Cell-specific role of protease 2A in poliovirus translation in relation to 5' noncoding region secondary structures.

Abstract

Polioviruses are single stranded RNA viruses and members of the picornavirus family. They have an unusually long non coding region at the 5’ end which has elaborate secondary structure predicted to be made up of seven domains. Part of the secondary structure constitutes an internal ribosome entry site (IRES) which allows the virus to utilise cap-independent initiation of translation whilst disabling the host cell’s cap-dependent translation. Translation inefficiencies originally caused by disruptions of the secondary structure of domain V could be compensated for in monkey kidney cells in vitro by coding changes in the protease 2A. These coding changes were found throughout the protease which is otherwise quite highly conserved in polioviruses. They appear to have no effect on monkey neurovirulence and their activity was found to be cell specific, having little or no compensatory effect in a mouse cell line. Using this cell line to investigate the effects of mutations in functionally significant secondary structure of domain V on virus growth highlighted unpaired loops as being important. Shortening one loop was detrimental to the virus whereas the sequence of the loop was much less important. In addition, flexibility at another position between two stems appeared to be critical and mutations that could potentially alter the folding in this area rendered the virus temperature sensitive.