Fig. 6: The structure of translocated tmRNA reveals how the right resume codon is selected.
From: Structures of tmRNA and SmpB as they transit through the ribosome
a Left, focus on the interactions between SmpB (purple) and the four nucleotides just upstream of the tmRNA (red) resume codon. The cryo-electron density map is displayed and coloured according to the local resolutions as computed with ResMap74. Right, same but without the map. For clarity, cartoon representation is used for SmpB and only the four residues involved in the codon selection are shown. b An A84U/U85G double mutation in tmRNA maintains a high level of trans-translation but also promotes -1 frameshifting41. c Mutation of tmRNA’s highly conserved A86 nucleotide into a pyrimidine nucleotide lowers the stacking interaction with SmpB Tyr55 and results in a +1 frameshift41,42. d An SmpB triple mutant (Y24C, E107V and V129A) can partially reverse the effect of the tmRNA A86C mutation, allowing for both +1 frameshifting and in-frame re-registration43. The boxes show part of the MLD sequence, with the wild-type sequence repeated at the top for reference. The first two codons are grey, the mutated nucleotides are green and the five nucleotides presented in the figure are in capital letters. Where appropriate, the sequences of the mutants are shifted to highlight the frameshifts caused by the mutations.
