Structures of tmRNA and SmpB as they transit through the ribosome

Charlotte Guyomar (1) , Gaetano D’urso (1) , Sophie Chat (1) , Emmanuel Giudice (1) , Reynald Gillet (1)

1 IGDR - Institut de Génétique et Développement de Rennes

In bacteria, trans-translation is the main rescue system, freeing ribosomes stalled on defective messenger RNAs. This mechanism is driven by small protein B (SmpB) and transfer-messenger RNA (tmRNA), a hybrid RNA known to have both a tRNA-like and an mRNA-like domain. Here we present four cryo-EM structures of the ribosome during trans-translation at resolutions from 3.0 to 3.4 Å. These include the high-resolution structure of the whole pre-accommodated state, as well as structures of the accommodated state, the translocated state, and a translocation intermediate. Together, they shed light on the movements of the tmRNA-SmpB complex in the ribosome, from its delivery by the elongation factor EF-Tu to its passage through the ribosomal A and P sites after the opening of the B1 bridges. Additionally, we describe the interactions between the tmRNA-SmpB complex and the ribosome. These explain why the process does not interfere with canonical translation.

Domains: Life Sciences [q-bio]

Charlotte Guyomar, Gaetano D’urso, Sophie Chat, Emmanuel Giudice, Reynald Gillet. Structures of tmRNA and SmpB as they transit through the ribosome. Nature Communications, 2021, 12 (1), pp.4909. ⟨10.1038/s41467-021-24881-4⟩. ⟨hal-03343248⟩