Regulation of orotidylic acid pyrophosphorylase in Saccharomyces cerevisiae

Yeast mutants deficient in orotidine-5'-phosphate (OMP) pyrophosphorylase activity have been obtained. The gene encoding this Enzyme is unlinked to the four pyrimidine genes previously described. The specific activity of OMP pyrophosphorylase remains constant under all of the physiological conditions used to repress, to derepress, or to induce pyrimidine biosynthesis. This Enzyme appears, therefore, to escape the scheme of regulation by mixed repression and induction controlling the other Enzymes of the pyrimidine pathway.