Evidence for a two membrane-spanning autonomous mitochondrial DNA replisome.
The unit of inheritance for mitochondrial DNA (mtDNA) is a complex nucleoprotein structure termed the nucleoid. The organization of the nucleoid as well as its role in mtDNA replication remain largely unknown. Here, we show in Saccharomyces cerevisiae that at least two populations of nucleoids exist within the same mitochondrion and can be distinguished by their association with a discrete proteinaceous structure that spans the outer and inner mitochondrial membranes. Surprisingly, this two membrane-spanning structure (TMS) persists and self-replicates in the absence of mtDNA. We tested whether TMS functions to direct the replication of mtDNA. By monitoring BrdU incorporation, we observed that actively replicating nucleoids are associated exclusively with TMS. Consistent with TMS's role in mtDNA replication, we found that Mip1, the mtDNA polymerase, is also a stable component of TMS. Taken together, our observations reveal the existence of an autonomous two membrane-spanning mitochondrial replisome as well as provide a mechanism for how mtDNA replication and inheritance may be physically linked.
Section of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA.
Shelly
S
Meeusen
Jodi
J
Nunnari
D002478:Cells, Cultured; D004256:DNA Polymerase I / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins; D007211:Indoles; D007425:Intracellular Membranes / Q000378:metabolism* / Q000648:ultrastructure; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D009698:Nucleoproteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
C072843:ABF2 protein, S cerevisiae; D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D007211:Indoles; D008164:Luminescent Proteins; C082519:MGM101 protein, S cerevisiae; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; D009698:Nucleoproteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; C007293:DAPI; D004256:DNA Polymerase I; D004259:DNA-Directed DNA Polymerase; C068352:MIP1 protein, S cerevisiae