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

To evaluate the connection between pulling forces on the nascent chain and frameshifting, we measured the tension on the nascent chain at the point of elongation when the slip site occupies the ribosomal active site (Supplemental Movie 1). 47 Pulling forces were highest for the LL variant, which averaged 4.2 pN higher than the WT. In contrast, the EE mutations reduce the pulling force on the nascent chain by an average 2.3 pN relative to WT. These results are consistent with the hypothesis that differences in frameshifting arise from the effects of these mutations on the pulling force on the nascent chain. Simulations of polyprotein variants bearing insertions or deletions that alter the distance between TM2 and the ribosomal slip-site indicate that the native distance (45 residues) is nearly optimal for the transmission of pulling force through the nascent chain (Supplemental Table 1 ), which is consistent with the observed patterns in frameshifting (Fig. 4B) .