URA3 is a

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

V in ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...

'' (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

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria and ...

s. URA3 encodes Orotidine 5'-phosphate decarboxylase (ODCase), which is an

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

that catalyzes one reaction in the synthesis of pyrimidine ribonucleotides (a component of

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

Use in yeast research

Loss of ODCase activity leads to a lack of cell growth unless

uracil Uracil () (nucleoside#List of nucleosides and corresponding nucleobases, symbol U or Ura) is one of the four nucleotide bases in the nucleic acid RNA. The others are adenine (A), cytosine (C), and guanine (G). In RNA, uracil binds to adenine via ...

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 Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

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

External links

* {{cite web , work = S. cerevisiae database , date = 2018 , title = URA3 gene , url = https://www.yeastgenome.org/locus/S000000747 Saccharomyces cerevisiae genes