Cotranslational Folding Stimulates Programmed Ribosomal Frameshifting in the Alphavirus Structural Polyprotein

Haley R. Harrington; Matthew H. Zimmer; Laura M. Chamness; Veronica Nash; Wesley D. Penn; Thomas F. Miller; Suchetana Mukhopadhyay; Jonathan P. Schlebach

An analysis of the spectrum of topological states sampled during translation reveals that the magnitude of the pulling force transmitted to the ribosome scales with the number of beads that occupy the translocon (Fig. 5C ). This finding suggests pulling forces are generated by the movement of hydrophobic transmembrane segments from the protein-conducting channel of the translocon to the hydrophobic membrane core, as has been established previously. 40, 41, 47 This . CC-BY 4.0 International license is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. It . https://doi.org/10.1101/790444 doi: bioRxiv preprint interpretation suggests differences in pulling forces arise from variations in the distribution of topological isomers that form during translation of these variants (Fig. 5D) . The LL mutant predominately samples conformations where the majority of TM2 beads are in the translocon (Fig. 5A, right) , whereas the EE mutant almost exclusively adopts conformations in which the majority of TM2 beads fall outside of the translocon and within the cytosol (Fig. 5A, left) . As passage through the translocon is a prerequisite for membrane integration, the relationship between pulling forces and residence of the nascent chain within the translocon is consistent with our model for structural polyprotein biogenesis (Fig. 3) and confirms that the translocon-mediated membrane integration of TM2 stimulates -1PRF.