Abstract
The 2A protein of Theiler’s murine encephalomyelitis virus (TMEV) is required for stimulating programmed −1 ribosomal frameshifting (PRF) during infection. However, the amino acid sequence of TMEV 2A shares only 27% identity with the 2A orthologue from the related cardiovirus encephalomyocarditis virus (EMCV) for which a structure has been recently determined. Here we present the X-ray crystal structure of TMEV 2A, revealing that, despite the low sequence identity, the overall beta-shell architecture is retained, and the location of previously described mutations on this structure suggests a common RNA binding mode. We determine the minimal stimulatory element in the viral RNA required for 2A binding and show that 2A binds to this element with 1:1 stoichiometry and nanomolar affinity. We also demonstrate a critical role for bases upstream of the originally predicted stem-loop, providing evidence that an alternative pseudoknot-like conformation recently demonstrated for EMCV is a conserved feature of cardiovirus stimulatory elements. We go on to examine frameshifting in infected cells by ribosome profiling and metabolic labelling. We observe PRF efficiencies of up to 85%, highlighting this as the most efficient example of −1 PRF in any natural system thus far characterised. Furthermore, we document a series of ribosomal pauses in and around the site of PRF with potential implications for our understanding of translational control in cardioviruses.
Competing Interest Statement
The authors have declared no competing interest.
