A 2ND DNA-POLYMERASE-ACTIVITY IN YEAST MITOCHONDRIA

In eukaryotic cells, there is much evidence to indicate that the repli cation of the mitochondrial genome is carried out by a specific DNA po lymerase named DNA polymerase gamma. In the yeast S. cerevisiae, a DNA polymerase gamma has been partially purified and the gene encoding th e catalytic subunit identified. The characteristics of this enzyme are the same as those found in higher eukaryotes, except for the requirem ent for a higher magnesium concentration. During a purification proced ure of yeast mitochondrial DNA polymerase, we have isolated a second D NA polymerase activity. Using different approaches we have ruled out t he possibility of nuclear contamination or a product of proteolysis. F rom its properties, this new DNA polymerase activity seems to be diffe rent from any yeast DNA polymerase. This new mitochondrial DNA polymer ase activity provides evidence that the animal model of mitochondrial DNA replication cannot be generalized. The presence of two DNA polymer ases in yeast mitochondria could reflect a different replication or re pair mechanism.