The ability of proteins to engage in nuclear-cytoplasmic shuttling is required for their proper function. The nuclear export of the von Hippel Lindau (VHL) tumour suppressor protein is necessary for the proteasomal degradation of the hypoxia inducible factor alpha (HIFα). Studies have identified that the nuclear export of VHL and other proteins encoding a Transcription-Dependent Nuclear Export Motif (TD-NEM) is independent of the classical CRM1 nuclear export pathway but requires ongoing transcription. Furthermore, the eukaryotic elongation factor 1 alpha (eEF1A) was identified as a mandatory component of the TD-NEM-mediated nuclear export machinery. In this study, we have uncovered the ability of eEF1A to mediate the nuclear export of proteins by accessing the nuclear compartment in its inactive, GDP-bound form. Although previously thought of as a strictly cytoplasmic protein, work conducted in this thesis has shown that eEF1A is a nuclear-cytoplasmic shuttling protein and this ability is required for the effective export of proteins encoding a TD-NEM.

The sexual functions of the mating type gene (mt) of Neurospora crassa include specification of mating identity (Shear and Dodge, 1927) and perithecial maturation (Griffiths and DeLange, 1978; Staben and Yanofsky, 1990). The gene also acts as a vegetative incompatibility locus, so that A + a heterokaryons (Beadle and Coonradt, 1944) or A/a duplication strains (Newmeyer and Taylor, 1967) grow poorly or not at all. An intriguing question regarding the mating type gene is this: How does it control both the switch between somatic and meiotic events and heterokaryon incompatibility? Several research groups (Glass, et al., 1990; Staben and Yanofsky, 1990) are presently studying the sexual functions of the mating type genes. I present a study of the incompatibility function. Two experiments were performed. The first was a search for new suppressors of mating type-associated incompatibility, which resulted in the identification of seven new suppressors, none of which was allelic with the one known suppressor, tol. The second was the comparison of growth rates of a mating type mutant (fertile, heterokaryon compatible) in a mixed mating type heterokaryon and in a mixed mating type duplication to determine whether or not cytoplasmic incompatibility is separable from nuclear incompatibility. The results obtained suggest that the mating type mutant, am33, eliminates heterokaryon incompatibility without eliminating nuclear incompatibility. The search for suppressors was attempted in order to define more of the genes involved in A/a incompatibility. The analysis of heterokaryon versus nuclear incompatibility was done to investigate the cellular interactions involved in A/a incompatibility. / Science, Faculty of / Botany, Department of / Graduate

No description available.

No description available.

<p> Barley coleoptiles were observed to be remarkably variable in height at 72 hr of germination. The objective or the study presented here was to analyze this variation in growth among coleoptiles and to attempt to determine its cause. The first step in this analysis of the variation was to determine the growth patterns of 900 individual coleoptiles by measuring their heights periodically during their growth period. In determining the cause for the variation, genetic, environmental, hormonal, metabolic and cytoplasmic factors were considered. For example, since gibberellin and kinetin have been implicated in the control of cell division and cell elongation these growth factors were supplied exogenously to germinating seedlings in an attempt to stimulate uniform growth of all coleoptiles. In similar studies, the effect or physical conditions and co2 on coleoptile growth was determined variation in growth is shown by any one of a number of parameters. Proteins, however, because they are closer to gene activity than the others are a better indicator of whether the variation in growth is caused at a fundamental level. Variations similar to those in coleoptile height were found in the amino acid analysis of different types of coleoptiles. Experiments were also done to determine if a genetic component was responsible for the variation in coleoptile growth. There was no correlation between germination pattern of a seedling and that of its progeny; therefore, the variation in growth was attributed to differences in cytoplasmic constituents of individual coleoptiles. </p> / Thesis / Doctor of Philosophy (PhD)

No description available.

Wolbachia est une bactérie endosymbiotique, intracellulaire et exclusivement transmise maternellement qui infecterait au moins 106 espèces d'insectes. Wolbachia manipule fréquemment la reproduction de ses hôte à son avantage, notamment en induisant une forme de stérilité conditionnelle appelée incompatibilité cytoplasmique (IC). Chez les moustiques du complexe Culex pipiens, une grande diversité de souches de Wolbachia et de types d'IC a été précédemment identifiée, mais plusieurs aspects de la biologie de cette association restaient peu connus. Les travaux présentés dans cette thèse ont notamment permis de caractériser (i) l'impact de Wolbachia sur la structuration génétique des populations hôtes et (ii) la diversité des souches de Wolbachia et, plus précisément d'appréhender le mécanisme de l'IC. Par un suivi de populations naturelles, nous avons mis en évidence que Wolbachia induisait une forte structuration de la diversité mitochondriale, mais aussi qu'elle participait à des événements répétés d'introgression cytoplasmique entre les différents membres du complexe Cx. pipiens. Nous avons également mené une étude de génomique comparative basée sur le séquençage de quatre génomes complets de Wolbachia très proches phylogénétiquement. Pour cela, nous avons mis en place une série d'analyses approfondies utilisant un large panel d'outils bioinformatiques couplés à des vérifications moléculaires. Nous avons montré qu'il existait peu de polymorphisme entre les groupes de Wolbachia infectant Cx. pipiens. De plus, ces études nous ont permis de mettre en évidence des gènes candidats qui pourraient être directement impliqués dans le mécanisme de l'IC. / Wolbachia is an intracellular bacterial symbiont, exclusively maternally inherited, infecting at least 106 species of insects. Wolbachia commonly manipulates insect reproduction to its own advantage, as well illustrated by a phenomenon of conditional sterility called cytoplasmic incompatibility (CI). In mosquitoes of Culex pipiens complex, a great diversity of Wolbachia strains and of CI types was previously identified, but several aspects of the biology of this symbiotic association remained unknown. The aim of the studies presented in this thesis is to characterize (i) the impact of Wolbachia on the host genetic structure and (ii) the Wolbachia strains diversity in order to attempt an identification of CI molecular basis. By a survey of natural populations, we highlighted that Wolbachia deeply impacts the population structure of mitochondrial diversity, but is also associated with repeated events of cytoplasmic introgression between members of complex Cx. pipiens. We also conducted a study of comparative genomics based on the sequencing of four complete genomes of very closely related Wolbachia strains. For that purpose, we performed a series of analyses using a wide panel of bioinformatic tools coupled with molecular validations. We showed a low polymorphism between two groups of Wolbachia infecting Cx. pipiens. These studies also allowed us to highlight promising candidate genes which could be directly involved in the CI mechanism.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.