Nucleic Acids Research, 2000, Vol. 28, No. 22 4479-4487
© 2000 Oxford University Press
Extragenomic double-stranded DNA circles in yeast with linear mitochondrial genomes: potential involvement in telomere maintenance
1Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599-27514, USA, 2Department of Genetics, Faculty of Natural Sciences, Comenius University, Mlynska dolina B-1 and 3Department of Biochemistry, Faculty of Natural Sciences, Comenius University, Mlynska dolina CH-1, 842 15 Bratislava, Slovakia
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 = 17). Similar results were obtained with two other yeast species (P.philodendra and C.salmanticensis) which possess analogous telomeric structure.
* To whom correspondence should be addressed. Tel: +1 919 966 2151; Fax: +1 919 966 3015; Email: jdg{at}med.unc.edu The authors wish it to be know that, in their opinion, the first two authors should be regarded as joint First Authors
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