The Saccharomyces cerevisiae oxysterol binding protein homologue Kes1/Osh4 is a member of an enigmatic class of proteins found throughout Eukarya. This family of proteins is united by a ?-barrel structure that binds sterols and oxysterols. An N-terminal lid is thought to both sequester sterols inside the core and promote localization of Kes1 to regions of high membrane curvature via a predicted ArfGAP lipid packing sensor motif. Additionally, a phosphoinositide-binding region on a discrete surface of Kes1 has also been identified. In this thesis, structure-function analysis of Kes1 determined that phosphoinositide binding is required for membrane association in vitro, and in vivo phosphoinositide binding is required for localization to the Golgi. Ergosterol, the major sterol in S. cerevisiae, and membrane curvature had minimal effects on membrane association. This study also revealed a role for Kes1 in the regulation of both phosphatidylinositol-4-phosphate and phosphatidylinositol-3-phosphate homeostasis. Phosphoinositide and sterol binding by Kes1 are necessary for it to alter phosphatidylinositol-4-phosphate, but not phosphatidylinositol-3-phosphate homeostasis. Misregulation of phosphatidylinositol-4-phosphate homeostasis by Kes1 manifested itself in an inability of the v-SNARE Snc1 to traffic properly and was consistent with a defect in trans-Golgi/endosome trafficking. I went on to demonstrate a role for Kes1 in regulating the conversion of phosphatidylinositol-4-phosphate to phosphatidylinositol for the synthesis of sphingolipids, and I present a model for the role of Kes1 at the Golgi. Kes1 acts as a sterol sensor that regulates phosphatidylinositol-4-phosphate to sphingolipids metabolism, which ultimately regulates the delivery of proteins that assemble into lipid rafts for their transport from the Golgi to the plasma membrane. I also uncovered a previously unknown role for Kes1 in the regulation of the cytoplasm-to-vacuole and autophagy trafficking pathways, which is mediated by the ability of Kes1 to regulate phosphatidylinositol-3-phosphate homeostasis.

"June 2002" / Bibliography: leaves 179-194. / 194 leaves : ill. (col.), plates (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The overall aim of the research presented in this thesis was to determine if the growth and function of external hyphae of Arbuscular Mycorrhizal (AM) fungi is affected by changes in soil pore size. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 2002

Thesis (Ph. D.)--University of Adelaide, Dept. of Soil Science, 1995? / Copies of author's previously published articles inserted. Includes bibliographical references (leaves 184-197).

Thesis (M.S.)--University of Wisconsin -- La Crosse, 2009. / Includes bibliographical references (leaves 42-46)

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Membrane fusion plays a crucial role in many biological processes from virus infection to release of neurotransmitters (Hughson 1999). Membrane -bound surface glycoproteins are involved in the fusion process. The enveloped animal virus infection is initiated by interactions between the virus and the cell membrane through the surface glycoproteins called fusion glycoproteins (Eckert and Kim 2001). The fusion glycoproteins are responsible for both receptor binding and membrane fusion activity. The fusion proteins are characterized by a large ectodomain containing fusion peptides, a transmembrane (TM) domain, and a cytoplasimic domain. The viruses can enter cells either at neutral pH or at acidic pH. When exposed to appropriate conditions, the fusion protein undergoes conformational changes, which in turn drives the fusion process. The fusion glycoproteins can be classified as Class I and Class II fusion proteins (Lescar eta/. 2001 ). The Class I fusion proteins are synthesized as a precursor molecule, which then undergoes proteolytic cleavage to generate a mature molecule containing the hydrophobic fusion peptide at the N -terminal. The class II fusion glycoproteins are not synthesized as precursor molecules, and they have internal fusion peptides. The vesicular stomatitis virus (VSV) glycoprotein G is a class Ill fusion protein. It has a neutral internal fusion peptide and upon exposure to low pH, the protein undergoes reversible conformational change (Gaudin 2000, Yao eta/. 2003). A 62kDa soluble ectodomain of VSV G (Gs) has been generated by limited trypsin digestion. The SDS PAGE gel electrophoresis indicates that the trypsin has possibly cleaved near the transmembrane (TM) domain. Liposome binding experiment suggests that Gs can bind to liposomes in a pH dependent manner. Liposome fusion studied by RET assay suggests that the Gs can induce significant amount of hemifusion. However, it failed to induce any content mixing mainly due to considerable amount of membrane leakage activity. This indicates that the binding to the membrane through the TM domain is required for complete membrane fusion. Unlike TBE E soluble ectodomain, Gs can form dimers and trimers at neutral and fusion active pH. Light scattering experiment shows that the aggregation of Gs increases with a decrease in pH. The conformational change with changes in pH was evident from the trypsin sensitivity assay and CD spectroscopy. It was observed that Gs became resistant to trypsin digestion at low pH and a-helicity content of the molecule increased upon lowering the pH. However, the maximum amount of a-helicity was observed at pH 6. The removal of the TM domain also shifts the optimum fusion pH towards more acidic pH in comparison to VSV G. These results indicate that the TM domain is not required for the oligomerization of G protein, but some role has been reserved for the TM domain during membrane fusion. The CD spectroscopic data also indicated that the G protein undergoes structural rearrangement between pH 7.4-6, which could be responsible for the exposure of fusion peptide and subsequent target membrane binding. / Thesis / Master of Science (MSc)

