Mitochondrial DNA in yeast recombination and subsequent modification following mating between a grande and a suppressive petite |
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Authors: | John Blamire Corinne A. Michels Jean M. Walsh Debra L. Friedenberg |
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Affiliation: | (1) National Institute for Medical Research, Mill Hill, NW7 1AA London, England;(2) Present address: Department of Molecular Biology and Biochemistry, University of California, 92717 Irvine, California, USA |
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Abstract: | Summary The fluorinated pyrimidines 5-fluorouracil (5FU) and 5-fluorocytosine (5FC) induce the cytoplasmic petite mutation in the yeastSaccharomyces cerevisiae with high efficiency. It was found that in order to induce the mutation, 5FC must first be deaminated to 5FU. However, mutagenesis does not depend on the further conversion of 5FU to its deoxyriboside (5FUDR) and subsequent blockade of intracellular thymidine synthesis, since 5FUDR itself was found not to be mutagenic, and 5FU-induced mutagenesis was not antagonised by supplying thymidine monophosphate (dTMP) to a dTMP permeable strain. In any case, observations of the molecular changes accompanying petite induction in log phase cells ruled out the possibility that mutagenesis resulted simply from the dilution out of replication-blocked mitDNA molecules, since the appearance of mutants coincided with the synthesis of altered mitDNA molecules. In different strains, the resulting defective molecules were either maintained, giving rise to suppressive – petites, or completely degraded, to give pure clones of neutral 0 mutants. It is suggested that this degradative process was a consequence of the incorporation of 5FU into RNA. |
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