Extragenomic double-stranded DNA circles in yeast with linear mitochondrial genomes: potential involvement in telomere maintenance

Although the typical mitochondrial DNA (mtDNA) is portrayed as a circular m olecule, a large number of organisms contain linear mitochondrial genomes c lassified by their telomere structure, The class of mitochondrial telomeres identified in three yeast species, Candida parapsilosis, Pichia philodendr a and Candida salmanticensis, is characterized by inverted terminal repeats each consisting of several tandemly repeating units and a 5' single-strand ed extension. The molecular mechanisms of the origin, replication and maint enance of this type of mitochondrial telomere remain unknown, While studyin g the replication of linear mtDNA of C. parapsilosis by 2-D gel electrophor esis distinct DNA fragments composed solely of mitochondrial telomeric sequ ences were detected and their properties were suggestive of a circular conf ormation, 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, correspon ding 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 analogo us telomeric structure.