Autonomous replication activity of a human mitochondrial DNA sequence inserted into genomic DNA

Mitochondrial DNA (mtDNA) fragments can be found inserted into nuclear DNA and may contribute to cancer and aging. A HeLaTG-cell nuclear transcript was shown to include human cytochrome oxidase subunit 3 (coxIII) mtDNA fused to c-myc sequences. Independently, a coxIII-containing cDNA was discovered to replicate autonomously in HeLa cells. We show that the HeLaTG mtDNA insertion has autonomous replication activity when transfected into HeLa cells and in a mammalian in vitro replication system. Replication in vitro starts within the fusion cDNA sequence. Insertion of an element which could function as a replication origin may affect cellular DNA replication and proliferation.