Assembly of the mitochondrial membrane system. Complete restriction map of the cytochrome b region of mitochondrial DNA in Saccharomyces cerevisiae D273-10B.

The cytoplasmic petite (rho-) mutant DS400/A12 has been obtained from the wild type strain of Saccharomyces cerevisiae D273-10B/A21. The DS400/A12 clone has a mitochondrial genome with a 7.6-kilobase pair, tandemly repeated segment of DNA. Genetic tests indicate that DS400/A12 contains all the cob1 and cob2 markers of the cytochrome b gene. The gene has been further dissected by mutagenesis of DS400/A12 and selection of secondary rho- clones with simpler genotypes. Restriction analysis of the mtDNAs of the rho- clones was used to construct the complete restriction map of the cytochrome b region and to map the mutations within narrowly defined physical limits. The cytochrome b mutants scatter over a maximal distance of 3.3 kilobase pairs. All the mutations assigned previously to the cob2 locus are found between 71.6 and 73.2 units. The cob1 mutations are located between 74.6 and 76.3 units. The estimated distance between the two loci is at least 1 kilobase pair.