The mapping of mutations in tRNA and cytochrome oxidase genes located in the cap-par segment of the mitochondrial genome of S. cerevisiae

Abstract

1. Two mutants have been isolated which carry mutations in mitochondrial tRNA genes; one in the aspartyl-tRNA gene and the other in one of the threonyl-tRNA genes. The mutant tRNAs are unable to be charged with their respective amino acids. 2. These two mutations are located on the mitochondrial genome in the cap-par segment. Analyses of genetic recombination frequencies and co-retention and co-deletion frequencies of markers in petite strains yield an unambiguous gene order cap-asp-oxi 1-thr 1-oxi 2-par. 3. Two loci involved in the specification of cytochrome oxidase (oxi1 and oxi2) show an average recombination frequency of 14% in pairwise crosses involving mutations of both loci. Although the two loci have a related function and are genetically linked they are shown to be separated by at least one tRNA gene. 4. Pairwise intralocus crosses involving mit- mutations within either the oxi1 or oxi2 locus yield recombination frequencies <0.02–3.2%. However, no unique order could be derived for 19 oxi 1 and 6 oxi 2 mutations based on these data. In addition, the separation of mutant alleles within a single locus as the result of petite mutation was very rare. Consequently, attempts to order mutations within the locus from an analysis of the flanking markers in petites where separation occurred, provided only limited resolution. 5. A discussion is presented of the limitations of the current mitochondrial genetic mapping techniques when applied to the fine resolution of glycerol negative mit- and syn- mutations.