Ribosomes enriched in messages for nuclear-encoded mitochondrial proteins are present in mitochondria preparations. To determine if this is due to a specific ribosome-mitochondria interaction, highly purified rat liver mitochondria were stripped of ribosomes by EDTA/high salt treatment and incubated with GTPase-depleted rat liver ribosomes in the absence or presence of ATP, GTP, GDP or guanosine-5'-[thioj-triphosphate (GTP7S). Ribosomemitochondria complexes were separated from free ribosomes by sedimentation and ribosome-mitochondria binding was determined both by electron microscopy, and by measuring the A2eo and A 280 of the resuspended mitochondria. Pre-formed complexes were sedimented, and the supernatants and pellets analyzed for ribosomal RNA and protein content. All four methods show that ribosomes bind to mitochondria in the absence of a trinucleotide but binding is attenuated or reversed by GTP, GDP, or GTP7S. When isolated ribosomes were programmed with a truncated mRNA coding for the first 93 amino acids of mitochondrial malate dehydrogenase, only GTP7S, but not GTP or GDP, attenuated binding- GTP, GDP and GTPiS all attenuated binding of ribosomes programmed with a truncated luciferase mRNA. Our findings show that, 1) ribosomes bind specifically to mitochondria, 2) binding is reversible, 3) binding is affected by GTP, and 4) binding is affected by the nature of nascent polypeptides carried on the ribosome. These results also show that mitochondria] polypeptides are targeted to the mitochondria before synthesis is complete, suggesting that mitochondrial proteins may be imported by co-translational translocation.
|Original language||English (US)|
|State||Published - Dec 1 1998|
ASJC Scopus subject areas
- Molecular Biology