(a) Schematic representation of the VemP-SecDF2 mRNA encoding VemP leader peptide with N-terminal signal sequence (SS) and C-terminal stalling region (green), followed by a stem-loop structure that sequesters the ribosome-binding site (RBS) of the SecDF2 gene (left). The translation arrest of VemP maintains the unfolded conformation of the mRNA allowing ribosome binding and induction of SecDF2 expression. The VemP stalling window H138–Q156 (boxed) is shown with critical (green bold) and important (green) residues highlighted (Ishii et al., 2015), and an asterisk indicating the stop codon (right). (b–c) In vivo pulse-chase analysis with different VemP constructs; VemP ‘short’ (H138–Q156, orange), VemP ‘long’ (F131–Q156, pink), VemP ‘GS’ (purple) and VemP mutants L153A and Q156*. (d) Schematic of the VemP-SRC used for cryo-EM. (e–f) Western blot against the N-terminal HA-tag of in vitro translated ∆SS-VemP detecting stalled peptidyl-tRNA (I), stalled free peptide (II) or full-length free peptide (III), (e) in the absence and presence of RNase A treatment, or (f) as a function of time (25, 40, 55, 70, 85, 100 min). (g) Transverse section of cryo-EM structure of the VemP-SRC showing the peptidyl-tRNA (green), with small and large subunits coloured in yellow and blue, respectively.