The long range objective of this work is to understand the control of gene expression in eucaryotic cells. We are using the allantoin degradative system of the yeast Sacchaormyces cerevisiae as a model system for these investigations. Allantoin is degraded in this organism by the action of five enzyme activities and requires the additional participation of four transport systems. All of the genes responsible for these functions have been mapped. In past work we have shown that production of the five enzyme activities and one of the transport systems is inducible; allophanate, the last intermediate in the pathway serves as inducer. We have recently isolated two new classes of mutants. One class of strains (mutated in the dur5 locus) produces all of the enzymes constitutively in the absence of added inducer. The second class of strains (mutated in the dal6 locus) are unable to synthesize any of the enzymes even though inducer can be shown to exist in the cells. In the present application we propose to use these mutants to elucidate the molecular events involved in control of the five distinct genes associated with allantoin degradation. The principal areas of study include: (1) characterization of mutants in which production of the allantoin degrading enzymes has been altered (dur5 and dal6), (2) elucidation of control element interactions by genetic studies and the isolation of second generation control mutants, (3) cloning of the dur5 and dal6 genes, (4) characterization of dur5 and dal6 gene expression and (5) purification of the dur5 and dal6 gene products.