A complex of Mgm101 (green) and Mmm1 (red) controls mtDNA (blue) replication.
The mitochondrial genome (mtDNA) is packaged into nucleoids, some of which attach to the mitochondrial membrane at sites that contain the outer membrane protein Mmm1. Mmm1 binds to the actin cytoskeleton, and mitochondrial movement depends on actin, so one obvious hypothesis is that this DNA–protein structure segregates mtDNA into buds. But Meeusen and Nunnari suggest that Mmm1 and associated proteins replicate, rather than actively segregate, the genome.
The authors find that Mmm1-linked nucleoids are associated with both replicating mtDNA and proteins necessary for its duplication, including Mgm101, an essential DNA repair protein, and Mip1, the mtDNA polymerase. These proteins make up an independent structure, spanning two membranes, that is replicated and inherited even in the absence of...
