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Ribosome binding to mitochondria is regulated by GTP and the transit peptide
1Department of Pediatrics, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1081, USA.
The Journal of Biological Chemistry
|June 27, 1998
Summary
Ribosomes bind to mitochondria, suggesting a co-translational protein import pathway. This GTP-dependent binding is influenced by nascent protein chains, similar to endoplasmic reticulum processes.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Ribosome association with the endoplasmic reticulum membrane facilitates co-translational translocation.
- The mechanism of protein import into mitochondria in higher eukaryotes remains incompletely understood.
Purpose of the Study:
- To investigate ribosome binding to mitochondrial membranes in higher eukaryotes.
- To determine if a co-translational translocation pathway exists for mitochondrial protein import.
Main Methods:
- In vitro binding assays using purified rat liver mitochondria and ribosomes.
- Spectral measurements and analysis of mitochondrial-associated RNA.
- Electron microscopy to visualize ribosome-mitochondria interactions.
- GTP hydrolysis assays to assess energy dependence.
Main Results:
- Ribosomes stably bind to isolated mitochondria in vitro.
- Ribosome-mitochondria binding is dependent on GTP hydrolysis, significantly reduced by GTP and GTPgammaS.
- Ribosomes increase the rate of mitochondrial GTP hydrolysis but not ATP hydrolysis.
- Binding characteristics are altered by the presence of a nascent polypeptide chain.
Conclusions:
- Mitochondrial membranes possess specific receptors for ribosomes.
- A GTP-dependent mechanism mediates ribosome-mitochondria binding.
- Evidence supports a co-translational translocation pathway for mitochondrial protein import.