Morphology and organization of mitochondrial nucleoids in life cycle of the yeast Saccharomyces cerevisiae

Abstract

Mitochondrial DNA (mtDNA) is associated with specific proteins to form mitochondrial nucleoids (mt-nucleoids). We investigated morphological changes in mt-nucleoids during life cycle of the yeast, Saccharomyces cerevisiae by DAPI-fluorescence microscopy. The mt-nucleoids showed a string-of-beads appearance in log-phase cells and a small spherical one in stationary-phase cells, respectively. During meiosis and sporulation, the mt-nucleoids formed a distinct network during meiotic prophase and were distributed into spores. During the course of anaerobic culture, the mt-nucleoids formed large aggregates in stationary-phase cells. These large mt-nucleoids elongated and were dynamically dispersed into small ones during the transition from anaerobic to aerobic culture. The morphology of mt-nucleoids in rho^- respiratory-deficient cells significantly varied depending on the unit length of their mtDNA sequence. We analyzed the protein components of the isolated mt-nucleoids. A DNA-binding protein Abf2p is a major component of the mt-nucleoids and plays roles in packaging mtDNA. A number of proteins other than Abf2p are also associated with mt-nucleoids. By comparison of Abf2p homologues in several yeast species, we revealed that Abf2p is a highly diverged protein among the mt-nucleoid proteins.