Poliovirus protease does not mediate cleavage of the 220,000-Da component of the cap binding protein complex.

Poliovirus infection of HeLa cells results in a rapid shutoff of host protein synthesis but does not inhibit the translation of poliovirus mRNA. It has been suggested that this virus-induced translational control is mediated by the inactivation of a cap binding protein (CBP) complex, and it has been shown that the 220,000-Da component(s) (p220) of the CBP complex is cleaved in infected HeLa cells to form antigenically related peptides of 100,000-130,000 Da. To determine whether the known viral protease (peptide 3C) was the mediator of the cleavage of p220, we used immunoblot techniques to analyze partially purified infected HeLa cell extracts for cleavage activity. We report here that p220 cleavage activity does not copurify with viral peptide 3C or with any precursors containing 3C sequences. We also show that cleavage of p220 can be demonstrated in vitro in HeLa cell extracts under conditions where the functional activity of the poliovirus protease is inhibited by specific antibody.