URA3

URA3 is a gene on chromosome V in Saccharomyces cerevisiae (yeast). Its systematic name is YEL021W. URA3 is often used in yeast research as a "marker gene", that is, a gene to label chromosomes or plasmids. URA3 encodes Orotidine 5'-phosphate decarboxylase (ODCase), which is an enzyme that catalyzes one reaction in the synthesis of pyrimidine ribonucleotides (a component of RNA).[1]

Orotidine 5'-phosphate decarboxylase
Identifiers
OrganismSaccharomyces cerevisiae
SymbolURA3
Alt. symbolsYEL021W, ODCase
Entrez856692
HomoloGene136914
RefSeq (mRNA)NM_001178836
RefSeq (Prot)NP_010893
UniProtP03962
Other data
EC number4.1.1.23
ChromosomeV: 0.12 - 0.12 Mb

Use in yeast research

Loss of ODCase activity leads to a lack of cell growth unless uracil or uridine is added to the media. The presence of the URA3 gene in yeast restores ODCase activity, facilitating growth on media not supplemented with uracil or uridine, thereby allowing selection for yeast carrying the gene. In contrast, if 5-FOA (5-Fluoroorotic acid) is added to the media, the active ODCase will convert 5-FOA into the toxic compound (a suicide inhibitor) 5-fluorouracil causing cell death, which allows for selection against yeast carrying the gene.

Since URA3 allows for both positive and negative selection, it has been developed as a genetic marker for DNA transformations and other genetic techniques in bacteria and many fungal species. It is one of the most important genetic markers in yeast genetic modification. While URA3 is a powerful selectable marker it has a high background. This background is because cells that pick up mutations in URA3 may also grow on 5-FOA. Colonies should be verified by a second assay such as PCR to confirm the desired strain has been created.

References
  1. Flynn PJ, Reece RJ (January 1999). "Activation of transcription by metabolic intermediates of the pyrimidine biosynthetic pathway". Molecular and Cellular Biology. 19 (1): 882–8. doi:10.1128/mcb.19.1.882. PMC 83945. PMID 9858611.
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