Le nucléole est un compartiment spécialisé où les ARN ribosomiques (ARNr) sont transcrits, maturent et sont assemblés pour former les sous-unités du ribosome. Chez la levure Saccharomyces cerevisiae, l'ADN ribosomique est transcrit en un précurseur de 35S qui code pour l'ARN 18S de la petite sous-unité ribosomique ainsi que les ARN 5.8S et 25S de la grande sous-unité du ribosome. Le nucléole contient environ 100 petites ribonucléoprotéines nucléolaires (snoRNP), qui sont constituées d'une molécule d'ARN (snoRNA) et de quelques protéines. Les snoRNA forment deux grandes familles: les familles à boîtes C/D et à boîtes H/ACA. Ces snoRNA servent de guides pour des modifications post-transcriptionnelles des ARNr, i.e. méthylation du ribose en 2'-OH (C/D) et pseudouridylation (H/ACA). Le snoRNA va d'abord s'apparier à l'ARNr et les protéines associées au snoRNA vont effectuer les modifIcations. Certains de ces snoRNA sont requis pour des réactions de clivage du précurseur des ARNr; ces clivages servent à éliminer des régions espaceur dans le pré-ARNr. Les snoRNP de la famille H/ACA contiennent quatre protéines essentielles, Cbf5p, Garlp, Nhp2p, et Nop10p. Contrairement aux autres snoRNA H/ACA, snR30 n'a pas de cible pour la pseudouridylation. Par contre, le snoRNA snR30 est essentiel dans les étapes de maturation menant à la production de l'ARNr 18S, ce qui n'est pas le cas des autres snoRNA H/ACA. Le but de cette recherche est de purifier le complexe snR30 et d'identifier ses composantes protéiques. snR30 possède probablement des protéines qui lui sont spécifiques, en plus des quatre protéines H/ACA, et qui contribuent à ses propriétés fonctionnelles uniques, à savoir, son rôle dans la maturation des ARNr. Afin de purifier snR30, l'aptamère SI a été utilisé et le contenu protéique de snR30 identifié par spectrométrie de masse. L'aptamère SI est une courte séquence d'acides nucléiques qui possède une haute affinité et spécificité pour la streptavidine. Cette séquence a été introduite par mutagenèse dirigée par PCR dans la séquence codant pour SNR30 et cette construction S1-SNR30 a été exprimée in vivo à partir d'un vecteur d'expression de levure. Il a ensuite été possible de purifier le complexe S1-snR30 par chromatographie d'affinité utilisant des billes couplées à la streptavidine. Le snoRNA SI-snR30 est associé non seulement aux protéines H/ACA Garlp et Nhp2p mais aussi à plusieurs autres protéines. Ces protéines doivent maintenant être identifiées afin de les caractériser et élucider leur(s) rôle(s) dans la maturation des ARNr. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : SnR30, Nucléole, Ribosome, ARN ribosomique (ARNr), Petit ARN nucléolaire (snoRNA), petite ribonucléoprotéine nucléolaire (snoRNP), H/ACA, Chromatographie d'affinité, Aptamère.

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published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Nitric oxide (NO) is one of the most important air pollutants in atmosphere mainly emitted from combustion exhaust gas. In this research, a biotrickling filter was designed and operated to remove this pollutant from an air stream using bacteria extracted from the sewage sludge of a municipal sewage-treatment plant. The bacteria were cultured and enriched by either petri dish’s cultivation or liquid cultivation. The adsorption capacity of the ceramic material, which was used as the packing material, was determined to be 34 g-NO/L under 37℃. However, the saturated adsorption capacity of the packing material with the recycling solution is 236 mg-NO/L under the operation temperature 37℃.The result suggested that the microporous structure of the ceramic material not the humidity is the main contributor to the ceramic material adsorption capacity. Both the ceramic material adsorption capacity and the removal capacity of the liquid were limited and saturated in 540 min and 2 min operation, respectively. To obtain the best operation conditions for the biotrickling filter, orthogonal experiments (L9 (34)) were designed. The experimental data were analyzed by the signal to noise (S/N) ratio and ANOVA. The optimal conditions of the biotrickling filter occurred at a temperature of 40℃, a pH of 8.00.05 and a chemical oxygen demand (COD) of 165 mg/L in the recycled water with no oxygen in the system. Inlet oxygen concentration was found to be the most significant factor of the biotrickling filter that has a significant negative effect on the NO removal efficiency. The DNA sequencing of four clones of bacteria showed 93-98% similarity to Pseudomonas mendocina strain. This strain has been analysed by full gene sequencing and proved to be a brand-new strain named as Pseudomonas mendocina DLHK. This strain can transfer nitrate to organic nitrogen. This result indicated the assimilation nitrogen process in this system and suggested that the main nitrogen removal capacity in this system was through biological function. Through the isotope experimental analysis, two intermediate products (15NO and 15N2O) have been found during the biological process of the system by using quantitative gas analysis (QGA). These results indicated the denitrification function in this biotrickling filter. A model was developed to explain the biological process in the biotrickling filter. The averaged error of the measured and modeled data is -0.047. The standard deviation of the error is 0.039. The model prediction is in good agreement with the experimental data, particularly at small packing height. Most NO removal capacity was achieved at the first 5 cm packing material. The effects of the axial interstitial velocity and the biofilm coverage to the NO elimination were studied by the model that provided a basic for the design of a biotrickling filter. The biotrickling filter could be used for exhaust gases treatment. The assimilation function in the biological system could be another way to utilize the nitrogen component in the waste gas from harmful to benign nature. The isotope labeling technology is a new method to detect gas components for complex gas samples. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

abstract / Civil Engineering / Doctoral / Doctor of Philosophy

Not available / text

M. Tech. Chemical Engineering

Thesis (DTech. degree in Environmental, Water & Earth Sciences)--Tshwane University of Technology, 2009. / The potential of tassel from R52 maize cultivar for the removal of heavy metals from simulated and environmental aqueous samples as well as the physicochemical characteristics of tassel were investigated. Milled tassel powder was employed in metal removal from simulated aqueous sample and thereafter, the developed method was applied to environmental samples. This research has demonstrated the potential of maize tassel to adsorb metal ions from both simulated and environmental samples. Furthermore, metals adsorbed on tassel were easily desorbed suggesting that tassel can be employed in metal recycling.

Thesis (DTech. degree in Environmental, Water and Earth Sciences)--Tshwane University of Technology, 2008.

published_or_final_version / Civil and Structural Engineering / Master / Master of Philosophy