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1979 T516 / Master of Science

The overall objective of this project was to investigate the effects of the symbiotic association of plants with vesicular - arbuscular mycorrhizal fungi on the intensity of intraspecific competition and its consequences on population structure I performed four main glasshouse experiments using a non - cultivated species, Rhodanthe chlorocephala ssp rosea, or a cultivated species, Trifolium subterraneum. I grew the plants at different plant densities, under different levels of resources ( phosphorus and / or light ), in environments with homogeneous and / or patchy distribution of phosphorus ( P ). In pots with homogeneous distribution of P, the addition of P to R. chlorocephala and mycorrhizal infection in T. subterraneum increased plant biomass of single plants. However, these beneficial effects were reduced by increasing plant density. Shading of plants of T. subterraneum did not generally alter these effects. Mycorrhizal symbiosis and the addition of P always increased the intensity of plant intraspecific competition. In trays with patchy or homogeneous distribution of P, mycorrhizal infection and patchy distribution of P increased the total biomass and size inequality of populations of plants of T. subterraneum. Individual biomass was determined by the local soil P concentration in patchy environments and by mycorrhizal infection in low density treatments. Mycorrhizal infection, but not patchy P distribution, increased relative competition intensity. Asymmetric or symmetric distribution of resources between plants will change these size hierarchies. The distinction between these two types of distributions has lead to two different models explaining the interaction between competition and size inequality ( degree to which the biomass is concentrated within a small fraction of the population &# 40 Weiner and Thomas 1986 ) ) the resource depletion and resource pre - emption models ( Weiner and Thomas 1986, Weiner 1988b ). In the first model ( resource depletion ) competition reduces the relative growth rate of all the individuals by the same proportion, reduces variance of growth rates and reduces variation in sizes. Thus, in this model resource acquisition is proportional to plant size ( Weiner 1990 ). This model is also called symmetric or two - sided competition and applies when competition for nutrients predominates. It predicts that at high density, plants will be smaller but the population will have less inequality than at low density ( Weiner and Thomas 1986 ). In the second model ( resource pre - emption ), competition increases the variation in relative growth rates and increases variation in sizes. Large plants obtain a more than proportional share of the resources ( relative to sizes ) ( Weiner 1990 ) and this increases their competitive ability which results in a positive feedback on plant size. This phenomenon is also called snowball cumulation, asymmetric or one - sided competition and it was observed only when competition for light was predominant ( Wilson 1988a ). This second model predicts that at high density plant populations will have more inequality than at low density ( Weiner and Thomas 1986 ). Although these two models are generally accepted, alternative analyses and recent experiments show that the degree of asymmetry of the interaction depends on the spatial and temporal distribution of the resource, the spatial distribution of the individuals in the population, neighbourhood competition and the mobility of the resource ( Huston 1986 ; Miller and Weiner 1989, Weiner 1990, Bonan 1991 ). Weiner ( 1990 ) suggested that if nutrients are distributed homogeneously and the uptake is proportional to root size, the competitive interaction will be more symmetric, whereas if patches with more nutrients can be reached by large individuals, asymmetric competition will predominate. This hypothesis has not been tested yet. Turner and Rabinowitz ( 1983 ) found that populations with an initial random spatial distribution of individuals had an unexpected increase in size inequality. My results emphasise that the main effects of mycorrhizas at the individual level cannot be expected to be apparent at the population level, because of the influence of density - dependent processes. However, infected individuals with a strong response to the symbiosis would have an advantage in situations of competition. This scenario can explain the maintenance of the symbiotic ability even under conditions such as dense populations, where there is no obvious advantage of the symbiosis at the population level. / Thesis (Ph.D.)--Department of Soil and Water, 1998.

Under field conditions, vesicles were the most frequently observed mycorrhizal structures in sugar maple, while greenhouse grown seedlings formed more arbuscules. Seasonal fluctuations of vesicular-arbuscular mycorrhizae existed. Mycorrhizal associations formed within 30 days in the greenhouse. Arbuscules were usually formed from hyphal coils and occasionally from linear hyphae spreading from cell to cell. Degenerating arbuscules were not observed. The addition of basic cations increased the number of vesicles formed and decreased the overall infection rates and seedling growth. The uptake of calcium, magnesium, and nitrogen decreased, and potassium uptake increased as fertilization rates increased. Positive correlations existed between the incidence of arbuscules and plant growth and health and between the incidence of arbuscules and the uptake of calcium, magnesium, nitrogen and phosphorus, and with the uptake ratios and these elements with potassium. This suggests that vesicular-arbuscular mycorrhizae may in some way be regulating ionic balance in these seedlings.