Osmotic stress and the yeast actin-based cytoskeleton
Gustin, Michael C.
Doctor of Philosophy
In order for cells to grow and survive, they must be able to overcome changes in their external environment. For example, stresses such as high or low temperatures and nutrient deprivation have been shown to elicit a response pathway which eventually results in the transcriptional or translational regulation of various genes. This study focuses on the ability of yeast cells to respond to and recover from the environmental stress of a change in external osmolarity. Because of its unicellular nature, it is vital that the sudden changes in internal turgor pressure caused by osmotic stress are compensated for, usually through the accumulation of glycerol inside the cell. Recently, it was found that strains with mutations in the single essential yeast actin gene, ACT1, were not able to grow at high temperatures or high osmolarity. This phenotype suggested that an underlying physiological process affecting cytoskeletal actin was involved in the response to osmotic stress. In order to understand this process, wild type yeast cells were analyzed at the morphological, genetic and molecular level. Results from this characterization led to the hypothesis that the response of actin to osmotic stress is regulated by interactions with other actin binding proteins. Potential candidates for these interactions were discovered by generating second site suppressors of an actin mutant and analysing them genetically. A dominant suppressor, RAH3, was found with four alleles, each having different phenotypes. Cloning of the recessive single mutant revealed that the gene product was the yeast homolog to fimbrin, a protein thought to regulate stress responses. Sequence analysis of the different alleles indicates that several sites dispersed throughout the fimbrin gene are important in regulating the cytoskeletal response to osmotic stress.
Cell biology; Genetics