As in Saccharomyces cerevisiae, aspartate transcarbamoylase is assembled on a multifunctional protein including a dihydroorotase-like cryptic domain in Schizosaccharomyces pombe.

The organisation of the URA1 gene of Schizosaccharomyces pombe was determined from the entire cDNA cloned by the transformation of an ATCase-deficient strain of Saccharomyces cerevisiae. The URA1 gene encodes the bifunctional protein GLNase/CPSase-ATCase which catalyses the first two steps of the pyrimidine biosynthesis pathway. The complete nucleotide sequence of the URA1 cDNA was elucidated and the deduced amino-acid sequence was used to define four domains in the protein; three functional domains, corresponding to GLNase (glutamine amidotransferase), CPSase (carbamoylphosphate synthetase) and ATCase (aspartate transcarbamoylase) activities, and one cryptic DHOase (dihydroorotase) domain. Genetic investigations confirmed that both GLNase/CPSase and ATCase activities are carried out by the same polypeptide. They are also both feedback-inhibited by UTP (uridine triphosphate). Its organization and regulation indicate that the S. pombe URA1 gene product appears very similar to the S. cerevisiae URA2 gene product.

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