A second DNA polymerase activity in yeast mitochondria

In eukaryotic cells, there is much evidence to indicate that the replication of the mitochondrial genome is carried out by a specific DNA polymerase named DNA polymerase gamma. In theyeast S, cerevisiae, a DNA polymerase gamma has been partially purified and the gene encoding the catalytic subunit identified. The characteristics of this enzyme are the same as those found in higher eukaryotes, except for the requirement for a higher magnesium concentration. During a purification procedure of yeast mitochondrial DNA polymerase, we have isolated a second DNA polymerase activity. Using different approaches we have ruled out the possibility of nuclear contamination oraproductofproteolysis. From its properties, this new DNA polymerase activity seems to be different from any yeast DNA polymerase. This new mitochondrial DNA polymerase activity provides evidence that the animal model of mitochondrial DNA replication cannot be generalized. The presence of two DNA polymerases in yeast mitochondria could reflect a different replication or repair mechanism.