Cryo-EM structure of the small subunit of the mammalian mitochondrial ribosome.

The mammalian mitochondrial ribosomes (mitoribosomes) are responsible for synthesizing 13 membrane proteins that form essential components of the complexes involved in oxidative phosphorylation or ATP generation for the eukaryotic cell. The mammalian 55S mitoribosome contains significantly smaller rRNAs and a large mass of mitochondrial ribosomal proteins (MRPs), including large mito-specific amino acid extensions and insertions in MRPs that are homologous to bacterial ribosomal proteins and an additional 35 mito-specific MRPs. Here we present the cryo-EM structure analysis of the small (28S) subunit (SSU) of the 55S mitoribosome.

Structure of a mitochondrial ribosome with minimal RNA.

The Leishmania tarentolae mitochondrial ribosome (Lmr) is a minimal ribosomal RNA (rRNA)-containing ribosome. We have obtained a cryo-EM map of the Lmr. The map reveals several features that have not been seen in previously-determined structures of eubacterial or eukaryotic (cytoplasmic or organellar) ribosomes to our knowledge.

Structural aspects of RbfA action during small ribosomal subunit assembly.

Ribosome binding factor A (RbfA) is a bacterial cold shock response protein, required for an efficient processing of the 5' end of the 16S ribosomal RNA (rRNA) during assembly of the small (30S) ribosomal subunit. Here we present a crystal structure of Thermus thermophilus (Tth) RbfA and a three-dimensional cryo-electron microscopic (EM) map of the Tth 30S*RbfA complex. RbfA binds to the 30S subunit in a position overlapping the binding sites of the A and P site tRNAs, and RbfA's functionally important C terminus extends toward the 5' end of the 16S rRNA.

Interaction of Era with the 30S ribosomal subunit implications for 30S subunit assembly.

Era (E. coliRas-like protein) is a highly conserved and essential GTPase in bacteria. It binds to the 16S ribosomal RNA (rRNA) of the small (30S) ribosomal subunit, and its depletion leads to accumulation of an unprocessed precursor of the 16S rRNA.

Visualization of ribosome-recycling factor on the Escherichia coli 70S ribosome: functional implications.

After the termination step of protein synthesis, a deacylated tRNA and mRNA remain associated with the ribosome. The ribosome-recycling factor (RRF), together with elongation factor G (EF-G), disassembles this posttermination complex into mRNA, tRNA, and the ribosome. We have obtained a three-dimensional cryo-electron microscopic map of a complex of the Escherichia coli 70S ribosome and RRF.

Structure of the mammalian mitochondrial ribosome reveals an expanded functional role for its component proteins.

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 (approximately 69:approximately 31) is the inverse of that of its prokaryotic counterpart (approximately 33:approximately 67), 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.