EUKARYOTIC INITIATION FACTOR-III IS REQUIRED FOR POLIOVIRUS-2A PROTEASE-INDUCED CLEAVAGE OF THE P220 COMPONENT OF EUKARYOTIC INITIATION FACTOR-4F

After cultured cells are infected with poliovirus, cellular mRNA fails to bind to ribosomes, and synthesis of the majority of cellular proteins ceases. The defective step has been localized to the cap-dependent activity of the eukaryotic translation initiation factor 4F. Inactivation of this factor correlates with the cleavage of its largest subunit, p220, into characteristic products observed in infected cells. This cleavage is mediated by the poliovirus protease 2A(pro). Previous work suggests that 2A(pro) does not catalyze the reaction directly, suggesting that one or more cellular proteins is required for the degradation of p220. To identify such a protein, we have developed an assay in which cleavage of a p220 substrate in the presence of poliovirus 2A(pro) is dependent upon the addition of HeLa cell proteins. By using this assay, we show that another factor, eukaryotic translation initiation factor 3, is required for 2A(pro)-dependent cleavage of p220.