5-Fluoroorotic Acid (5-FOA) is widely used in the field of yeast molecular genetics. The toxicity of 5-FOA to yeast cells with a functioning URA3 gene which encodes orotidine-5′-P decarboxylase (OMP decarboxylase), makes it especially useful for the selection and identification of mutant yeast strains. 5-FOA is most often applied with Saccharomyces cerevisiae (URA3), although it has been used in other strains including Schizosaccharomyces pombe (URA4 and URA5), Candida albicans (URA3) and the bacterium E. coli (pyrF). The use of 5-FOA in the yeast 2-hybrid system allows for the construction of activation domain hybrid libraries to identify protein-protein interactions.