The ogd1 and kgd1 mutants lacking 2-oxoglutarate dehydrogenase activity in yeast are allelic and can be differentiated by the cloned amber suppressor.

The activity of mitochondrial 2-oxoglutarate dehydrogenase in S. cerevisiae can be impaired either by the ogd1 or the kgd1 mutation. The OGD1 gene and two suppressor genes were isolated by complementation of the ogd1 mutant. The complementation of the kdg1 mutant by the OGD1 gene, an allelism test, and meiotic mapping, revealed that the ogd1 and kgd1 mutations are allelic. The two mutations were differentiated by the cloned suppressor gene which was able to partially complement ogd1, but not kgd1. The molecular analysis of the suppressor gene revealed its identity with the natural tRNA(GlnCAG) gene found in the upstream region of URA10.