Pyrimidine ribonucleotide salvage pathways (WP95)

Saccharomyces cerevisiae

Pyrimidine nucleotides are essential as components of nucleic acids, as substrates for amino acid synthesis and as energy sources, but defects in the de novo biosynthesis of pyrimidines are not lethal in S. cerevisiae cells (CITS:10501935). This is because salvage pathways are able to utilize preformed bases (either from exogenous sources or internal turnover sources) for the synthesis of pyrimidines (CITS:2189783). If the required substrates are available, salvage pathways are preferred over de novo synthesis pathways for pyrimidine biosynthesis (CITS:12111094). The salvage pathways of pyrimidine ribonucleotides consist of 1) importing exogenous bases into the cell, and 2) the interconversion of various bases (CITS:2189783)(CITS:12111094). Three proteins are involved in the import of exogenous bases used by the salvage pathway for pyrimidine ribonucleotide biosynthesis. Uracil enters the cell via the Fur4p uracil permease (CITS:6290876)(CITS:3276521), cytosine enters the cell via the Fcy2p purine-cytosine transporter (CITS:6387700)(CITS:2191181), and uridine enters the cell via the Fui1p uridine permease (CITS:9485596). As with many of the metabolic pathways of S. cerevisiae, the pathways for the salvage of pyrimidine ribonucleotides are under both transcriptional and post-transcriptional catabolite repression at a variety of points (CITS:10074071)(CITS:11125145)(CITS:12111094)(CITS:12570998)(CITS:12791685)(CITS:1429716)(CITS:14657252). This pathway is of biomedical interest because cytosine deaminase (Fcy1p) is not found in mammals (CITS:12637534) and is capable of catalyzing the deamination of the prodrug 5-fluorocytosine (5FC) to form the anticancer drug 5-fluorouracil (5FU) (CITS:15823054). Expression of Fcy1p in tumor cells increases their sensitivity to 5FC, and expression of Fur1p increases tumor cell sensitivity to 5FU (CITS:10919655). Tumor cells expressing a novel chimeric protein, produced from a gene containing the FCY1 and FUR1 coding sequences fused in frame, display significantly increased sensitivity to 5-FC suggesting that this novel suicide gene may constitute an original and potent candidate therapeutic gene for cancer gene therapy (CITS:10919655). SOURCE: SGD pathways,


Meredith Braymer , Egon Willighagen , Daniela Digles , Martina Summer-Kutmon , and Eric Weitz


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Saccharomyces cerevisiae



Pathway Ontology

pyrimidine salvage pathway


Label Type Compact URI Comment
uracil Metabolite cas:66-22-8
CDP Metabolite cas:63-38-7
pyrophosphate Metabolite cas:2466-09-3
cytidine Metabolite cas:65-46-3
ATP Metabolite cas:1927-31-7
ribose Metabolite cas:50-69-1
ribose Metabolite cas:50-69-1
ATP Metabolite cas:1927-31-7
ADP Metabolite cas:58-64-0
ADP Metabolite cas:58-64-0
PRPP Metabolite cas:97-55-2
GTP Metabolite cas:2564-35-4
GDP Metabolite cas:146-91-8
cytosine Metabolite cas:71-30-7
ADP Metabolite cas:58-64-0
uridine Metabolite cas:58-96-8
ATP Metabolite cas:1927-31-7
URK1 GeneProduct sgd:S000005295
URH1 GeneProduct sgd:S000002808
FUR1 GeneProduct sgd:S000001170
URK1 GeneProduct sgd:S000005295
YNK1 GeneProduct sgd:S000001550
FCY1 GeneProduct sgd:S000006266
CDD1 GeneProduct sgd:S000004235
URH1 GeneProduct sgd:S000002808


  1. New insights into the pyrimidine salvage pathway of Saccharomyces cerevisiae: requirement of six genes for cytidine metabolism. Kurtz JE, Exinger F, Erbs P, Jund R. Curr Genet. 1999 Sep;36(3):130–6. PubMed Europe PMC Scholia
  2. The URH1 uridine ribohydrolase of Saccharomyces cerevisiae. Kurtz JE, Exinger F, Erbs P, Jund R. Curr Genet. 2002 Jun;41(3):132–41. PubMed Europe PMC Scholia