CARBAMYL-PHOSPHATE SYNTHETASE DOMAIN OF THE YEAST MULTIFUNCTIONAL PROTEIN URA2 IS NECESSARY FOR ASPARTATE-TRANSCARBAMYLASE INHIBITION BY UTP

In Saccharomyces cerevisiae, the first two reactions of pyrimidine bio synthesis are catalyzed by the multifunctional protein Ura2 carrying b oth carbamyl-phosphate synthetase (CPSase) and aspartate transcarbamyl ase (ATCase) enzyme activities. In order to study how UTP regulates bo th of these activities mutant strains were constructed: one strain whi ch expressed the Ura2 protein fused to the green fluorescent protein, and two strains expressed truncated Ura2 proteins. These strains exhib ited a phenotype associated with a modified regulation of the pyrimidi ne pathway. Results presented in this report provide arguments in favo r of a single UTP binding site located on the CPSase domain, and suppo rt a model in which ATCase activity is inhibited by UTP only when it c an interact with the CPSase domain. (C) 1998 Federation of European Bi ochemical Societies.