Repair of Radiation-Induced Strand Scissions in Nuclear and Mitochondrial DNAs in Tetrahymena pyriformis

Exposure of Tetrahymena pyriformis (W) cells to gamma-radiation (200 krad) caused strand-breaks in nuclear and mitochondrial DNAs as assayed by sedimentation analysis in alkaline sucrose density gradients using lysates of nuclei and mitochondria (prelabeled with [³ H]thymidine). Postirradiation incubation of the cells in the growth medium at 25°C resulted in restitution of single-strand breaks in these DNAs. Both the subcellular organelles exhibited ability to rejoin single-strand scissions in their DNAs (caused by 200 krad gamma-radiation in vitro) when incubated in isotonic buffer at 25°C. The in vitro repair by the subcellular organelles was inhibited by EDTA (1× 10^-3 M). 2,4-Dinitrophenol (5× 10^-5 M) and procaine hydrochloride (3× 10^-3 M) effectively inhibited mitochondrial DNA repair but nuclear DNA repair was not inhibited even at higher concentrations of the chemicals.