Molecular mimicry of tRNA / mRNA during trans‐translation

Abstract

In trans-translation, transfer-messanger RNA (tmRNA) rescues the stalled ribosome, which is caused by truncated or other problemtic mRNAs. When tmRNA enters the stalled ribosome, there is no codon-anticodon interaction, but with a protein factor SmpB. Here, we studied the binding site of SmpB on the ribosome by directed hydroxyl radical probing. It revealed that there are two SmpB binding sites on a ribosome, the A-site and P-site, suggesting that these binding sites reflect pre- and post-translocation states of SmpB during trans-translation. It is also suggested that the N-terminal region (1–133) and the C-terminal tail (134–160) of SmpB mimic the lower half of tRNA and mRNA, respectively. We also examined the role of the C-terminal tail of SmpB using an in vitro trans-translation system. Our data indicate that the residues of the C-terminal tail of SmpB are involved in the early stage of trans-translation. This work was supported by a grant-in-aid for Young Scientists (Start-up) from Japan Society for the Promotion of Science (JSPS) to D.K. (No. 21880009) and a Research Fellowship of Hirosaki University for D.K.