Fig. 4.

Hypothetical models for conformational changes of the ribosome and mRNA stimulatory structure during −1 PRF. Refolding of the downstream RNA intermediate structure occurs when the ribosome translocates to (A) the first half of the slippery sequence (step a1) or (B) the second half of the slippery sequence (step b2). The slippery sequence and the sequence under tension are shown in yellow and red, respectively. The partially-unwound downstream RNA structures before refolding are shown in red. See the text for details. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)