Analyses of genes involved in yeast cell wall $ beta$1,6-glucan assembly have identified CWH41, PTC1/CWH47, EXG1, PBS2 and a family of genes related to the human oxysterol binding protein, OSBP. CWH41 encodes a novel membrane N-glycoprotein located in the ER. Disruption of CWH41 leads to a K1 killer toxin resistant phenotype, and a 50% reduction in the $ beta$1,6-glucan level The $cwh{ it 41 /} Delta$ mutant displayed strong synergistic defects with $kre{ it 1 /} Delta$ or $kre{ it 1 /} Delta$ null mutations: the $cwh{ it 41 /} Delta kre{ it 6 /} Delta$ double mutant showed a slow-growth phenotype and a 75% reduction in $ beta$1,6-glucan level, and cells containing $cwh{ it 41 /} Delta kre{ it 6 /} Delta$ double mutations were nonviable. These results indicate that CWH41 is involved in the assembly of $ beta$1,6-glucan. / PTC1/CWH47 encodes a serine/threonine phosphatase, PBS2 is the structural gene for a MAPK kinase, and EXG1 codes for an exo-$ beta$-glucanase. Overexpression of EXG1 led to a killer resistant phenotype and a reduction in ($ beta$1,6-glucan level; whereas the $exg{ it 1 /} Delta$ mutant displayed modest increases in killer sensitivity and $ beta$1,6-glucan levels. Disruption of PTC1/CWH47 and overexpression of PBS2 resulted in similar $ beta$-glucan related phenotypes, with elevated EXG1 transcription, increased Exg1p activity, reduced $ beta$1,6-glucan levels, and resistance to killer toxin. The killer resistant phenotype caused by PTC1/CWH47 disruption or PBS2 overproduction were partially suppressed by the $exg{ it 1 /} Delta$ null mutation. These results suggest that Ptc1p/Cwh47p and Pbs2p play opposing regulatory roles in $ beta$-glucan assembly, and this is effected in part by modulating Exg1p activity. / Three yeast genes, KES1, HES1 and OSH1, whose products show homology to the human oxysterol binding protein, were also identified. Mutations in these genes resulted in sterol-related phenotypes, which include tryptophan-transport defects and nystatin resistance. In addition, mutant combinations showed small but cumulative reductions in membrane ergosterol levels. The three genes are also functionally related; since overexpression of HES1 or KES1 alleviated the tryptophan-transport defect in $kes{ it 1 /} Delta$ or $osh{ it 1 /} Delta$ mutants, respectively. These observations implicate the KES1-related gene family in ergosterol synthesis and provide comparative evidence of a role for human OSBP in cholesterol synthesis.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.40149 |
| Date | January 1995 |
| Creators | Jiang, Bo, 1964- |
| Contributors | Bussey, Howard (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001484907, proquestno: NN12392, Theses scanned by UMI/ProQuest. |
Page generated in 0.0024 seconds