Composition and Structure of the 80 S Ribosome from the Green Alga Chlamydomonas reinhardtii: 80 S Ribosomes are Conserved in Plants and Animals

We have conducted a proteomic analysis of the 80 S cytosolic ribosome from the eukaryotic green alga Chlamydomonas reinhardtii, and accompany this with a cryo-electron microscopy structure of the ribosome. Proteins homologous to all but one rat 40 S subunit protein, including a homolog of RACK1, and all but three rat 60 S subunit proteins were identified as components of the C. reinhardtii ribosome. Expressed Sequence Tag (EST) evidence and annotation of the completed C. reinhardtii genome identified genes for each of the four proteins not identified by proteomic analysis, showing that algae potentially have a complete set of orthologs to mammalian 80 S ribosomal proteins. Presented at 25 Å, the algal 80 S ribosome is very similar in structure to the yeast 80 S ribosome, with only minor distinguishable differences. These data show that, although separated by billions of years of evolution, cytosolic ribosomes from photosynthetic organisms are highly conserved with their yeast and animal counterparts.