Translation without eIF2 promoted by poliovirus 2A protease

Poliovirus RNA utilizes eIF2 for the initiation of translation in cell free systems. Remarkably, we now describe that poliovirus translation takes place at late times of infection when eIF2 is inactivated by phosphorylation. By contrast, translation directed by poliovirus RNA is blocked when eIF2 is inactivated at earlier times. Thus, poliovirus RNA translation exhibits a dual mechanism for the initiation of protein synthesis as regards to the requirement for eIF2. Analysis of individual poliovirus non-structural proteins indicates that the presence of 2A(pro) alone is sufficient to provide eIF2 independence for IRES-driven translation. This effect is not observed with a 2A(pro) variant unable to cleave eIF4G. The level of 2A(pro) synthesized in culture cells is crucial for obtaining eIF2 independence. Expression of the N-or C-terminus fragments of eIF4G did not stimulate IRES-driven translation, nor provide eIF2 independence, consistent with the idea that the presence of 2A(pro) at high concentrations is necessary. The finding that 2A(pro) provides eIF2-independent translation opens a new and unsuspected area of research in the field of picornavirus protein synthesis.