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  • American Society for Cell Biology (ASCB)  (5)
  • 1
    Online Resource
    Online Resource
    American Society for Cell Biology (ASCB) ; 1998
    In:  Molecular Biology of the Cell Vol. 9, No. 9 ( 1998-09), p. 2375-2382
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 9, No. 9 ( 1998-09), p. 2375-2382
    Abstract: Mammalian mitochondrial ribosomes contain two prokaryotic-like rRNAs, 12S and 16S, both encoded by mitochondrial DNA. As opposed to cytosolic ribosomes, however, these ribosomes are not thought to contain 5S rRNA. For this reason, it has been unclear whether 5S rRNA, which can be detected in mitochondrial preparations, is an authentic organellar species imported from the cytosol or is merely a copurifying cytosol-derived contaminant. We now show that 5S rRNA is tightly associated with highly purified mitochondrial fractions of human and rat cells and that 5S rRNA transcripts derived from a synthetic gene transfected transiently into human cells are both expressed in vivo and present in highly purified mitochondria and mitoplasts. We conclude that 5S rRNA is imported into mammalian mitochondria, but its function there still remains to be clarified.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 1998
    detail.hit.zdb_id: 1474922-1
    SSG: 12
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  • 2
    Online Resource
    Online Resource
    American Society for Cell Biology (ASCB) ; 2003
    In:  Molecular Biology of the Cell Vol. 14, No. 9 ( 2003-09), p. 3628-3635
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 14, No. 9 ( 2003-09), p. 3628-3635
    Abstract: Mutations in mitochondrial DNA (mtDNA) cause impairment of ATP synthesis. It was hypothesized that high-energy compounds, such as ATP, are compartmentalized within cells and that different cell functions are sustained by different pools of ATP, some deriving from mitochondrial oxidative phosphorylation (OXPHOS) and others from glycolysis. Therefore, an OXPHOS dysfunction may affect different cell compartments to different extents. To address this issue, we have used recombinant forms of the ATP reporter luciferase localized in different cell compartments— the cytosol, the subplasma membrane region, the mitochondrial matrix, and the nucleus— of cells containing either wild-type or mutant mtDNA. We found that with glycolytic substrates, both wild-type and mutant cells were able to maintain adequate ATP supplies in all compartments. Conversely, with the OXPHOS substrate pyruvate ATP levels collapsed in all cell compartments of mutant cells. In wild-type cells normal levels of ATP were maintained with pyruvate in the cytosol and in the subplasma membrane region, but, surprisingly, they were reduced in the mitochondria and, to a greater extent, in the nucleus. The severe decrease in nuclear ATP content under “OXPHOS-only” conditions implies that depletion of nuclear ATP plays an important, and hitherto unappreciated, role in patients with mitochondrial dysfunction.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2003
    detail.hit.zdb_id: 1474922-1
    SSG: 12
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  • 3
    Online Resource
    Online Resource
    American Society for Cell Biology (ASCB) ; 2000
    In:  Molecular Biology of the Cell Vol. 11, No. 4 ( 2000-04), p. 1471-1485
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 11, No. 4 ( 2000-04), p. 1471-1485
    Abstract: Mitochondria from patients with Kearns–Sayre syndrome harboring large-scale rearrangements of human mitochondrial DNA (mtDNA; both partial deletions and a partial duplication) were introduced into human cells lacking endogenous mtDNA. Cytoplasmic hybrids containing 100% wild-type mtDNA, 100% mtDNA with partial duplications, and 100% mtDNA with partial deletions were isolated and characterized. The cell lines with 100% deleted mtDNAs exhibited a complete impairment of respiratory chain function and oxidative phosphorylation. In contrast, there were no detectable respiratory chain or protein synthesis defects in the cell lines with 100% duplicated mtDNAs. Unexpectedly, the mass of mtDNA was identical in all cell lines, despite the fact that different lines contained mtDNAs of vastly different sizes and with different numbers of replication origins, suggesting that mtDNA copy number may be regulated by tightly controlled mitochondrial dNTP pools. In addition, quantitation of mtDNA-encoded RNAs and polypeptides in these lines provided evidence that mtDNA gene copy number affects gene expression, which, in turn, is regulated at both the post-transcriptional and translational levels.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2000
    detail.hit.zdb_id: 1474922-1
    SSG: 12
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  • 4
    Online Resource
    Online Resource
    American Society for Cell Biology (ASCB) ; 2000
    In:  Molecular Biology of the Cell Vol. 11, No. 7 ( 2000-07), p. 2349-2358
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 11, No. 7 ( 2000-07), p. 2349-2358
    Abstract: Large-scale rearrangements of mitochondrial DNA (mtDNA; i.e., partial duplications [dup-mtDNAs] and deletions [Δ-mtDNAs] ) coexist in tissues in a subset of patients with sporadic mitochondrial disorders. In order to study the dynamic relationship among rearranged and wild-type mtDNA (wt-mtDNA) species, we created transmitochondrial cell lines harboring various proportions of wt-, Δ-, and dup-mtDNAs from two patients. After prolonged culture in nonselective media, cells that contained initially 100% dup-mtDNAs became heteroplasmic, containing both wild-type and rearranged mtDNAs, likely generated via intramolecular recombination events. However, in cells that contained initially a mixture of both wt- and Δ-mtDNAs, we did not observe any dup-mtDNAs or other new forms of rearranged mtDNAs, perhaps because the two species were physically separated and were therefore unable to recombine. The ratio of wt-mtDNA to Δ-mtDNAs remained stable in all cells examined, suggesting that there was no replicative advantage for the smaller deleted molecules. Finally, in cells containing a mixture of monomeric and dimeric forms of a specific Δ-mtDNA, we found that the mtDNA population shifted towards homoplasmic dimers, suggesting that there may be circumstances under which the cells favor molecules with multiple replication origins, independent of the size of the molecule.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2000
    detail.hit.zdb_id: 1474922-1
    SSG: 12
    Location Call Number Limitation Availability
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  • 5
    Online Resource
    Online Resource
    American Society for Cell Biology (ASCB) ; 2002
    In:  Molecular Biology of the Cell Vol. 13, No. 11 ( 2002-11), p. 3836-3844
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 13, No. 11 ( 2002-11), p. 3836-3844
    Abstract: Unlike most organisms, the mitochondrial DNA (mtDNA) ofChlamydomonas reinhardtii, a green alga, does not encode subunit 6 of F 0 F 1 -ATP synthase. We hypothesized that C. reinhardtii ATPase 6 is nucleus encoded and identified cDNAs and a single-copy nuclear gene specifying this subunit (CrATP6, with eight exons, four of which encode a mitochondrial targeting signal). Although the algal and humanATP6 genes are in different subcellular compartments and the encoded polypeptides are highly diverged, their secondary structures are remarkably similar. When CrATP6 was expressed in human cells, a significant amount of the precursor polypeptide was targeted to mitochondria, the mitochondrial targeting signal was cleaved within the organelle, and the mature polypeptide was assembled into human ATP synthase. In spite of the evolutionary distance between algae and mammals, C. reinhardtii ATPase 6 functioned in human cells, because deficiencies in both cell viability and ATP synthesis in transmitochondrial cell lines harboring a pathogenic mutation in the human mtDNA-encoded ATP6 gene were overcome by expression of CrATP6. The ability to express a nucleus-encoded version of a mammalian mtDNA-encoded protein may provide a way to import other highly hydrophobic proteins into mitochondria and could serve as the basis for a gene therapy approach to treat human mitochondrial diseases.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2002
    detail.hit.zdb_id: 1474922-1
    SSG: 12
    Location Call Number Limitation Availability
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