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Linear mitochondrial DNAs of yeasts: frequency of occurrence and general features
1Section de Biologie, Institut Curie, Centre Universitaire Paris XI, Orsay, France.
Abstract:
In most yeast species, the mitochondrial DNA (mtDNA) has been reported to be a circular molecule. However, two cases of linear mtDNA with specific termini have previously been described. We examined the frequency of occurrence of linear forms of mtDNA among yeasts by pulsed-field gel electrophoresis. Among the 58 species from the genera Pichia and Williopsis that we examined, linear mtDNA was found with unexpectedly high frequency. Thirteen species contained a linear mtDNA, as confirmed by restriction mapping, and labeling, and electron microscopy. The mtDNAs from Pichia pijperi, Williopsis mrakii, and P. jadinii were studied in detail. In each case, the left and right terminal fragments shared homologous sequences. Between the terminal repeats, the order of mitochondrial genes was the same in all of the linear mtDNAs examined, despite a large variation of the genome size. This constancy of gene order is in contrast with the great variation of gene arrangement in circular mitochondrial genomes of yeasts. The coding sequences determined on several genes were highly homologous to those of the circular mtDNAs, suggesting that these two forms of mtDNA are not of distant origins.
Insights
Linear mitochondrial DNA (mtDNA) occurs frequently in Pichia and Williopsis yeasts. Despite genome size variation, these linear mtDNAs share conserved gene order and homologous termini, suggesting a common origin with circular mtDNA.
Area of Science:
- Mycology
- Molecular Biology
- Genetics
Background:
- Most yeast mitochondrial DNA (mtDNA) is circular.
- Linear mtDNA with specific termini is rare, with only two previously documented cases.
- Understanding mtDNA structure diversity is crucial for evolutionary studies.
Purpose of the Study:
- To investigate the frequency of linear mtDNA in yeast species.
- To characterize the structure and gene organization of linear mtDNA.
- To compare linear and circular mtDNA to infer evolutionary relationships.
Main Methods:
- Pulsed-field gel electrophoresis to detect linear mtDNA.
- Restriction mapping, labeling, and electron microscopy for confirmation.
- Sequence analysis of terminal fragments and gene order determination.
Main Results:
- Linear mtDNA was found in 13 out of 58 examined species of Pichia and Williopsis.
- Terminal fragments of linear mtDNA exhibited homologous sequences.
- Conserved gene order was observed across linear mtDNAs, irrespective of genome size.
- Coding sequences showed high homology to circular mtDNAs.
Conclusions:
- Linear mtDNA is unexpectedly common in certain yeast genera.
- Homologous termini and conserved gene order suggest a shared evolutionary origin between linear and circular mtDNA.
- The findings challenge the paradigm of exclusively circular mtDNA in most yeasts.