Reference: Baichwal V, et al. (1983) Leucine biosynthesis in yeast. Identification of two genes (LEU4, LEU5) that affect alpha-Isopropylmalate synthase activity and evidence that LEU1 and LEU2 gene expression is controlled by alpha-Isopropylmalate and the product of a regulatory gene. Curr Genet 7(5):369-377