A Phylogenetic Study on Vertebrate Mitochondria1 DNA Polymerase

Abstract

A phylogenetic survey for the mitochondrial DNA polymerase is presented with the results obtained for all the different classes for the vertebrates [Salmo fario liver, Emys orbicularis liver, Pleurodeles waltlii oocytes, Xenopus laevis oocytes, Cercopithecus aethiops kidney cells (CV-1) mouse fibroblast L-cells and chick embryo]. The operating conditions include the purification of mitochondria, the analysis of the DNA polymerase activity in the extract and the determination of the sedimentation coefficient on sucrose gradients. The utilization of digitonin for removing the external membrane of the orangelle and contaminating proteins was generalized since this detergent shows no effect on the activities of either DNA polymerase .alpha. or .gamma.. The results obtained for the mitochondria of different classes of vertebrates show that the activity responding to the specific assay of DNA polymerase .gamma. tended invariably to increase during purification while that of DNA polymerase .alpha. tended to decrease. In almost all the cases the .gamma.-polymerase represented the only DNA polymerase activity found in the mitochondria after digitonin treatment. The analysis of the sedimentation patterns of the mitochondrial DNA polymerase straongly suggests the presence of a single type of DNA polymerase showing the typical properties of the .gamma.-polymerase. The vertebrate mitochondria contain a well-defined and unique form of DNA polymerase which corresponds to the DNA polymerase .gamma.