INTACT EUKARYOTIC INITIATION-FACTOR 4G IS REQUIRED FOR HEPATITIS-A VIRUS INTERNAL INITIATION OF TRANSLATION

The requirements for optimal activity of the hepatitis A virus (HAV) i nternal ribosome entry segment (IRES) differ substantially from those of other picornavirus IRESes. One such difference is that, to dale, th e HAV IRES is the only one whose efficiency is severely inhibited in t he presence of the picornaviral 2A proteinase. Here we describe experi ments designed to dissect the mechanism of proteinase-mediated inhibit ion of HAV translation. Using dicistronic mRNAs translated in vitro, w e show that the HAV IRES is inhibited by the foot-and-mouth disease vi rus Lb proteinase, as well as by the human rhinovirus 2A proteinase. F urthermore, using mutant Lb proteinase, we demonstrate that proteolyti c activity is required for inhibition of HAV IRES activity, Translatio n inhibition correlated closely with the extent of cleavage of the one identified common cellular target for the 2A and Lb proteinases, euka ryotic initiation factor (eIf) 4G, a component of the eIF4F cap-bindin g protein complex. Total rescue of HAV IRES activity was possible if p urified eIF4F was added to translation extracts. In contrast, if the a dded eIF4F contained cleaved eIF4G, no rescue of HAV IRES activity was evidenced. Thus the HAV IRES requires intact eIF4G for activity. This is unique among the picornavirus IRESes studied to date and may help explain why HAV does not inhibit host cell translation during viral in fection. (C) 1997 Academic Press.