Evidence for the dark repair of ultraviolet damage in Saccharomyces cerevisiae mitochondrial DNA.

Evidence for the dark repair of ultraviolet damage to yeast mitochondrial DNA has been observed. The ultraviolet dose necessary to inflict significant damage to both nuclear and mitochondrial DNA was determined. Cell survival at large doses of ultraviolet light was observed after immediate and delayed plating of yeast onto 1% pyruvate and 1% glucose media. In the highly lethal dose ranges of irradiation an increase in the number of normal colonies appeared after a period of liquid holding and delayed plating. This increase, demonstrated separately on 1% glucose and 1% pyruvate media suggested that the repair of both mitochondrial and nuclear DNA had occurred. After low doses of ultraviolet light an actual decrease in the number of petite survivors was seen after delayed plating, even though the total number of survivors increased. When a known repair inhibitor, caffeine, was added to the liquid holding buffer prior to the delayed plating of yeast, a marked decrease in the number of petites did not occur after delayed plating. Therefore, the decrease in the number of petite survivors after delayed plating following low doses of ultraviolet light is attributed to the repair of yeast mitochondrial DNA.