A novel mitochondrial DNA replication intermediate in the yeast saccharomyces cerevisiae /

Abstract

Mitochondria are small organelles that function as the biological powerhouses of the cell by acting as the principal site ofATP production in aerobic cells. They contain their own genome (mtDNA) that replicates independently from chromosomal DNA in the nucleus. Several human degenerative diseases including neuropathies, myopathies, diabetes and some cancers have been recently discovered that involve large-scale rearrangements of mtDNA. MtDNA mutations are also the cause of many inherited human diseases such as MELAS, LOHN and MERRF. It has also been proposed that the aging process is influenced by accumulated damage (referred to as common deletions) in ~tDNA. Very little is known concerning the relative transmission of normal or mutant mtDNAs, or for that matter, control of mitochondrial DNA replication itself. In the yeast Saccharomyces cervisiae, Mutant yeast mtDNAs that contain deletions termed (p-) can create a phenotype called hupersuppressive (HSp-) that possess a huge replication advantage over wild-type mtDNA and are preferentially inherited. Our studies using 2-D gel DNA electrophoresis to analyze mtDNA replication intermediate structures from both wild-type and mutant strains during log phase growth, when mtDNA production is high, show novel replication intermediates of single stranded and supercoiled mtDNA forms. The current theory ofmtDNA replication in yeast is based on a mammalian D loop model (Clayton, 1985). This method is asynchronous asymmetrical replication that does not include single stranded mtDNA or supercoiled DNA forms. From our data we suggest that there are alternative mtDNA replication mechanisms, i.e. Rolling Circle or recombination dependant replication, in yeast, which account for these novel forms.