ULTRAVIOLET IRRADIATION STUDIES ON CYTOPLASMIC DETERMINANT OF YEAST MITOCHONDRION

Ultraviolet induction of the cytoplasmic petite mutation in yeast was studied under a variety of growth conditions both before and after irradiation. The induction curves were found to be single-event for anaerobically-grown cells, and multiple-event for aerobic cells. By using a split dose technique, both photo-reactivation and dark-repair were investigated. No significant difference in repair ability was found between aerobic and anaerobic cells. A target theory interpretation of the induction curves suggests that mitochondrial DNA, assumed to be the genetic determinant, exists as a single heritable unit in anaerobic cells, and as multiple units in aerobic cells; moreover, the number of genetically effective copies in the aerobic cells appears to be far smaller than the number of mitochondria. These results are shown to be in accord with an independent estimate of the number of cytoplasmic determinants derived from recent genetic studies on mitochondrial recombination in aerobic and anaerobic yeast cells. © 1968.