Electron microscopic analysis of the yeast mitochondrial DNA segment conferring chloramphenicol resistance.

Mitochondrial DNAs from six p- mutants carrying the genetic locus Rib1 and deleted for the rest of the genome were analyzed. Distribution of circular molecules from one mutant followed exactly the frequency rule, l/n, for multimers with discreet classes n, 2n, 3n, etc. Another, genetically unstable mutant displayed a continuous spectrum of circular molecules of various lengths. Four other mutants contained multiple series of circular molecules. Partial denaturation maps show that the mutants analyzed show a common segment ca. 1.0 micron long and differ by characteristic deletions of extremites of this segment. Short terminal deletions of the right i.e. pointing towards the Rib3 locus, terminus of this segment are correlated with modifications of the recombination properties related to the omega locus.