Sequence rearrangements between mitochondrial DNAs of Torulopsis glabrata and Kloeckera africana identified by hybridization with six polypeptide encoding regions from Saccharomyces cerevisiae mitochondrial DNA

Sequences hybridizing to six mitochondrial DNA encoded polypeptide genes of Saccharomyces cerevisiae have been mapped in the 18·9 and 27·1 kbp² circular mitochondrial DNAs from Torulopsis glabrata and Kloeckera africana. With the possible exception of cytochrome oxidase subunit 1 and ATPase subunit 6 genes, no two hybridizable sequences share the same order in the two mtDNAs nor is there any topographical similarity to S. cerevisiae mtDNA apart from the grouping mentioned above. Because sequence rearrangements are prevalent in yeast mitochondrial DNAs we infer that order is not critical for mitochondrial gene expression and that prokaryotic-like operons do not exist. In contrast to S. cerevisiae, the cytochrome b region in T. glabrata and K. africana is confined to 1·46 or 1·58 kbp, respectively, which suggests that intervening sequences in this gene are either small or absent. On the other hand, hybridizable sequences to a 5·2 kbp portion of the S. cerevisiae cytochrome oxidase subunit 1 gene, retaining exons 3 to 7 or 8, span 3 to 4 kbp in the two mtDNAs. In addition an 0·8 to 0·9 kbp intervening sequence is present in each case, which does not hybridize to either exon or intron regions of the S. cerevisiae probe. These results imply that the cytochrome oxidase subunit 1 gene in both mtDNAs has a mosaic organization of coding and noncoding sequences.