Mitochondrial aspartate aminotransferase ( ) inactivation causes glutamate-requiring mutation in .

Two genomic genes, which rescue ammonium assimilation defect in the glutamate-requiring mutant, were identified. The , encoding a mitochondrial aspartate aminotransferase, is the causative gene of mutation because an inseparable linkage between and on the chromosome, and also the mutant strain has a nonsense mutation within the coding region, which is responsible for its defective phenotype. The , a mitochondrial 2-oxoglutarate carrier, was also isolated as a weak multicopy suppressor gene. These findings reiterate the importance of the mitochondria in utilizing the amino acids for cellular nitrogen metabolism.