LEU2

LEU2 is a gene in the yeast Saccharomyces cerevisiae that encodes beta-isopropylmalate dehydrogenase, an enzyme in the leucine biosynthesis pathway. The enzyme catalyzes the NAD+-dependent oxidative decarboxylation of beta-isopropylmalate to alpha-ketoisocaproate, a key step that leads to leucine production.

In laboratory strains, loss of LEU2 causes leucine auxotrophy, meaning the organism cannot synthesize leucine and must obtain it from the environment. A functional LEU2 gene restores the ability to grow on media lacking leucine, providing a basis for genetic selection.

Because LEU2 can restore prototrophy, the gene is widely used as a selectable marker in Saccharomyces cerevisiae genetics. Vectors carrying LEU2 are used to select transformants that have incorporated the marker by growing on media without added leucine, allowing researchers to identify cells that have taken up the desired DNA.

LEU2 homologs exist in other fungi, and the gene is commonly used in fungal genetics as a standard marker for leucine prototrophy. Beyond its role in metabolism, LEU2 serves as a practical tool in genetic engineering and functional studies of amino acid biosynthesis in yeast.