REGULATION OF MITOCHONDRIAL TRANSCRIPTION BY MITOCHONDRIAL TRANSCRIPTION FACTOR-A

In order to test the hypothesis that mitochondrial transcription facto r A (mtTFA) regulates mitochondrial transcription in vivo, mtTFA was o verexpressed in HeLa cells and imported into isolated rat liver mitoch ondria. Five hours after transfection with an eukaryotic expression ve ctor, mitochondrial transcripts for cytochrome-c-oxidase subunit I and 12 S rRNA were increased over controls. In the presence of rat liver mitochondria, the 29 kDa mtTFA, generated by in vitro, translation, wa s processed to a 24 kDa protein which was protected from protease dige stion. This demonstrates that mtTFA was imported into the matrix. Inco rporation of P-32-UTP into mitochondrial transcripts was stimulated fo llowing import of mtTFA. We conclude that the intracellular and intram itochondrial concentration of mtTFA, respectively, indeed regulates mi tochondrial transcription.