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Extragenomic double-stranded DNA circles in yeast with linear mitochondrial genomes: potential involvement in
L Tomaska1, J Nosek, A M Makhov
1Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599-27514, USA.
Abstract:
Although the typical mitochondrial DNA (mtDNA) is portrayed as a circular molecule, a large number of organisms contain linear mitochondrial genomes classified by their telomere structure. The class of mitochondrial telomeres identified in three yeast species, Candida parapsilosis, Pichia philodendra and Candida salmanticensis, is characterized by inverted terminal repeats each consisting of several tandemly repeating units and a 5' single-stranded extension. The molecular mechanisms of the origin, replication and maintenance of this type of mitochondrial telomere remain unknown. While studying the replication of linear mtDNA of C.parapsilosis by 2-D gel electrophoresis distinct DNA fragments composed solely of mitochondrial telomeric sequences were detected and their properties were suggestive of a circular conformation. Electron microscopic analysis of these DNAs revealed the presence of highly supertwisted circular molecules which could be relaxed by DNase I. The minicircles fell into distinct categories based on length, corresponding to n x 0.75 kb (n = 1-7). Similar results were obtained with two other yeast species (P.philodendra and C. salmanticensis) which possess analogous telomeric structure.
Insights
Linear mitochondrial DNA (mtDNA) in certain yeasts, characterized by unique telomeres, can form circular minicircles. These minicircles, detected during replication studies, suggest novel structures in mitochondrial genomes.
Area of Science:
- Molecular Biology
- Genetics
- Yeast Biology
Background:
- Mitochondrial DNA (mtDNA) is typically circular, but linear forms exist in many organisms.
- Linear mtDNA telomeres in yeast species like Candida parapsilosis feature inverted terminal repeats and single-stranded extensions.
- The replication and maintenance mechanisms of these linear mitochondrial telomeres are not well understood.
Purpose of the Study:
- To investigate the replication of linear mtDNA in Candida parapsilosis.
- To characterize the molecular mechanisms underlying the formation and structure of linear mtDNA telomeres.
Main Methods:
- Two-dimensional (2-D) gel electrophoresis was employed to study mtDNA replication.
- Electron microscopy was used to visualize DNA structures.
- DNase I treatment was applied to analyze DNA molecule properties.
Main Results:
- Distinct DNA fragments composed solely of mitochondrial telomeric sequences were detected.
- These fragments exhibited properties indicative of a circular conformation.
- Electron microscopy revealed highly supercoiled circular molecules (minicircles) of varying lengths (n x 0.75 kb, n=1-7), reducible by DNase I, in C. parapsilosis, P. philodendra, and C. salmanticensis.
Conclusions:
- Linear mtDNA in these yeast species can form circular minicircles composed of telomeric sequences.
- These findings suggest a unique mode of replication or maintenance for linear mitochondrial genomes.
- The presence of these minicircles provides new insights into the structural diversity of mitochondrial DNA.