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MMM1 encodes a mitochondrial outer membrane protein essential for establishing and maintaining the structure of yeast
S M Burgess1, M Delannoy, R E Jensen
1Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Abstract:
In the yeast Saccharomyces cerevisiae, mitochondria are elongated organelles which form a reticulum around the cell periphery. To determine the mechanism by which mitochondrial shape is established and maintained, we screened yeast mutants for those defective in mitochondrial morphology. One of these mutants, mmm1, is temperature-sensitive for the external shape of its mitochondria. At the restrictive temperature, elongated mitochondria appear to quickly collapse into large, spherical organelles. Upon return to the permissive temperature, wild-type mitochondrial structure is restored. The morphology of other cellular organelles is not affected in mmm1 mutants, and mmm1 does not disrupt normal actin or tubulin organization. Cells disrupted in the MMM1 gene are inviable when grown on nonfermentable carbon sources and show abnormal mitochondrial morphology at all temperatures. The lethality of mmm1 mutants appears to result from the inability to segregate the aberrant-shaped mitochondria into daughter cells. Mitochondrial structure is therefore important for normal cell function. Mmm1p is located in the mitochondrial outer membrane, with a large carboxyl-terminal domain facing the cytosol. We propose that Mmm1p maintains mitochondria in an elongated shape by attaching the mitochondrion to an external framework, such as the cytoskeleton.
Insights
The MMM1 gene is crucial for maintaining mitochondrial shape in yeast. Mutations disrupt mitochondrial structure, leading to cell inviability due to segregation defects.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Mitochondria in yeast (Saccharomyces cerevisiae) form an elongated, reticular network.
- Understanding the mechanisms of mitochondrial shape maintenance is essential for cell function.
Purpose of the Study:
- To identify genes involved in establishing and maintaining mitochondrial morphology.
- To elucidate the function of the MMM1 gene in mitochondrial shape control.
Main Methods:
- Screening of yeast mutants for defects in mitochondrial morphology.
- Temperature-shift experiments to assess temperature sensitivity.
- Analysis of cellular organelle morphology, actin, and tubulin organization.
- Growth assays on nonfermentable carbon sources.
Main Results:
- The mmm1 mutant exhibits temperature-sensitive defects in mitochondrial shape, collapsing into spherical organelles at restrictive temperatures.
- Mmm1p is localized to the mitochondrial outer membrane.
- Cells with disrupted MMM1 are inviable on nonfermentable media and display abnormal mitochondrial morphology.
- Mitochondrial shape defects, not actin or tubulin disorganization, cause inviability due to segregation issues.
Conclusions:
- Mitochondrial structure is vital for normal cell function and proper segregation into daughter cells.
- Mmm1p likely maintains mitochondrial shape by anchoring mitochondria to external cellular structures.
- The MMM1 gene product plays a critical role in mitochondrial morphology and cell viability.