title: Mitochondrial fusion increases the mitochondrial DNA copy number in budding yeast.
abstract: Mitochondrial fusion plays an important role in mitochondrial DNA (mtDNA) maintenance, although the underlying mechanisms are unclear. In budding yeast, certain levels of reactive oxygen species (ROS) can promote recombination-mediated mtDNA replication, and mtDNA maintenance depends on the homologous DNA pairing protein Mhr1. Here, we show that the fusion of isolated yeast mitochondria, which can be monitored by the bimolecular fluorescence complementation-derived green fluorescent protein (GFP) fluorescence, increases the mtDNA copy number in a manner dependent on Mhr1. The fusion event, accompanied by the degradation of dissociated electron transport chain complex IV and transient reductions in the complex IV subunits by the inner membrane AAA proteases such as Yme1, increases ROS levels. Analysis of the initial stage of mitochondrial fusion in early log-phase cells produced similar results. Moreover, higher ROS levels in mitochondrial fusion-deficient mutant cells increased the amount of newly synthesized mtDNA, resulting in increases in the mtDNA copy number. In contrast, reducing ROS levels in yme1 null mutant cells significantly decreased the mtDNA copy number, leading to an increase in cells lacking mtDNA. Our results indicate that mitochondrial fusion induces mtDNA synthesis by facilitating ROS-triggered, recombination-mediated replication and thereby prevents the generation of mitochondria lacking DNA.
authors.affiliation: Chemical Genetics Laboratory, RIKEN Advanced Science Institute, Hirosawa, Wako-shi, Saitama, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Hori
authors.forename: Minoru
authors.initials: M
authors.lastname: Yoshida
authors.forename: Feng
authors.initials: F
authors.lastname: Ling
mesh_terms: D049069:ATP-Dependent Proteases / Q000235:genetics / Q000378:metabolism; D015139:Blotting, Southern; D015153:Blotting, Western; D004272:DNA, Mitochondrial / Q000235:genetics*; D003576:Electron Transport Complex IV / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D017382:Reactive Oxygen Species / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; C417727:MHR1 protein, S cerevisiae; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D017382:Reactive Oxygen Species; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; C117108:cytochrome C oxidase subunit II; C093750:COX3 protein, S cerevisiae; D003576:Electron Transport Complex IV; D049069:ATP-Dependent Proteases; C082702:YME1 protein, S cerevisiae; C401395:FZO1 protein, S cerevisiae; D020558:GTP Phosphohydrolases