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Control of the Mitochondrial Genome in Saccharomyces cerevisiae

THE FATE OF MITOCHONDRIAL MEMBRANE PROTEINS AND MITOCHONDRIAL DEOXYRIBONUCLEIC ACID DURING PETITE INDUCTION

From the ¹ From the Department of Biochemical Sciences, Frick Chemical Laboratory, Princeton University, Princeton, New Jersey 08540

A mutant of Saccharomyces cerevisiae which issues cytoplasmic petite (^-) progeny at 18° or during growth at 28° on medium containing 3 mg per ml of chloramphenicol was examined to determine the fate of mitochondrial membrane proteins and mitochondrial DNA during the petite induction process. Labeling of mitochondria in vivo with radioactive leucine in the presence of 200 µg per ml of cycloheximide and subsequent separation of the labeled proteins on sodium dodecyl sulfate acrylamide gels yields a gel pattern consisting of seven or eight protein species ranging in molecular weight from 13,000 to 45,000. This pattern is much simpler than that obtained from mitochondria isolated from cells labeled in vivo without drugs and presumably represents products of mitochondrial protein synthesis.

The mitochondrial gel profile of the mutant strain 1121, when compared with that of parent strain 55-R5-3C, undergoes striking alterations during petite induction at 18° which include (a) a loss of a molecular weight 41,000 component, (b) a decrease in the synthesis of a 24,000 component, and (c) an apparent increase in low molecular weight (13,000) material. Changes in the mitochondrial gel profile of strain 1121 during petite induction by growth at 28° in the presence of chloramphenicol are restricted to a decrease in the appearance of a molecular weight 41,000 component.

Growth of strain 1121 at 18° results in an apparent decrease of mitochondrial DNA from the bulk population. The subcloning of randomly selected cytoplasmic petites issued at 18° by strain 1121 gives two types of cells, those with detectable mitochondrial DNA and those apparently lacking mitochondrial DNA, illustrating a genetic heterogeneity in the 18° petite population.

We suggest that the alterations in the 1121 gel profiles of mitochondria obtained from cells during 18° growth or growth at 28° with chloramphenicol reflect the improper formation of a membrane component related to the maintenance of the ⁺ genotype.

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