Journal
CELL
Volume 115, Issue 1, Pages 97-108Publisher
CELL PRESS
DOI: 10.1016/S0092-8674(03)00762-1
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Funding
- NIGMS NIH HHS [R01 GM061576, GM32734, GM61576] Funding Source: Medline
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The mitochondrial ribosome is responsible for the biosynthesis of protein components crucial to the generation of ATP in the eukaryotic cell. Because the protein:RNA ratio in the mitochondrial ribosome (similar to69:similar to31) is the inverse of that of its prokaryotic counterpart (similar to33:similar to67), it was thought that the additional and/or larger proteins of the mitochondrial ribosome must compensate for the shortened rRNAs. Here, we present a three-dimensional cryo-electron microscopic map of the mammalian mitochondrial 55S ribosome carrying a tRNA at its P site, and we find that instead, many of the proteins occupy new positions in the ribosome. Furthermore, unlike cytoplasmic ribosomes, the mitochondrial ribosome possesses inter-subunit bridges composed largely of proteins; it has a gatelike structure at its mRNA entrance, perhaps involved in recruiting unique mitochondrial mRNAs; and it has a polypeptide exit tunnel that allows access to the solvent before the exit site, suggesting a unique nascent-polypeptide exit mechanism.
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