Mutational analysis of the EMCV 2A protein identifies a nuclear localization signal and an eIF4E binding site

Cardioviruses have a unique 2A protein (143 aa). During genome translation, the encephalomyocarditis virus (EMCV) 2A is released through a ribosome skipping event mitigated through C-terminal 2A sequences and by subsequent N-terminal reaction with viral 3C^pro. Although viral replication is cytoplasmic, mature 2A accumulates in nucleoli shortly after infection. Some protein also transiently associates with cytoplasmic 40S ribosomal subunits, an activity contributing to inhibition of cellular cap-dependent translation. Cardiovirus sequences predict an eIF4E binding site (aa 126-134) and a nuclear localization signal (NLS, aa 91-102), within 2A, both of which are functional during EMCV infection. Point mutations preventing eIF4E:2A interactions gave small-plaque phenotype viruses, but still inhibited cellular cap-dependent translation. Deletions within the NLS motif relocalized 2A to the cytoplasm and abrogated the inhibition of cap-dependent translation. A fusion protein linking the 2A NLS to eGFP was sufficient to redirect the reporter to the nucleus but not into nucleoli.