Biogenesis of Mitochondria: Analysis of Deletion of Mitochondrial Antibiotic Resistance Markers in Petite Mutants of Saccharomyces cerevisiae1

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Yeast strains carrying markers in several mitochondrial antibiotic resistance loci have been employed in a study of the retention and deletion of mitochondrial genes in cytoplasmic petite mutants. An assessment is made of the results in terms of the probable arrangement and linkage of mitochondrial genetic markers. The results are indicative of the retention of continuous stretches of the mitochondrial genome in most petite mutants, and it is therefore possible to propose a gene order based on co-retention of different markers. The order par, mik1, oli1 is suggested from the petite studies in the case of three markers not previously assigned an unambiguous order by analysis of mitochondrial gene recombination. The frequency of separation of markers by deletion in petites was of an order similar to that obtained by recombination in polar crosses, except in the case of the ery1 and cap1 loci, which were rarely separated in petite mutants. The deletion or retention of the locus determining polarity of recombination (ω) was also demonstrated and shown to coincide with deletion or retention of the ery1, cap1 region of the mitochondrial genome. Petites retaining this region, when crossed with rho+ strains, display features of polarity of recombination and transmission similar to the parent rho+ strain. By contrast a petite determined to have lost the ω+ locus did not show normal polarity of marker transmission. Differences were observed in the relative frequency of retention of markers in a number of strains and also when comparing petites derived spontaneously with those obtained after ultraviolet light mutagenesis. By contrast, a similar pattern of marker retention was seen when comparing spontaneous with ethidium bromide-induced petites.

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