DNA biosynthesis by isolated mitochondria. Stimulation by cytoplasmic factors from neoplastic and regenerating tissues.

The incorporation of radioactively labeled dTTP or dATP by rat liver mitochondria in vitro is stimulated by factors present in the postmicrosomal fraction of rat and mouse tumors and in regenerating and fetal rat liver, but not in normal liver. The observed stimulation is completely abolished by ethidium bromide, a specific inhibitor of mitochondrial DNA polymerase in mammalian systems. The stimulatory activity is nondialyzable, heat labile, insensitive to DNase and RNase, and precipitated by 30 to 50% ammonium sulfate. Fractionation of the crude rat hepatoma supernatant on a DNA-cellulose column has led to the separation of two active peaks containing negatively charged proteins which bind specifically to DNA and which are eluted by 0.15 and 0.30 M NaCl, respectively. These eluates contain all of the stimulatory activity of unfractionated hepatoma supernatant.