Characterization of components required to maintain mitochondrial DNA and mitochondrial morphology in the yeast, Saccharomyces cerevisiae

Mitochondria are highly dynamic organelles bound by both an outer and inner membrane and contain their own genome, which is separate from the cell nucleus. In Saccharomyces cerevisiae, mitochondria are branched reticular structures localized to the cell cortex that are maintained by a balance of fission and fusion. Since they can not be made de novo , both mitochondria and mitochondrial DNA (mtDNA) must be inherited from mother to daughter cell. Within the organelle, mtDNA is packaged into higher order structures, termed nucleoids. A number of components have been identified in S. cerevisiae that are required for maintaining nucleoids, including components required for DNA replication, recombination, repair, and packaging. A number of components have also been identified to be required for maintaining mitochondrial morphology, including cytoskeletal elements as well as proteins that are directly associated with mitochondria. Here, a combination of genetics and biochemistry has been used to characterize two proteins, Mgm101p and Mgm1p. Mgm101p is required for maintaining mtDNA, but not mitochondrial morphology, whereas Mgm1p is essential for maintaining branched, reticular mitochondria as well as mtDNA. Mgm101p was found to interact directly with mtDNA and is required for mtDNA repair. In contrast, Mgm1p was identified to be an intermembrane space protein required for mitochondrial fusion, and has been hypothesized to coordinate inner and outer membrane actions during fusion.