Basil J. Greber, Philipp Bieri, Marc Leibundgut, Alexander Leitner, Ruedi Aebersold, Daniel Boehringer, Nenad Ban
Mitochondria contain their own genomes, as well as their own transcription and translation machinery. In this study, the authors solve the structure of the mammalian mitochondrial ribosome using electron microscopy. It highlights many differences that exist between ribosomes which translate nuclear DNA in the cytosol, and mitoribosomes which exist in the mitochondrial matrix, tethered to the inner mitochondrial membrane. For instance, the mitoribosome contains a structurally-incorporated valine tRNA (perhaps explaining the pathogenicity of mitochondrial tRNA mutations?). Furthermore, mitoribosomes contain substantially less rRNA than their cytosolic counterparts - which is restricted to the catalytic core of the particle. Instead, mitoribosomes contain a substantially higher protein content, perhaps to protect itself from oxidative damage inside the matrix. It is currently unknown how the mitoribosome recognises mRNAs, but this structural insight suggests that protein, rather than rRNA, may have a larger role to play.
(see also http://www.sciencemag.org/content/348/6232/288.full
Roland Beckmann, Johannes M. Herrmann)