PICORNAVIRUS INTERNAL RIBOSOME ENTRY SEGMENTS - COMPARISON OF TRANSLATION EFFICIENCY AND THE REQUIREMENTS FOR OPTIMAL INTERNAL INITIATION OF TRANSLATION IN-VITRO

On the basis of primary sequence comparisons and secondary structure p redictions, picornavirus internal ribosome entry segments (IRESes) hav e been divided into three groups (entero- and rhinoviruses; cardio- an d aphthoviruses; and hepatitis A virus). Here, we describe a detailed comparison of the ability of IRESes from each group to direct internal initiation of translation in vitro using a single dicistronic mRNA (t he only variable being the IRES inserted into the dicistronic region), We studied the influence of various parameters on the capacity of six different picornaviral IRESes, and the non-picornaviral hepatitis C v irus IRES, to direct internal initiation of translation: salt concentr ation, the addition of HeLa cell proteins to rabbit reticulocyte lysat e translation reactions, the presence of foot-and-mouth disease virus Lb or human rhinovirus 2A proteinase, On the basis of the characterist ics of IRES-driven translation in vitro, the picornaviral IRESes can b e classified in a similar manner to when sequence homologies are consi dered, IRESes from each of the three groups responded differently to a ll of the parameters tested, indicating that while all of these elemen ts can direct internal ribosome entry, the functional requirements for efficient IRES activity vary dramatically, In the individual optimal conditions for translation initiation, the best IRESes were those from the cardio- and aphthoviruses, followed by those from the enterovirus es, which exhibited up to 70% of the efficiency of the EMCV element in directing internal initiation of translation.