A ROLE FOR RECOMBINATION JUNCTIONS IN THE SEGREGATION OF MITOCHONDRIAL-DNA IN YEAST

In S. cerevisiae, mitochondrial DNA (mtDNA) molecules, in spite of the ir high copy number, segregate as if there were a small number of heri table units. The rapid segregation of mitochondrial genomes can be ana lyzed using mtDNA deletion variants. These small, amplified genomes se gregate preferentially from mixed zygotes relative to wild-type mtDNA. This segregation advantage is abolished by mutations in a gene, MGT1, that encodes a recombination junction-resolving enzyme. We show here that resolvase deficiency causes a larger proportion of molecules to b e linked together by recombination junctions, resulting in the aggrega tion of mtDNA into a small number of cytological structures. This chan ge in mtDNA structure can account far the increased mitotic loss of mt DNA and the altered pattern of mtDNA segregation from zygotes. We prop ose that the level of unresolved recombination junctions influences th e number of heritable units of mtDNA.