Accommodation of tmRNA-SmpB into stalled ribosomes: a cryo-EM study.
In eubacteria, translation of defective messenger RNAs (mRNAs) produces truncated polypeptides that stall on the ribosome. A quality control mechanism referred to as trans-translation is performed by transfer-messenger RNA (tmRNA), a specialized RNA acting as both a tRNA and an mRNA, associated with small protein B (SmpB). So far, a clear view of the structural movements of both the protein and RNA necessary to perform accommodation is still lacking. By using a construct containing the tRNA-like domain as well as the extended helix H2 of tmRNA, we present a cryo-electron microscopy study of the process of accommodation. The structure suggests how tmRNA and SmpB move into the ribosome decoding site after the release of EF-Tu.GDP. While two SmpB molecules are bound per ribosome in a preaccommodated state, our results show that during accommodation the SmpB protein interacting with the small subunit decoding site stays in place while the one interacting with the large subunit moves away. Relative to canonical translation, an additional movement is observed due to the rotation of H2. This suggests that the larger movement required to resume translation on a tmRNA internal open reading frame starts during accommodation.
Weis
Felix
F
Universite de Rennes 1, INSERM U835, Laboratoire de Biochimie Pharmaceutique, 35043 Rennes Cedex, France.
Bron
Patrick
P
Rolland
Jean-Paul
JP
Thomas
Daniel
D
Felden
Brice
B
Gillet
Reynald
R
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D021621:Imaging, Three-Dimensional; D046911:Macromolecular Substances; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D011487:Protein Conformation; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism* / Q000648:ultrastructure*; D016963:Thermus thermophilus / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure
D001426:Bacterial Proteins; D046911:Macromolecular Substances; D012329:RNA, Bacterial; D016601:RNA-Binding Proteins; C430328:small protein B; C096222:tmRNA