This article provides insufficient context for those unfamiliar with the subject. Please help improve the article with a good introductory style. (October 2009)

URA3 is gene on Chromosome V in Saccharomyces (yeast). Its systematic name is YEL021W. URA3 is a gene that encodes orotidine 5-phosphate decarboxylase (ODCase), which is an enzyme that catalyzes one reaction involved in the synthesis of pyrimidine ribonucleotides in yeast RNA.

Loss of ODCase activity leads to a lack of cell growth unless uracil or uridine is added to the media. When the URA3 gene is added, auxotrophic bacteria can now grow (positive selection). In contrast, if 5-FOA (5-Fluoroorotic acid) is added to the media, the ODCase of prototrophic bacteria can convert 5-FOA into the toxic compound (a suicide inhibitor) 5-fluorouracil causing death (negative selection).

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.

References [link]

S. cerevisiae database (2005) URA3 gene. https://db.yeastgenome.org/cgi-bin/locus.pl?locus=ura3#summaryParagraph (accessed 16/10/07).

PAUL J. FLYNN AND RICHARD J. REECE. Activation of Transcription by Metabolic Intermediates of the Pyrimidine Biosynthetic Pathway. MOLECULAR AND CELLULAR BIOLOGY,Vol. 19, No. 1, 882–888