Restriction site variation, length polymorphism and changes in gene order in the mitochondrial DNA of the yeast Kluyveromyces lactics

Complete nucleotide sequence of the mitochondrial DNA from Kluyveromyces lactis

The total nucleotide sequence of the mitochondrial genome of the yeast Kluyveromyces lactis was determined. The DNA is a circular molecule of 40,291 base pairs, with 26.1% GC. It contains a set of protein- and RNA-coding genes equivalent to those of the Saccharomyces cerevisiae mitochondrial genome. The genome size is about one half of that of S. cerevisiae mitochondrial DNA. The difference in size is due essentially to a reduced proportion of intergenic and intronic sequences. The coding sequences occupy about one third of the genome, the rest being composed of AT-rich sequences and numerous short GC-rich clusters that are dispersed mostly in the non-coding regions and a few within coding sequences. The presence of these GC clusters is a characteristic feature common to K. lactis and S. cerevisiae mitochondrial DNA, although their sequence patterns are different. The absence of the NADH dehydrogenase subunit genes distinguishes this yeast and S. cerevisiae from the typically aerobic species. The genetic code appears to be that of the standard fungal mitochondrial genomes, with UGA as a tryptophan codon. There are only 22 transfer RNA genes, those corresponding to CUN and CGN codons being missing. CUN codons are absent in the protein-coding sequences. There are five CGN codons within the open reading frames, but they are located exclusively in the introns, rendering them untranslatable. Introns are found only the genes in KlCOX1 and LrRNA. The transcription promoter motif known in S. cerevisiae and several other yeast species is also present. All genes are transcribed from the same strand, except those on a single 7-kilobase pairs segment (EMBL Accession No. AY654900).

Assessment of phenotypic and genetic diversity in the yeast genus Metschnikowia

The taxonomy of the yeast genus Metschnikowia has undergone profound changes over the past century. Major developments, from the capacity to obtain pure cultures of parasitic species to progress associated with the extensive use of molecular biology tools in yeast systematics, are briefly reviewed. Results from past work and new data are combined to evaluate evolutionary relationships and clarify the classification of both terrestrial and aquatic species. Recent physiological studies, including the utilization of non-conventional carbon and nitrogen sources, and characteristics like lipolytic activity and maximum temperatures for growth, are presented. The assessment of the genetic diversity within the genus by restriction analysis of the mitochondrial DNA and by the production of specific DNA probes has been explored. The results indicate the potential application of the latter in rapid identification procedures.

Larger rearranged mitochondrial genomes in Dekkera/Brettanomyces yeasts are more closely related than smaller genomes with a conserved gene order

Mitochondrial genomes from yeasts in the Dekkera/Brettanomyces/Eeniella group vary in size from 28 to 101 kb. Mapping of genes has shown that the three smallest genomes, of 28-42 kb, have the same gene order, whereas the three larger mitochondrial DNAs of 57-101 kb are rearranged relative to the smaller molecules and between themselves. To examine the relationships between these genomes, a phylogenetic tree has been constructed by sequence comparison of the mitochondrial-encoded cytochrome oxidase subunit gene (COX2) from the six species. Contrary to expectation, the tree shows that the larger rearranged genomes are more closely related than the smaller mtDNAs. This result indicates that the gene order of the smaller mtDNAs (28-42 kb) is ancestral and that larger mtDNA molecules (57-101 kb) are more prone to rearrangement than smaller forms.