The FUR1 gene of Saccharomyces cerevisiae: cloning, structure and expression of wild-type and mutant alleles

Abstract The FUR1 gene of Saccharomyces cerevisiae encodes uracil phosphoribosyltransferase (UPRTase) which catalyses the conversion of uracil into uridine 5′-monophosphate (UMP) in the pyrimidine salvage pathway. The FUR1 gene is included in a 2.1 kb genomic segment of DNA and is transcribed into a 1 kb poly(A) + mRNA. Sequencing has determined a 753 bp open reading frame capable of encoding a protein of 251 amino acids. The FUR1 genes for three recessive fur1 alleles, having different sensibilities to 5-fluorouridine (5-FU r ) but identical levels of resistance to 5-fluorouracil (5-FU), were cloned and sequenced. Single bp changes located in different regions of the gene were found in each mutant. Two in vitro-constructed deletions of the FUR1 gene have been integrated at the chromosomal locus, giving strains with 5-FUR R and 5-FU R R mutant phenotype. Assays of UPRTase, uridine kinase, uridine ribohydrolase and uridine 5′-monophosphate nucleotidase enzymatic activities, in extracts of strains where the FUR1 gene is overexpressedor deleted, indicate that the FUR1 encoded protein possesses only UPRTase activity.