends development of guidelines for graphical disclosure, and advises preparers and users of annual reports to be aware of misleading graphs.

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La cigarette électronique (E-cigarette) est un phénomène relativement récent qui est en train de prendre une ampleur inattendue, surtout chez les jeunes. La littérature scientifique à ce sujet est encore relativement rare et surtout centrée sur les taux de prévalence. Bien que théoriquement conçues pour les adultes qui voudraient arrêter de fumer, les adolescents sont devenus un public cible pour ces produits, dont beaucoup n'ayant jamais fumé de cigarettes traditionnelles. Du point de vue de la santé publique, une des préoccupations majeures correspond au possible effet indésirable des cigarettes électroniques d'inciter les jeunes au tabagisme. Beaucoup de questions restent sans réponse quant à l'impact des cigarettes électroniques sur la santé publique. Par exemple, il n'est pas clair si les cigarettes électroniques sont juste une nouveauté que les jeunes n'essayent qu'une fois ou si elles ont le potentiel de concurrencer les cigarettes traditionnelles. Même si les cigarettes électroniques sont disponibles en Suisse depuis près de 10 ans, peu de données existent quant aux motifs de consommation des jeunes, les modalités de consommation, les effets recherchés et la perception de leur nocivité.

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Langattomien lähiverkkojen yleistyessä nopeasti suurten verkkojen teknologiana käyttösääntöjen valvonta tulee tarpeelliseksi. Tässä työssä kuvataan, kuinka käyttäjät voidaan pakottaa noudattamaan käyttösääntöjä julkisissa WLAN-verkoissa. Työssä käsiteltävät ongelmat koskevat menetelmiä epäluotettavien DHCP-palvelinten paljastamiseksi sekä omia IP-osoitteita käyttävien käyttäjien paljastamiseksi tilanteissa, jolloin IP-osoite ei ole virallisen DHCP-palvelimen myöntämä. Jokaisen menetelmän kohdalla pohditaan, kuinka tällaisia käyttäjiä voidaan estää rikkomasta käyttösääntöjä. Lisäksi pohditaan keskitetyn tietojen keruun hyödyntämistä kuvattujen tehtävien suorittamiseksi. Esitetyt ratkaisut on erityisesti suunniteltu testiverkkoa varten, mutta yleiset ideat ovat toimivia missä tahansa langattomassa verkossa.