The structure of the small mitochondrial DNA of Kluyveromyces thermotolerans is likely to reflect the ancestral gene order in fungi.

Mapping the 23-kb circular mitochondrial DNA from the yeast Kluyveromyces thermotolerans has shown that only one change occurs in the gene order in comparison to the 19-kb mtDNA of Candida (Torulopsis) glabrata. Sequence analysis of the mitochondrially encoded cytochrome oxidase subunit 2 gene reveals that despite their conserved gene order, the two small genomes are more distantly related than larger mtDNA molecules with multiple rearrangements. This result supports a previous observation that larger mitochondrial genomes are more prone to rearrange than smaller forms and suggests that the architecture of the two small molecules is likely to represent the structure of an ancestor.