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 biosynthesis are catalyzed by the multifunctional protein Ura2 carrying both carbamyl-phosphate synthetase (CPSase) and aspartate transcarbamylase (ATCase) enzyme activities. In order to study how UTP regulates both of these activities mutant strains were constructed: one strain which expressed the Ura2 protein fused to the green fluorescent protein, and two strains expressed truncated Ura2 proteins. These strains exhibited a phenotype associated with a modified regulation of the pyrimidine pathway. Results presented in this report provide arguments in favor of a single UTP binding site located on the CPSase domain, and support a model in which ATCase activity is inhibited by UTP only when it can interact with the CPSase domain.