Viral proteins and site-specific cleavage

The protease coded by a picornavirus is central in the control of the viral replication. It is essential in the production of virus structural proteins, and regulates the viral RNA replicase in infected cells. The properties of the poliovirus protease are summarized and compared with other viruses. The interaction of polio protease with host defenses was examined. A cellular ribosomal protease degrades poliovirus and other "foreign" proteins, thus restricting viral functions. However, shortly after infection, ribosomal protease activity is suppressed, and in virus-infected extracts the enzyme is degraded. A second line of defense are the protein antiproteases of animal sera. Some of these inhibitors are able to complex the polio protease. A regulatory pathway summarizing the possible interactions of viral protease and the host defenses is presented.