Mitochondrial genetics. VI. The petite mutation in Saccharomyces cerevisiae: interrelations between the loss of the p+ factor and the loss of the drug resistance mitochondrial genetic markers.

The survival of the rho(+) factor and of Drug(R) mitochondrial genetic markers after exposure to ethidium bromide has been studied. A technique allowing the determination of Drug(R) genetic markers among a great number of both grande and petite colonies has been developed. The results have been analyzed by the target theory. The survival of the rho(+) factor is always less than the survival of any Drug(R) genetic marker. The survivals of C(R) and E(R) are similar to each other, while that of O(R) is greater than that of the other two Drug(R) markers. All possible combinations of Drug(R) markers have been found among the rho(-) petite cells induced, while the only type found among the grande colonies is the preexisting one. The loss of the C(R) and E(R) genetic markers was found to be the most frequently concomitant, while the correlation between the loss of the O(R) marker and the other two Drug(R) markers is less strong. Similar results have been obtained after U.V. irradiation. Interpretations concerning the structure of the yeast mitochondrial genome are given and hypotheses on the mechanism of petite mutation discussed.