Pyruvate carboxylase in the yeast pyc mutant.

Pyruvate carboxylase deficiency was previously reported to be the biochemical lesion in a yeast mutant, designated pyc, which cannot utilize ethanol, acetate, pyruvate, aspartate, or oxaloacetate as the sole carbon source [C. Wills and T. Melham (1985) Arch. Biochem. Biophys. 236, 782-791; C. Wills et al. (1986) Arch. Biochem. Biophys. 246, 306-320]. We present evidence here that the level of pyruvate carboxylase activity as well as the native and subunit molecular weights of this enzyme are identical in the mutant and the wild type. In addition we have used immunocytochemical labeling to demonstrate the exclusively cytosolic localization of this enzyme in both the mutant and wild-type yeast.