Genome-wide screen in yeast to identify modulators of mutant SOD1 toxicity

Yeast (Saccharomyces cerevisiae) cultures can be handled in a partially automated manner, and about 80% of the yeast genes have their homologous counterpart in mammalian cells. Thus, yeast mutant strains are a versatile tool for genetic studies on protein function and toxicity. In order to identify modulators and mechanisms of SOD1 toxicity, we performed a genome wide screen in Saccharomyces cerevisiae. Yeast strains were transformed with wild-type SOD1, as well as several mutant SOD1 species known to cause ALS. A screen for SOD1 toxicity was then performed for each mutant using >4000 haploid mutant yeast strains containing deletions of non-essential genes. We identified 4 yeast homologues of mammalian genes that modified mutant SOD1 toxicity. For example, mutant SOD1-susceptible yeast strains included deletion mutants for a mitochondrial co-chaperone or a key enzyme of the N-end rule pathway of protein degradation. We are currently transferring these findings to higher eukaryotic systems and studying the contribution of the N-end rule pathway-mediated protein degradation for SOD1 toxicity. Moreover, yeast deletion strains susceptible to mutant SOD1 toxicity could potentially be used for automated high-throughput screening of chemical libraries in order to identify therapeutic compounds.