Mitochondrial autonomy: Synthesis of DNA from RNA templates in isolated mammalian mitochondria

RNA-dependent DNA polymerases, since their initial identification [ 1,2] , have been identified in a variety of cells and viruses [3-lo] including the bacterium E. coli [l l-131 . The presence of RNA directed DNA synthesis in E. coli and in particular the information flow from RNA to DNA documented earlier [ 1 l] raises the question as to whether such information flow occurs in mammalian mitochondria. E. coli and mammalian mitochondria are similar in several respects [ 141 (autonomous synthesis of some macromolecules; response to certain antibiotics such as chloramphenicol, cycloheximide and camptothecin; and possession of DNA without a “nuclear” membrane) and mitochondria are thought by some to have arisen from an evolutionary standpoint from an invasion of eukaryotic cells by prokaryote bacteria and subsequent formation of symbios. The present report describes low levels of an enzyme which could be termed an RNA-dependent DNA polymerase in crude homogenates of mammalian mitochondria.