STUDIES ON BIOSYNTHESIS OF DNA POLYMERASE OF RAT LIVER MITOCHONDRIA

The biosynthesis of mitochondrial DNA polymerase was studied by determining the extent of isotope incorporated into the partially purified enzyme which had been isolated from mitochondria labeled in both in vivo and in vitro experiments. The DNA polymerase, isolated from mitochondria incubated with 14C-leucine or 14C-mixed l-amino acids in vitro, showed no incorporation of radioactivity under conditions where the residue fraction of mitochondria (membranes) from the enzyme isolation contained a level of radioactivity which approached the specific activity of whole mitochondria. Kinetic studies carried out in vivo showed that 3H-leucine was rapidly incorporated into the residue fraction of mitochondria and at time periods as short as 2 min, had a specific activity almost equal to that of whole mitochondria. The partially purified enzyme incorporated radioactivity more slowly and only after 60 min exposure to the 3H-leucine did the enzyme have a specific radioactivity equal to that of whole mitochondria. Moreover, the incorporation of radioactivity observed in the enzyme after 60 min was prevented by the prior injection of cycloheximide, an inhibitor of microsomal incorporation. These results tentatively support the hypothesis that mitochondrial DNA polymerase, like cytochrome c, may be synthesized extramitochondrially and transported into the organelle. © 1969.