Abstract
Programmed −1 ribosomal frameshifting (PRF) in cardioviruses is activated by the 2A protein: a multi-functional virulence factor that also inhibits cap-dependent translational initiation. Here we present the X-ray crystal structure of 2A and show that it selectively binds to and stabilises the PRF stimulatory RNA element in the viral genome. Using optical tweezers, we define the conformational repertoire of this element and measure changes in unfolding pathways arising from mutation and 2A binding. Next, we demonstrate a strong interaction between 2A and the small ribosomal subunit and present a cryo-EM structure of 2A bound to initiated 70S ribosomes. Multiple copies of 2A bind to the 16S rRNA where they may compete for binding with initiation and elongation factors. Together, these results define the structural basis for RNA recognition by 2A, expand our understanding of the 2A-dependent gene expression switch and reveal how 2A accumulation may shut down translation during virus infection.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
↵‡ Lead contact: ib103{at}cam.ac.uk
Changes to Title and Abstract; Minor alterations to text, formatting and figures to enhance clarity; New presentation of optical tweezer data (Figures 3 and S4); New MST data (Figure 4); Replacement data in Figure S3C with better signal and clearer gels; New 2A mutagenesis and biochemical data (Figure S5) with new section in results text; Minor updates to Methods and References; Inclusion of Table 5 (oligonucleotide sequences) and Key Resources Table.
