Using 5-Fluoroorotic Acid (5-FOA) for the counter-selection of yeast is a common genetic screening method. Curing yeast strains of plasmids, plasmid shuffling, allelic replacement, and two-hybrid screens are methods that can employ the use of 5-FOA. Otherwise nontoxic to yeast, 5-FOA is converted to the toxic form (i.e., 5-flurouracil) in strains expressing the functional URA3 gene coding for orotine-5-monophosphate decarboxylase that is involved in the synthesis of uracil. Yeast strains that are phenotypically Ura+ become Ura- and 5-FOA(R) (resistant) after selection. The question of 5-FOA solubility is often raised by customers using ultra-pure (< 98%) 5-FOA powder because of its insolubility in water. Thus, we provide a 100X concentrated (100 mg/ml) 5-FOA solution in DMSO and synthetic 5-FOA monohydrate powder. Both have been tested and validated on the basis of counter selection activity.

Format	Synthetic 5-FOA monohydrate powder or 100X liquid (100 mg/ml in DMSO)
Molecular Weight	174 g/mol
Product Storage	Store at -20°C
Purity	≥ 98% (estimated) by TLC, melting point, and lot comparison
Solubility	50 mg in 1 ml (1:1 1:1 NH4 OH:H2O) with gentle heating; >100 mg/ml in DMSO
Structure	C5H3FN2O4• H2O