| Investigating the targets of superoxide in the budding yeast Saccharomyces cerevisiae has increased our understanding of the physiological role that reactive oxygen species (ROS) play in eukaryotic systems. Superoxide stress in yeast induces a number of phenotypes; in most instances, the cause of these phenotypes remains poorly understood. There are some cases in which the targets of superoxide have been characterized and linked to specific phenotypes; these targets of oxidation are primarily protein-bound iron-sulfur (Fe-S) clusters. In this work, the cause of several superoxide-induced phenotypes, including altered iron homeostasis, the inability to biosynthesize lysine, and inhibited growth in alkaline medium are investigated utilizing biophysical, biochemical, and genetic approaches. Much of the evidence compiled in this study indicates that a defect in glucose repression, which is a transcriptional program employed by yeast to streamline growth and out-compete other organisms, is responsible for a superoxide-induced iron-starvation phenotype, the appearance of an iron pool that is detectable by electron paramagnetic resonance (EPR) spectroscopy, and the growth inhibition exhibited when cultured at alkaline pH. Superoxide stress also renders yeast auxotrophic for lysine, the cause of which was previously linked to an Fe-S cluster-containing enzyme of the biosynthetic pathway. In this study, the basis of the lysine auxotrophy is revisited through investigations of other potential targets of superoxide stress in the lysine biosynthetic pathway. |
