Thèses (Ph.D.)--Université de Sherbrooke (Canada), 1999. / Titre de l'écran-titre (visionné le 20 juin 2006). Publié aussi en version papier.

Thèses (M.Sc.)--Université de Sherbrooke (Canada), 2001. / Titre de l'écran-titre (visionné le 20 juin 2006). Publié aussi en version papier.

Thèses (M.Sc.)--Université de Sherbrooke (Canada), 2003. / Titre de l'écran-titre (visionné le 20 juin 2006). Publié aussi en version papier.

No description available.

No description available.

Thèses (M.Sc.)--Université de Sherbrooke (Canada), 1998. / Titre de l'écran-titre (visionné le 20 juin 2006). Publié aussi en version papier.

Thèse doctorat : Sciences de la Vie et de la Terre : Strasbourg 1 : 2006. / Thèse soutenue sur un ensemble de travaux. Titre provenant de l'écran-titre. Bibliogr. 7 p.

The main objective of this research is to advance our understanding of the biochemical properties and the structure-function relationships of the chloroplast glycerol-3-phosphate acyltransferases in plants. De novo synthesised fatty acyl chains are diverted into the prokaryotic pathway of plant lipid biosynthesis by a soluble glycerol-3-phosphate acyltransferase (GPAT [EC. 2.3.1.15]) in the chloroplast. GPAT catalyses acylation at the sn- 1 position of sn-glycerol-3-phosphate to form lysophosphatidic acid. Recombinant GPAT from squash and Arabidopsis were overproduced in Escherichia coli, purified to about 23- fold and 90% pure enzyme using a procedure developed in this study. Antibodies were raised in rabbits against these denatured recombinant GPAT preparations and four peptide antigens, and preliminary experiments were performed to test their suitability for use in Western blotting. In collaboration with the University of Sheffield, squash GPAT was successfully crystallised, isomorphous heavy metal derivatives prepared and the complete 3-dimensional structure of the protein at 2.3 Angstrom resolution determined. The cloning, functional expression and characterisation of a novel GPAT from oil palm, 'domainswap' chimeric recombinant proteins of Arabidopsis and squash GPAT, and spinach and squash GPAT respectively, and the influence of the N-terminal domain and amino acid substitutions in the C-terminal domain of the squash GPAT, was described. By determining the apparent kinetic constants for acyl-ACP substrates of most of the enzymes and by in vitro assays using mixtures of two acyl-ACP substrates under physiologically relevant conditions, it was found that their substrate selectivities could be dramatically altered. The development of ribozyme- technology as a molecular tool to down-regulate the gene expression of one out of multiple GPATs, was initiated. The strategy would allow for a phenotypic indication of ribozyme- efficacy in vivo and may help further contribute to the role of glycerol-3-phosphate acyltransferase in processes determining the phenomenon of chilling-sensitivity of plants.

No description available.

Evolutionary relationships amongst strains of the fungal genus Leptographium and related taxa were inferred using the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA repeat. To generate robust sequence alignments for phylogenetic analysis the relationship between DNA sequence variability and RNA structural conservation of ITS segments was examined. The results demonstrate that structural conservation of helical regions is facilitated by compensatory base changes, compensating insertions/deletions, and, possibly, RNA strand slippage. A high mol % G+C bias for ITS1 and ITS2 and structural constraints at the RNA level appear to limit the types of changes observed. Fifty strains of Leptographium were screened for the presence of introns within mitochondrial genes. Superimposing intron survey data onto the ITS-derived phylogenetic tree reveals that introns are absent from the small ribosomal RNA (rns) gene of all strains of L. procerum yet are found in all strains of L. lundbergii. Amongst members of L. wingfieldii, L. terebrantis, and L. truncatum intron distribution is stochastic and is not correlated to the evolutionary relationships amongst strains. A group II intron/LAGLIDADG homing endonuclease gene (HEG) composite element from the mt rns gene of L. truncatum strain CBS929.85 was characterized. Intron-catalyzed splicing was tested using ORF-less and ORF-containing precursor transcripts, and both versions of the intron readily self-splice under moderate temperature and ionic conditions (37 °C and 6 mM MgCl2). Cleavage activity of the intron-encoded protein (I-LtrII) was tested using an N-terminal His6-tagged and near native protein. The homing endonuclease cleaves double-stranded DNA 2 nucleotides upstream of the intron insertion site within the exon, generating 4 nucleotide 3’ OH overhangs. Intron splicing is not enhanced by the addition of I-LtrII and RNA-binding assays indicate that the His6-tagged protein does not bind to the intron. Phylogenetic relationships amongst the rns gene, intron, and amino acid sequences were inferred. An evolutionary model of the composite element is proposed in which the HEG invaded a group II intron and mobilized it. The mobile genetic element may be transmitted vertically amongst L. lundbergii strains and horizontally through lateral gene transfer amongst strains of L. wingfieldii, L. terebrantis, and L. truncatum.