DNA Biosynthesis by Isolated Mitochondria: A Replicative Rather Than a Repair Process

Abstract

The previously observed incorporation of deoxynucleoside triphosphate precursors into DNA by isolated rat liver mitochondria could reflect either replication of DNA or a repair process. Density labeling experiments in cesium chloride demonstrate that DNA synthesized in the presence of 5-bromodeoxyuridine triphosphate instead of thymidine triphosphate shows an appreciable increase in density. In some of the molecules undergoing synthesis, the amount of the density increase indicated a replacement of thymine by bromouracil to the extent of 33 percent. This extensive replacement, which would compute to twice this amount if only a single strand of the duplex is labeled, provides evidence for the synthesis of fairly long pieces of DNA. Such synthesis is characteristic of replication rather than repair, and the results thus suggest that mitochondria are able to replicate their own DNA.