Although aneuploidy is known to play a significant role in major human health problems such as birth defects and cancer, we know little the about the possible aneugenicity of our chemicals and drugs. This proposal is aimed at developing a rapid, economical aneugenicity assay in yeast strains optimized for toxicity testing. We will examine two assays for suitability to high throughput aneugenicity testing. The first is a GFP- based assay that uses lox/Cre recombination between mis-segregated homologues to generate GFP expression. The other assay takes advantage of the increased copper resistance displayed by yeast cells that get extra copies of a chromosomes carrying the CUP1 gene. Once a practicable assay has been constructed, we will attempt to increase the sensitivity of the assay using permeabilizing agents and mutations in yeast transporter genes, mitotic checkpoint genes and centromere sequences. Because many of the modifications that we introduce into our tester strain will affect sensitivity of yeast to toxins other than antigens, we predict that the optimized tester will facilitate the development of a variety of yeast-based toxicity assays. PROPOSED COMMERCIAL APPLICATIONS: The yeast based aneugen assays proposed here will be commercialized through: 1) application to very early stage drug development, 2) application to redesign of a drugs with aneugenic activities, and 3) use in surveying chemical portfolios for potential aneugenicity based liability exposure by insurers. The development of yeast strains optimized for toxicity testing may have a very larger commercial impact. We will use these optimized strains and strategies to develop a range of toxicity tests.